FreeBSD/Linux Kernel Cross Reference
sys/kern/vfs_subr.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1989, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)vfs_subr.c  8.31 (Berkeley) 5/26/95
     */
    
    /*
     * External virtual filesystem routines
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_ddb.h"
    #include "opt_watchdog.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/asan.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/capsicum.h>
    #include <sys/condvar.h>
    #include <sys/conf.h>
    #include <sys/counter.h>
    #include <sys/dirent.h>
    #include <sys/event.h>
    #include <sys/eventhandler.h>
    #include <sys/extattr.h>
    #include <sys/file.h>
    #include <sys/fcntl.h>
    #include <sys/jail.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/ktr.h>
    #include <sys/lockf.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/namei.h>
    #include <sys/pctrie.h>
    #include <sys/priv.h>
    #include <sys/reboot.h>
    #include <sys/refcount.h>
    #include <sys/rwlock.h>
    #include <sys/sched.h>
    #include <sys/sleepqueue.h>
    #include <sys/smr.h>
    #include <sys/smp.h>
    #include <sys/stat.h>
    #include <sys/sysctl.h>
    #include <sys/syslog.h>
    #include <sys/vmmeter.h>
    #include <sys/vnode.h>
    #include <sys/watchdog.h>
    
    #include <machine/stdarg.h>
    
    #include <security/mac/mac_framework.h>
    
    #include <vm/vm.h>
    #include <vm/vm_object.h>
    #include <vm/vm_extern.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_page.h>
    #include <vm/vm_kern.h>
   #include <vm/uma.h>
   
   #if defined(DEBUG_VFS_LOCKS) && (!defined(INVARIANTS) || !defined(WITNESS))
   #error DEBUG_VFS_LOCKS requires INVARIANTS and WITNESS
   #endif
   
   #ifdef DDB
   #include <ddb/ddb.h>
   #endif
   
   static void     delmntque(struct vnode *vp);
   static int      flushbuflist(struct bufv *bufv, int flags, struct bufobj *bo,
                       int slpflag, int slptimeo);
   static void     syncer_shutdown(void *arg, int howto);
   static int      vtryrecycle(struct vnode *vp);
   static void     v_init_counters(struct vnode *);
   static void     vn_seqc_init(struct vnode *);
   static void     vn_seqc_write_end_free(struct vnode *vp);
   static void     vgonel(struct vnode *);
   static bool     vhold_recycle_free(struct vnode *);
   static void     vdropl_recycle(struct vnode *vp);
   static void     vdrop_recycle(struct vnode *vp);
   static void     vfs_knllock(void *arg);
   static void     vfs_knlunlock(void *arg);
   static void     vfs_knl_assert_lock(void *arg, int what);
   static void     destroy_vpollinfo(struct vpollinfo *vi);
   static int      v_inval_buf_range_locked(struct vnode *vp, struct bufobj *bo,
                       daddr_t startlbn, daddr_t endlbn);
   static void     vnlru_recalc(void);
   
   /*
    * Number of vnodes in existence.  Increased whenever getnewvnode()
    * allocates a new vnode, decreased in vdropl() for VIRF_DOOMED vnode.
    */
   static u_long __exclusive_cache_line numvnodes;
   
   SYSCTL_ULONG(_vfs, OID_AUTO, numvnodes, CTLFLAG_RD, &numvnodes, 0,
       "Number of vnodes in existence");
   
   static counter_u64_t vnodes_created;
   SYSCTL_COUNTER_U64(_vfs, OID_AUTO, vnodes_created, CTLFLAG_RD, &vnodes_created,
       "Number of vnodes created by getnewvnode");
   
   /*
    * Conversion tables for conversion from vnode types to inode formats
    * and back.
    */
   enum vtype iftovt_tab[16] = {
           VNON, VFIFO, VCHR, VNON, VDIR, VNON, VBLK, VNON,
           VREG, VNON, VLNK, VNON, VSOCK, VNON, VNON, VNON
   };
   int vttoif_tab[10] = {
           0, S_IFREG, S_IFDIR, S_IFBLK, S_IFCHR, S_IFLNK,
           S_IFSOCK, S_IFIFO, S_IFMT, S_IFMT
   };
   
   /*
    * List of allocates vnodes in the system.
    */
   static TAILQ_HEAD(freelst, vnode) vnode_list;
   static struct vnode *vnode_list_free_marker;
   static struct vnode *vnode_list_reclaim_marker;
   
   /*
    * "Free" vnode target.  Free vnodes are rarely completely free, but are
    * just ones that are cheap to recycle.  Usually they are for files which
    * have been stat'd but not read; these usually have inode and namecache
    * data attached to them.  This target is the preferred minimum size of a
    * sub-cache consisting mostly of such files. The system balances the size
    * of this sub-cache with its complement to try to prevent either from
    * thrashing while the other is relatively inactive.  The targets express
    * a preference for the best balance.
    *
    * "Above" this target there are 2 further targets (watermarks) related
    * to recyling of free vnodes.  In the best-operating case, the cache is
    * exactly full, the free list has size between vlowat and vhiwat above the
    * free target, and recycling from it and normal use maintains this state.
    * Sometimes the free list is below vlowat or even empty, but this state
    * is even better for immediate use provided the cache is not full.
    * Otherwise, vnlru_proc() runs to reclaim enough vnodes (usually non-free
    * ones) to reach one of these states.  The watermarks are currently hard-
    * coded as 4% and 9% of the available space higher.  These and the default
    * of 25% for wantfreevnodes are too large if the memory size is large.
    * E.g., 9% of 75% of MAXVNODES is more than 566000 vnodes to reclaim
    * whenever vnlru_proc() becomes active.
    */
   static long wantfreevnodes;
   static long __exclusive_cache_line freevnodes;
   SYSCTL_ULONG(_vfs, OID_AUTO, freevnodes, CTLFLAG_RD,
       &freevnodes, 0, "Number of \"free\" vnodes");
   static long freevnodes_old;
   
   static counter_u64_t recycles_count;
   SYSCTL_COUNTER_U64(_vfs, OID_AUTO, recycles, CTLFLAG_RD, &recycles_count,
       "Number of vnodes recycled to meet vnode cache targets");
   
   static counter_u64_t recycles_free_count;
   SYSCTL_COUNTER_U64(_vfs, OID_AUTO, recycles_free, CTLFLAG_RD, &recycles_free_count,
       "Number of free vnodes recycled to meet vnode cache targets");
   
   static counter_u64_t deferred_inact;
   SYSCTL_COUNTER_U64(_vfs, OID_AUTO, deferred_inact, CTLFLAG_RD, &deferred_inact,
       "Number of times inactive processing was deferred");
   
   /* To keep more than one thread at a time from running vfs_getnewfsid */
   static struct mtx mntid_mtx;
   
   /*
    * Lock for any access to the following:
    *      vnode_list
    *      numvnodes
    *      freevnodes
    */
   static struct mtx __exclusive_cache_line vnode_list_mtx;
   
   /* Publicly exported FS */
   struct nfs_public nfs_pub;
   
   static uma_zone_t buf_trie_zone;
   static smr_t buf_trie_smr;
   
   /* Zone for allocation of new vnodes - used exclusively by getnewvnode() */
   static uma_zone_t vnode_zone;
   MALLOC_DEFINE(M_VNODEPOLL, "VN POLL", "vnode poll");
   
   __read_frequently smr_t vfs_smr;
   
   /*
    * The workitem queue.
    *
    * It is useful to delay writes of file data and filesystem metadata
    * for tens of seconds so that quickly created and deleted files need
    * not waste disk bandwidth being created and removed. To realize this,
    * we append vnodes to a "workitem" queue. When running with a soft
    * updates implementation, most pending metadata dependencies should
    * not wait for more than a few seconds. Thus, mounted on block devices
    * are delayed only about a half the time that file data is delayed.
    * Similarly, directory updates are more critical, so are only delayed
    * about a third the time that file data is delayed. Thus, there are
    * SYNCER_MAXDELAY queues that are processed round-robin at a rate of
    * one each second (driven off the filesystem syncer process). The
    * syncer_delayno variable indicates the next queue that is to be processed.
    * Items that need to be processed soon are placed in this queue:
    *
    *      syncer_workitem_pending[syncer_delayno]
    *
    * A delay of fifteen seconds is done by placing the request fifteen
    * entries later in the queue:
    *
    *      syncer_workitem_pending[(syncer_delayno + 15) & syncer_mask]
    *
    */
   static int syncer_delayno;
   static long syncer_mask;
   LIST_HEAD(synclist, bufobj);
   static struct synclist *syncer_workitem_pending;
   /*
    * The sync_mtx protects:
    *      bo->bo_synclist
    *      sync_vnode_count
    *      syncer_delayno
    *      syncer_state
    *      syncer_workitem_pending
    *      syncer_worklist_len
    *      rushjob
    */
   static struct mtx sync_mtx;
   static struct cv sync_wakeup;
   
   #define SYNCER_MAXDELAY         32
   static int syncer_maxdelay = SYNCER_MAXDELAY;   /* maximum delay time */
   static int syncdelay = 30;              /* max time to delay syncing data */
   static int filedelay = 30;              /* time to delay syncing files */
   SYSCTL_INT(_kern, OID_AUTO, filedelay, CTLFLAG_RW, &filedelay, 0,
       "Time to delay syncing files (in seconds)");
   static int dirdelay = 29;               /* time to delay syncing directories */
   SYSCTL_INT(_kern, OID_AUTO, dirdelay, CTLFLAG_RW, &dirdelay, 0,
       "Time to delay syncing directories (in seconds)");
   static int metadelay = 28;              /* time to delay syncing metadata */
   SYSCTL_INT(_kern, OID_AUTO, metadelay, CTLFLAG_RW, &metadelay, 0,
       "Time to delay syncing metadata (in seconds)");
   static int rushjob;             /* number of slots to run ASAP */
   static int stat_rush_requests;  /* number of times I/O speeded up */
   SYSCTL_INT(_debug, OID_AUTO, rush_requests, CTLFLAG_RW, &stat_rush_requests, 0,
       "Number of times I/O speeded up (rush requests)");
   
   #define VDBATCH_SIZE 8
   struct vdbatch {
           u_int index;
           long freevnodes;
           struct mtx lock;
           struct vnode *tab[VDBATCH_SIZE];
   };
   DPCPU_DEFINE_STATIC(struct vdbatch, vd);
   
   static void     vdbatch_dequeue(struct vnode *vp);
   
   /*
    * When shutting down the syncer, run it at four times normal speed.
    */
   #define SYNCER_SHUTDOWN_SPEEDUP         4
   static int sync_vnode_count;
   static int syncer_worklist_len;
   static enum { SYNCER_RUNNING, SYNCER_SHUTTING_DOWN, SYNCER_FINAL_DELAY }
       syncer_state;
   
   /* Target for maximum number of vnodes. */
   u_long desiredvnodes;
   static u_long gapvnodes;                /* gap between wanted and desired */
   static u_long vhiwat;           /* enough extras after expansion */
   static u_long vlowat;           /* minimal extras before expansion */
   static u_long vstir;            /* nonzero to stir non-free vnodes */
   static volatile int vsmalltrigger = 8;  /* pref to keep if > this many pages */
   
   static u_long vnlru_read_freevnodes(void);
   
   /*
    * Note that no attempt is made to sanitize these parameters.
    */
   static int
   sysctl_maxvnodes(SYSCTL_HANDLER_ARGS)
   {
           u_long val;
           int error;
   
           val = desiredvnodes;
           error = sysctl_handle_long(oidp, &val, 0, req);
           if (error != 0 || req->newptr == NULL)
                   return (error);
   
           if (val == desiredvnodes)
                   return (0);
           mtx_lock(&vnode_list_mtx);
           desiredvnodes = val;
           wantfreevnodes = desiredvnodes / 4;
           vnlru_recalc();
           mtx_unlock(&vnode_list_mtx);
           /*
            * XXX There is no protection against multiple threads changing
            * desiredvnodes at the same time. Locking above only helps vnlru and
            * getnewvnode.
            */
           vfs_hash_changesize(desiredvnodes);
           cache_changesize(desiredvnodes);
           return (0);
   }
   
   SYSCTL_PROC(_kern, KERN_MAXVNODES, maxvnodes,
       CTLTYPE_ULONG | CTLFLAG_MPSAFE | CTLFLAG_RW, NULL, 0, sysctl_maxvnodes,
       "LU", "Target for maximum number of vnodes");
   
   static int
   sysctl_wantfreevnodes(SYSCTL_HANDLER_ARGS)
   {
           u_long val;
           int error;
   
           val = wantfreevnodes;
           error = sysctl_handle_long(oidp, &val, 0, req);
           if (error != 0 || req->newptr == NULL)
                   return (error);
   
           if (val == wantfreevnodes)
                   return (0);
           mtx_lock(&vnode_list_mtx);
           wantfreevnodes = val;
           vnlru_recalc();
           mtx_unlock(&vnode_list_mtx);
           return (0);
   }
   
   SYSCTL_PROC(_vfs, OID_AUTO, wantfreevnodes,
       CTLTYPE_ULONG | CTLFLAG_MPSAFE | CTLFLAG_RW, NULL, 0, sysctl_wantfreevnodes,
       "LU", "Target for minimum number of \"free\" vnodes");
   
   SYSCTL_ULONG(_kern, OID_AUTO, minvnodes, CTLFLAG_RW,
       &wantfreevnodes, 0, "Old name for vfs.wantfreevnodes (legacy)");
   static int vnlru_nowhere;
   SYSCTL_INT(_debug, OID_AUTO, vnlru_nowhere, CTLFLAG_RW,
       &vnlru_nowhere, 0, "Number of times the vnlru process ran without success");
   
   static int
   sysctl_try_reclaim_vnode(SYSCTL_HANDLER_ARGS)
   {
           struct vnode *vp;
           struct nameidata nd;
           char *buf;
           unsigned long ndflags;
           int error;
   
           if (req->newptr == NULL)
                   return (EINVAL);
           if (req->newlen >= PATH_MAX)
                   return (E2BIG);
   
           buf = malloc(PATH_MAX, M_TEMP, M_WAITOK);
           error = SYSCTL_IN(req, buf, req->newlen);
           if (error != 0)
                   goto out;
   
           buf[req->newlen] = '\0';
   
           ndflags = LOCKLEAF | NOFOLLOW | AUDITVNODE1 | SAVENAME;
           NDINIT(&nd, LOOKUP, ndflags, UIO_SYSSPACE, buf, curthread);
           if ((error = namei(&nd)) != 0)
                   goto out;
           vp = nd.ni_vp;
   
           if (VN_IS_DOOMED(vp)) {
                   /*
                    * This vnode is being recycled.  Return != 0 to let the caller
                    * know that the sysctl had no effect.  Return EAGAIN because a
                    * subsequent call will likely succeed (since namei will create
                    * a new vnode if necessary)
                    */
                   error = EAGAIN;
                   goto putvnode;
           }
   
           counter_u64_add(recycles_count, 1);
           vgone(vp);
   putvnode:
           NDFREE(&nd, 0);
   out:
           free(buf, M_TEMP);
           return (error);
   }
   
   static int
   sysctl_ftry_reclaim_vnode(SYSCTL_HANDLER_ARGS)
   {
           struct thread *td = curthread;
           struct vnode *vp;
           struct file *fp;
           int error;
           int fd;
   
           if (req->newptr == NULL)
                   return (EBADF);
   
           error = sysctl_handle_int(oidp, &fd, 0, req);
           if (error != 0)
                   return (error);
           error = getvnode(curthread, fd, &cap_fcntl_rights, &fp);
           if (error != 0)
                   return (error);
           vp = fp->f_vnode;
   
           error = vn_lock(vp, LK_EXCLUSIVE);
           if (error != 0)
                   goto drop;
   
           counter_u64_add(recycles_count, 1);
           vgone(vp);
           VOP_UNLOCK(vp);
   drop:
           fdrop(fp, td);
           return (error);
   }
   
   SYSCTL_PROC(_debug, OID_AUTO, try_reclaim_vnode,
       CTLTYPE_STRING | CTLFLAG_MPSAFE | CTLFLAG_WR, NULL, 0,
       sysctl_try_reclaim_vnode, "A", "Try to reclaim a vnode by its pathname");
   SYSCTL_PROC(_debug, OID_AUTO, ftry_reclaim_vnode,
       CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_WR, NULL, 0,
       sysctl_ftry_reclaim_vnode, "I",
       "Try to reclaim a vnode by its file descriptor");
   
   /* Shift count for (uintptr_t)vp to initialize vp->v_hash. */
   static int vnsz2log;
   
   /*
    * Support for the bufobj clean & dirty pctrie.
    */
   static void *
   buf_trie_alloc(struct pctrie *ptree)
   {
           return (uma_zalloc_smr(buf_trie_zone, M_NOWAIT));
   }
   
   static void
   buf_trie_free(struct pctrie *ptree, void *node)
   {
           uma_zfree_smr(buf_trie_zone, node);
   }
   PCTRIE_DEFINE_SMR(BUF, buf, b_lblkno, buf_trie_alloc, buf_trie_free,
       buf_trie_smr);
   
   /*
    * Initialize the vnode management data structures.
    *
    * Reevaluate the following cap on the number of vnodes after the physical
    * memory size exceeds 512GB.  In the limit, as the physical memory size
    * grows, the ratio of the memory size in KB to vnodes approaches 64:1.
    */
   #ifndef MAXVNODES_MAX
   #define MAXVNODES_MAX   (512UL * 1024 * 1024 / 64)      /* 8M */
   #endif
   
   static MALLOC_DEFINE(M_VNODE_MARKER, "vnodemarker", "vnode marker");
   
   static struct vnode *
   vn_alloc_marker(struct mount *mp)
   {
           struct vnode *vp;
   
           vp = malloc(sizeof(struct vnode), M_VNODE_MARKER, M_WAITOK | M_ZERO);
           vp->v_type = VMARKER;
           vp->v_mount = mp;
   
           return (vp);
   }
   
   static void
   vn_free_marker(struct vnode *vp)
   {
   
           MPASS(vp->v_type == VMARKER);
           free(vp, M_VNODE_MARKER);
   }
   
   #ifdef KASAN
   static int
   vnode_ctor(void *mem, int size, void *arg __unused, int flags __unused)
   {
           kasan_mark(mem, size, roundup2(size, UMA_ALIGN_PTR + 1), 0);
           return (0);
   }
   
   static void
   vnode_dtor(void *mem, int size, void *arg __unused)
   {
           size_t end1, end2, off1, off2;
   
           _Static_assert(offsetof(struct vnode, v_vnodelist) <
               offsetof(struct vnode, v_dbatchcpu),
               "KASAN marks require updating");
   
           off1 = offsetof(struct vnode, v_vnodelist);
           off2 = offsetof(struct vnode, v_dbatchcpu);
           end1 = off1 + sizeof(((struct vnode *)NULL)->v_vnodelist);
           end2 = off2 + sizeof(((struct vnode *)NULL)->v_dbatchcpu);
   
           /*
            * Access to the v_vnodelist and v_dbatchcpu fields are permitted even
            * after the vnode has been freed.  Try to get some KASAN coverage by
            * marking everything except those two fields as invalid.  Because
            * KASAN's tracking is not byte-granular, any preceding fields sharing
            * the same 8-byte aligned word must also be marked valid.
            */
   
           /* Handle the area from the start until v_vnodelist... */
           off1 = rounddown2(off1, KASAN_SHADOW_SCALE);
           kasan_mark(mem, off1, off1, KASAN_UMA_FREED);
   
           /* ... then the area between v_vnodelist and v_dbatchcpu ... */
           off1 = roundup2(end1, KASAN_SHADOW_SCALE);
           off2 = rounddown2(off2, KASAN_SHADOW_SCALE);
           if (off2 > off1)
                   kasan_mark((void *)((char *)mem + off1), off2 - off1,
                       off2 - off1, KASAN_UMA_FREED);
   
           /* ... and finally the area from v_dbatchcpu to the end. */
           off2 = roundup2(end2, KASAN_SHADOW_SCALE);
           kasan_mark((void *)((char *)mem + off2), size - off2, size - off2,
               KASAN_UMA_FREED);
   }
   #endif /* KASAN */
   
   /*
    * Initialize a vnode as it first enters the zone.
    */
   static int
   vnode_init(void *mem, int size, int flags)
   {
           struct vnode *vp;
   
           vp = mem;
           bzero(vp, size);
           /*
            * Setup locks.
            */
           vp->v_vnlock = &vp->v_lock;
           mtx_init(&vp->v_interlock, "vnode interlock", NULL, MTX_DEF);
           /*
            * By default, don't allow shared locks unless filesystems opt-in.
            */
           lockinit(vp->v_vnlock, PVFS, "vnode", VLKTIMEOUT,
               LK_NOSHARE | LK_IS_VNODE);
           /*
            * Initialize bufobj.
            */
           bufobj_init(&vp->v_bufobj, vp);
           /*
            * Initialize namecache.
            */
           cache_vnode_init(vp);
           /*
            * Initialize rangelocks.
            */
           rangelock_init(&vp->v_rl);
   
           vp->v_dbatchcpu = NOCPU;
   
           /*
            * Check vhold_recycle_free for an explanation.
            */
           vp->v_holdcnt = VHOLD_NO_SMR;
           vp->v_type = VNON;
           mtx_lock(&vnode_list_mtx);
           TAILQ_INSERT_BEFORE(vnode_list_free_marker, vp, v_vnodelist);
           mtx_unlock(&vnode_list_mtx);
           return (0);
   }
   
   /*
    * Free a vnode when it is cleared from the zone.
    */
   static void
   vnode_fini(void *mem, int size)
   {
           struct vnode *vp;
           struct bufobj *bo;
   
           vp = mem;
           vdbatch_dequeue(vp);
           mtx_lock(&vnode_list_mtx);
           TAILQ_REMOVE(&vnode_list, vp, v_vnodelist);
           mtx_unlock(&vnode_list_mtx);
           rangelock_destroy(&vp->v_rl);
           lockdestroy(vp->v_vnlock);
           mtx_destroy(&vp->v_interlock);
           bo = &vp->v_bufobj;
           rw_destroy(BO_LOCKPTR(bo));
   
           kasan_mark(mem, size, size, 0);
   }
   
   /*
    * Provide the size of NFS nclnode and NFS fh for calculation of the
    * vnode memory consumption.  The size is specified directly to
    * eliminate dependency on NFS-private header.
    *
    * Other filesystems may use bigger or smaller (like UFS and ZFS)
    * private inode data, but the NFS-based estimation is ample enough.
    * Still, we care about differences in the size between 64- and 32-bit
    * platforms.
    *
    * Namecache structure size is heuristically
    * sizeof(struct namecache_ts) + CACHE_PATH_CUTOFF + 1.
    */
   #ifdef _LP64
   #define NFS_NCLNODE_SZ  (528 + 64)
   #define NC_SZ           148
   #else
   #define NFS_NCLNODE_SZ  (360 + 32)
   #define NC_SZ           92
   #endif
   
   static void
   vntblinit(void *dummy __unused)
   {
           struct vdbatch *vd;
           uma_ctor ctor;
           uma_dtor dtor;
           int cpu, physvnodes, virtvnodes;
           u_int i;
   
           /*
            * Desiredvnodes is a function of the physical memory size and the
            * kernel's heap size.  Generally speaking, it scales with the
            * physical memory size.  The ratio of desiredvnodes to the physical
            * memory size is 1:16 until desiredvnodes exceeds 98,304.
            * Thereafter, the
            * marginal ratio of desiredvnodes to the physical memory size is
            * 1:64.  However, desiredvnodes is limited by the kernel's heap
            * size.  The memory required by desiredvnodes vnodes and vm objects
            * must not exceed 1/10th of the kernel's heap size.
            */
           physvnodes = maxproc + pgtok(vm_cnt.v_page_count) / 64 +
               3 * min(98304 * 16, pgtok(vm_cnt.v_page_count)) / 64;
           virtvnodes = vm_kmem_size / (10 * (sizeof(struct vm_object) +
               sizeof(struct vnode) + NC_SZ * ncsizefactor + NFS_NCLNODE_SZ));
           desiredvnodes = min(physvnodes, virtvnodes);
           if (desiredvnodes > MAXVNODES_MAX) {
                   if (bootverbose)
                           printf("Reducing kern.maxvnodes %lu -> %lu\n",
                               desiredvnodes, MAXVNODES_MAX);
                   desiredvnodes = MAXVNODES_MAX;
           }
           wantfreevnodes = desiredvnodes / 4;
           mtx_init(&mntid_mtx, "mntid", NULL, MTX_DEF);
           TAILQ_INIT(&vnode_list);
           mtx_init(&vnode_list_mtx, "vnode_list", NULL, MTX_DEF);
           /*
            * The lock is taken to appease WITNESS.
            */
           mtx_lock(&vnode_list_mtx);
           vnlru_recalc();
           mtx_unlock(&vnode_list_mtx);
           vnode_list_free_marker = vn_alloc_marker(NULL);
           TAILQ_INSERT_HEAD(&vnode_list, vnode_list_free_marker, v_vnodelist);
           vnode_list_reclaim_marker = vn_alloc_marker(NULL);
           TAILQ_INSERT_HEAD(&vnode_list, vnode_list_reclaim_marker, v_vnodelist);
   
   #ifdef KASAN
           ctor = vnode_ctor;
           dtor = vnode_dtor;
   #else
           ctor = NULL;
           dtor = NULL;
   #endif
           vnode_zone = uma_zcreate("VNODE", sizeof(struct vnode), ctor, dtor,
               vnode_init, vnode_fini, UMA_ALIGN_PTR, UMA_ZONE_NOKASAN);
           uma_zone_set_smr(vnode_zone, vfs_smr);
   
           /*
            * Preallocate enough nodes to support one-per buf so that
            * we can not fail an insert.  reassignbuf() callers can not
            * tolerate the insertion failure.
            */
           buf_trie_zone = uma_zcreate("BUF TRIE", pctrie_node_size(),
               NULL, NULL, pctrie_zone_init, NULL, UMA_ALIGN_PTR, 
               UMA_ZONE_NOFREE | UMA_ZONE_SMR);
           buf_trie_smr = uma_zone_get_smr(buf_trie_zone);
           uma_prealloc(buf_trie_zone, nbuf);
   
           vnodes_created = counter_u64_alloc(M_WAITOK);
           recycles_count = counter_u64_alloc(M_WAITOK);
           recycles_free_count = counter_u64_alloc(M_WAITOK);
           deferred_inact = counter_u64_alloc(M_WAITOK);
   
           /*
            * Initialize the filesystem syncer.
            */
           syncer_workitem_pending = hashinit(syncer_maxdelay, M_VNODE,
               &syncer_mask);
           syncer_maxdelay = syncer_mask + 1;
           mtx_init(&sync_mtx, "Syncer mtx", NULL, MTX_DEF);
           cv_init(&sync_wakeup, "syncer");
           for (i = 1; i <= sizeof(struct vnode); i <<= 1)
                   vnsz2log++;
           vnsz2log--;
   
           CPU_FOREACH(cpu) {
                   vd = DPCPU_ID_PTR((cpu), vd);
                   bzero(vd, sizeof(*vd));
                   mtx_init(&vd->lock, "vdbatch", NULL, MTX_DEF);
           }
   }
   SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_FIRST, vntblinit, NULL);
   
   /*
    * Mark a mount point as busy. Used to synchronize access and to delay
    * unmounting. Eventually, mountlist_mtx is not released on failure.
    *
    * vfs_busy() is a custom lock, it can block the caller.
    * vfs_busy() only sleeps if the unmount is active on the mount point.
    * For a mountpoint mp, vfs_busy-enforced lock is before lock of any
    * vnode belonging to mp.
    *
    * Lookup uses vfs_busy() to traverse mount points.
    * root fs                      var fs
    * / vnode lock         A       / vnode lock (/var)             D
    * /var vnode lock      B       /log vnode lock(/var/log)       E
    * vfs_busy lock        C       vfs_busy lock                   F
    *
    * Within each file system, the lock order is C->A->B and F->D->E.
    *
    * When traversing across mounts, the system follows that lock order:
    *
    *        C->A->B
    *              |
    *              +->F->D->E
    *
    * The lookup() process for namei("/var") illustrates the process:
    *  VOP_LOOKUP() obtains B while A is held
    *  vfs_busy() obtains a shared lock on F while A and B are held
    *  vput() releases lock on B
    *  vput() releases lock on A
    *  VFS_ROOT() obtains lock on D while shared lock on F is held
    *  vfs_unbusy() releases shared lock on F
    *  vn_lock() obtains lock on deadfs vnode vp_crossmp instead of A.
    *    Attempt to lock A (instead of vp_crossmp) while D is held would
    *    violate the global order, causing deadlocks.
    *
    * dounmount() locks B while F is drained.
    */
   int
   vfs_busy(struct mount *mp, int flags)
   {
           struct mount_pcpu *mpcpu;
   
           MPASS((flags & ~MBF_MASK) == 0);
           CTR3(KTR_VFS, "%s: mp %p with flags %d", __func__, mp, flags);
   
           if (vfs_op_thread_enter(mp, mpcpu)) {
                   MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
                   MPASS((mp->mnt_kern_flag & MNTK_UNMOUNT) == 0);
                   MPASS((mp->mnt_kern_flag & MNTK_REFEXPIRE) == 0);
                   vfs_mp_count_add_pcpu(mpcpu, ref, 1);
                   vfs_mp_count_add_pcpu(mpcpu, lockref, 1);
                   vfs_op_thread_exit(mp, mpcpu);
                   if (flags & MBF_MNTLSTLOCK)
                           mtx_unlock(&mountlist_mtx);
                   return (0);
           }
   
           MNT_ILOCK(mp);
           vfs_assert_mount_counters(mp);
           MNT_REF(mp);
           /*
            * If mount point is currently being unmounted, sleep until the
            * mount point fate is decided.  If thread doing the unmounting fails,
            * it will clear MNTK_UNMOUNT flag before waking us up, indicating
            * that this mount point has survived the unmount attempt and vfs_busy
            * should retry.  Otherwise the unmounter thread will set MNTK_REFEXPIRE
            * flag in addition to MNTK_UNMOUNT, indicating that mount point is
            * about to be really destroyed.  vfs_busy needs to release its
            * reference on the mount point in this case and return with ENOENT,
            * telling the caller that mount mount it tried to busy is no longer
            * valid.
            */
           while (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                   if (flags & MBF_NOWAIT || mp->mnt_kern_flag & MNTK_REFEXPIRE) {
                           MNT_REL(mp);
                           MNT_IUNLOCK(mp);
                           CTR1(KTR_VFS, "%s: failed busying before sleeping",
                               __func__);
                           return (ENOENT);
                   }
                   if (flags & MBF_MNTLSTLOCK)
                           mtx_unlock(&mountlist_mtx);
                   mp->mnt_kern_flag |= MNTK_MWAIT;
                   msleep(mp, MNT_MTX(mp), PVFS | PDROP, "vfs_busy", 0);
                   if (flags & MBF_MNTLSTLOCK)
                           mtx_lock(&mountlist_mtx);
                   MNT_ILOCK(mp);
           }
           if (flags & MBF_MNTLSTLOCK)
                   mtx_unlock(&mountlist_mtx);
           mp->mnt_lockref++;
           MNT_IUNLOCK(mp);
           return (0);
   }
   
   /*
    * Free a busy filesystem.
    */
   void
   vfs_unbusy(struct mount *mp)
   {
           struct mount_pcpu *mpcpu;
           int c;
   
           CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
   
           if (vfs_op_thread_enter(mp, mpcpu)) {
                   MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
                   vfs_mp_count_sub_pcpu(mpcpu, lockref, 1);
                   vfs_mp_count_sub_pcpu(mpcpu, ref, 1);
                   vfs_op_thread_exit(mp, mpcpu);
                   return;
           }
   
           MNT_ILOCK(mp);
           vfs_assert_mount_counters(mp);
           MNT_REL(mp);
           c = --mp->mnt_lockref;
           if (mp->mnt_vfs_ops == 0) {
                   MPASS((mp->mnt_kern_flag & MNTK_DRAINING) == 0);
                   MNT_IUNLOCK(mp);
                   return;
           }
           if (c < 0)
                   vfs_dump_mount_counters(mp);
           if (c == 0 && (mp->mnt_kern_flag & MNTK_DRAINING) != 0) {
                   MPASS(mp->mnt_kern_flag & MNTK_UNMOUNT);
                   CTR1(KTR_VFS, "%s: waking up waiters", __func__);
                   mp->mnt_kern_flag &= ~MNTK_DRAINING;
                   wakeup(&mp->mnt_lockref);
           }
           MNT_IUNLOCK(mp);
   }
   
   /*
    * Lookup a mount point by filesystem identifier.
    */
   struct mount *
   vfs_getvfs(fsid_t *fsid)
   {
           struct mount *mp;
   
           CTR2(KTR_VFS, "%s: fsid %p", __func__, fsid);
           mtx_lock(&mountlist_mtx);
           TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                   if (fsidcmp(&mp->mnt_stat.f_fsid, fsid) == 0) {
                           vfs_ref(mp);
                           mtx_unlock(&mountlist_mtx);
                           return (mp);
                   }
           }
           mtx_unlock(&mountlist_mtx);
           CTR2(KTR_VFS, "%s: lookup failed for %p id", __func__, fsid);
           return ((struct mount *) 0);
   }
   
   /*
    * Lookup a mount point by filesystem identifier, busying it before
    * returning.
    *
    * To avoid congestion on mountlist_mtx, implement simple direct-mapped
    * cache for popular filesystem identifiers.  The cache is lockess, using
    * the fact that struct mount's are never freed.  In worst case we may
    * get pointer to unmounted or even different filesystem, so we have to
    * check what we got, and go slow way if so.
    */
   struct mount *
   vfs_busyfs(fsid_t *fsid)
   {
   #define FSID_CACHE_SIZE 256
           typedef struct mount * volatile vmp_t;
           static vmp_t cache[FSID_CACHE_SIZE];
           struct mount *mp;
           int error;
           uint32_t hash;
   
           CTR2(KTR_VFS, "%s: fsid %p", __func__, fsid);
           hash = fsid->val[0] ^ fsid->val[1];
           hash = (hash >> 16 ^ hash) & (FSID_CACHE_SIZE - 1);
           mp = cache[hash];
           if (mp == NULL || fsidcmp(&mp->mnt_stat.f_fsid, fsid) != 0)
                   goto slow;
           if (vfs_busy(mp, 0) != 0) {
                   cache[hash] = NULL;
                   goto slow;
           }
           if (fsidcmp(&mp->mnt_stat.f_fsid, fsid) == 0)
                   return (mp);
           else
               vfs_unbusy(mp);
   
   slow:
           mtx_lock(&mountlist_mtx);
           TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                   if (fsidcmp(&mp->mnt_stat.f_fsid, fsid) == 0) {
                           error = vfs_busy(mp, MBF_MNTLSTLOCK);
                           if (error) {
                                   cache[hash] = NULL;
                                   mtx_unlock(&mountlist_mtx);
                                   return (NULL);
                           }
                           cache[hash] = mp;
                           return (mp);
                   }
           }
           CTR2(KTR_VFS, "%s: lookup failed for %p id", __func__, fsid);
           mtx_unlock(&mountlist_mtx);
           return ((struct mount *) 0);
   }
   
   /*
    * Check if a user can access privileged mount options.
    */
   int
   vfs_suser(struct mount *mp, struct thread *td)
   {
           int error;
   
           if (jailed(td->td_ucred)) {
                   /*
                    * If the jail of the calling thread lacks permission for
                    * this type of file system, deny immediately.
                    */
                   if (!prison_allow(td->td_ucred, mp->mnt_vfc->vfc_prison_flag))
                           return (EPERM);
   
                   /*
                    * If the file system was mounted outside the jail of the
                    * calling thread, deny immediately.
                    */
                   if (prison_check(td->td_ucred, mp->mnt_cred) != 0)
                           return (EPERM);
           }
   
           /*
            * If file system supports delegated administration, we don't check
            * for the PRIV_VFS_MOUNT_OWNER privilege - it will be better verified
            * by the file system itself.
            * If this is not the user that did original mount, we check for
            * the PRIV_VFS_MOUNT_OWNER privilege.
            */
           if (!(mp->mnt_vfc->vfc_flags & VFCF_DELEGADMIN) &&
               mp->mnt_cred->cr_uid != td->td_ucred->cr_uid) {
                   if ((error = priv_check(td, PRIV_VFS_MOUNT_OWNER)) != 0)
                           return (error);
           }
           return (0);
   }
   
  /*
   * Get a new unique fsid.  Try to make its val[0] unique, since this value
   * will be used to create fake device numbers for stat().  Also try (but
   * not so hard) make its val[0] unique mod 2^16, since some emulators only
   * support 16-bit device numbers.  We end up with unique val[0]'s for the
   * first 2^16 calls and unique val[0]'s mod 2^16 for the first 2^8 calls.
   *
   * Keep in mind that several mounts may be running in parallel.  Starting
   * the search one past where the previous search terminated is both a
   * micro-optimization and a defense against returning the same fsid to
   * different mounts.
   */
  void
  vfs_getnewfsid(struct mount *mp)
  {
          static uint16_t mntid_base;
          struct mount *nmp;
          fsid_t tfsid;
          int mtype;
  
          CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
          mtx_lock(&mntid_mtx);
          mtype = mp->mnt_vfc->vfc_typenum;
          tfsid.val[1] = mtype;
          mtype = (mtype & 0xFF) << 24;
          for (;;) {
                  tfsid.val[0] = makedev(255,
                      mtype | ((mntid_base & 0xFF00) << 8) | (mntid_base & 0xFF));
                  mntid_base++;
                  if ((nmp = vfs_getvfs(&tfsid)) == NULL)
                          break;
                  vfs_rel(nmp);
          }
          mp->mnt_stat.f_fsid.val[0] = tfsid.val[0];
          mp->mnt_stat.f_fsid.val[1] = tfsid.val[1];
          mtx_unlock(&mntid_mtx);
  }
  
  /*
   * Knob to control the precision of file timestamps:
   *
   *   0 = seconds only; nanoseconds zeroed.
   *   1 = seconds and nanoseconds, accurate within 1/HZ.
   *   2 = seconds and nanoseconds, truncated to microseconds.
   * >=3 = seconds and nanoseconds, maximum precision.
   */
  enum { TSP_SEC, TSP_HZ, TSP_USEC, TSP_NSEC };
  
  static int timestamp_precision = TSP_USEC;
  SYSCTL_INT(_vfs, OID_AUTO, timestamp_precision, CTLFLAG_RW,
      &timestamp_precision, 0, "File timestamp precision (0: seconds, "
      "1: sec + ns accurate to 1/HZ, 2: sec + ns truncated to us, "
      "3+: sec + ns (max. precision))");
  
  /*
   * Get a current timestamp.
   */
  void
  vfs_timestamp(struct timespec *tsp)
  {
          struct timeval tv;
  
          switch (timestamp_precision) {
          case TSP_SEC:
                  tsp->tv_sec = time_second;
                  tsp->tv_nsec = 0;
                  break;
          case TSP_HZ:
                  getnanotime(tsp);
                  break;
          case TSP_USEC:
                  microtime(&tv);
                  TIMEVAL_TO_TIMESPEC(&tv, tsp);
                  break;
          case TSP_NSEC:
          default:
                  nanotime(tsp);
                  break;
          }
  }
  
  /*
   * Set vnode attributes to VNOVAL
   */
  void
  vattr_null(struct vattr *vap)
  {
  
          vap->va_type = VNON;
          vap->va_size = VNOVAL;
          vap->va_bytes = VNOVAL;
          vap->va_mode = VNOVAL;
          vap->va_nlink = VNOVAL;
          vap->va_uid = VNOVAL;
          vap->va_gid = VNOVAL;
          vap->va_fsid = VNOVAL;
          vap->va_fileid = VNOVAL;
          vap->va_blocksize = VNOVAL;
          vap->va_rdev = VNOVAL;
          vap->va_atime.tv_sec = VNOVAL;
          vap->va_atime.tv_nsec = VNOVAL;
          vap->va_mtime.tv_sec = VNOVAL;
          vap->va_mtime.tv_nsec = VNOVAL;
          vap->va_ctime.tv_sec = VNOVAL;
          vap->va_ctime.tv_nsec = VNOVAL;
          vap->va_birthtime.tv_sec = VNOVAL;
          vap->va_birthtime.tv_nsec = VNOVAL;
          vap->va_flags = VNOVAL;
          vap->va_gen = VNOVAL;
          vap->va_vaflags = 0;
  }
  
  /*
   * Try to reduce the total number of vnodes.
   *
   * This routine (and its user) are buggy in at least the following ways:
   * - all parameters were picked years ago when RAM sizes were significantly
   *   smaller
   * - it can pick vnodes based on pages used by the vm object, but filesystems
   *   like ZFS don't use it making the pick broken
   * - since ZFS has its own aging policy it gets partially combated by this one
   * - a dedicated method should be provided for filesystems to let them decide
   *   whether the vnode should be recycled
   *
   * This routine is called when we have too many vnodes.  It attempts
   * to free <count> vnodes and will potentially free vnodes that still
   * have VM backing store (VM backing store is typically the cause
   * of a vnode blowout so we want to do this).  Therefore, this operation
   * is not considered cheap.
   *
   * A number of conditions may prevent a vnode from being reclaimed.
   * the buffer cache may have references on the vnode, a directory
   * vnode may still have references due to the namei cache representing
   * underlying files, or the vnode may be in active use.   It is not
   * desirable to reuse such vnodes.  These conditions may cause the
   * number of vnodes to reach some minimum value regardless of what
   * you set kern.maxvnodes to.  Do not set kern.maxvnodes too low.
   *
   * @param reclaim_nc_src Only reclaim directories with outgoing namecache
   *                       entries if this argument is strue
   * @param trigger        Only reclaim vnodes with fewer than this many resident
   *                       pages.
   * @param target         How many vnodes to reclaim.
   * @return               The number of vnodes that were reclaimed.
   */
  static int
  vlrureclaim(bool reclaim_nc_src, int trigger, u_long target)
  {
          struct vnode *vp, *mvp;
          struct mount *mp;
          struct vm_object *object;
          u_long done;
          bool retried;
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
  
          retried = false;
          done = 0;
  
          mvp = vnode_list_reclaim_marker;
  restart:
          vp = mvp;
          while (done < target) {
                  vp = TAILQ_NEXT(vp, v_vnodelist);
                  if (__predict_false(vp == NULL))
                          break;
  
                  if (__predict_false(vp->v_type == VMARKER))
                          continue;
  
                  /*
                   * If it's been deconstructed already, it's still
                   * referenced, or it exceeds the trigger, skip it.
                   * Also skip free vnodes.  We are trying to make space
                   * to expand the free list, not reduce it.
                   */
                  if (vp->v_usecount > 0 || vp->v_holdcnt == 0 ||
                      (!reclaim_nc_src && !LIST_EMPTY(&vp->v_cache_src)))
                          goto next_iter;
  
                  if (vp->v_type == VBAD || vp->v_type == VNON)
                          goto next_iter;
  
                  object = atomic_load_ptr(&vp->v_object);
                  if (object == NULL || object->resident_page_count > trigger) {
                          goto next_iter;
                  }
  
                  /*
                   * Handle races against vnode allocation. Filesystems lock the
                   * vnode some time after it gets returned from getnewvnode,
                   * despite type and hold count being manipulated earlier.
                   * Resorting to checking v_mount restores guarantees present
                   * before the global list was reworked to contain all vnodes.
                   */
                  if (!VI_TRYLOCK(vp))
                          goto next_iter;
                  if (__predict_false(vp->v_type == VBAD || vp->v_type == VNON)) {
                          VI_UNLOCK(vp);
                          goto next_iter;
                  }
                  if (vp->v_mount == NULL) {
                          VI_UNLOCK(vp);
                          goto next_iter;
                  }
                  vholdl(vp);
                  VI_UNLOCK(vp);
                  TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                  TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
                  mtx_unlock(&vnode_list_mtx);
  
                  if (vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                          vdrop_recycle(vp);
                          goto next_iter_unlocked;
                  }
                  if (VOP_LOCK(vp, LK_EXCLUSIVE|LK_NOWAIT) != 0) {
                          vdrop_recycle(vp);
                          vn_finished_write(mp);
                          goto next_iter_unlocked;
                  }
  
                  VI_LOCK(vp);
                  if (vp->v_usecount > 0 ||
                      (!reclaim_nc_src && !LIST_EMPTY(&vp->v_cache_src)) ||
                      (vp->v_object != NULL && vp->v_object->handle == vp &&
                      vp->v_object->resident_page_count > trigger)) {
                          VOP_UNLOCK(vp);
                          vdropl_recycle(vp);
                          vn_finished_write(mp);
                          goto next_iter_unlocked;
                  }
                  counter_u64_add(recycles_count, 1);
                  vgonel(vp);
                  VOP_UNLOCK(vp);
                  vdropl_recycle(vp);
                  vn_finished_write(mp);
                  done++;
  next_iter_unlocked:
                  if (should_yield())
                          kern_yield(PRI_USER);
                  mtx_lock(&vnode_list_mtx);
                  goto restart;
  next_iter:
                  MPASS(vp->v_type != VMARKER);
                  if (!should_yield())
                          continue;
                  TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                  TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
                  mtx_unlock(&vnode_list_mtx);
                  kern_yield(PRI_USER);
                  mtx_lock(&vnode_list_mtx);
                  goto restart;
          }
          if (done == 0 && !retried) {
                  TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                  TAILQ_INSERT_HEAD(&vnode_list, mvp, v_vnodelist);
                  retried = true;
                  goto restart;
          }
          return (done);
  }
  
  static int max_vnlru_free = 10000; /* limit on vnode free requests per call */
  SYSCTL_INT(_debug, OID_AUTO, max_vnlru_free, CTLFLAG_RW, &max_vnlru_free,
      0,
      "limit on vnode free requests per call to the vnlru_free routine");
  
  /*
   * Attempt to reduce the free list by the requested amount.
   */
  static int
  vnlru_free_impl(int count, struct vfsops *mnt_op, struct vnode *mvp)
  {
          struct vnode *vp;
          struct mount *mp;
          int ocount;
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
          if (count > max_vnlru_free)
                  count = max_vnlru_free;
          ocount = count;
          vp = mvp;
          for (;;) {
                  if (count == 0) {
                          break;
                  }
                  vp = TAILQ_NEXT(vp, v_vnodelist);
                  if (__predict_false(vp == NULL)) {
                          TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                          TAILQ_INSERT_TAIL(&vnode_list, mvp, v_vnodelist);
                          break;
                  }
                  if (__predict_false(vp->v_type == VMARKER))
                          continue;
                  if (vp->v_holdcnt > 0)
                          continue;
                  /*
                   * Don't recycle if our vnode is from different type
                   * of mount point.  Note that mp is type-safe, the
                   * check does not reach unmapped address even if
                   * vnode is reclaimed.
                   */
                  if (mnt_op != NULL && (mp = vp->v_mount) != NULL &&
                      mp->mnt_op != mnt_op) {
                          continue;
                  }
                  if (__predict_false(vp->v_type == VBAD || vp->v_type == VNON)) {
                          continue;
                  }
                  if (!vhold_recycle_free(vp))
                          continue;
                  TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                  TAILQ_INSERT_AFTER(&vnode_list, vp, mvp, v_vnodelist);
                  mtx_unlock(&vnode_list_mtx);
                  /*
                   * FIXME: ignores the return value, meaning it may be nothing
                   * got recycled but it claims otherwise to the caller.
                   *
                   * Originally the value started being ignored in 2005 with
                   * 114a1006a8204aa156e1f9ad6476cdff89cada7f .
                   *
                   * Respecting the value can run into significant stalls if most
                   * vnodes belong to one file system and it has writes
                   * suspended.  In presence of many threads and millions of
                   * vnodes they keep contending on the vnode_list_mtx lock only
                   * to find vnodes they can't recycle.
                   *
                   * The solution would be to pre-check if the vnode is likely to
                   * be recycle-able, but it needs to happen with the
                   * vnode_list_mtx lock held. This runs into a problem where
                   * VOP_GETWRITEMOUNT (currently needed to find out about if
                   * writes are frozen) can take locks which LOR against it.
                   *
                   * Check nullfs for one example (null_getwritemount).
                   */
                  vtryrecycle(vp);
                  count--;
                  mtx_lock(&vnode_list_mtx);
                  vp = mvp;
          }
          return (ocount - count);
  }
  
  static int
  vnlru_free_locked(int count)
  {
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
          return (vnlru_free_impl(count, NULL, vnode_list_free_marker));
  }
  
  void
  vnlru_free_vfsops(int count, struct vfsops *mnt_op, struct vnode *mvp)
  {
  
          MPASS(mnt_op != NULL);
          MPASS(mvp != NULL);
          VNPASS(mvp->v_type == VMARKER, mvp);
          mtx_lock(&vnode_list_mtx);
          vnlru_free_impl(count, mnt_op, mvp);
          mtx_unlock(&vnode_list_mtx);
  }
  
  /*
   * Temporary binary compat, don't use. Call vnlru_free_vfsops instead.
   */
  void
  vnlru_free(int count, struct vfsops *mnt_op)
  {
          struct vnode *mvp;
  
          if (count == 0)
                  return;
          mtx_lock(&vnode_list_mtx);
          mvp = vnode_list_free_marker;
          if (vnlru_free_impl(count, mnt_op, mvp) == 0) {
                  /*
                   * It is possible the marker was moved over eligible vnodes by
                   * callers which filtered by different ops. If so, start from
                   * scratch.
                   */
                  if (vnlru_read_freevnodes() > 0) {
                          TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
                          TAILQ_INSERT_HEAD(&vnode_list, mvp, v_vnodelist);
                  }
                  vnlru_free_impl(count, mnt_op, mvp);
          }
          mtx_unlock(&vnode_list_mtx);
  }
  
  struct vnode *
  vnlru_alloc_marker(void)
  {
          struct vnode *mvp;
  
          mvp = vn_alloc_marker(NULL);
          mtx_lock(&vnode_list_mtx);
          TAILQ_INSERT_BEFORE(vnode_list_free_marker, mvp, v_vnodelist);
          mtx_unlock(&vnode_list_mtx);
          return (mvp);
  }
  
  void
  vnlru_free_marker(struct vnode *mvp)
  {
          mtx_lock(&vnode_list_mtx);
          TAILQ_REMOVE(&vnode_list, mvp, v_vnodelist);
          mtx_unlock(&vnode_list_mtx);
          vn_free_marker(mvp);
  }
  
  static void
  vnlru_recalc(void)
  {
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
          gapvnodes = imax(desiredvnodes - wantfreevnodes, 100);
          vhiwat = gapvnodes / 11; /* 9% -- just under the 10% in vlrureclaim() */
          vlowat = vhiwat / 2;
  }
  
  /*
   * Attempt to recycle vnodes in a context that is always safe to block.
   * Calling vlrurecycle() from the bowels of filesystem code has some
   * interesting deadlock problems.
   */
  static struct proc *vnlruproc;
  static int vnlruproc_sig;
  
  /*
   * The main freevnodes counter is only updated when threads requeue their vnode
   * batches. CPUs are conditionally walked to compute a more accurate total.
   *
   * Limit how much of a slop are we willing to tolerate. Note: the actual value
   * at any given moment can still exceed slop, but it should not be by significant
   * margin in practice.
   */
  #define VNLRU_FREEVNODES_SLOP 128
  
  static __inline void
  vfs_freevnodes_inc(void)
  {
          struct vdbatch *vd;
  
          critical_enter();
          vd = DPCPU_PTR(vd);
          vd->freevnodes++;
          critical_exit();
  }
  
  static __inline void
  vfs_freevnodes_dec(void)
  {
          struct vdbatch *vd;
  
          critical_enter();
          vd = DPCPU_PTR(vd);
          vd->freevnodes--;
          critical_exit();
  }
  
  static u_long
  vnlru_read_freevnodes(void)
  {
          struct vdbatch *vd;
          long slop;
          int cpu;
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
          if (freevnodes > freevnodes_old)
                  slop = freevnodes - freevnodes_old;
          else
                  slop = freevnodes_old - freevnodes;
          if (slop < VNLRU_FREEVNODES_SLOP)
                  return (freevnodes >= 0 ? freevnodes : 0);
          freevnodes_old = freevnodes;
          CPU_FOREACH(cpu) {
                  vd = DPCPU_ID_PTR((cpu), vd);
                  freevnodes_old += vd->freevnodes;
          }
          return (freevnodes_old >= 0 ? freevnodes_old : 0);
  }
  
  static bool
  vnlru_under(u_long rnumvnodes, u_long limit)
  {
          u_long rfreevnodes, space;
  
          if (__predict_false(rnumvnodes > desiredvnodes))
                  return (true);
  
          space = desiredvnodes - rnumvnodes;
          if (space < limit) {
                  rfreevnodes = vnlru_read_freevnodes();
                  if (rfreevnodes > wantfreevnodes)
                          space += rfreevnodes - wantfreevnodes;
          }
          return (space < limit);
  }
  
  static bool
  vnlru_under_unlocked(u_long rnumvnodes, u_long limit)
  {
          long rfreevnodes, space;
  
          if (__predict_false(rnumvnodes > desiredvnodes))
                  return (true);
  
          space = desiredvnodes - rnumvnodes;
          if (space < limit) {
                  rfreevnodes = atomic_load_long(&freevnodes);
                  if (rfreevnodes > wantfreevnodes)
                          space += rfreevnodes - wantfreevnodes;
          }
          return (space < limit);
  }
  
  static void
  vnlru_kick(void)
  {
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
          if (vnlruproc_sig == 0) {
                  vnlruproc_sig = 1;
                  wakeup(vnlruproc);
          }
  }
  
  static void
  vnlru_proc(void)
  {
          u_long rnumvnodes, rfreevnodes, target;
          unsigned long onumvnodes;
          int done, force, trigger, usevnodes;
          bool reclaim_nc_src, want_reread;
  
          EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, vnlruproc,
              SHUTDOWN_PRI_FIRST);
  
          force = 0;
          want_reread = false;
          for (;;) {
                  kproc_suspend_check(vnlruproc);
                  mtx_lock(&vnode_list_mtx);
                  rnumvnodes = atomic_load_long(&numvnodes);
  
                  if (want_reread) {
                          force = vnlru_under(numvnodes, vhiwat) ? 1 : 0;
                          want_reread = false;
                  }
  
                  /*
                   * If numvnodes is too large (due to desiredvnodes being
                   * adjusted using its sysctl, or emergency growth), first
                   * try to reduce it by discarding from the free list.
                   */
                  if (rnumvnodes > desiredvnodes) {
                          vnlru_free_locked(rnumvnodes - desiredvnodes);
                          rnumvnodes = atomic_load_long(&numvnodes);
                  }
                  /*
                   * Sleep if the vnode cache is in a good state.  This is
                   * when it is not over-full and has space for about a 4%
                   * or 9% expansion (by growing its size or inexcessively
                   * reducing its free list).  Otherwise, try to reclaim
                   * space for a 10% expansion.
                   */
                  if (vstir && force == 0) {
                          force = 1;
                          vstir = 0;
                  }
                  if (force == 0 && !vnlru_under(rnumvnodes, vlowat)) {
                          vnlruproc_sig = 0;
                          wakeup(&vnlruproc_sig);
                          msleep(vnlruproc, &vnode_list_mtx,
                              PVFS|PDROP, "vlruwt", hz);
                          continue;
                  }
                  rfreevnodes = vnlru_read_freevnodes();
  
                  onumvnodes = rnumvnodes;
                  /*
                   * Calculate parameters for recycling.  These are the same
                   * throughout the loop to give some semblance of fairness.
                   * The trigger point is to avoid recycling vnodes with lots
                   * of resident pages.  We aren't trying to free memory; we
                   * are trying to recycle or at least free vnodes.
                   */
                  if (rnumvnodes <= desiredvnodes)
                          usevnodes = rnumvnodes - rfreevnodes;
                  else
                          usevnodes = rnumvnodes;
                  if (usevnodes <= 0)
                          usevnodes = 1;
                  /*
                   * The trigger value is chosen to give a conservatively
                   * large value to ensure that it alone doesn't prevent
                   * making progress.  The value can easily be so large that
                   * it is effectively infinite in some congested and
                   * misconfigured cases, and this is necessary.  Normally
                   * it is about 8 to 100 (pages), which is quite large.
                   */
                  trigger = vm_cnt.v_page_count * 2 / usevnodes;
                  if (force < 2)
                          trigger = vsmalltrigger;
                  reclaim_nc_src = force >= 3;
                  target = rnumvnodes * (int64_t)gapvnodes / imax(desiredvnodes, 1);
                  target = target / 10 + 1;
                  done = vlrureclaim(reclaim_nc_src, trigger, target);
                  mtx_unlock(&vnode_list_mtx);
                  if (onumvnodes > desiredvnodes && numvnodes <= desiredvnodes)
                          uma_reclaim(UMA_RECLAIM_DRAIN);
                  if (done == 0) {
                          if (force == 0 || force == 1) {
                                  force = 2;
                                  continue;
                          }
                          if (force == 2) {
                                  force = 3;
                                  continue;
                          }
                          want_reread = true;
                          force = 0;
                          vnlru_nowhere++;
                          tsleep(vnlruproc, PPAUSE, "vlrup", hz * 3);
                  } else {
                          want_reread = true;
                          kern_yield(PRI_USER);
                  }
          }
  }
  
  static struct kproc_desc vnlru_kp = {
          "vnlru",
          vnlru_proc,
          &vnlruproc
  };
  SYSINIT(vnlru, SI_SUB_KTHREAD_UPDATE, SI_ORDER_FIRST, kproc_start,
      &vnlru_kp);
  
  /*
   * Routines having to do with the management of the vnode table.
   */
  
  /*
   * Try to recycle a freed vnode.  We abort if anyone picks up a reference
   * before we actually vgone().  This function must be called with the vnode
   * held to prevent the vnode from being returned to the free list midway
   * through vgone().
   */
  static int
  vtryrecycle(struct vnode *vp)
  {
          struct mount *vnmp;
  
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          VNASSERT(vp->v_holdcnt, vp,
              ("vtryrecycle: Recycling vp %p without a reference.", vp));
          /*
           * This vnode may found and locked via some other list, if so we
           * can't recycle it yet.
           */
          if (VOP_LOCK(vp, LK_EXCLUSIVE | LK_NOWAIT) != 0) {
                  CTR2(KTR_VFS,
                      "%s: impossible to recycle, vp %p lock is already held",
                      __func__, vp);
                  vdrop_recycle(vp);
                  return (EWOULDBLOCK);
          }
          /*
           * Don't recycle if its filesystem is being suspended.
           */
          if (vn_start_write(vp, &vnmp, V_NOWAIT) != 0) {
                  VOP_UNLOCK(vp);
                  CTR2(KTR_VFS,
                      "%s: impossible to recycle, cannot start the write for %p",
                      __func__, vp);
                  vdrop_recycle(vp);
                  return (EBUSY);
          }
          /*
           * If we got this far, we need to acquire the interlock and see if
           * anyone picked up this vnode from another list.  If not, we will
           * mark it with DOOMED via vgonel() so that anyone who does find it
           * will skip over it.
           */
          VI_LOCK(vp);
          if (vp->v_usecount) {
                  VOP_UNLOCK(vp);
                  vdropl_recycle(vp);
                  vn_finished_write(vnmp);
                  CTR2(KTR_VFS,
                      "%s: impossible to recycle, %p is already referenced",
                      __func__, vp);
                  return (EBUSY);
          }
          if (!VN_IS_DOOMED(vp)) {
                  counter_u64_add(recycles_free_count, 1);
                  vgonel(vp);
          }
          VOP_UNLOCK(vp);
          vdropl_recycle(vp);
          vn_finished_write(vnmp);
          return (0);
  }
  
  /*
   * Allocate a new vnode.
   *
   * The operation never returns an error. Returning an error was disabled
   * in r145385 (dated 2005) with the following comment:
   *
   * XXX Not all VFS_VGET/ffs_vget callers check returns.
   *
   * Given the age of this commit (almost 15 years at the time of writing this
   * comment) restoring the ability to fail requires a significant audit of
   * all codepaths.
   *
   * The routine can try to free a vnode or stall for up to 1 second waiting for
   * vnlru to clear things up, but ultimately always performs a M_WAITOK allocation.
   */
  static u_long vn_alloc_cyclecount;
  
  static struct vnode * __noinline
  vn_alloc_hard(struct mount *mp)
  {
          u_long rnumvnodes, rfreevnodes;
  
          mtx_lock(&vnode_list_mtx);
          rnumvnodes = atomic_load_long(&numvnodes);
          if (rnumvnodes + 1 < desiredvnodes) {
                  vn_alloc_cyclecount = 0;
                  goto alloc;
          }
          rfreevnodes = vnlru_read_freevnodes();
          if (vn_alloc_cyclecount++ >= rfreevnodes) {
                  vn_alloc_cyclecount = 0;
                  vstir = 1;
          }
          /*
           * Grow the vnode cache if it will not be above its target max
           * after growing.  Otherwise, if the free list is nonempty, try
           * to reclaim 1 item from it before growing the cache (possibly
           * above its target max if the reclamation failed or is delayed).
           * Otherwise, wait for some space.  In all cases, schedule
           * vnlru_proc() if we are getting short of space.  The watermarks
           * should be chosen so that we never wait or even reclaim from
           * the free list to below its target minimum.
           */
          if (vnlru_free_locked(1) > 0)
                  goto alloc;
          if (mp == NULL || (mp->mnt_kern_flag & MNTK_SUSPEND) == 0) {
                  /*
                   * Wait for space for a new vnode.
                   */
                  vnlru_kick();
                  msleep(&vnlruproc_sig, &vnode_list_mtx, PVFS, "vlruwk", hz);
                  if (atomic_load_long(&numvnodes) + 1 > desiredvnodes &&
                      vnlru_read_freevnodes() > 1)
                          vnlru_free_locked(1);
          }
  alloc:
          rnumvnodes = atomic_fetchadd_long(&numvnodes, 1) + 1;
          if (vnlru_under(rnumvnodes, vlowat))
                  vnlru_kick();
          mtx_unlock(&vnode_list_mtx);
          return (uma_zalloc_smr(vnode_zone, M_WAITOK));
  }
  
  static struct vnode *
  vn_alloc(struct mount *mp)
  {
          u_long rnumvnodes;
  
          if (__predict_false(vn_alloc_cyclecount != 0))
                  return (vn_alloc_hard(mp));
          rnumvnodes = atomic_fetchadd_long(&numvnodes, 1) + 1;
          if (__predict_false(vnlru_under_unlocked(rnumvnodes, vlowat))) {
                  atomic_subtract_long(&numvnodes, 1);
                  return (vn_alloc_hard(mp));
          }
  
          return (uma_zalloc_smr(vnode_zone, M_WAITOK));
  }
  
  static void
  vn_free(struct vnode *vp)
  {
  
          atomic_subtract_long(&numvnodes, 1);
          uma_zfree_smr(vnode_zone, vp);
  }
  
  /*
   * Return the next vnode from the free list.
   */
  int
  getnewvnode(const char *tag, struct mount *mp, struct vop_vector *vops,
      struct vnode **vpp)
  {
          struct vnode *vp;
          struct thread *td;
          struct lock_object *lo;
  
          CTR3(KTR_VFS, "%s: mp %p with tag %s", __func__, mp, tag);
  
          KASSERT(vops->registered,
              ("%s: not registered vector op %p\n", __func__, vops));
  
          td = curthread;
          if (td->td_vp_reserved != NULL) {
                  vp = td->td_vp_reserved;
                  td->td_vp_reserved = NULL;
          } else {
                  vp = vn_alloc(mp);
          }
          counter_u64_add(vnodes_created, 1);
          /*
           * Locks are given the generic name "vnode" when created.
           * Follow the historic practice of using the filesystem
           * name when they allocated, e.g., "zfs", "ufs", "nfs, etc.
           *
           * Locks live in a witness group keyed on their name. Thus,
           * when a lock is renamed, it must also move from the witness
           * group of its old name to the witness group of its new name.
           *
           * The change only needs to be made when the vnode moves
           * from one filesystem type to another. We ensure that each
           * filesystem use a single static name pointer for its tag so
           * that we can compare pointers rather than doing a strcmp().
           */
          lo = &vp->v_vnlock->lock_object;
  #ifdef WITNESS
          if (lo->lo_name != tag) {
  #endif
                  lo->lo_name = tag;
  #ifdef WITNESS
                  WITNESS_DESTROY(lo);
                  WITNESS_INIT(lo, tag);
          }
  #endif
          /*
           * By default, don't allow shared locks unless filesystems opt-in.
           */
          vp->v_vnlock->lock_object.lo_flags |= LK_NOSHARE;
          /*
           * Finalize various vnode identity bits.
           */
          KASSERT(vp->v_object == NULL, ("stale v_object %p", vp));
          KASSERT(vp->v_lockf == NULL, ("stale v_lockf %p", vp));
          KASSERT(vp->v_pollinfo == NULL, ("stale v_pollinfo %p", vp));
          vp->v_type = VNON;
          vp->v_op = vops;
          vp->v_irflag = 0;
          v_init_counters(vp);
          vn_seqc_init(vp);
          vp->v_bufobj.bo_ops = &buf_ops_bio;
  #ifdef DIAGNOSTIC
          if (mp == NULL && vops != &dead_vnodeops)
                  printf("NULL mp in getnewvnode(9), tag %s\n", tag);
  #endif
  #ifdef MAC
          mac_vnode_init(vp);
          if (mp != NULL && (mp->mnt_flag & MNT_MULTILABEL) == 0)
                  mac_vnode_associate_singlelabel(mp, vp);
  #endif
          if (mp != NULL) {
                  vp->v_bufobj.bo_bsize = mp->mnt_stat.f_iosize;
                  if ((mp->mnt_kern_flag & MNTK_NOKNOTE) != 0)
                          vp->v_vflag |= VV_NOKNOTE;
          }
  
          /*
           * For the filesystems which do not use vfs_hash_insert(),
           * still initialize v_hash to have vfs_hash_index() useful.
           * E.g., nullfs uses vfs_hash_index() on the lower vnode for
           * its own hashing.
           */
          vp->v_hash = (uintptr_t)vp >> vnsz2log;
  
          *vpp = vp;
          return (0);
  }
  
  void
  getnewvnode_reserve(void)
  {
          struct thread *td;
  
          td = curthread;
          MPASS(td->td_vp_reserved == NULL);
          td->td_vp_reserved = vn_alloc(NULL);
  }
  
  void
  getnewvnode_drop_reserve(void)
  {
          struct thread *td;
  
          td = curthread;
          if (td->td_vp_reserved != NULL) {
                  vn_free(td->td_vp_reserved);
                  td->td_vp_reserved = NULL;
          }
  }
  
  static void __noinline
  freevnode(struct vnode *vp)
  {
          struct bufobj *bo;
  
          /*
           * The vnode has been marked for destruction, so free it.
           *
           * The vnode will be returned to the zone where it will
           * normally remain until it is needed for another vnode. We
           * need to cleanup (or verify that the cleanup has already
           * been done) any residual data left from its current use
           * so as not to contaminate the freshly allocated vnode.
           */
          CTR2(KTR_VFS, "%s: destroying the vnode %p", __func__, vp);
          /*
           * Paired with vgone.
           */
          vn_seqc_write_end_free(vp);
  
          bo = &vp->v_bufobj;
          VNASSERT(vp->v_data == NULL, vp, ("cleaned vnode isn't"));
          VNPASS(vp->v_holdcnt == VHOLD_NO_SMR, vp);
          VNASSERT(vp->v_usecount == 0, vp, ("Non-zero use count"));
          VNASSERT(vp->v_writecount == 0, vp, ("Non-zero write count"));
          VNASSERT(bo->bo_numoutput == 0, vp, ("Clean vnode has pending I/O's"));
          VNASSERT(bo->bo_clean.bv_cnt == 0, vp, ("cleanbufcnt not 0"));
          VNASSERT(pctrie_is_empty(&bo->bo_clean.bv_root), vp,
              ("clean blk trie not empty"));
          VNASSERT(bo->bo_dirty.bv_cnt == 0, vp, ("dirtybufcnt not 0"));
          VNASSERT(pctrie_is_empty(&bo->bo_dirty.bv_root), vp,
              ("dirty blk trie not empty"));
          VNASSERT(TAILQ_EMPTY(&vp->v_cache_dst), vp, ("vp has namecache dst"));
          VNASSERT(LIST_EMPTY(&vp->v_cache_src), vp, ("vp has namecache src"));
          VNASSERT(vp->v_cache_dd == NULL, vp, ("vp has namecache for .."));
          VNASSERT(TAILQ_EMPTY(&vp->v_rl.rl_waiters), vp,
              ("Dangling rangelock waiters"));
          VNASSERT((vp->v_iflag & (VI_DOINGINACT | VI_OWEINACT)) == 0, vp,
              ("Leaked inactivation"));
          VI_UNLOCK(vp);
  #ifdef MAC
          mac_vnode_destroy(vp);
  #endif
          if (vp->v_pollinfo != NULL) {
                  vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                  destroy_vpollinfo(vp->v_pollinfo);
                  VOP_UNLOCK(vp);
                  vp->v_pollinfo = NULL;
          }
          vp->v_mountedhere = NULL;
          vp->v_unpcb = NULL;
          vp->v_rdev = NULL;
          vp->v_fifoinfo = NULL;
          vp->v_lasta = vp->v_clen = vp->v_cstart = vp->v_lastw = 0;
          vp->v_iflag = 0;
          vp->v_vflag = 0;
          bo->bo_flag = 0;
          vn_free(vp);
  }
  
  /*
   * Delete from old mount point vnode list, if on one.
   */
  static void
  delmntque(struct vnode *vp)
  {
          struct mount *mp;
  
          VNPASS((vp->v_mflag & VMP_LAZYLIST) == 0, vp);
  
          mp = vp->v_mount;
          if (mp == NULL)
                  return;
          MNT_ILOCK(mp);
          VI_LOCK(vp);
          vp->v_mount = NULL;
          VI_UNLOCK(vp);
          VNASSERT(mp->mnt_nvnodelistsize > 0, vp,
                  ("bad mount point vnode list size"));
          TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
          mp->mnt_nvnodelistsize--;
          MNT_REL(mp);
          MNT_IUNLOCK(mp);
  }
  
  static void
  insmntque_stddtr(struct vnode *vp, void *dtr_arg)
  {
  
          vp->v_data = NULL;
          vp->v_op = &dead_vnodeops;
          vgone(vp);
          vput(vp);
  }
  
  /*
   * Insert into list of vnodes for the new mount point, if available.
   */
  int
  insmntque1(struct vnode *vp, struct mount *mp,
          void (*dtr)(struct vnode *, void *), void *dtr_arg)
  {
  
          KASSERT(vp->v_mount == NULL,
                  ("insmntque: vnode already on per mount vnode list"));
          VNASSERT(mp != NULL, vp, ("Don't call insmntque(foo, NULL)"));
          ASSERT_VOP_ELOCKED(vp, "insmntque: non-locked vp");
  
          /*
           * We acquire the vnode interlock early to ensure that the
           * vnode cannot be recycled by another process releasing a
           * holdcnt on it before we get it on both the vnode list
           * and the active vnode list. The mount mutex protects only
           * manipulation of the vnode list and the vnode freelist
           * mutex protects only manipulation of the active vnode list.
           * Hence the need to hold the vnode interlock throughout.
           */
          MNT_ILOCK(mp);
          VI_LOCK(vp);
          if (((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 &&
              ((mp->mnt_kern_flag & MNTK_UNMOUNTF) != 0 ||
              mp->mnt_nvnodelistsize == 0)) &&
              (vp->v_vflag & VV_FORCEINSMQ) == 0) {
                  VI_UNLOCK(vp);
                  MNT_IUNLOCK(mp);
                  if (dtr != NULL)
                          dtr(vp, dtr_arg);
                  return (EBUSY);
          }
          vp->v_mount = mp;
          MNT_REF(mp);
          TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
          VNASSERT(mp->mnt_nvnodelistsize >= 0, vp,
                  ("neg mount point vnode list size"));
          mp->mnt_nvnodelistsize++;
          VI_UNLOCK(vp);
          MNT_IUNLOCK(mp);
          return (0);
  }
  
  int
  insmntque(struct vnode *vp, struct mount *mp)
  {
  
          return (insmntque1(vp, mp, insmntque_stddtr, NULL));
  }
  
  /*
   * Flush out and invalidate all buffers associated with a bufobj
   * Called with the underlying object locked.
   */
  int
  bufobj_invalbuf(struct bufobj *bo, int flags, int slpflag, int slptimeo)
  {
          int error;
  
          BO_LOCK(bo);
          if (flags & V_SAVE) {
                  error = bufobj_wwait(bo, slpflag, slptimeo);
                  if (error) {
                          BO_UNLOCK(bo);
                          return (error);
                  }
                  if (bo->bo_dirty.bv_cnt > 0) {
                          BO_UNLOCK(bo);
                          do {
                                  error = BO_SYNC(bo, MNT_WAIT);
                          } while (error == ERELOOKUP);
                          if (error != 0)
                                  return (error);
                          BO_LOCK(bo);
                          if (bo->bo_numoutput > 0 || bo->bo_dirty.bv_cnt > 0) {
                                  BO_UNLOCK(bo);
                                  return (EBUSY);
                          }
                  }
          }
          /*
           * If you alter this loop please notice that interlock is dropped and
           * reacquired in flushbuflist.  Special care is needed to ensure that
           * no race conditions occur from this.
           */
          do {
                  error = flushbuflist(&bo->bo_clean,
                      flags, bo, slpflag, slptimeo);
                  if (error == 0 && !(flags & V_CLEANONLY))
                          error = flushbuflist(&bo->bo_dirty,
                              flags, bo, slpflag, slptimeo);
                  if (error != 0 && error != EAGAIN) {
                          BO_UNLOCK(bo);
                          return (error);
                  }
          } while (error != 0);
  
          /*
           * Wait for I/O to complete.  XXX needs cleaning up.  The vnode can
           * have write I/O in-progress but if there is a VM object then the
           * VM object can also have read-I/O in-progress.
           */
          do {
                  bufobj_wwait(bo, 0, 0);
                  if ((flags & V_VMIO) == 0 && bo->bo_object != NULL) {
                          BO_UNLOCK(bo);
                          vm_object_pip_wait_unlocked(bo->bo_object, "bovlbx");
                          BO_LOCK(bo);
                  }
          } while (bo->bo_numoutput > 0);
          BO_UNLOCK(bo);
  
          /*
           * Destroy the copy in the VM cache, too.
           */
          if (bo->bo_object != NULL &&
              (flags & (V_ALT | V_NORMAL | V_CLEANONLY | V_VMIO)) == 0) {
                  VM_OBJECT_WLOCK(bo->bo_object);
                  vm_object_page_remove(bo->bo_object, 0, 0, (flags & V_SAVE) ?
                      OBJPR_CLEANONLY : 0);
                  VM_OBJECT_WUNLOCK(bo->bo_object);
          }
  
  #ifdef INVARIANTS
          BO_LOCK(bo);
          if ((flags & (V_ALT | V_NORMAL | V_CLEANONLY | V_VMIO |
              V_ALLOWCLEAN)) == 0 && (bo->bo_dirty.bv_cnt > 0 ||
              bo->bo_clean.bv_cnt > 0))
                  panic("vinvalbuf: flush failed");
          if ((flags & (V_ALT | V_NORMAL | V_CLEANONLY | V_VMIO)) == 0 &&
              bo->bo_dirty.bv_cnt > 0)
                  panic("vinvalbuf: flush dirty failed");
          BO_UNLOCK(bo);
  #endif
          return (0);
  }
  
  /*
   * Flush out and invalidate all buffers associated with a vnode.
   * Called with the underlying object locked.
   */
  int
  vinvalbuf(struct vnode *vp, int flags, int slpflag, int slptimeo)
  {
  
          CTR3(KTR_VFS, "%s: vp %p with flags %d", __func__, vp, flags);
          ASSERT_VOP_LOCKED(vp, "vinvalbuf");
          if (vp->v_object != NULL && vp->v_object->handle != vp)
                  return (0);
          return (bufobj_invalbuf(&vp->v_bufobj, flags, slpflag, slptimeo));
  }
  
  /*
   * Flush out buffers on the specified list.
   *
   */
  static int
  flushbuflist(struct bufv *bufv, int flags, struct bufobj *bo, int slpflag,
      int slptimeo)
  {
          struct buf *bp, *nbp;
          int retval, error;
          daddr_t lblkno;
          b_xflags_t xflags;
  
          ASSERT_BO_WLOCKED(bo);
  
          retval = 0;
          TAILQ_FOREACH_SAFE(bp, &bufv->bv_hd, b_bobufs, nbp) {
                  /*
                   * If we are flushing both V_NORMAL and V_ALT buffers then
                   * do not skip any buffers. If we are flushing only V_NORMAL
                   * buffers then skip buffers marked as BX_ALTDATA. If we are
                   * flushing only V_ALT buffers then skip buffers not marked
                   * as BX_ALTDATA.
                   */
                  if (((flags & (V_NORMAL | V_ALT)) != (V_NORMAL | V_ALT)) &&
                     (((flags & V_NORMAL) && (bp->b_xflags & BX_ALTDATA) != 0) ||
                      ((flags & V_ALT) && (bp->b_xflags & BX_ALTDATA) == 0))) {
                          continue;
                  }
                  if (nbp != NULL) {
                          lblkno = nbp->b_lblkno;
                          xflags = nbp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN);
                  }
                  retval = EAGAIN;
                  error = BUF_TIMELOCK(bp,
                      LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK, BO_LOCKPTR(bo),
                      "flushbuf", slpflag, slptimeo);
                  if (error) {
                          BO_LOCK(bo);
                          return (error != ENOLCK ? error : EAGAIN);
                  }
                  KASSERT(bp->b_bufobj == bo,
                      ("bp %p wrong b_bufobj %p should be %p",
                      bp, bp->b_bufobj, bo));
                  /*
                   * XXX Since there are no node locks for NFS, I
                   * believe there is a slight chance that a delayed
                   * write will occur while sleeping just above, so
                   * check for it.
                   */
                  if (((bp->b_flags & (B_DELWRI | B_INVAL)) == B_DELWRI) &&
                      (flags & V_SAVE)) {
                          bremfree(bp);
                          bp->b_flags |= B_ASYNC;
                          bwrite(bp);
                          BO_LOCK(bo);
                          return (EAGAIN);        /* XXX: why not loop ? */
                  }
                  bremfree(bp);
                  bp->b_flags |= (B_INVAL | B_RELBUF);
                  bp->b_flags &= ~B_ASYNC;
                  brelse(bp);
                  BO_LOCK(bo);
                  if (nbp == NULL)
                          break;
                  nbp = gbincore(bo, lblkno);
                  if (nbp == NULL || (nbp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN))
                      != xflags)
                          break;                  /* nbp invalid */
          }
          return (retval);
  }
  
  int
  bnoreuselist(struct bufv *bufv, struct bufobj *bo, daddr_t startn, daddr_t endn)
  {
          struct buf *bp;
          int error;
          daddr_t lblkno;
  
          ASSERT_BO_LOCKED(bo);
  
          for (lblkno = startn;;) {
  again:
                  bp = BUF_PCTRIE_LOOKUP_GE(&bufv->bv_root, lblkno);
                  if (bp == NULL || bp->b_lblkno >= endn ||
                      bp->b_lblkno < startn)
                          break;
                  error = BUF_TIMELOCK(bp, LK_EXCLUSIVE | LK_SLEEPFAIL |
                      LK_INTERLOCK, BO_LOCKPTR(bo), "brlsfl", 0, 0);
                  if (error != 0) {
                          BO_RLOCK(bo);
                          if (error == ENOLCK)
                                  goto again;
                          return (error);
                  }
                  KASSERT(bp->b_bufobj == bo,
                      ("bp %p wrong b_bufobj %p should be %p",
                      bp, bp->b_bufobj, bo));
                  lblkno = bp->b_lblkno + 1;
                  if ((bp->b_flags & B_MANAGED) == 0)
                          bremfree(bp);
                  bp->b_flags |= B_RELBUF;
                  /*
                   * In the VMIO case, use the B_NOREUSE flag to hint that the
                   * pages backing each buffer in the range are unlikely to be
                   * reused.  Dirty buffers will have the hint applied once
                   * they've been written.
                   */
                  if ((bp->b_flags & B_VMIO) != 0)
                          bp->b_flags |= B_NOREUSE;
                  brelse(bp);
                  BO_RLOCK(bo);
          }
          return (0);
  }
  
  /*
   * Truncate a file's buffer and pages to a specified length.  This
   * is in lieu of the old vinvalbuf mechanism, which performed unneeded
   * sync activity.
   */
  int
  vtruncbuf(struct vnode *vp, off_t length, int blksize)
  {
          struct buf *bp, *nbp;
          struct bufobj *bo;
          daddr_t startlbn;
  
          CTR4(KTR_VFS, "%s: vp %p with block %d:%ju", __func__,
              vp, blksize, (uintmax_t)length);
  
          /*
           * Round up to the *next* lbn.
           */
          startlbn = howmany(length, blksize);
  
          ASSERT_VOP_LOCKED(vp, "vtruncbuf");
  
          bo = &vp->v_bufobj;
  restart_unlocked:
          BO_LOCK(bo);
  
          while (v_inval_buf_range_locked(vp, bo, startlbn, INT64_MAX) == EAGAIN)
                  ;
  
          if (length > 0) {
  restartsync:
                  TAILQ_FOREACH_SAFE(bp, &bo->bo_dirty.bv_hd, b_bobufs, nbp) {
                          if (bp->b_lblkno > 0)
                                  continue;
                          /*
                           * Since we hold the vnode lock this should only
                           * fail if we're racing with the buf daemon.
                           */
                          if (BUF_LOCK(bp,
                              LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                              BO_LOCKPTR(bo)) == ENOLCK)
                                  goto restart_unlocked;
  
                          VNASSERT((bp->b_flags & B_DELWRI), vp,
                              ("buf(%p) on dirty queue without DELWRI", bp));
  
                          bremfree(bp);
                          bawrite(bp);
                          BO_LOCK(bo);
                          goto restartsync;
                  }
          }
  
          bufobj_wwait(bo, 0, 0);
          BO_UNLOCK(bo);
          vnode_pager_setsize(vp, length);
  
          return (0);
  }
  
  /*
   * Invalidate the cached pages of a file's buffer within the range of block
   * numbers [startlbn, endlbn).
   */
  void
  v_inval_buf_range(struct vnode *vp, daddr_t startlbn, daddr_t endlbn,
      int blksize)
  {
          struct bufobj *bo;
          off_t start, end;
  
          ASSERT_VOP_LOCKED(vp, "v_inval_buf_range");
  
          start = blksize * startlbn;
          end = blksize * endlbn;
  
          bo = &vp->v_bufobj;
          BO_LOCK(bo);
          MPASS(blksize == bo->bo_bsize);
  
          while (v_inval_buf_range_locked(vp, bo, startlbn, endlbn) == EAGAIN)
                  ;
  
          BO_UNLOCK(bo);
          vn_pages_remove(vp, OFF_TO_IDX(start), OFF_TO_IDX(end + PAGE_SIZE - 1));
  }
  
  static int
  v_inval_buf_range_locked(struct vnode *vp, struct bufobj *bo,
      daddr_t startlbn, daddr_t endlbn)
  {
          struct buf *bp, *nbp;
          bool anyfreed;
  
          ASSERT_VOP_LOCKED(vp, "v_inval_buf_range_locked");
          ASSERT_BO_LOCKED(bo);
  
          do {
                  anyfreed = false;
                  TAILQ_FOREACH_SAFE(bp, &bo->bo_clean.bv_hd, b_bobufs, nbp) {
                          if (bp->b_lblkno < startlbn || bp->b_lblkno >= endlbn)
                                  continue;
                          if (BUF_LOCK(bp,
                              LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                              BO_LOCKPTR(bo)) == ENOLCK) {
                                  BO_LOCK(bo);
                                  return (EAGAIN);
                          }
  
                          bremfree(bp);
                          bp->b_flags |= B_INVAL | B_RELBUF;
                          bp->b_flags &= ~B_ASYNC;
                          brelse(bp);
                          anyfreed = true;
  
                          BO_LOCK(bo);
                          if (nbp != NULL &&
                              (((nbp->b_xflags & BX_VNCLEAN) == 0) ||
                              nbp->b_vp != vp ||
                              (nbp->b_flags & B_DELWRI) != 0))
                                  return (EAGAIN);
                  }
  
                  TAILQ_FOREACH_SAFE(bp, &bo->bo_dirty.bv_hd, b_bobufs, nbp) {
                          if (bp->b_lblkno < startlbn || bp->b_lblkno >= endlbn)
                                  continue;
                          if (BUF_LOCK(bp,
                              LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                              BO_LOCKPTR(bo)) == ENOLCK) {
                                  BO_LOCK(bo);
                                  return (EAGAIN);
                          }
                          bremfree(bp);
                          bp->b_flags |= B_INVAL | B_RELBUF;
                          bp->b_flags &= ~B_ASYNC;
                          brelse(bp);
                          anyfreed = true;
  
                          BO_LOCK(bo);
                          if (nbp != NULL &&
                              (((nbp->b_xflags & BX_VNDIRTY) == 0) ||
                              (nbp->b_vp != vp) ||
                              (nbp->b_flags & B_DELWRI) == 0))
                                  return (EAGAIN);
                  }
          } while (anyfreed);
          return (0);
  }
  
  static void
  buf_vlist_remove(struct buf *bp)
  {
          struct bufv *bv;
          b_xflags_t flags;
  
          flags = bp->b_xflags;
  
          KASSERT(bp->b_bufobj != NULL, ("No b_bufobj %p", bp));
          ASSERT_BO_WLOCKED(bp->b_bufobj);
          KASSERT((flags & (BX_VNDIRTY | BX_VNCLEAN)) != 0 &&
              (flags & (BX_VNDIRTY | BX_VNCLEAN)) != (BX_VNDIRTY | BX_VNCLEAN),
              ("%s: buffer %p has invalid queue state", __func__, bp));
  
          if ((flags & BX_VNDIRTY) != 0)
                  bv = &bp->b_bufobj->bo_dirty;
          else
                  bv = &bp->b_bufobj->bo_clean;
          BUF_PCTRIE_REMOVE(&bv->bv_root, bp->b_lblkno);
          TAILQ_REMOVE(&bv->bv_hd, bp, b_bobufs);
          bv->bv_cnt--;
          bp->b_xflags &= ~(BX_VNDIRTY | BX_VNCLEAN);
  }
  
  /*
   * Add the buffer to the sorted clean or dirty block list.
   *
   * NOTE: xflags is passed as a constant, optimizing this inline function!
   */
  static void
  buf_vlist_add(struct buf *bp, struct bufobj *bo, b_xflags_t xflags)
  {
          struct bufv *bv;
          struct buf *n;
          int error;
  
          ASSERT_BO_WLOCKED(bo);
          KASSERT((bo->bo_flag & BO_NOBUFS) == 0,
              ("buf_vlist_add: bo %p does not allow bufs", bo));
          KASSERT((xflags & BX_VNDIRTY) == 0 || (bo->bo_flag & BO_DEAD) == 0,
              ("dead bo %p", bo));
          KASSERT((bp->b_xflags & (BX_VNDIRTY|BX_VNCLEAN)) == 0,
              ("buf_vlist_add: Buf %p has existing xflags %d", bp, bp->b_xflags));
          bp->b_xflags |= xflags;
          if (xflags & BX_VNDIRTY)
                  bv = &bo->bo_dirty;
          else
                  bv = &bo->bo_clean;
  
          /*
           * Keep the list ordered.  Optimize empty list insertion.  Assume
           * we tend to grow at the tail so lookup_le should usually be cheaper
           * than _ge. 
           */
          if (bv->bv_cnt == 0 ||
              bp->b_lblkno > TAILQ_LAST(&bv->bv_hd, buflists)->b_lblkno)
                  TAILQ_INSERT_TAIL(&bv->bv_hd, bp, b_bobufs);
          else if ((n = BUF_PCTRIE_LOOKUP_LE(&bv->bv_root, bp->b_lblkno)) == NULL)
                  TAILQ_INSERT_HEAD(&bv->bv_hd, bp, b_bobufs);
          else
                  TAILQ_INSERT_AFTER(&bv->bv_hd, n, bp, b_bobufs);
          error = BUF_PCTRIE_INSERT(&bv->bv_root, bp);
          if (error)
                  panic("buf_vlist_add:  Preallocated nodes insufficient.");
          bv->bv_cnt++;
  }
  
  /*
   * Look up a buffer using the buffer tries.
   */
  struct buf *
  gbincore(struct bufobj *bo, daddr_t lblkno)
  {
          struct buf *bp;
  
          ASSERT_BO_LOCKED(bo);
          bp = BUF_PCTRIE_LOOKUP(&bo->bo_clean.bv_root, lblkno);
          if (bp != NULL)
                  return (bp);
          return (BUF_PCTRIE_LOOKUP(&bo->bo_dirty.bv_root, lblkno));
  }
  
  /*
   * Look up a buf using the buffer tries, without the bufobj lock.  This relies
   * on SMR for safe lookup, and bufs being in a no-free zone to provide type
   * stability of the result.  Like other lockless lookups, the found buf may
   * already be invalid by the time this function returns.
   */
  struct buf *
  gbincore_unlocked(struct bufobj *bo, daddr_t lblkno)
  {
          struct buf *bp;
  
          ASSERT_BO_UNLOCKED(bo);
          bp = BUF_PCTRIE_LOOKUP_UNLOCKED(&bo->bo_clean.bv_root, lblkno);
          if (bp != NULL)
                  return (bp);
          return (BUF_PCTRIE_LOOKUP_UNLOCKED(&bo->bo_dirty.bv_root, lblkno));
  }
  
  /*
   * Associate a buffer with a vnode.
   */
  void
  bgetvp(struct vnode *vp, struct buf *bp)
  {
          struct bufobj *bo;
  
          bo = &vp->v_bufobj;
          ASSERT_BO_WLOCKED(bo);
          VNASSERT(bp->b_vp == NULL, bp->b_vp, ("bgetvp: not free"));
  
          CTR3(KTR_BUF, "bgetvp(%p) vp %p flags %X", bp, vp, bp->b_flags);
          VNASSERT((bp->b_xflags & (BX_VNDIRTY|BX_VNCLEAN)) == 0, vp,
              ("bgetvp: bp already attached! %p", bp));
  
          vhold(vp);
          bp->b_vp = vp;
          bp->b_bufobj = bo;
          /*
           * Insert onto list for new vnode.
           */
          buf_vlist_add(bp, bo, BX_VNCLEAN);
  }
  
  /*
   * Disassociate a buffer from a vnode.
   */
  void
  brelvp(struct buf *bp)
  {
          struct bufobj *bo;
          struct vnode *vp;
  
          CTR3(KTR_BUF, "brelvp(%p) vp %p flags %X", bp, bp->b_vp, bp->b_flags);
          KASSERT(bp->b_vp != NULL, ("brelvp: NULL"));
  
          /*
           * Delete from old vnode list, if on one.
           */
          vp = bp->b_vp;          /* XXX */
          bo = bp->b_bufobj;
          BO_LOCK(bo);
          buf_vlist_remove(bp);
          if ((bo->bo_flag & BO_ONWORKLST) && bo->bo_dirty.bv_cnt == 0) {
                  bo->bo_flag &= ~BO_ONWORKLST;
                  mtx_lock(&sync_mtx);
                  LIST_REMOVE(bo, bo_synclist);
                  syncer_worklist_len--;
                  mtx_unlock(&sync_mtx);
          }
          bp->b_vp = NULL;
          bp->b_bufobj = NULL;
          BO_UNLOCK(bo);
          vdrop(vp);
  }
  
  /*
   * Add an item to the syncer work queue.
   */
  static void
  vn_syncer_add_to_worklist(struct bufobj *bo, int delay)
  {
          int slot;
  
          ASSERT_BO_WLOCKED(bo);
  
          mtx_lock(&sync_mtx);
          if (bo->bo_flag & BO_ONWORKLST)
                  LIST_REMOVE(bo, bo_synclist);
          else {
                  bo->bo_flag |= BO_ONWORKLST;
                  syncer_worklist_len++;
          }
  
          if (delay > syncer_maxdelay - 2)
                  delay = syncer_maxdelay - 2;
          slot = (syncer_delayno + delay) & syncer_mask;
  
          LIST_INSERT_HEAD(&syncer_workitem_pending[slot], bo, bo_synclist);
          mtx_unlock(&sync_mtx);
  }
  
  static int
  sysctl_vfs_worklist_len(SYSCTL_HANDLER_ARGS)
  {
          int error, len;
  
          mtx_lock(&sync_mtx);
          len = syncer_worklist_len - sync_vnode_count;
          mtx_unlock(&sync_mtx);
          error = SYSCTL_OUT(req, &len, sizeof(len));
          return (error);
  }
  
  SYSCTL_PROC(_vfs, OID_AUTO, worklist_len,
      CTLTYPE_INT | CTLFLAG_MPSAFE| CTLFLAG_RD, NULL, 0,
      sysctl_vfs_worklist_len, "I", "Syncer thread worklist length");
  
  static struct proc *updateproc;
  static void sched_sync(void);
  static struct kproc_desc up_kp = {
          "syncer",
          sched_sync,
          &updateproc
  };
  SYSINIT(syncer, SI_SUB_KTHREAD_UPDATE, SI_ORDER_FIRST, kproc_start, &up_kp);
  
  static int
  sync_vnode(struct synclist *slp, struct bufobj **bo, struct thread *td)
  {
          struct vnode *vp;
          struct mount *mp;
  
          *bo = LIST_FIRST(slp);
          if (*bo == NULL)
                  return (0);
          vp = bo2vnode(*bo);
          if (VOP_ISLOCKED(vp) != 0 || VI_TRYLOCK(vp) == 0)
                  return (1);
          /*
           * We use vhold in case the vnode does not
           * successfully sync.  vhold prevents the vnode from
           * going away when we unlock the sync_mtx so that
           * we can acquire the vnode interlock.
           */
          vholdl(vp);
          mtx_unlock(&sync_mtx);
          VI_UNLOCK(vp);
          if (vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                  vdrop(vp);
                  mtx_lock(&sync_mtx);
                  return (*bo == LIST_FIRST(slp));
          }
          vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
          (void) VOP_FSYNC(vp, MNT_LAZY, td);
          VOP_UNLOCK(vp);
          vn_finished_write(mp);
          BO_LOCK(*bo);
          if (((*bo)->bo_flag & BO_ONWORKLST) != 0) {
                  /*
                   * Put us back on the worklist.  The worklist
                   * routine will remove us from our current
                   * position and then add us back in at a later
                   * position.
                   */
                  vn_syncer_add_to_worklist(*bo, syncdelay);
          }
          BO_UNLOCK(*bo);
          vdrop(vp);
          mtx_lock(&sync_mtx);
          return (0);
  }
  
  static int first_printf = 1;
  
  /*
   * System filesystem synchronizer daemon.
   */
  static void
  sched_sync(void)
  {
          struct synclist *next, *slp;
          struct bufobj *bo;
          long starttime;
          struct thread *td = curthread;
          int last_work_seen;
          int net_worklist_len;
          int syncer_final_iter;
          int error;
  
          last_work_seen = 0;
          syncer_final_iter = 0;
          syncer_state = SYNCER_RUNNING;
          starttime = time_uptime;
          td->td_pflags |= TDP_NORUNNINGBUF;
  
          EVENTHANDLER_REGISTER(shutdown_pre_sync, syncer_shutdown, td->td_proc,
              SHUTDOWN_PRI_LAST);
  
          mtx_lock(&sync_mtx);
          for (;;) {
                  if (syncer_state == SYNCER_FINAL_DELAY &&
                      syncer_final_iter == 0) {
                          mtx_unlock(&sync_mtx);
                          kproc_suspend_check(td->td_proc);
                          mtx_lock(&sync_mtx);
                  }
                  net_worklist_len = syncer_worklist_len - sync_vnode_count;
                  if (syncer_state != SYNCER_RUNNING &&
                      starttime != time_uptime) {
                          if (first_printf) {
                                  printf("\nSyncing disks, vnodes remaining... ");
                                  first_printf = 0;
                          }
                          printf("%d ", net_worklist_len);
                  }
                  starttime = time_uptime;
  
                  /*
                   * Push files whose dirty time has expired.  Be careful
                   * of interrupt race on slp queue.
                   *
                   * Skip over empty worklist slots when shutting down.
                   */
                  do {
                          slp = &syncer_workitem_pending[syncer_delayno];
                          syncer_delayno += 1;
                          if (syncer_delayno == syncer_maxdelay)
                                  syncer_delayno = 0;
                          next = &syncer_workitem_pending[syncer_delayno];
                          /*
                           * If the worklist has wrapped since the
                           * it was emptied of all but syncer vnodes,
                           * switch to the FINAL_DELAY state and run
                           * for one more second.
                           */
                          if (syncer_state == SYNCER_SHUTTING_DOWN &&
                              net_worklist_len == 0 &&
                              last_work_seen == syncer_delayno) {
                                  syncer_state = SYNCER_FINAL_DELAY;
                                  syncer_final_iter = SYNCER_SHUTDOWN_SPEEDUP;
                          }
                  } while (syncer_state != SYNCER_RUNNING && LIST_EMPTY(slp) &&
                      syncer_worklist_len > 0);
  
                  /*
                   * Keep track of the last time there was anything
                   * on the worklist other than syncer vnodes.
                   * Return to the SHUTTING_DOWN state if any
                   * new work appears.
                   */
                  if (net_worklist_len > 0 || syncer_state == SYNCER_RUNNING)
                          last_work_seen = syncer_delayno;
                  if (net_worklist_len > 0 && syncer_state == SYNCER_FINAL_DELAY)
                          syncer_state = SYNCER_SHUTTING_DOWN;
                  while (!LIST_EMPTY(slp)) {
                          error = sync_vnode(slp, &bo, td);
                          if (error == 1) {
                                  LIST_REMOVE(bo, bo_synclist);
                                  LIST_INSERT_HEAD(next, bo, bo_synclist);
                                  continue;
                          }
  
                          if (first_printf == 0) {
                                  /*
                                   * Drop the sync mutex, because some watchdog
                                   * drivers need to sleep while patting
                                   */
                                  mtx_unlock(&sync_mtx);
                                  wdog_kern_pat(WD_LASTVAL);
                                  mtx_lock(&sync_mtx);
                          }
                  }
                  if (syncer_state == SYNCER_FINAL_DELAY && syncer_final_iter > 0)
                          syncer_final_iter--;
                  /*
                   * The variable rushjob allows the kernel to speed up the
                   * processing of the filesystem syncer process. A rushjob
                   * value of N tells the filesystem syncer to process the next
                   * N seconds worth of work on its queue ASAP. Currently rushjob
                   * is used by the soft update code to speed up the filesystem
                   * syncer process when the incore state is getting so far
                   * ahead of the disk that the kernel memory pool is being
                   * threatened with exhaustion.
                   */
                  if (rushjob > 0) {
                          rushjob -= 1;
                          continue;
                  }
                  /*
                   * Just sleep for a short period of time between
                   * iterations when shutting down to allow some I/O
                   * to happen.
                   *
                   * If it has taken us less than a second to process the
                   * current work, then wait. Otherwise start right over
                   * again. We can still lose time if any single round
                   * takes more than two seconds, but it does not really
                   * matter as we are just trying to generally pace the
                   * filesystem activity.
                   */
                  if (syncer_state != SYNCER_RUNNING ||
                      time_uptime == starttime) {
                          thread_lock(td);
                          sched_prio(td, PPAUSE);
                          thread_unlock(td);
                  }
                  if (syncer_state != SYNCER_RUNNING)
                          cv_timedwait(&sync_wakeup, &sync_mtx,
                              hz / SYNCER_SHUTDOWN_SPEEDUP);
                  else if (time_uptime == starttime)
                          cv_timedwait(&sync_wakeup, &sync_mtx, hz);
          }
  }
  
  /*
   * Request the syncer daemon to speed up its work.
   * We never push it to speed up more than half of its
   * normal turn time, otherwise it could take over the cpu.
   */
  int
  speedup_syncer(void)
  {
          int ret = 0;
  
          mtx_lock(&sync_mtx);
          if (rushjob < syncdelay / 2) {
                  rushjob += 1;
                  stat_rush_requests += 1;
                  ret = 1;
          }
          mtx_unlock(&sync_mtx);
          cv_broadcast(&sync_wakeup);
          return (ret);
  }
  
  /*
   * Tell the syncer to speed up its work and run though its work
   * list several times, then tell it to shut down.
   */
  static void
  syncer_shutdown(void *arg, int howto)
  {
  
          if (howto & RB_NOSYNC)
                  return;
          mtx_lock(&sync_mtx);
          syncer_state = SYNCER_SHUTTING_DOWN;
          rushjob = 0;
          mtx_unlock(&sync_mtx);
          cv_broadcast(&sync_wakeup);
          kproc_shutdown(arg, howto);
  }
  
  void
  syncer_suspend(void)
  {
  
          syncer_shutdown(updateproc, 0);
  }
  
  void
  syncer_resume(void)
  {
  
          mtx_lock(&sync_mtx);
          first_printf = 1;
          syncer_state = SYNCER_RUNNING;
          mtx_unlock(&sync_mtx);
          cv_broadcast(&sync_wakeup);
          kproc_resume(updateproc);
  }
  
  /*
   * Move the buffer between the clean and dirty lists of its vnode.
   */
  void
  reassignbuf(struct buf *bp)
  {
          struct vnode *vp;
          struct bufobj *bo;
          int delay;
  #ifdef INVARIANTS
          struct bufv *bv;
  #endif
  
          vp = bp->b_vp;
          bo = bp->b_bufobj;
  
          KASSERT((bp->b_flags & B_PAGING) == 0,
              ("%s: cannot reassign paging buffer %p", __func__, bp));
  
          CTR3(KTR_BUF, "reassignbuf(%p) vp %p flags %X",
              bp, bp->b_vp, bp->b_flags);
  
          BO_LOCK(bo);
          buf_vlist_remove(bp);
  
          /*
           * If dirty, put on list of dirty buffers; otherwise insert onto list
           * of clean buffers.
           */
          if (bp->b_flags & B_DELWRI) {
                  if ((bo->bo_flag & BO_ONWORKLST) == 0) {
                          switch (vp->v_type) {
                          case VDIR:
                                  delay = dirdelay;
                                  break;
                          case VCHR:
                                  delay = metadelay;
                                  break;
                          default:
                                  delay = filedelay;
                          }
                          vn_syncer_add_to_worklist(bo, delay);
                  }
                  buf_vlist_add(bp, bo, BX_VNDIRTY);
          } else {
                  buf_vlist_add(bp, bo, BX_VNCLEAN);
  
                  if ((bo->bo_flag & BO_ONWORKLST) && bo->bo_dirty.bv_cnt == 0) {
                          mtx_lock(&sync_mtx);
                          LIST_REMOVE(bo, bo_synclist);
                          syncer_worklist_len--;
                          mtx_unlock(&sync_mtx);
                          bo->bo_flag &= ~BO_ONWORKLST;
                  }
          }
  #ifdef INVARIANTS
          bv = &bo->bo_clean;
          bp = TAILQ_FIRST(&bv->bv_hd);
          KASSERT(bp == NULL || bp->b_bufobj == bo,
              ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
          bp = TAILQ_LAST(&bv->bv_hd, buflists);
          KASSERT(bp == NULL || bp->b_bufobj == bo,
              ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
          bv = &bo->bo_dirty;
          bp = TAILQ_FIRST(&bv->bv_hd);
          KASSERT(bp == NULL || bp->b_bufobj == bo,
              ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
          bp = TAILQ_LAST(&bv->bv_hd, buflists);
          KASSERT(bp == NULL || bp->b_bufobj == bo,
              ("bp %p wrong b_bufobj %p should be %p", bp, bp->b_bufobj, bo));
  #endif
          BO_UNLOCK(bo);
  }
  
  static void
  v_init_counters(struct vnode *vp)
  {
  
          VNASSERT(vp->v_type == VNON && vp->v_data == NULL && vp->v_iflag == 0,
              vp, ("%s called for an initialized vnode", __FUNCTION__));
          ASSERT_VI_UNLOCKED(vp, __FUNCTION__);
  
          refcount_init(&vp->v_holdcnt, 1);
          refcount_init(&vp->v_usecount, 1);
  }
  
  /*
   * Grab a particular vnode from the free list, increment its
   * reference count and lock it.  VIRF_DOOMED is set if the vnode
   * is being destroyed.  Only callers who specify LK_RETRY will
   * see doomed vnodes.  If inactive processing was delayed in
   * vput try to do it here.
   *
   * usecount is manipulated using atomics without holding any locks.
   *
   * holdcnt can be manipulated using atomics without holding any locks,
   * except when transitioning 1<->0, in which case the interlock is held.
   *
   * Consumers which don't guarantee liveness of the vnode can use SMR to
   * try to get a reference. Note this operation can fail since the vnode
   * may be awaiting getting freed by the time they get to it.
   */
  enum vgetstate
  vget_prep_smr(struct vnode *vp)
  {
          enum vgetstate vs;
  
          VFS_SMR_ASSERT_ENTERED();
  
          if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
                  vs = VGET_USECOUNT;
          } else {
                  if (vhold_smr(vp))
                          vs = VGET_HOLDCNT;
                  else
                          vs = VGET_NONE;
          }
          return (vs);
  }
  
  enum vgetstate
  vget_prep(struct vnode *vp)
  {
          enum vgetstate vs;
  
          if (refcount_acquire_if_not_zero(&vp->v_usecount)) {
                  vs = VGET_USECOUNT;
          } else {
                  vhold(vp);
                  vs = VGET_HOLDCNT;
          }
          return (vs);
  }
  
  void
  vget_abort(struct vnode *vp, enum vgetstate vs)
  {
  
          switch (vs) {
          case VGET_USECOUNT:
                  vrele(vp);
                  break;
          case VGET_HOLDCNT:
                  vdrop(vp);
                  break;
          default:
                  __assert_unreachable();
          }
  }
  
  int
  vget(struct vnode *vp, int flags)
  {
          enum vgetstate vs;
  
          vs = vget_prep(vp);
          return (vget_finish(vp, flags, vs));
  }
  
  int
  vget_finish(struct vnode *vp, int flags, enum vgetstate vs)
  {
          int error;
  
          if ((flags & LK_INTERLOCK) != 0)
                  ASSERT_VI_LOCKED(vp, __func__);
          else
                  ASSERT_VI_UNLOCKED(vp, __func__);
          VNPASS(vs == VGET_HOLDCNT || vs == VGET_USECOUNT, vp);
          VNPASS(vp->v_holdcnt > 0, vp);
          VNPASS(vs == VGET_HOLDCNT || vp->v_usecount > 0, vp);
  
          error = vn_lock(vp, flags);
          if (__predict_false(error != 0)) {
                  vget_abort(vp, vs);
                  CTR2(KTR_VFS, "%s: impossible to lock vnode %p", __func__,
                      vp);
                  return (error);
          }
  
          vget_finish_ref(vp, vs);
          return (0);
  }
  
  void
  vget_finish_ref(struct vnode *vp, enum vgetstate vs)
  {
          int old;
  
          VNPASS(vs == VGET_HOLDCNT || vs == VGET_USECOUNT, vp);
          VNPASS(vp->v_holdcnt > 0, vp);
          VNPASS(vs == VGET_HOLDCNT || vp->v_usecount > 0, vp);
  
          if (vs == VGET_USECOUNT)
                  return;
  
          /*
           * We hold the vnode. If the usecount is 0 it will be utilized to keep
           * the vnode around. Otherwise someone else lended their hold count and
           * we have to drop ours.
           */
          old = atomic_fetchadd_int(&vp->v_usecount, 1);
          VNASSERT(old >= 0, vp, ("%s: wrong use count %d", __func__, old));
          if (old != 0) {
  #ifdef INVARIANTS
                  old = atomic_fetchadd_int(&vp->v_holdcnt, -1);
                  VNASSERT(old > 1, vp, ("%s: wrong hold count %d", __func__, old));
  #else
                  refcount_release(&vp->v_holdcnt);
  #endif
          }
  }
  
  void
  vref(struct vnode *vp)
  {
          enum vgetstate vs;
  
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          vs = vget_prep(vp);
          vget_finish_ref(vp, vs);
  }
  
  void
  vrefact(struct vnode *vp)
  {
  
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
  #ifdef INVARIANTS
          int old = atomic_fetchadd_int(&vp->v_usecount, 1);
          VNASSERT(old > 0, vp, ("%s: wrong use count %d", __func__, old));
  #else
          refcount_acquire(&vp->v_usecount);
  #endif
  }
  
  void
  vlazy(struct vnode *vp)
  {
          struct mount *mp;
  
          VNASSERT(vp->v_holdcnt > 0, vp, ("%s: vnode not held", __func__));
  
          if ((vp->v_mflag & VMP_LAZYLIST) != 0)
                  return;
          /*
           * We may get here for inactive routines after the vnode got doomed.
           */
          if (VN_IS_DOOMED(vp))
                  return;
          mp = vp->v_mount;
          mtx_lock(&mp->mnt_listmtx);
          if ((vp->v_mflag & VMP_LAZYLIST) == 0) {
                  vp->v_mflag |= VMP_LAZYLIST;
                  TAILQ_INSERT_TAIL(&mp->mnt_lazyvnodelist, vp, v_lazylist);
                  mp->mnt_lazyvnodelistsize++;
          }
          mtx_unlock(&mp->mnt_listmtx);
  }
  
  static void
  vunlazy(struct vnode *vp)
  {
          struct mount *mp;
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNPASS(!VN_IS_DOOMED(vp), vp);
  
          mp = vp->v_mount;
          mtx_lock(&mp->mnt_listmtx);
          VNPASS(vp->v_mflag & VMP_LAZYLIST, vp);
          /*
           * Don't remove the vnode from the lazy list if another thread
           * has increased the hold count. It may have re-enqueued the
           * vnode to the lazy list and is now responsible for its
           * removal.
           */
          if (vp->v_holdcnt == 0) {
                  vp->v_mflag &= ~VMP_LAZYLIST;
                  TAILQ_REMOVE(&mp->mnt_lazyvnodelist, vp, v_lazylist);
                  mp->mnt_lazyvnodelistsize--;
          }
          mtx_unlock(&mp->mnt_listmtx);
  }
  
  /*
   * This routine is only meant to be called from vgonel prior to dooming
   * the vnode.
   */
  static void
  vunlazy_gone(struct vnode *vp)
  {
          struct mount *mp;
  
          ASSERT_VOP_ELOCKED(vp, __func__);
          ASSERT_VI_LOCKED(vp, __func__);
          VNPASS(!VN_IS_DOOMED(vp), vp);
  
          if (vp->v_mflag & VMP_LAZYLIST) {
                  mp = vp->v_mount;
                  mtx_lock(&mp->mnt_listmtx);
                  VNPASS(vp->v_mflag & VMP_LAZYLIST, vp);
                  vp->v_mflag &= ~VMP_LAZYLIST;
                  TAILQ_REMOVE(&mp->mnt_lazyvnodelist, vp, v_lazylist);
                  mp->mnt_lazyvnodelistsize--;
                  mtx_unlock(&mp->mnt_listmtx);
          }
  }
  
  static void
  vdefer_inactive(struct vnode *vp)
  {
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNASSERT(vp->v_holdcnt > 0, vp,
              ("%s: vnode without hold count", __func__));
          if (VN_IS_DOOMED(vp)) {
                  vdropl(vp);
                  return;
          }
          if (vp->v_iflag & VI_DEFINACT) {
                  VNASSERT(vp->v_holdcnt > 1, vp, ("lost hold count"));
                  vdropl(vp);
                  return;
          }
          if (vp->v_usecount > 0) {
                  vp->v_iflag &= ~VI_OWEINACT;
                  vdropl(vp);
                  return;
          }
          vlazy(vp);
          vp->v_iflag |= VI_DEFINACT;
          VI_UNLOCK(vp);
          counter_u64_add(deferred_inact, 1);
  }
  
  static void
  vdefer_inactive_unlocked(struct vnode *vp)
  {
  
          VI_LOCK(vp);
          if ((vp->v_iflag & VI_OWEINACT) == 0) {
                  vdropl(vp);
                  return;
          }
          vdefer_inactive(vp);
  }
  
  enum vput_op { VRELE, VPUT, VUNREF };
  
  /*
   * Handle ->v_usecount transitioning to 0.
   *
   * By releasing the last usecount we take ownership of the hold count which
   * provides liveness of the vnode, meaning we have to vdrop.
   *
   * For all vnodes we may need to perform inactive processing. It requires an
   * exclusive lock on the vnode, while it is legal to call here with only a
   * shared lock (or no locks). If locking the vnode in an expected manner fails,
   * inactive processing gets deferred to the syncer.
   *
   * XXX Some filesystems pass in an exclusively locked vnode and strongly depend
   * on the lock being held all the way until VOP_INACTIVE. This in particular
   * happens with UFS which adds half-constructed vnodes to the hash, where they
   * can be found by other code.
   */
  static void
  vput_final(struct vnode *vp, enum vput_op func)
  {
          int error;
          bool want_unlock;
  
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          VNPASS(vp->v_holdcnt > 0, vp);
  
          VI_LOCK(vp);
  
          /*
           * By the time we got here someone else might have transitioned
           * the count back to > 0.
           */
          if (vp->v_usecount > 0)
                  goto out;
  
          /*
           * If the vnode is doomed vgone already performed inactive processing
           * (if needed).
           */
          if (VN_IS_DOOMED(vp))
                  goto out;
  
          if (__predict_true(VOP_NEED_INACTIVE(vp) == 0))
                  goto out;
  
          if (vp->v_iflag & VI_DOINGINACT)
                  goto out;
  
          /*
           * Locking operations here will drop the interlock and possibly the
           * vnode lock, opening a window where the vnode can get doomed all the
           * while ->v_usecount is 0. Set VI_OWEINACT to let vgone know to
           * perform inactive.
           */
          vp->v_iflag |= VI_OWEINACT;
          want_unlock = false;
          error = 0;
          switch (func) {
          case VRELE:
                  switch (VOP_ISLOCKED(vp)) {
                  case LK_EXCLUSIVE:
                          break;
                  case LK_EXCLOTHER:
                  case 0:
                          want_unlock = true;
                          error = vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK);
                          VI_LOCK(vp);
                          break;
                  default:
                          /*
                           * The lock has at least one sharer, but we have no way
                           * to conclude whether this is us. Play it safe and
                           * defer processing.
                           */
                          error = EAGAIN;
                          break;
                  }
                  break;
          case VPUT:
                  want_unlock = true;
                  if (VOP_ISLOCKED(vp) != LK_EXCLUSIVE) {
                          error = VOP_LOCK(vp, LK_UPGRADE | LK_INTERLOCK |
                              LK_NOWAIT);
                          VI_LOCK(vp);
                  }
                  break;
          case VUNREF:
                  if (VOP_ISLOCKED(vp) != LK_EXCLUSIVE) {
                          error = VOP_LOCK(vp, LK_TRYUPGRADE | LK_INTERLOCK);
                          VI_LOCK(vp);
                  }
                  break;
          }
          if (error == 0) {
                  if (func == VUNREF) {
                          VNASSERT((vp->v_vflag & VV_UNREF) == 0, vp,
                              ("recursive vunref"));
                          vp->v_vflag |= VV_UNREF;
                  }
                  for (;;) {
                          error = vinactive(vp);
                          if (want_unlock)
                                  VOP_UNLOCK(vp);
                          if (error != ERELOOKUP || !want_unlock)
                                  break;
                          VOP_LOCK(vp, LK_EXCLUSIVE);
                  }
                  if (func == VUNREF)
                          vp->v_vflag &= ~VV_UNREF;
                  vdropl(vp);
          } else {
                  vdefer_inactive(vp);
          }
          return;
  out:
          if (func == VPUT)
                  VOP_UNLOCK(vp);
          vdropl(vp);
  }
  
  /*
   * Decrement ->v_usecount for a vnode.
   *
   * Releasing the last use count requires additional processing, see vput_final
   * above for details.
   *
   * Comment above each variant denotes lock state on entry and exit.
   */
  
  /*
   * in: any
   * out: same as passed in
   */
  void
  vrele(struct vnode *vp)
  {
  
          ASSERT_VI_UNLOCKED(vp, __func__);
          if (!refcount_release(&vp->v_usecount))
                  return;
          vput_final(vp, VRELE);
  }
  
  /*
   * in: locked
   * out: unlocked
   */
  void
  vput(struct vnode *vp)
  {
  
          ASSERT_VOP_LOCKED(vp, __func__);
          ASSERT_VI_UNLOCKED(vp, __func__);
          if (!refcount_release(&vp->v_usecount)) {
                  VOP_UNLOCK(vp);
                  return;
          }
          vput_final(vp, VPUT);
  }
  
  /*
   * in: locked
   * out: locked
   */
  void
  vunref(struct vnode *vp)
  {
  
          ASSERT_VOP_LOCKED(vp, __func__);
          ASSERT_VI_UNLOCKED(vp, __func__);
          if (!refcount_release(&vp->v_usecount))
                  return;
          vput_final(vp, VUNREF);
  }
  
  void
  vhold(struct vnode *vp)
  {
          int old;
  
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          old = atomic_fetchadd_int(&vp->v_holdcnt, 1);
          VNASSERT(old >= 0 && (old & VHOLD_ALL_FLAGS) == 0, vp,
              ("%s: wrong hold count %d", __func__, old));
          if (old == 0)
                  vfs_freevnodes_dec();
  }
  
  void
  vholdnz(struct vnode *vp)
  {
  
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
  #ifdef INVARIANTS
          int old = atomic_fetchadd_int(&vp->v_holdcnt, 1);
          VNASSERT(old > 0 && (old & VHOLD_ALL_FLAGS) == 0, vp,
              ("%s: wrong hold count %d", __func__, old));
  #else
          atomic_add_int(&vp->v_holdcnt, 1);
  #endif
  }
  
  /*
   * Grab a hold count unless the vnode is freed.
   *
   * Only use this routine if vfs smr is the only protection you have against
   * freeing the vnode.
   *
   * The code loops trying to add a hold count as long as the VHOLD_NO_SMR flag
   * is not set.  After the flag is set the vnode becomes immutable to anyone but
   * the thread which managed to set the flag.
   *
   * It may be tempting to replace the loop with:
   * count = atomic_fetchadd_int(&vp->v_holdcnt, 1);
   * if (count & VHOLD_NO_SMR) {
   *     backpedal and error out;
   * }
   *
   * However, while this is more performant, it hinders debugging by eliminating
   * the previously mentioned invariant.
   */
  bool
  vhold_smr(struct vnode *vp)
  {
          int count;
  
          VFS_SMR_ASSERT_ENTERED();
  
          count = atomic_load_int(&vp->v_holdcnt);
          for (;;) {
                  if (count & VHOLD_NO_SMR) {
                          VNASSERT((count & ~VHOLD_NO_SMR) == 0, vp,
                              ("non-zero hold count with flags %d\n", count));
                          return (false);
                  }
                  VNASSERT(count >= 0, vp, ("invalid hold count %d\n", count));
                  if (atomic_fcmpset_int(&vp->v_holdcnt, &count, count + 1)) {
                          if (count == 0)
                                  vfs_freevnodes_dec();
                          return (true);
                  }
          }
  }
  
  /*
   * Hold a free vnode for recycling.
   *
   * Note: vnode_init references this comment.
   *
   * Attempts to recycle only need the global vnode list lock and have no use for
   * SMR.
   *
   * However, vnodes get inserted into the global list before they get fully
   * initialized and stay there until UMA decides to free the memory. This in
   * particular means the target can be found before it becomes usable and after
   * it becomes recycled. Picking up such vnodes is guarded with v_holdcnt set to
   * VHOLD_NO_SMR.
   *
   * Note: the vnode may gain more references after we transition the count 0->1.
   */
  static bool
  vhold_recycle_free(struct vnode *vp)
  {
          int count;
  
          mtx_assert(&vnode_list_mtx, MA_OWNED);
  
          count = atomic_load_int(&vp->v_holdcnt);
          for (;;) {
                  if (count & VHOLD_NO_SMR) {
                          VNASSERT((count & ~VHOLD_NO_SMR) == 0, vp,
                              ("non-zero hold count with flags %d\n", count));
                          return (false);
                  }
                  VNASSERT(count >= 0, vp, ("invalid hold count %d\n", count));
                  if (count > 0) {
                          return (false);
                  }
                  if (atomic_fcmpset_int(&vp->v_holdcnt, &count, count + 1)) {
                          vfs_freevnodes_dec();
                          return (true);
                  }
          }
  }
  
  static void __noinline
  vdbatch_process(struct vdbatch *vd)
  {
          struct vnode *vp;
          int i;
  
          mtx_assert(&vd->lock, MA_OWNED);
          MPASS(curthread->td_pinned > 0);
          MPASS(vd->index == VDBATCH_SIZE);
  
          mtx_lock(&vnode_list_mtx);
          critical_enter();
          freevnodes += vd->freevnodes;
          for (i = 0; i < VDBATCH_SIZE; i++) {
                  vp = vd->tab[i];
                  TAILQ_REMOVE(&vnode_list, vp, v_vnodelist);
                  TAILQ_INSERT_TAIL(&vnode_list, vp, v_vnodelist);
                  MPASS(vp->v_dbatchcpu != NOCPU);
                  vp->v_dbatchcpu = NOCPU;
          }
          mtx_unlock(&vnode_list_mtx);
          vd->freevnodes = 0;
          bzero(vd->tab, sizeof(vd->tab));
          vd->index = 0;
          critical_exit();
  }
  
  static void
  vdbatch_enqueue(struct vnode *vp)
  {
          struct vdbatch *vd;
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNASSERT(!VN_IS_DOOMED(vp), vp,
              ("%s: deferring requeue of a doomed vnode", __func__));
  
          if (vp->v_dbatchcpu != NOCPU) {
                  VI_UNLOCK(vp);
                  return;
          }
  
          sched_pin();
          vd = DPCPU_PTR(vd);
          mtx_lock(&vd->lock);
          MPASS(vd->index < VDBATCH_SIZE);
          MPASS(vd->tab[vd->index] == NULL);
          /*
           * A hack: we depend on being pinned so that we know what to put in
           * ->v_dbatchcpu.
           */
          vp->v_dbatchcpu = curcpu;
          vd->tab[vd->index] = vp;
          vd->index++;
          VI_UNLOCK(vp);
          if (vd->index == VDBATCH_SIZE)
                  vdbatch_process(vd);
          mtx_unlock(&vd->lock);
          sched_unpin();
  }
  
  /*
   * This routine must only be called for vnodes which are about to be
   * deallocated. Supporting dequeue for arbitrary vndoes would require
   * validating that the locked batch matches.
   */
  static void
  vdbatch_dequeue(struct vnode *vp)
  {
          struct vdbatch *vd;
          int i;
          short cpu;
  
          VNASSERT(vp->v_type == VBAD || vp->v_type == VNON, vp,
              ("%s: called for a used vnode\n", __func__));
  
          cpu = vp->v_dbatchcpu;
          if (cpu == NOCPU)
                  return;
  
          vd = DPCPU_ID_PTR(cpu, vd);
          mtx_lock(&vd->lock);
          for (i = 0; i < vd->index; i++) {
                  if (vd->tab[i] != vp)
                          continue;
                  vp->v_dbatchcpu = NOCPU;
                  vd->index--;
                  vd->tab[i] = vd->tab[vd->index];
                  vd->tab[vd->index] = NULL;
                  break;
          }
          mtx_unlock(&vd->lock);
          /*
           * Either we dequeued the vnode above or the target CPU beat us to it.
           */
          MPASS(vp->v_dbatchcpu == NOCPU);
  }
  
  /*
   * Drop the hold count of the vnode.  If this is the last reference to
   * the vnode we place it on the free list unless it has been vgone'd
   * (marked VIRF_DOOMED) in which case we will free it.
   *
   * Because the vnode vm object keeps a hold reference on the vnode if
   * there is at least one resident non-cached page, the vnode cannot
   * leave the active list without the page cleanup done.
   */
  static void __noinline
  vdropl_final(struct vnode *vp)
  {
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNPASS(VN_IS_DOOMED(vp), vp);
          /*
           * Set the VHOLD_NO_SMR flag.
           *
           * We may be racing against vhold_smr. If they win we can just pretend
           * we never got this far, they will vdrop later.
           */
          if (__predict_false(!atomic_cmpset_int(&vp->v_holdcnt, 0, VHOLD_NO_SMR))) {
                  vfs_freevnodes_inc();
                  VI_UNLOCK(vp);
                  /*
                   * We lost the aforementioned race. Any subsequent access is
                   * invalid as they might have managed to vdropl on their own.
                   */
                  return;
          }
          /*
           * Don't bump freevnodes as this one is going away.
           */
          freevnode(vp);
  }
  
  void
  vdrop(struct vnode *vp)
  {
  
          ASSERT_VI_UNLOCKED(vp, __func__);
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          if (refcount_release_if_not_last(&vp->v_holdcnt))
                  return;
          VI_LOCK(vp);
          vdropl(vp);
  }
  
  static void __always_inline
  vdropl_impl(struct vnode *vp, bool enqueue)
  {
  
          ASSERT_VI_LOCKED(vp, __func__);
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          if (!refcount_release(&vp->v_holdcnt)) {
                  VI_UNLOCK(vp);
                  return;
          }
          VNPASS((vp->v_iflag & VI_OWEINACT) == 0, vp);
          VNPASS((vp->v_iflag & VI_DEFINACT) == 0, vp);
          if (VN_IS_DOOMED(vp)) {
                  vdropl_final(vp);
                  return;
          }
  
          vfs_freevnodes_inc();
          if (vp->v_mflag & VMP_LAZYLIST) {
                  vunlazy(vp);
          }
  
          if (!enqueue) {
                  VI_UNLOCK(vp);
                  return;
          }
  
          /*
           * Also unlocks the interlock. We can't assert on it as we
           * released our hold and by now the vnode might have been
           * freed.
           */
          vdbatch_enqueue(vp);
  }
  
  void
  vdropl(struct vnode *vp)
  {
  
          vdropl_impl(vp, true);
  }
  
  /*
   * vdrop a vnode when recycling
   *
   * This is a special case routine only to be used when recycling, differs from
   * regular vdrop by not requeieing the vnode on LRU.
   *
   * Consider a case where vtryrecycle continuously fails with all vnodes (due to
   * e.g., frozen writes on the filesystem), filling the batch and causing it to
   * be requeued. Then vnlru will end up revisiting the same vnodes. This is a
   * loop which can last for as long as writes are frozen.
   */
  static void
  vdropl_recycle(struct vnode *vp)
  {
  
          vdropl_impl(vp, false);
  }
  
  static void
  vdrop_recycle(struct vnode *vp)
  {
  
          VI_LOCK(vp);
          vdropl_recycle(vp);
  }
  
  /*
   * Call VOP_INACTIVE on the vnode and manage the DOINGINACT and OWEINACT
   * flags.  DOINGINACT prevents us from recursing in calls to vinactive.
   */
  static int
  vinactivef(struct vnode *vp)
  {
          struct vm_object *obj;
          int error;
  
          ASSERT_VOP_ELOCKED(vp, "vinactive");
          ASSERT_VI_LOCKED(vp, "vinactive");
          VNASSERT((vp->v_iflag & VI_DOINGINACT) == 0, vp,
              ("vinactive: recursed on VI_DOINGINACT"));
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          vp->v_iflag |= VI_DOINGINACT;
          vp->v_iflag &= ~VI_OWEINACT;
          VI_UNLOCK(vp);
          /*
           * Before moving off the active list, we must be sure that any
           * modified pages are converted into the vnode's dirty
           * buffers, since these will no longer be checked once the
           * vnode is on the inactive list.
           *
           * The write-out of the dirty pages is asynchronous.  At the
           * point that VOP_INACTIVE() is called, there could still be
           * pending I/O and dirty pages in the object.
           */
          if ((obj = vp->v_object) != NULL && (vp->v_vflag & VV_NOSYNC) == 0 &&
              vm_object_mightbedirty(obj)) {
                  VM_OBJECT_WLOCK(obj);
                  vm_object_page_clean(obj, 0, 0, 0);
                  VM_OBJECT_WUNLOCK(obj);
          }
          error = VOP_INACTIVE(vp);
          VI_LOCK(vp);
          VNASSERT(vp->v_iflag & VI_DOINGINACT, vp,
              ("vinactive: lost VI_DOINGINACT"));
          vp->v_iflag &= ~VI_DOINGINACT;
          return (error);
  }
  
  int
  vinactive(struct vnode *vp)
  {
  
          ASSERT_VOP_ELOCKED(vp, "vinactive");
          ASSERT_VI_LOCKED(vp, "vinactive");
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
  
          if ((vp->v_iflag & VI_OWEINACT) == 0)
                  return (0);
          if (vp->v_iflag & VI_DOINGINACT)
                  return (0);
          if (vp->v_usecount > 0) {
                  vp->v_iflag &= ~VI_OWEINACT;
                  return (0);
          }
          return (vinactivef(vp));
  }
  
  /*
   * Remove any vnodes in the vnode table belonging to mount point mp.
   *
   * If FORCECLOSE is not specified, there should not be any active ones,
   * return error if any are found (nb: this is a user error, not a
   * system error). If FORCECLOSE is specified, detach any active vnodes
   * that are found.
   *
   * If WRITECLOSE is set, only flush out regular file vnodes open for
   * writing.
   *
   * SKIPSYSTEM causes any vnodes marked VV_SYSTEM to be skipped.
   *
   * `rootrefs' specifies the base reference count for the root vnode
   * of this filesystem. The root vnode is considered busy if its
   * v_usecount exceeds this value. On a successful return, vflush(, td)
   * will call vrele() on the root vnode exactly rootrefs times.
   * If the SKIPSYSTEM or WRITECLOSE flags are specified, rootrefs must
   * be zero.
   */
  #ifdef DIAGNOSTIC
  static int busyprt = 0;         /* print out busy vnodes */
  SYSCTL_INT(_debug, OID_AUTO, busyprt, CTLFLAG_RW, &busyprt, 0, "Print out busy vnodes");
  #endif
  
  int
  vflush(struct mount *mp, int rootrefs, int flags, struct thread *td)
  {
          struct vnode *vp, *mvp, *rootvp = NULL;
          struct vattr vattr;
          int busy = 0, error;
  
          CTR4(KTR_VFS, "%s: mp %p with rootrefs %d and flags %d", __func__, mp,
              rootrefs, flags);
          if (rootrefs > 0) {
                  KASSERT((flags & (SKIPSYSTEM | WRITECLOSE)) == 0,
                      ("vflush: bad args"));
                  /*
                   * Get the filesystem root vnode. We can vput() it
                   * immediately, since with rootrefs > 0, it won't go away.
                   */
                  if ((error = VFS_ROOT(mp, LK_EXCLUSIVE, &rootvp)) != 0) {
                          CTR2(KTR_VFS, "%s: vfs_root lookup failed with %d",
                              __func__, error);
                          return (error);
                  }
                  vput(rootvp);
          }
  loop:
          MNT_VNODE_FOREACH_ALL(vp, mp, mvp) {
                  vholdl(vp);
                  error = vn_lock(vp, LK_INTERLOCK | LK_EXCLUSIVE);
                  if (error) {
                          vdrop(vp);
                          MNT_VNODE_FOREACH_ALL_ABORT(mp, mvp);
                          goto loop;
                  }
                  /*
                   * Skip over a vnodes marked VV_SYSTEM.
                   */
                  if ((flags & SKIPSYSTEM) && (vp->v_vflag & VV_SYSTEM)) {
                          VOP_UNLOCK(vp);
                          vdrop(vp);
                          continue;
                  }
                  /*
                   * If WRITECLOSE is set, flush out unlinked but still open
                   * files (even if open only for reading) and regular file
                   * vnodes open for writing.
                   */
                  if (flags & WRITECLOSE) {
                          if (vp->v_object != NULL) {
                                  VM_OBJECT_WLOCK(vp->v_object);
                                  vm_object_page_clean(vp->v_object, 0, 0, 0);
                                  VM_OBJECT_WUNLOCK(vp->v_object);
                          }
                          do {
                                  error = VOP_FSYNC(vp, MNT_WAIT, td);
                          } while (error == ERELOOKUP);
                          if (error != 0) {
                                  VOP_UNLOCK(vp);
                                  vdrop(vp);
                                  MNT_VNODE_FOREACH_ALL_ABORT(mp, mvp);
                                  return (error);
                          }
                          error = VOP_GETATTR(vp, &vattr, td->td_ucred);
                          VI_LOCK(vp);
  
                          if ((vp->v_type == VNON ||
                              (error == 0 && vattr.va_nlink > 0)) &&
                              (vp->v_writecount <= 0 || vp->v_type != VREG)) {
                                  VOP_UNLOCK(vp);
                                  vdropl(vp);
                                  continue;
                          }
                  } else
                          VI_LOCK(vp);
                  /*
                   * With v_usecount == 0, all we need to do is clear out the
                   * vnode data structures and we are done.
                   *
                   * If FORCECLOSE is set, forcibly close the vnode.
                   */
                  if (vp->v_usecount == 0 || (flags & FORCECLOSE)) {
                          vgonel(vp);
                  } else {
                          busy++;
  #ifdef DIAGNOSTIC
                          if (busyprt)
                                  vn_printf(vp, "vflush: busy vnode ");
  #endif
                  }
                  VOP_UNLOCK(vp);
                  vdropl(vp);
          }
          if (rootrefs > 0 && (flags & FORCECLOSE) == 0) {
                  /*
                   * If just the root vnode is busy, and if its refcount
                   * is equal to `rootrefs', then go ahead and kill it.
                   */
                  VI_LOCK(rootvp);
                  KASSERT(busy > 0, ("vflush: not busy"));
                  VNASSERT(rootvp->v_usecount >= rootrefs, rootvp,
                      ("vflush: usecount %d < rootrefs %d",
                       rootvp->v_usecount, rootrefs));
                  if (busy == 1 && rootvp->v_usecount == rootrefs) {
                          VOP_LOCK(rootvp, LK_EXCLUSIVE|LK_INTERLOCK);
                          vgone(rootvp);
                          VOP_UNLOCK(rootvp);
                          busy = 0;
                  } else
                          VI_UNLOCK(rootvp);
          }
          if (busy) {
                  CTR2(KTR_VFS, "%s: failing as %d vnodes are busy", __func__,
                      busy);
                  return (EBUSY);
          }
          for (; rootrefs > 0; rootrefs--)
                  vrele(rootvp);
          return (0);
  }
  
  /*
   * Recycle an unused vnode to the front of the free list.
   */
  int
  vrecycle(struct vnode *vp)
  {
          int recycled;
  
          VI_LOCK(vp);
          recycled = vrecyclel(vp);
          VI_UNLOCK(vp);
          return (recycled);
  }
  
  /*
   * vrecycle, with the vp interlock held.
   */
  int
  vrecyclel(struct vnode *vp)
  {
          int recycled;
  
          ASSERT_VOP_ELOCKED(vp, __func__);
          ASSERT_VI_LOCKED(vp, __func__);
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          recycled = 0;
          if (vp->v_usecount == 0) {
                  recycled = 1;
                  vgonel(vp);
          }
          return (recycled);
  }
  
  /*
   * Eliminate all activity associated with a vnode
   * in preparation for reuse.
   */
  void
  vgone(struct vnode *vp)
  {
          VI_LOCK(vp);
          vgonel(vp);
          VI_UNLOCK(vp);
  }
  
  static void
  notify_lowervp_vfs_dummy(struct mount *mp __unused,
      struct vnode *lowervp __unused)
  {
  }
  
  /*
   * Notify upper mounts about reclaimed or unlinked vnode.
   */
  void
  vfs_notify_upper(struct vnode *vp, int event)
  {
          static struct vfsops vgonel_vfsops = {
                  .vfs_reclaim_lowervp = notify_lowervp_vfs_dummy,
                  .vfs_unlink_lowervp = notify_lowervp_vfs_dummy,
          };
          struct mount *mp, *ump, *mmp;
  
          mp = vp->v_mount;
          if (mp == NULL)
                  return;
          if (TAILQ_EMPTY(&mp->mnt_uppers))
                  return;
  
          mmp = malloc(sizeof(struct mount), M_TEMP, M_WAITOK | M_ZERO);
          mmp->mnt_op = &vgonel_vfsops;
          mmp->mnt_kern_flag |= MNTK_MARKER;
          MNT_ILOCK(mp);
          mp->mnt_kern_flag |= MNTK_VGONE_UPPER;
          for (ump = TAILQ_FIRST(&mp->mnt_uppers); ump != NULL;) {
                  if ((ump->mnt_kern_flag & MNTK_MARKER) != 0) {
                          ump = TAILQ_NEXT(ump, mnt_upper_link);
                          continue;
                  }
                  TAILQ_INSERT_AFTER(&mp->mnt_uppers, ump, mmp, mnt_upper_link);
                  MNT_IUNLOCK(mp);
                  switch (event) {
                  case VFS_NOTIFY_UPPER_RECLAIM:
                          VFS_RECLAIM_LOWERVP(ump, vp);
                          break;
                  case VFS_NOTIFY_UPPER_UNLINK:
                          VFS_UNLINK_LOWERVP(ump, vp);
                          break;
                  default:
                          KASSERT(0, ("invalid event %d", event));
                          break;
                  }
                  MNT_ILOCK(mp);
                  ump = TAILQ_NEXT(mmp, mnt_upper_link);
                  TAILQ_REMOVE(&mp->mnt_uppers, mmp, mnt_upper_link);
          }
          free(mmp, M_TEMP);
          mp->mnt_kern_flag &= ~MNTK_VGONE_UPPER;
          if ((mp->mnt_kern_flag & MNTK_VGONE_WAITER) != 0) {
                  mp->mnt_kern_flag &= ~MNTK_VGONE_WAITER;
                  wakeup(&mp->mnt_uppers);
          }
          MNT_IUNLOCK(mp);
  }
  
  /*
   * vgone, with the vp interlock held.
   */
  static void
  vgonel(struct vnode *vp)
  {
          struct thread *td;
          struct mount *mp;
          vm_object_t object;
          bool active, doinginact, oweinact;
  
          ASSERT_VOP_ELOCKED(vp, "vgonel");
          ASSERT_VI_LOCKED(vp, "vgonel");
          VNASSERT(vp->v_holdcnt, vp,
              ("vgonel: vp %p has no reference.", vp));
          CTR2(KTR_VFS, "%s: vp %p", __func__, vp);
          td = curthread;
  
          /*
           * Don't vgonel if we're already doomed.
           */
          if (VN_IS_DOOMED(vp))
                  return;
          /*
           * Paired with freevnode.
           */
          vn_seqc_write_begin_locked(vp);
          vunlazy_gone(vp);
          vn_irflag_set_locked(vp, VIRF_DOOMED);
  
          /*
           * Check to see if the vnode is in use.  If so, we have to
           * call VOP_CLOSE() and VOP_INACTIVE().
           *
           * It could be that VOP_INACTIVE() requested reclamation, in
           * which case we should avoid recursion, so check
           * VI_DOINGINACT.  This is not precise but good enough.
           */
          active = vp->v_usecount > 0;
          oweinact = (vp->v_iflag & VI_OWEINACT) != 0;
          doinginact = (vp->v_iflag & VI_DOINGINACT) != 0;
  
          /*
           * If we need to do inactive VI_OWEINACT will be set.
           */
          if (vp->v_iflag & VI_DEFINACT) {
                  VNASSERT(vp->v_holdcnt > 1, vp, ("lost hold count"));
                  vp->v_iflag &= ~VI_DEFINACT;
                  vdropl(vp);
          } else {
                  VNASSERT(vp->v_holdcnt > 0, vp, ("vnode without hold count"));
                  VI_UNLOCK(vp);
          }
          cache_purge_vgone(vp);
          vfs_notify_upper(vp, VFS_NOTIFY_UPPER_RECLAIM);
  
          /*
           * If purging an active vnode, it must be closed and
           * deactivated before being reclaimed.
           */
          if (active)
                  VOP_CLOSE(vp, FNONBLOCK, NOCRED, td);
          if (!doinginact) {
                  do {
                          if (oweinact || active) {
                                  VI_LOCK(vp);
                                  vinactivef(vp);
                                  oweinact = (vp->v_iflag & VI_OWEINACT) != 0;
                                  VI_UNLOCK(vp);
                          }
                  } while (oweinact);
          }
          if (vp->v_type == VSOCK)
                  vfs_unp_reclaim(vp);
  
          /*
           * Clean out any buffers associated with the vnode.
           * If the flush fails, just toss the buffers.
           */
          mp = NULL;
          if (!TAILQ_EMPTY(&vp->v_bufobj.bo_dirty.bv_hd))
                  (void) vn_start_secondary_write(vp, &mp, V_WAIT);
          if (vinvalbuf(vp, V_SAVE, 0, 0) != 0) {
                  while (vinvalbuf(vp, 0, 0, 0) != 0)
                          ;
          }
  
          BO_LOCK(&vp->v_bufobj);
          KASSERT(TAILQ_EMPTY(&vp->v_bufobj.bo_dirty.bv_hd) &&
              vp->v_bufobj.bo_dirty.bv_cnt == 0 &&
              TAILQ_EMPTY(&vp->v_bufobj.bo_clean.bv_hd) &&
              vp->v_bufobj.bo_clean.bv_cnt == 0,
              ("vp %p bufobj not invalidated", vp));
  
          /*
           * For VMIO bufobj, BO_DEAD is set later, or in
           * vm_object_terminate() after the object's page queue is
           * flushed.
           */
          object = vp->v_bufobj.bo_object;
          if (object == NULL)
                  vp->v_bufobj.bo_flag |= BO_DEAD;
          BO_UNLOCK(&vp->v_bufobj);
  
          /*
           * Handle the VM part.  Tmpfs handles v_object on its own (the
           * OBJT_VNODE check).  Nullfs or other bypassing filesystems
           * should not touch the object borrowed from the lower vnode
           * (the handle check).
           */
          if (object != NULL && object->type == OBJT_VNODE &&
              object->handle == vp)
                  vnode_destroy_vobject(vp);
  
          /*
           * Reclaim the vnode.
           */
          if (VOP_RECLAIM(vp))
                  panic("vgone: cannot reclaim");
          if (mp != NULL)
                  vn_finished_secondary_write(mp);
          VNASSERT(vp->v_object == NULL, vp,
              ("vop_reclaim left v_object vp=%p", vp));
          /*
           * Clear the advisory locks and wake up waiting threads.
           */
          (void)VOP_ADVLOCKPURGE(vp);
          vp->v_lockf = NULL;
          /*
           * Delete from old mount point vnode list.
           */
          delmntque(vp);
          /*
           * Done with purge, reset to the standard lock and invalidate
           * the vnode.
           */
          VI_LOCK(vp);
          vp->v_vnlock = &vp->v_lock;
          vp->v_op = &dead_vnodeops;
          vp->v_type = VBAD;
  }
  
  /*
   * Print out a description of a vnode.
   */
  static const char * const typename[] =
  {"VNON", "VREG", "VDIR", "VBLK", "VCHR", "VLNK", "VSOCK", "VFIFO", "VBAD",
   "VMARKER"};
  
  _Static_assert((VHOLD_ALL_FLAGS & ~VHOLD_NO_SMR) == 0,
      "new hold count flag not added to vn_printf");
  
  void
  vn_printf(struct vnode *vp, const char *fmt, ...)
  {
          va_list ap;
          char buf[256], buf2[16];
          u_long flags;
          u_int holdcnt;
          short irflag;
  
          va_start(ap, fmt);
          vprintf(fmt, ap);
          va_end(ap);
          printf("%p: ", (void *)vp);
          printf("type %s\n", typename[vp->v_type]);
          holdcnt = atomic_load_int(&vp->v_holdcnt);
          printf("    usecount %d, writecount %d, refcount %d seqc users %d",
              vp->v_usecount, vp->v_writecount, holdcnt & ~VHOLD_ALL_FLAGS,
              vp->v_seqc_users);
          switch (vp->v_type) {
          case VDIR:
                  printf(" mountedhere %p\n", vp->v_mountedhere);
                  break;
          case VCHR:
                  printf(" rdev %p\n", vp->v_rdev);
                  break;
          case VSOCK:
                  printf(" socket %p\n", vp->v_unpcb);
                  break;
          case VFIFO:
                  printf(" fifoinfo %p\n", vp->v_fifoinfo);
                  break;
          default:
                  printf("\n");
                  break;
          }
          buf[0] = '\0';
          buf[1] = '\0';
          if (holdcnt & VHOLD_NO_SMR)
                  strlcat(buf, "|VHOLD_NO_SMR", sizeof(buf));
          printf("    hold count flags (%s)\n", buf + 1);
  
          buf[0] = '\0';
          buf[1] = '\0';
          irflag = vn_irflag_read(vp);
          if (irflag & VIRF_DOOMED)
                  strlcat(buf, "|VIRF_DOOMED", sizeof(buf));
          if (irflag & VIRF_PGREAD)
                  strlcat(buf, "|VIRF_PGREAD", sizeof(buf));
          if (irflag & VIRF_MOUNTPOINT)
                  strlcat(buf, "|VIRF_MOUNTPOINT", sizeof(buf));
          flags = irflag & ~(VIRF_DOOMED | VIRF_PGREAD | VIRF_MOUNTPOINT);
          if (flags != 0) {
                  snprintf(buf2, sizeof(buf2), "|VIRF(0x%lx)", flags);
                  strlcat(buf, buf2, sizeof(buf));
          }
          if (vp->v_vflag & VV_ROOT)
                  strlcat(buf, "|VV_ROOT", sizeof(buf));
          if (vp->v_vflag & VV_ISTTY)
                  strlcat(buf, "|VV_ISTTY", sizeof(buf));
          if (vp->v_vflag & VV_NOSYNC)
                  strlcat(buf, "|VV_NOSYNC", sizeof(buf));
          if (vp->v_vflag & VV_ETERNALDEV)
                  strlcat(buf, "|VV_ETERNALDEV", sizeof(buf));
          if (vp->v_vflag & VV_CACHEDLABEL)
                  strlcat(buf, "|VV_CACHEDLABEL", sizeof(buf));
          if (vp->v_vflag & VV_VMSIZEVNLOCK)
                  strlcat(buf, "|VV_VMSIZEVNLOCK", sizeof(buf));
          if (vp->v_vflag & VV_COPYONWRITE)
                  strlcat(buf, "|VV_COPYONWRITE", sizeof(buf));
          if (vp->v_vflag & VV_SYSTEM)
                  strlcat(buf, "|VV_SYSTEM", sizeof(buf));
          if (vp->v_vflag & VV_PROCDEP)
                  strlcat(buf, "|VV_PROCDEP", sizeof(buf));
          if (vp->v_vflag & VV_NOKNOTE)
                  strlcat(buf, "|VV_NOKNOTE", sizeof(buf));
          if (vp->v_vflag & VV_DELETED)
                  strlcat(buf, "|VV_DELETED", sizeof(buf));
          if (vp->v_vflag & VV_MD)
                  strlcat(buf, "|VV_MD", sizeof(buf));
          if (vp->v_vflag & VV_FORCEINSMQ)
                  strlcat(buf, "|VV_FORCEINSMQ", sizeof(buf));
          if (vp->v_vflag & VV_READLINK)
                  strlcat(buf, "|VV_READLINK", sizeof(buf));
          flags = vp->v_vflag & ~(VV_ROOT | VV_ISTTY | VV_NOSYNC | VV_ETERNALDEV |
              VV_CACHEDLABEL | VV_VMSIZEVNLOCK | VV_COPYONWRITE | VV_SYSTEM |
              VV_PROCDEP | VV_NOKNOTE | VV_DELETED | VV_MD | VV_FORCEINSMQ |
              VV_READLINK);
          if (flags != 0) {
                  snprintf(buf2, sizeof(buf2), "|VV(0x%lx)", flags);
                  strlcat(buf, buf2, sizeof(buf));
          }
          if (vp->v_iflag & VI_TEXT_REF)
                  strlcat(buf, "|VI_TEXT_REF", sizeof(buf));
          if (vp->v_iflag & VI_MOUNT)
                  strlcat(buf, "|VI_MOUNT", sizeof(buf));
          if (vp->v_iflag & VI_DOINGINACT)
                  strlcat(buf, "|VI_DOINGINACT", sizeof(buf));
          if (vp->v_iflag & VI_OWEINACT)
                  strlcat(buf, "|VI_OWEINACT", sizeof(buf));
          if (vp->v_iflag & VI_DEFINACT)
                  strlcat(buf, "|VI_DEFINACT", sizeof(buf));
          if (vp->v_iflag & VI_FOPENING)
                  strlcat(buf, "|VI_FOPENING", sizeof(buf));
          flags = vp->v_iflag & ~(VI_TEXT_REF | VI_MOUNT | VI_DOINGINACT |
              VI_OWEINACT | VI_DEFINACT | VI_FOPENING);
          if (flags != 0) {
                  snprintf(buf2, sizeof(buf2), "|VI(0x%lx)", flags);
                  strlcat(buf, buf2, sizeof(buf));
          }
          if (vp->v_mflag & VMP_LAZYLIST)
                  strlcat(buf, "|VMP_LAZYLIST", sizeof(buf));
          flags = vp->v_mflag & ~(VMP_LAZYLIST);
          if (flags != 0) {
                  snprintf(buf2, sizeof(buf2), "|VMP(0x%lx)", flags);
                  strlcat(buf, buf2, sizeof(buf));
          }
          printf("    flags (%s)", buf + 1);
          if (mtx_owned(VI_MTX(vp)))
                  printf(" VI_LOCKed");
          printf("\n");
          if (vp->v_object != NULL)
                  printf("    v_object %p ref %d pages %d "
                      "cleanbuf %d dirtybuf %d\n",
                      vp->v_object, vp->v_object->ref_count,
                      vp->v_object->resident_page_count,
                      vp->v_bufobj.bo_clean.bv_cnt,
                      vp->v_bufobj.bo_dirty.bv_cnt);
          printf("    ");
          lockmgr_printinfo(vp->v_vnlock);
          if (vp->v_data != NULL)
                  VOP_PRINT(vp);
  }
  
  #ifdef DDB
  /*
   * List all of the locked vnodes in the system.
   * Called when debugging the kernel.
   */
  DB_SHOW_COMMAND(lockedvnods, lockedvnodes)
  {
          struct mount *mp;
          struct vnode *vp;
  
          /*
           * Note: because this is DDB, we can't obey the locking semantics
           * for these structures, which means we could catch an inconsistent
           * state and dereference a nasty pointer.  Not much to be done
           * about that.
           */
          db_printf("Locked vnodes\n");
          TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                  TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                          if (vp->v_type != VMARKER && VOP_ISLOCKED(vp))
                                  vn_printf(vp, "vnode ");
                  }
          }
  }
  
  /*
   * Show details about the given vnode.
   */
  DB_SHOW_COMMAND(vnode, db_show_vnode)
  {
          struct vnode *vp;
  
          if (!have_addr)
                  return;
          vp = (struct vnode *)addr;
          vn_printf(vp, "vnode ");
  }
  
  /*
   * Show details about the given mount point.
   */
  DB_SHOW_COMMAND(mount, db_show_mount)
  {
          struct mount *mp;
          struct vfsopt *opt;
          struct statfs *sp;
          struct vnode *vp;
          char buf[512];
          uint64_t mflags;
          u_int flags;
  
          if (!have_addr) {
                  /* No address given, print short info about all mount points. */
                  TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                          db_printf("%p %s on %s (%s)\n", mp,
                              mp->mnt_stat.f_mntfromname,
                              mp->mnt_stat.f_mntonname,
                              mp->mnt_stat.f_fstypename);
                          if (db_pager_quit)
                                  break;
                  }
                  db_printf("\nMore info: show mount <addr>\n");
                  return;
          }
  
          mp = (struct mount *)addr;
          db_printf("%p %s on %s (%s)\n", mp, mp->mnt_stat.f_mntfromname,
              mp->mnt_stat.f_mntonname, mp->mnt_stat.f_fstypename);
  
          buf[0] = '\0';
          mflags = mp->mnt_flag;
  #define MNT_FLAG(flag)  do {                                            \
          if (mflags & (flag)) {                                          \
                  if (buf[0] != '\0')                                     \
                          strlcat(buf, ", ", sizeof(buf));                \
                  strlcat(buf, (#flag) + 4, sizeof(buf));                 \
                  mflags &= ~(flag);                                      \
          }                                                               \
  } while (0)
          MNT_FLAG(MNT_RDONLY);
          MNT_FLAG(MNT_SYNCHRONOUS);
          MNT_FLAG(MNT_NOEXEC);
          MNT_FLAG(MNT_NOSUID);
          MNT_FLAG(MNT_NFS4ACLS);
          MNT_FLAG(MNT_UNION);
          MNT_FLAG(MNT_ASYNC);
          MNT_FLAG(MNT_SUIDDIR);
          MNT_FLAG(MNT_SOFTDEP);
          MNT_FLAG(MNT_NOSYMFOLLOW);
          MNT_FLAG(MNT_GJOURNAL);
          MNT_FLAG(MNT_MULTILABEL);
          MNT_FLAG(MNT_ACLS);
          MNT_FLAG(MNT_NOATIME);
          MNT_FLAG(MNT_NOCLUSTERR);
          MNT_FLAG(MNT_NOCLUSTERW);
          MNT_FLAG(MNT_SUJ);
          MNT_FLAG(MNT_EXRDONLY);
          MNT_FLAG(MNT_EXPORTED);
          MNT_FLAG(MNT_DEFEXPORTED);
          MNT_FLAG(MNT_EXPORTANON);
          MNT_FLAG(MNT_EXKERB);
          MNT_FLAG(MNT_EXPUBLIC);
          MNT_FLAG(MNT_LOCAL);
          MNT_FLAG(MNT_QUOTA);
          MNT_FLAG(MNT_ROOTFS);
          MNT_FLAG(MNT_USER);
          MNT_FLAG(MNT_IGNORE);
          MNT_FLAG(MNT_UPDATE);
          MNT_FLAG(MNT_DELEXPORT);
          MNT_FLAG(MNT_RELOAD);
          MNT_FLAG(MNT_FORCE);
          MNT_FLAG(MNT_SNAPSHOT);
          MNT_FLAG(MNT_BYFSID);
  #undef MNT_FLAG
          if (mflags != 0) {
                  if (buf[0] != '\0')
                          strlcat(buf, ", ", sizeof(buf));
                  snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf),
                      "0x%016jx", mflags);
          }
          db_printf("    mnt_flag = %s\n", buf);
  
          buf[0] = '\0';
          flags = mp->mnt_kern_flag;
  #define MNT_KERN_FLAG(flag)     do {                                    \
          if (flags & (flag)) {                                           \
                  if (buf[0] != '\0')                                     \
                          strlcat(buf, ", ", sizeof(buf));                \
                  strlcat(buf, (#flag) + 5, sizeof(buf));                 \
                  flags &= ~(flag);                                       \
          }                                                               \
  } while (0)
          MNT_KERN_FLAG(MNTK_UNMOUNTF);
          MNT_KERN_FLAG(MNTK_ASYNC);
          MNT_KERN_FLAG(MNTK_SOFTDEP);
          MNT_KERN_FLAG(MNTK_DRAINING);
          MNT_KERN_FLAG(MNTK_REFEXPIRE);
          MNT_KERN_FLAG(MNTK_EXTENDED_SHARED);
          MNT_KERN_FLAG(MNTK_SHARED_WRITES);
          MNT_KERN_FLAG(MNTK_NO_IOPF);
          MNT_KERN_FLAG(MNTK_VGONE_UPPER);
          MNT_KERN_FLAG(MNTK_VGONE_WAITER);
          MNT_KERN_FLAG(MNTK_LOOKUP_EXCL_DOTDOT);
          MNT_KERN_FLAG(MNTK_MARKER);
          MNT_KERN_FLAG(MNTK_USES_BCACHE);
          MNT_KERN_FLAG(MNTK_FPLOOKUP);
          MNT_KERN_FLAG(MNTK_NOASYNC);
          MNT_KERN_FLAG(MNTK_UNMOUNT);
          MNT_KERN_FLAG(MNTK_MWAIT);
          MNT_KERN_FLAG(MNTK_SUSPEND);
          MNT_KERN_FLAG(MNTK_SUSPEND2);
          MNT_KERN_FLAG(MNTK_SUSPENDED);
          MNT_KERN_FLAG(MNTK_LOOKUP_SHARED);
          MNT_KERN_FLAG(MNTK_NOKNOTE);
  #undef MNT_KERN_FLAG
          if (flags != 0) {
                  if (buf[0] != '\0')
                          strlcat(buf, ", ", sizeof(buf));
                  snprintf(buf + strlen(buf), sizeof(buf) - strlen(buf),
                      "0x%08x", flags);
          }
          db_printf("    mnt_kern_flag = %s\n", buf);
  
          db_printf("    mnt_opt = ");
          opt = TAILQ_FIRST(mp->mnt_opt);
          if (opt != NULL) {
                  db_printf("%s", opt->name);
                  opt = TAILQ_NEXT(opt, link);
                  while (opt != NULL) {
                          db_printf(", %s", opt->name);
                          opt = TAILQ_NEXT(opt, link);
                  }
          }
          db_printf("\n");
  
          sp = &mp->mnt_stat;
          db_printf("    mnt_stat = { version=%u type=%u flags=0x%016jx "
              "bsize=%ju iosize=%ju blocks=%ju bfree=%ju bavail=%jd files=%ju "
              "ffree=%jd syncwrites=%ju asyncwrites=%ju syncreads=%ju "
              "asyncreads=%ju namemax=%u owner=%u fsid=[%d, %d] }\n",
              (u_int)sp->f_version, (u_int)sp->f_type, (uintmax_t)sp->f_flags,
              (uintmax_t)sp->f_bsize, (uintmax_t)sp->f_iosize,
              (uintmax_t)sp->f_blocks, (uintmax_t)sp->f_bfree,
              (intmax_t)sp->f_bavail, (uintmax_t)sp->f_files,
              (intmax_t)sp->f_ffree, (uintmax_t)sp->f_syncwrites,
              (uintmax_t)sp->f_asyncwrites, (uintmax_t)sp->f_syncreads,
              (uintmax_t)sp->f_asyncreads, (u_int)sp->f_namemax,
              (u_int)sp->f_owner, (int)sp->f_fsid.val[0], (int)sp->f_fsid.val[1]);
  
          db_printf("    mnt_cred = { uid=%u ruid=%u",
              (u_int)mp->mnt_cred->cr_uid, (u_int)mp->mnt_cred->cr_ruid);
          if (jailed(mp->mnt_cred))
                  db_printf(", jail=%d", mp->mnt_cred->cr_prison->pr_id);
          db_printf(" }\n");
          db_printf("    mnt_ref = %d (with %d in the struct)\n",
              vfs_mount_fetch_counter(mp, MNT_COUNT_REF), mp->mnt_ref);
          db_printf("    mnt_gen = %d\n", mp->mnt_gen);
          db_printf("    mnt_nvnodelistsize = %d\n", mp->mnt_nvnodelistsize);
          db_printf("    mnt_lazyvnodelistsize = %d\n",
              mp->mnt_lazyvnodelistsize);
          db_printf("    mnt_writeopcount = %d (with %d in the struct)\n",
              vfs_mount_fetch_counter(mp, MNT_COUNT_WRITEOPCOUNT), mp->mnt_writeopcount);
          db_printf("    mnt_iosize_max = %d\n", mp->mnt_iosize_max);
          db_printf("    mnt_hashseed = %u\n", mp->mnt_hashseed);
          db_printf("    mnt_lockref = %d (with %d in the struct)\n",
              vfs_mount_fetch_counter(mp, MNT_COUNT_LOCKREF), mp->mnt_lockref);
          db_printf("    mnt_secondary_writes = %d\n", mp->mnt_secondary_writes);
          db_printf("    mnt_secondary_accwrites = %d\n",
              mp->mnt_secondary_accwrites);
          db_printf("    mnt_gjprovider = %s\n",
              mp->mnt_gjprovider != NULL ? mp->mnt_gjprovider : "NULL");
          db_printf("    mnt_vfs_ops = %d\n", mp->mnt_vfs_ops);
  
          db_printf("\n\nList of active vnodes\n");
          TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                  if (vp->v_type != VMARKER && vp->v_holdcnt > 0) {
                          vn_printf(vp, "vnode ");
                          if (db_pager_quit)
                                  break;
                  }
          }
          db_printf("\n\nList of inactive vnodes\n");
          TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                  if (vp->v_type != VMARKER && vp->v_holdcnt == 0) {
                          vn_printf(vp, "vnode ");
                          if (db_pager_quit)
                                  break;
                  }
          }
  }
  #endif  /* DDB */
  
  /*
   * Fill in a struct xvfsconf based on a struct vfsconf.
   */
  static int
  vfsconf2x(struct sysctl_req *req, struct vfsconf *vfsp)
  {
          struct xvfsconf xvfsp;
  
          bzero(&xvfsp, sizeof(xvfsp));
          strcpy(xvfsp.vfc_name, vfsp->vfc_name);
          xvfsp.vfc_typenum = vfsp->vfc_typenum;
          xvfsp.vfc_refcount = vfsp->vfc_refcount;
          xvfsp.vfc_flags = vfsp->vfc_flags;
          /*
           * These are unused in userland, we keep them
           * to not break binary compatibility.
           */
          xvfsp.vfc_vfsops = NULL;
          xvfsp.vfc_next = NULL;
          return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
  }
  
  #ifdef COMPAT_FREEBSD32
  struct xvfsconf32 {
          uint32_t        vfc_vfsops;
          char            vfc_name[MFSNAMELEN];
          int32_t         vfc_typenum;
          int32_t         vfc_refcount;
          int32_t         vfc_flags;
          uint32_t        vfc_next;
  };
  
  static int
  vfsconf2x32(struct sysctl_req *req, struct vfsconf *vfsp)
  {
          struct xvfsconf32 xvfsp;
  
          bzero(&xvfsp, sizeof(xvfsp));
          strcpy(xvfsp.vfc_name, vfsp->vfc_name);
          xvfsp.vfc_typenum = vfsp->vfc_typenum;
          xvfsp.vfc_refcount = vfsp->vfc_refcount;
          xvfsp.vfc_flags = vfsp->vfc_flags;
          return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
  }
  #endif
  
  /*
   * Top level filesystem related information gathering.
   */
  static int
  sysctl_vfs_conflist(SYSCTL_HANDLER_ARGS)
  {
          struct vfsconf *vfsp;
          int error;
  
          error = 0;
          vfsconf_slock();
          TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
  #ifdef COMPAT_FREEBSD32
                  if (req->flags & SCTL_MASK32)
                          error = vfsconf2x32(req, vfsp);
                  else
  #endif
                          error = vfsconf2x(req, vfsp);
                  if (error)
                          break;
          }
          vfsconf_sunlock();
          return (error);
  }
  
  SYSCTL_PROC(_vfs, OID_AUTO, conflist, CTLTYPE_OPAQUE | CTLFLAG_RD |
      CTLFLAG_MPSAFE, NULL, 0, sysctl_vfs_conflist,
      "S,xvfsconf", "List of all configured filesystems");
  
  #ifndef BURN_BRIDGES
  static int      sysctl_ovfs_conf(SYSCTL_HANDLER_ARGS);
  
  static int
  vfs_sysctl(SYSCTL_HANDLER_ARGS)
  {
          int *name = (int *)arg1 - 1;    /* XXX */
          u_int namelen = arg2 + 1;       /* XXX */
          struct vfsconf *vfsp;
  
          log(LOG_WARNING, "userland calling deprecated sysctl, "
              "please rebuild world\n");
  
  #if 1 || defined(COMPAT_PRELITE2)
          /* Resolve ambiguity between VFS_VFSCONF and VFS_GENERIC. */
          if (namelen == 1)
                  return (sysctl_ovfs_conf(oidp, arg1, arg2, req));
  #endif
  
          switch (name[1]) {
          case VFS_MAXTYPENUM:
                  if (namelen != 2)
                          return (ENOTDIR);
                  return (SYSCTL_OUT(req, &maxvfsconf, sizeof(int)));
          case VFS_CONF:
                  if (namelen != 3)
                          return (ENOTDIR);       /* overloaded */
                  vfsconf_slock();
                  TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
                          if (vfsp->vfc_typenum == name[2])
                                  break;
                  }
                  vfsconf_sunlock();
                  if (vfsp == NULL)
                          return (EOPNOTSUPP);
  #ifdef COMPAT_FREEBSD32
                  if (req->flags & SCTL_MASK32)
                          return (vfsconf2x32(req, vfsp));
                  else
  #endif
                          return (vfsconf2x(req, vfsp));
          }
          return (EOPNOTSUPP);
  }
  
  static SYSCTL_NODE(_vfs, VFS_GENERIC, generic, CTLFLAG_RD | CTLFLAG_SKIP |
      CTLFLAG_MPSAFE, vfs_sysctl,
      "Generic filesystem");
  
  #if 1 || defined(COMPAT_PRELITE2)
  
  static int
  sysctl_ovfs_conf(SYSCTL_HANDLER_ARGS)
  {
          int error;
          struct vfsconf *vfsp;
          struct ovfsconf ovfs;
  
          vfsconf_slock();
          TAILQ_FOREACH(vfsp, &vfsconf, vfc_list) {
                  bzero(&ovfs, sizeof(ovfs));
                  ovfs.vfc_vfsops = vfsp->vfc_vfsops;     /* XXX used as flag */
                  strcpy(ovfs.vfc_name, vfsp->vfc_name);
                  ovfs.vfc_index = vfsp->vfc_typenum;
                  ovfs.vfc_refcount = vfsp->vfc_refcount;
                  ovfs.vfc_flags = vfsp->vfc_flags;
                  error = SYSCTL_OUT(req, &ovfs, sizeof ovfs);
                  if (error != 0) {
                          vfsconf_sunlock();
                          return (error);
                  }
          }
          vfsconf_sunlock();
          return (0);
  }
  
  #endif /* 1 || COMPAT_PRELITE2 */
  #endif /* !BURN_BRIDGES */
  
  #define KINFO_VNODESLOP         10
  #ifdef notyet
  /*
   * Dump vnode list (via sysctl).
   */
  /* ARGSUSED */
  static int
  sysctl_vnode(SYSCTL_HANDLER_ARGS)
  {
          struct xvnode *xvn;
          struct mount *mp;
          struct vnode *vp;
          int error, len, n;
  
          /*
           * Stale numvnodes access is not fatal here.
           */
          req->lock = 0;
          len = (numvnodes + KINFO_VNODESLOP) * sizeof *xvn;
          if (!req->oldptr)
                  /* Make an estimate */
                  return (SYSCTL_OUT(req, 0, len));
  
          error = sysctl_wire_old_buffer(req, 0);
          if (error != 0)
                  return (error);
          xvn = malloc(len, M_TEMP, M_ZERO | M_WAITOK);
          n = 0;
          mtx_lock(&mountlist_mtx);
          TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                  if (vfs_busy(mp, MBF_NOWAIT | MBF_MNTLSTLOCK))
                          continue;
                  MNT_ILOCK(mp);
                  TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                          if (n == len)
                                  break;
                          vref(vp);
                          xvn[n].xv_size = sizeof *xvn;
                          xvn[n].xv_vnode = vp;
                          xvn[n].xv_id = 0;       /* XXX compat */
  #define XV_COPY(field) xvn[n].xv_##field = vp->v_##field
                          XV_COPY(usecount);
                          XV_COPY(writecount);
                          XV_COPY(holdcnt);
                          XV_COPY(mount);
                          XV_COPY(numoutput);
                          XV_COPY(type);
  #undef XV_COPY
                          xvn[n].xv_flag = vp->v_vflag;
  
                          switch (vp->v_type) {
                          case VREG:
                          case VDIR:
                          case VLNK:
                                  break;
                          case VBLK:
                          case VCHR:
                                  if (vp->v_rdev == NULL) {
                                          vrele(vp);
                                          continue;
                                  }
                                  xvn[n].xv_dev = dev2udev(vp->v_rdev);
                                  break;
                          case VSOCK:
                                  xvn[n].xv_socket = vp->v_socket;
                                  break;
                          case VFIFO:
                                  xvn[n].xv_fifo = vp->v_fifoinfo;
                                  break;
                          case VNON:
                          case VBAD:
                          default:
                                  /* shouldn't happen? */
                                  vrele(vp);
                                  continue;
                          }
                          vrele(vp);
                          ++n;
                  }
                  MNT_IUNLOCK(mp);
                  mtx_lock(&mountlist_mtx);
                  vfs_unbusy(mp);
                  if (n == len)
                          break;
          }
          mtx_unlock(&mountlist_mtx);
  
          error = SYSCTL_OUT(req, xvn, n * sizeof *xvn);
          free(xvn, M_TEMP);
          return (error);
  }
  
  SYSCTL_PROC(_kern, KERN_VNODE, vnode, CTLTYPE_OPAQUE | CTLFLAG_RD |
      CTLFLAG_MPSAFE, 0, 0, sysctl_vnode, "S,xvnode",
      "");
  #endif
  
  static void
  unmount_or_warn(struct mount *mp)
  {
          int error;
  
          error = dounmount(mp, MNT_FORCE, curthread);
          if (error != 0) {
                  printf("unmount of %s failed (", mp->mnt_stat.f_mntonname);
                  if (error == EBUSY)
                          printf("BUSY)\n");
                  else
                          printf("%d)\n", error);
          }
  }
  
  /*
   * Unmount all filesystems. The list is traversed in reverse order
   * of mounting to avoid dependencies.
   */
  void
  vfs_unmountall(void)
  {
          struct mount *mp, *tmp;
  
          CTR1(KTR_VFS, "%s: unmounting all filesystems", __func__);
  
          /*
           * Since this only runs when rebooting, it is not interlocked.
           */
          TAILQ_FOREACH_REVERSE_SAFE(mp, &mountlist, mntlist, mnt_list, tmp) {
                  vfs_ref(mp);
  
                  /*
                   * Forcibly unmounting "/dev" before "/" would prevent clean
                   * unmount of the latter.
                   */
                  if (mp == rootdevmp)
                          continue;
  
                  unmount_or_warn(mp);
          }
  
          if (rootdevmp != NULL)
                  unmount_or_warn(rootdevmp);
  }
  
  static void
  vfs_deferred_inactive(struct vnode *vp, int lkflags)
  {
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNASSERT((vp->v_iflag & VI_DEFINACT) == 0, vp, ("VI_DEFINACT still set"));
          if ((vp->v_iflag & VI_OWEINACT) == 0) {
                  vdropl(vp);
                  return;
          }
          if (vn_lock(vp, lkflags) == 0) {
                  VI_LOCK(vp);
                  vinactive(vp);
                  VOP_UNLOCK(vp);
                  vdropl(vp);
                  return;
          }
          vdefer_inactive_unlocked(vp);
  }
  
  static int
  vfs_periodic_inactive_filter(struct vnode *vp, void *arg)
  {
  
          return (vp->v_iflag & VI_DEFINACT);
  }
  
  static void __noinline
  vfs_periodic_inactive(struct mount *mp, int flags)
  {
          struct vnode *vp, *mvp;
          int lkflags;
  
          lkflags = LK_EXCLUSIVE | LK_INTERLOCK;
          if (flags != MNT_WAIT)
                  lkflags |= LK_NOWAIT;
  
          MNT_VNODE_FOREACH_LAZY(vp, mp, mvp, vfs_periodic_inactive_filter, NULL) {
                  if ((vp->v_iflag & VI_DEFINACT) == 0) {
                          VI_UNLOCK(vp);
                          continue;
                  }
                  vp->v_iflag &= ~VI_DEFINACT;
                  vfs_deferred_inactive(vp, lkflags);
          }
  }
  
  static inline bool
  vfs_want_msync(struct vnode *vp)
  {
          struct vm_object *obj;
  
          /*
           * This test may be performed without any locks held.
           * We rely on vm_object's type stability.
           */
          if (vp->v_vflag & VV_NOSYNC)
                  return (false);
          obj = vp->v_object;
          return (obj != NULL && vm_object_mightbedirty(obj));
  }
  
  static int
  vfs_periodic_msync_inactive_filter(struct vnode *vp, void *arg __unused)
  {
  
          if (vp->v_vflag & VV_NOSYNC)
                  return (false);
          if (vp->v_iflag & VI_DEFINACT)
                  return (true);
          return (vfs_want_msync(vp));
  }
  
  static void __noinline
  vfs_periodic_msync_inactive(struct mount *mp, int flags)
  {
          struct vnode *vp, *mvp;
          struct vm_object *obj;
          int lkflags, objflags;
          bool seen_defer;
  
          lkflags = LK_EXCLUSIVE | LK_INTERLOCK;
          if (flags != MNT_WAIT) {
                  lkflags |= LK_NOWAIT;
                  objflags = OBJPC_NOSYNC;
          } else {
                  objflags = OBJPC_SYNC;
          }
  
          MNT_VNODE_FOREACH_LAZY(vp, mp, mvp, vfs_periodic_msync_inactive_filter, NULL) {
                  seen_defer = false;
                  if (vp->v_iflag & VI_DEFINACT) {
                          vp->v_iflag &= ~VI_DEFINACT;
                          seen_defer = true;
                  }
                  if (!vfs_want_msync(vp)) {
                          if (seen_defer)
                                  vfs_deferred_inactive(vp, lkflags);
                          else
                                  VI_UNLOCK(vp);
                          continue;
                  }
                  if (vget(vp, lkflags) == 0) {
                          obj = vp->v_object;
                          if (obj != NULL && (vp->v_vflag & VV_NOSYNC) == 0) {
                                  VM_OBJECT_WLOCK(obj);
                                  vm_object_page_clean(obj, 0, 0, objflags);
                                  VM_OBJECT_WUNLOCK(obj);
                          }
                          vput(vp);
                          if (seen_defer)
                                  vdrop(vp);
                  } else {
                          if (seen_defer)
                                  vdefer_inactive_unlocked(vp);
                  }
          }
  }
  
  void
  vfs_periodic(struct mount *mp, int flags)
  {
  
          CTR2(KTR_VFS, "%s: mp %p", __func__, mp);
  
          if ((mp->mnt_kern_flag & MNTK_NOMSYNC) != 0)
                  vfs_periodic_inactive(mp, flags);
          else
                  vfs_periodic_msync_inactive(mp, flags);
  }
  
  static void
  destroy_vpollinfo_free(struct vpollinfo *vi)
  {
  
          knlist_destroy(&vi->vpi_selinfo.si_note);
          mtx_destroy(&vi->vpi_lock);
          free(vi, M_VNODEPOLL);
  }
  
  static void
  destroy_vpollinfo(struct vpollinfo *vi)
  {
  
          knlist_clear(&vi->vpi_selinfo.si_note, 1);
          seldrain(&vi->vpi_selinfo);
          destroy_vpollinfo_free(vi);
  }
  
  /*
   * Initialize per-vnode helper structure to hold poll-related state.
   */
  void
  v_addpollinfo(struct vnode *vp)
  {
          struct vpollinfo *vi;
  
          if (vp->v_pollinfo != NULL)
                  return;
          vi = malloc(sizeof(*vi), M_VNODEPOLL, M_WAITOK | M_ZERO);
          mtx_init(&vi->vpi_lock, "vnode pollinfo", NULL, MTX_DEF);
          knlist_init(&vi->vpi_selinfo.si_note, vp, vfs_knllock,
              vfs_knlunlock, vfs_knl_assert_lock);
          VI_LOCK(vp);
          if (vp->v_pollinfo != NULL) {
                  VI_UNLOCK(vp);
                  destroy_vpollinfo_free(vi);
                  return;
          }
          vp->v_pollinfo = vi;
          VI_UNLOCK(vp);
  }
  
  /*
   * Record a process's interest in events which might happen to
   * a vnode.  Because poll uses the historic select-style interface
   * internally, this routine serves as both the ``check for any
   * pending events'' and the ``record my interest in future events''
   * functions.  (These are done together, while the lock is held,
   * to avoid race conditions.)
   */
  int
  vn_pollrecord(struct vnode *vp, struct thread *td, int events)
  {
  
          v_addpollinfo(vp);
          mtx_lock(&vp->v_pollinfo->vpi_lock);
          if (vp->v_pollinfo->vpi_revents & events) {
                  /*
                   * This leaves events we are not interested
                   * in available for the other process which
                   * which presumably had requested them
                   * (otherwise they would never have been
                   * recorded).
                   */
                  events &= vp->v_pollinfo->vpi_revents;
                  vp->v_pollinfo->vpi_revents &= ~events;
  
                  mtx_unlock(&vp->v_pollinfo->vpi_lock);
                  return (events);
          }
          vp->v_pollinfo->vpi_events |= events;
          selrecord(td, &vp->v_pollinfo->vpi_selinfo);
          mtx_unlock(&vp->v_pollinfo->vpi_lock);
          return (0);
  }
  
  /*
   * Routine to create and manage a filesystem syncer vnode.
   */
  #define sync_close ((int (*)(struct  vop_close_args *))nullop)
  static int      sync_fsync(struct  vop_fsync_args *);
  static int      sync_inactive(struct  vop_inactive_args *);
  static int      sync_reclaim(struct  vop_reclaim_args *);
  
  static struct vop_vector sync_vnodeops = {
          .vop_bypass =   VOP_EOPNOTSUPP,
          .vop_close =    sync_close,             /* close */
          .vop_fsync =    sync_fsync,             /* fsync */
          .vop_inactive = sync_inactive,  /* inactive */
          .vop_need_inactive = vop_stdneed_inactive, /* need_inactive */
          .vop_reclaim =  sync_reclaim,   /* reclaim */
          .vop_lock1 =    vop_stdlock,    /* lock */
          .vop_unlock =   vop_stdunlock,  /* unlock */
          .vop_islocked = vop_stdislocked,        /* islocked */
  };
  VFS_VOP_VECTOR_REGISTER(sync_vnodeops);
  
  /*
   * Create a new filesystem syncer vnode for the specified mount point.
   */
  void
  vfs_allocate_syncvnode(struct mount *mp)
  {
          struct vnode *vp;
          struct bufobj *bo;
          static long start, incr, next;
          int error;
  
          /* Allocate a new vnode */
          error = getnewvnode("syncer", mp, &sync_vnodeops, &vp);
          if (error != 0)
                  panic("vfs_allocate_syncvnode: getnewvnode() failed");
          vp->v_type = VNON;
          vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
          vp->v_vflag |= VV_FORCEINSMQ;
          error = insmntque(vp, mp);
          if (error != 0)
                  panic("vfs_allocate_syncvnode: insmntque() failed");
          vp->v_vflag &= ~VV_FORCEINSMQ;
          VOP_UNLOCK(vp);
          /*
           * Place the vnode onto the syncer worklist. We attempt to
           * scatter them about on the list so that they will go off
           * at evenly distributed times even if all the filesystems
           * are mounted at once.
           */
          next += incr;
          if (next == 0 || next > syncer_maxdelay) {
                  start /= 2;
                  incr /= 2;
                  if (start == 0) {
                          start = syncer_maxdelay / 2;
                          incr = syncer_maxdelay;
                  }
                  next = start;
          }
          bo = &vp->v_bufobj;
          BO_LOCK(bo);
          vn_syncer_add_to_worklist(bo, syncdelay > 0 ? next % syncdelay : 0);
          /* XXX - vn_syncer_add_to_worklist() also grabs and drops sync_mtx. */
          mtx_lock(&sync_mtx);
          sync_vnode_count++;
          if (mp->mnt_syncer == NULL) {
                  mp->mnt_syncer = vp;
                  vp = NULL;
          }
          mtx_unlock(&sync_mtx);
          BO_UNLOCK(bo);
          if (vp != NULL) {
                  vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
                  vgone(vp);
                  vput(vp);
          }
  }
  
  void
  vfs_deallocate_syncvnode(struct mount *mp)
  {
          struct vnode *vp;
  
          mtx_lock(&sync_mtx);
          vp = mp->mnt_syncer;
          if (vp != NULL)
                  mp->mnt_syncer = NULL;
          mtx_unlock(&sync_mtx);
          if (vp != NULL)
                  vrele(vp);
  }
  
  /*
   * Do a lazy sync of the filesystem.
   */
  static int
  sync_fsync(struct vop_fsync_args *ap)
  {
          struct vnode *syncvp = ap->a_vp;
          struct mount *mp = syncvp->v_mount;
          int error, save;
          struct bufobj *bo;
  
          /*
           * We only need to do something if this is a lazy evaluation.
           */
          if (ap->a_waitfor != MNT_LAZY)
                  return (0);
  
          /*
           * Move ourselves to the back of the sync list.
           */
          bo = &syncvp->v_bufobj;
          BO_LOCK(bo);
          vn_syncer_add_to_worklist(bo, syncdelay);
          BO_UNLOCK(bo);
  
          /*
           * Walk the list of vnodes pushing all that are dirty and
           * not already on the sync list.
           */
          if (vfs_busy(mp, MBF_NOWAIT) != 0)
                  return (0);
          VOP_UNLOCK(syncvp);
          save = curthread_pflags_set(TDP_SYNCIO);
          /*
           * The filesystem at hand may be idle with free vnodes stored in the
           * batch.  Return them instead of letting them stay there indefinitely.
           */
          vfs_periodic(mp, MNT_NOWAIT);
          error = VFS_SYNC(mp, MNT_LAZY);
          curthread_pflags_restore(save);
          vn_lock(syncvp, LK_EXCLUSIVE | LK_RETRY);
          vfs_unbusy(mp);
          return (error);
  }
  
  /*
   * The syncer vnode is no referenced.
   */
  static int
  sync_inactive(struct vop_inactive_args *ap)
  {
  
          vgone(ap->a_vp);
          return (0);
  }
  
  /*
   * The syncer vnode is no longer needed and is being decommissioned.
   *
   * Modifications to the worklist must be protected by sync_mtx.
   */
  static int
  sync_reclaim(struct vop_reclaim_args *ap)
  {
          struct vnode *vp = ap->a_vp;
          struct bufobj *bo;
  
          bo = &vp->v_bufobj;
          BO_LOCK(bo);
          mtx_lock(&sync_mtx);
          if (vp->v_mount->mnt_syncer == vp)
                  vp->v_mount->mnt_syncer = NULL;
          if (bo->bo_flag & BO_ONWORKLST) {
                  LIST_REMOVE(bo, bo_synclist);
                  syncer_worklist_len--;
                  sync_vnode_count--;
                  bo->bo_flag &= ~BO_ONWORKLST;
          }
          mtx_unlock(&sync_mtx);
          BO_UNLOCK(bo);
  
          return (0);
  }
  
  int
  vn_need_pageq_flush(struct vnode *vp)
  {
          struct vm_object *obj;
  
          obj = vp->v_object;
          return (obj != NULL && (vp->v_vflag & VV_NOSYNC) == 0 &&
              vm_object_mightbedirty(obj));
  }
  
  /*
   * Check if vnode represents a disk device
   */
  bool
  vn_isdisk_error(struct vnode *vp, int *errp)
  {
          int error;
  
          if (vp->v_type != VCHR) {
                  error = ENOTBLK;
                  goto out;
          }
          error = 0;
          dev_lock();
          if (vp->v_rdev == NULL)
                  error = ENXIO;
          else if (vp->v_rdev->si_devsw == NULL)
                  error = ENXIO;
          else if (!(vp->v_rdev->si_devsw->d_flags & D_DISK))
                  error = ENOTBLK;
          dev_unlock();
  out:
          *errp = error;
          return (error == 0);
  }
  
  bool
  vn_isdisk(struct vnode *vp)
  {
          int error;
  
          return (vn_isdisk_error(vp, &error));
  }
  
  /*
   * VOP_FPLOOKUP_VEXEC routines are subject to special circumstances, see
   * the comment above cache_fplookup for details.
   */
  int
  vaccess_vexec_smr(mode_t file_mode, uid_t file_uid, gid_t file_gid, struct ucred *cred)
  {
          int error;
  
          VFS_SMR_ASSERT_ENTERED();
  
          /* Check the owner. */
          if (cred->cr_uid == file_uid) {
                  if (file_mode & S_IXUSR)
                          return (0);
                  goto out_error;
          }
  
          /* Otherwise, check the groups (first match) */
          if (groupmember(file_gid, cred)) {
                  if (file_mode & S_IXGRP)
                          return (0);
                  goto out_error;
          }
  
          /* Otherwise, check everyone else. */
          if (file_mode & S_IXOTH)
                  return (0);
  out_error:
          /*
           * Permission check failed, but it is possible denial will get overwritten
           * (e.g., when root is traversing through a 700 directory owned by someone
           * else).
           *
           * vaccess() calls priv_check_cred which in turn can descent into MAC
           * modules overriding this result. It's quite unclear what semantics
           * are allowed for them to operate, thus for safety we don't call them
           * from within the SMR section. This also means if any such modules
           * are present, we have to let the regular lookup decide.
           */
          error = priv_check_cred_vfs_lookup_nomac(cred);
          switch (error) {
          case 0:
                  return (0);
          case EAGAIN:
                  /*
                   * MAC modules present.
                   */
                  return (EAGAIN);
          case EPERM:
                  return (EACCES);
          default:
                  return (error);
          }
  }
  
  /*
   * Common filesystem object access control check routine.  Accepts a
   * vnode's type, "mode", uid and gid, requested access mode, and credentials.
   * Returns 0 on success, or an errno on failure.
   */
  int
  vaccess(enum vtype type, mode_t file_mode, uid_t file_uid, gid_t file_gid,
      accmode_t accmode, struct ucred *cred)
  {
          accmode_t dac_granted;
          accmode_t priv_granted;
  
          KASSERT((accmode & ~(VEXEC | VWRITE | VREAD | VADMIN | VAPPEND)) == 0,
              ("invalid bit in accmode"));
          KASSERT((accmode & VAPPEND) == 0 || (accmode & VWRITE),
              ("VAPPEND without VWRITE"));
  
          /*
           * Look for a normal, non-privileged way to access the file/directory
           * as requested.  If it exists, go with that.
           */
  
          dac_granted = 0;
  
          /* Check the owner. */
          if (cred->cr_uid == file_uid) {
                  dac_granted |= VADMIN;
                  if (file_mode & S_IXUSR)
                          dac_granted |= VEXEC;
                  if (file_mode & S_IRUSR)
                          dac_granted |= VREAD;
                  if (file_mode & S_IWUSR)
                          dac_granted |= (VWRITE | VAPPEND);
  
                  if ((accmode & dac_granted) == accmode)
                          return (0);
  
                  goto privcheck;
          }
  
          /* Otherwise, check the groups (first match) */
          if (groupmember(file_gid, cred)) {
                  if (file_mode & S_IXGRP)
                          dac_granted |= VEXEC;
                  if (file_mode & S_IRGRP)
                          dac_granted |= VREAD;
                  if (file_mode & S_IWGRP)
                          dac_granted |= (VWRITE | VAPPEND);
  
                  if ((accmode & dac_granted) == accmode)
                          return (0);
  
                  goto privcheck;
          }
  
          /* Otherwise, check everyone else. */
          if (file_mode & S_IXOTH)
                  dac_granted |= VEXEC;
          if (file_mode & S_IROTH)
                  dac_granted |= VREAD;
          if (file_mode & S_IWOTH)
                  dac_granted |= (VWRITE | VAPPEND);
          if ((accmode & dac_granted) == accmode)
                  return (0);
  
  privcheck:
          /*
           * Build a privilege mask to determine if the set of privileges
           * satisfies the requirements when combined with the granted mask
           * from above.  For each privilege, if the privilege is required,
           * bitwise or the request type onto the priv_granted mask.
           */
          priv_granted = 0;
  
          if (type == VDIR) {
                  /*
                   * For directories, use PRIV_VFS_LOOKUP to satisfy VEXEC
                   * requests, instead of PRIV_VFS_EXEC.
                   */
                  if ((accmode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                      !priv_check_cred(cred, PRIV_VFS_LOOKUP))
                          priv_granted |= VEXEC;
          } else {
                  /*
                   * Ensure that at least one execute bit is on. Otherwise,
                   * a privileged user will always succeed, and we don't want
                   * this to happen unless the file really is executable.
                   */
                  if ((accmode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                      (file_mode & (S_IXUSR | S_IXGRP | S_IXOTH)) != 0 &&
                      !priv_check_cred(cred, PRIV_VFS_EXEC))
                          priv_granted |= VEXEC;
          }
  
          if ((accmode & VREAD) && ((dac_granted & VREAD) == 0) &&
              !priv_check_cred(cred, PRIV_VFS_READ))
                  priv_granted |= VREAD;
  
          if ((accmode & VWRITE) && ((dac_granted & VWRITE) == 0) &&
              !priv_check_cred(cred, PRIV_VFS_WRITE))
                  priv_granted |= (VWRITE | VAPPEND);
  
          if ((accmode & VADMIN) && ((dac_granted & VADMIN) == 0) &&
              !priv_check_cred(cred, PRIV_VFS_ADMIN))
                  priv_granted |= VADMIN;
  
          if ((accmode & (priv_granted | dac_granted)) == accmode) {
                  return (0);
          }
  
          return ((accmode & VADMIN) ? EPERM : EACCES);
  }
  
  /*
   * Credential check based on process requesting service, and per-attribute
   * permissions.
   */
  int
  extattr_check_cred(struct vnode *vp, int attrnamespace, struct ucred *cred,
      struct thread *td, accmode_t accmode)
  {
  
          /*
           * Kernel-invoked always succeeds.
           */
          if (cred == NOCRED)
                  return (0);
  
          /*
           * Do not allow privileged processes in jail to directly manipulate
           * system attributes.
           */
          switch (attrnamespace) {
          case EXTATTR_NAMESPACE_SYSTEM:
                  /* Potentially should be: return (EPERM); */
                  return (priv_check_cred(cred, PRIV_VFS_EXTATTR_SYSTEM));
          case EXTATTR_NAMESPACE_USER:
                  return (VOP_ACCESS(vp, accmode, cred, td));
          default:
                  return (EPERM);
          }
  }
  
  #ifdef DEBUG_VFS_LOCKS
  int vfs_badlock_ddb = 1;        /* Drop into debugger on violation. */
  SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_ddb, CTLFLAG_RW, &vfs_badlock_ddb, 0,
      "Drop into debugger on lock violation");
  
  int vfs_badlock_mutex = 1;      /* Check for interlock across VOPs. */
  SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_mutex, CTLFLAG_RW, &vfs_badlock_mutex,
      0, "Check for interlock across VOPs");
  
  int vfs_badlock_print = 1;      /* Print lock violations. */
  SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_print, CTLFLAG_RW, &vfs_badlock_print,
      0, "Print lock violations");
  
  int vfs_badlock_vnode = 1;      /* Print vnode details on lock violations. */
  SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_vnode, CTLFLAG_RW, &vfs_badlock_vnode,
      0, "Print vnode details on lock violations");
  
  #ifdef KDB
  int vfs_badlock_backtrace = 1;  /* Print backtrace at lock violations. */
  SYSCTL_INT(_debug, OID_AUTO, vfs_badlock_backtrace, CTLFLAG_RW,
      &vfs_badlock_backtrace, 0, "Print backtrace at lock violations");
  #endif
  
  static void
  vfs_badlock(const char *msg, const char *str, struct vnode *vp)
  {
  
  #ifdef KDB
          if (vfs_badlock_backtrace)
                  kdb_backtrace();
  #endif
          if (vfs_badlock_vnode)
                  vn_printf(vp, "vnode ");
          if (vfs_badlock_print)
                  printf("%s: %p %s\n", str, (void *)vp, msg);
          if (vfs_badlock_ddb)
                  kdb_enter(KDB_WHY_VFSLOCK, "lock violation");
  }
  
  void
  assert_vi_locked(struct vnode *vp, const char *str)
  {
  
          if (vfs_badlock_mutex && !mtx_owned(VI_MTX(vp)))
                  vfs_badlock("interlock is not locked but should be", str, vp);
  }
  
  void
  assert_vi_unlocked(struct vnode *vp, const char *str)
  {
  
          if (vfs_badlock_mutex && mtx_owned(VI_MTX(vp)))
                  vfs_badlock("interlock is locked but should not be", str, vp);
  }
  
  void
  assert_vop_locked(struct vnode *vp, const char *str)
  {
          int locked;
  
          if (KERNEL_PANICKED() || vp == NULL)
                  return;
  
          locked = VOP_ISLOCKED(vp);
          if (locked == 0 || locked == LK_EXCLOTHER)
                  vfs_badlock("is not locked but should be", str, vp);
  }
  
  void
  assert_vop_unlocked(struct vnode *vp, const char *str)
  {
          if (KERNEL_PANICKED() || vp == NULL)
                  return;
  
          if (VOP_ISLOCKED(vp) == LK_EXCLUSIVE)
                  vfs_badlock("is locked but should not be", str, vp);
  }
  
  void
  assert_vop_elocked(struct vnode *vp, const char *str)
  {
          if (KERNEL_PANICKED() || vp == NULL)
                  return;
  
          if (VOP_ISLOCKED(vp) != LK_EXCLUSIVE)
                  vfs_badlock("is not exclusive locked but should be", str, vp);
  }
  #endif /* DEBUG_VFS_LOCKS */
  
  void
  vop_rename_fail(struct vop_rename_args *ap)
  {
  
          if (ap->a_tvp != NULL)
                  vput(ap->a_tvp);
          if (ap->a_tdvp == ap->a_tvp)
                  vrele(ap->a_tdvp);
          else
                  vput(ap->a_tdvp);
          vrele(ap->a_fdvp);
          vrele(ap->a_fvp);
  }
  
  void
  vop_rename_pre(void *ap)
  {
          struct vop_rename_args *a = ap;
  
  #ifdef DEBUG_VFS_LOCKS
          if (a->a_tvp)
                  ASSERT_VI_UNLOCKED(a->a_tvp, "VOP_RENAME");
          ASSERT_VI_UNLOCKED(a->a_tdvp, "VOP_RENAME");
          ASSERT_VI_UNLOCKED(a->a_fvp, "VOP_RENAME");
          ASSERT_VI_UNLOCKED(a->a_fdvp, "VOP_RENAME");
  
          /* Check the source (from). */
          if (a->a_tdvp->v_vnlock != a->a_fdvp->v_vnlock &&
              (a->a_tvp == NULL || a->a_tvp->v_vnlock != a->a_fdvp->v_vnlock))
                  ASSERT_VOP_UNLOCKED(a->a_fdvp, "vop_rename: fdvp locked");
          if (a->a_tvp == NULL || a->a_tvp->v_vnlock != a->a_fvp->v_vnlock)
                  ASSERT_VOP_UNLOCKED(a->a_fvp, "vop_rename: fvp locked");
  
          /* Check the target. */
          if (a->a_tvp)
                  ASSERT_VOP_LOCKED(a->a_tvp, "vop_rename: tvp not locked");
          ASSERT_VOP_LOCKED(a->a_tdvp, "vop_rename: tdvp not locked");
  #endif
          /*
           * It may be tempting to add vn_seqc_write_begin/end calls here and
           * in vop_rename_post but that's not going to work out since some
           * filesystems relookup vnodes mid-rename. This is probably a bug.
           *
           * For now filesystems are expected to do the relevant calls after they
           * decide what vnodes to operate on.
           */
          if (a->a_tdvp != a->a_fdvp)
                  vhold(a->a_fdvp);
          if (a->a_tvp != a->a_fvp)
                  vhold(a->a_fvp);
          vhold(a->a_tdvp);
          if (a->a_tvp)
                  vhold(a->a_tvp);
  }
  
  #ifdef DEBUG_VFS_LOCKS
  void
  vop_fplookup_vexec_debugpre(void *ap __unused)
  {
  
          VFS_SMR_ASSERT_ENTERED();
  }
  
  void
  vop_fplookup_vexec_debugpost(void *ap __unused, int rc __unused)
  {
  
          VFS_SMR_ASSERT_ENTERED();
  }
  
  void
  vop_fplookup_symlink_debugpre(void *ap __unused)
  {
  
          VFS_SMR_ASSERT_ENTERED();
  }
  
  void
  vop_fplookup_symlink_debugpost(void *ap __unused, int rc __unused)
  {
  
          VFS_SMR_ASSERT_ENTERED();
  }
  
  static void
  vop_fsync_debugprepost(struct vnode *vp, const char *name)
  {
          if (vp->v_type == VCHR)
                  ;
          else if (MNT_EXTENDED_SHARED(vp->v_mount))
                  ASSERT_VOP_LOCKED(vp, name);
          else
                  ASSERT_VOP_ELOCKED(vp, name);
  }
  
  void
  vop_fsync_debugpre(void *a)
  {
          struct vop_fsync_args *ap;
  
          ap = a;
          vop_fsync_debugprepost(ap->a_vp, "fsync");
  }
  
  void
  vop_fsync_debugpost(void *a, int rc __unused)
  {
          struct vop_fsync_args *ap;
  
          ap = a;
          vop_fsync_debugprepost(ap->a_vp, "fsync");
  }
  
  void
  vop_fdatasync_debugpre(void *a)
  {
          struct vop_fdatasync_args *ap;
  
          ap = a;
          vop_fsync_debugprepost(ap->a_vp, "fsync");
  }
  
  void
  vop_fdatasync_debugpost(void *a, int rc __unused)
  {
          struct vop_fdatasync_args *ap;
  
          ap = a;
          vop_fsync_debugprepost(ap->a_vp, "fsync");
  }
  
  void
  vop_strategy_debugpre(void *ap)
  {
          struct vop_strategy_args *a;
          struct buf *bp;
  
          a = ap;
          bp = a->a_bp;
  
          /*
           * Cluster ops lock their component buffers but not the IO container.
           */
          if ((bp->b_flags & B_CLUSTER) != 0)
                  return;
  
          if (!KERNEL_PANICKED() && !BUF_ISLOCKED(bp)) {
                  if (vfs_badlock_print)
                          printf(
                              "VOP_STRATEGY: bp is not locked but should be\n");
                  if (vfs_badlock_ddb)
                          kdb_enter(KDB_WHY_VFSLOCK, "lock violation");
          }
  }
  
  void
  vop_lock_debugpre(void *ap)
  {
          struct vop_lock1_args *a = ap;
  
          if ((a->a_flags & LK_INTERLOCK) == 0)
                  ASSERT_VI_UNLOCKED(a->a_vp, "VOP_LOCK");
          else
                  ASSERT_VI_LOCKED(a->a_vp, "VOP_LOCK");
  }
  
  void
  vop_lock_debugpost(void *ap, int rc)
  {
          struct vop_lock1_args *a = ap;
  
          ASSERT_VI_UNLOCKED(a->a_vp, "VOP_LOCK");
          if (rc == 0 && (a->a_flags & LK_EXCLOTHER) == 0)
                  ASSERT_VOP_LOCKED(a->a_vp, "VOP_LOCK");
  }
  
  void
  vop_unlock_debugpre(void *ap)
  {
          struct vop_unlock_args *a = ap;
  
          ASSERT_VOP_LOCKED(a->a_vp, "VOP_UNLOCK");
  }
  
  void
  vop_need_inactive_debugpre(void *ap)
  {
          struct vop_need_inactive_args *a = ap;
  
          ASSERT_VI_LOCKED(a->a_vp, "VOP_NEED_INACTIVE");
  }
  
  void
  vop_need_inactive_debugpost(void *ap, int rc)
  {
          struct vop_need_inactive_args *a = ap;
  
          ASSERT_VI_LOCKED(a->a_vp, "VOP_NEED_INACTIVE");
  }
  #endif
  
  void
  vop_create_pre(void *ap)
  {
          struct vop_create_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_begin(dvp);
  }
  
  void
  vop_create_post(void *ap, int rc)
  {
          struct vop_create_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_end(dvp);
          if (!rc)
                  VFS_KNOTE_LOCKED(dvp, NOTE_WRITE);
  }
  
  void
  vop_whiteout_pre(void *ap)
  {
          struct vop_whiteout_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_begin(dvp);
  }
  
  void
  vop_whiteout_post(void *ap, int rc)
  {
          struct vop_whiteout_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_end(dvp);
  }
  
  void
  vop_deleteextattr_pre(void *ap)
  {
          struct vop_deleteextattr_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_begin(vp);
  }
  
  void
  vop_deleteextattr_post(void *ap, int rc)
  {
          struct vop_deleteextattr_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_end(vp);
          if (!rc)
                  VFS_KNOTE_LOCKED(a->a_vp, NOTE_ATTRIB);
  }
  
  void
  vop_link_pre(void *ap)
  {
          struct vop_link_args *a;
          struct vnode *vp, *tdvp;
  
          a = ap;
          vp = a->a_vp;
          tdvp = a->a_tdvp;
          vn_seqc_write_begin(vp);
          vn_seqc_write_begin(tdvp);
  }
  
  void
  vop_link_post(void *ap, int rc)
  {
          struct vop_link_args *a;
          struct vnode *vp, *tdvp;
  
          a = ap;
          vp = a->a_vp;
          tdvp = a->a_tdvp;
          vn_seqc_write_end(vp);
          vn_seqc_write_end(tdvp);
          if (!rc) {
                  VFS_KNOTE_LOCKED(vp, NOTE_LINK);
                  VFS_KNOTE_LOCKED(tdvp, NOTE_WRITE);
          }
  }
  
  void
  vop_mkdir_pre(void *ap)
  {
          struct vop_mkdir_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_begin(dvp);
  }
  
  void
  vop_mkdir_post(void *ap, int rc)
  {
          struct vop_mkdir_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_end(dvp);
          if (!rc)
                  VFS_KNOTE_LOCKED(dvp, NOTE_WRITE | NOTE_LINK);
  }
  
  #ifdef DEBUG_VFS_LOCKS
  void
  vop_mkdir_debugpost(void *ap, int rc)
  {
          struct vop_mkdir_args *a;
  
          a = ap;
          if (!rc)
                  cache_validate(a->a_dvp, *a->a_vpp, a->a_cnp);
  }
  #endif
  
  void
  vop_mknod_pre(void *ap)
  {
          struct vop_mknod_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_begin(dvp);
  }
  
  void
  vop_mknod_post(void *ap, int rc)
  {
          struct vop_mknod_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_end(dvp);
          if (!rc)
                  VFS_KNOTE_LOCKED(dvp, NOTE_WRITE);
  }
  
  void
  vop_reclaim_post(void *ap, int rc)
  {
          struct vop_reclaim_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          ASSERT_VOP_IN_SEQC(vp);
          if (!rc)
                  VFS_KNOTE_LOCKED(vp, NOTE_REVOKE);
  }
  
  void
  vop_remove_pre(void *ap)
  {
          struct vop_remove_args *a;
          struct vnode *dvp, *vp;
  
          a = ap;
          dvp = a->a_dvp;
          vp = a->a_vp;
          vn_seqc_write_begin(dvp);
          vn_seqc_write_begin(vp);
  }
  
  void
  vop_remove_post(void *ap, int rc)
  {
          struct vop_remove_args *a;
          struct vnode *dvp, *vp;
  
          a = ap;
          dvp = a->a_dvp;
          vp = a->a_vp;
          vn_seqc_write_end(dvp);
          vn_seqc_write_end(vp);
          if (!rc) {
                  VFS_KNOTE_LOCKED(dvp, NOTE_WRITE);
                  VFS_KNOTE_LOCKED(vp, NOTE_DELETE);
          }
  }
  
  void
  vop_rename_post(void *ap, int rc)
  {
          struct vop_rename_args *a = ap;
          long hint;
  
          if (!rc) {
                  hint = NOTE_WRITE;
                  if (a->a_fdvp == a->a_tdvp) {
                          if (a->a_tvp != NULL && a->a_tvp->v_type == VDIR)
                                  hint |= NOTE_LINK;
                          VFS_KNOTE_UNLOCKED(a->a_fdvp, hint);
                          VFS_KNOTE_UNLOCKED(a->a_tdvp, hint);
                  } else {
                          hint |= NOTE_EXTEND;
                          if (a->a_fvp->v_type == VDIR)
                                  hint |= NOTE_LINK;
                          VFS_KNOTE_UNLOCKED(a->a_fdvp, hint);
  
                          if (a->a_fvp->v_type == VDIR && a->a_tvp != NULL &&
                              a->a_tvp->v_type == VDIR)
                                  hint &= ~NOTE_LINK;
                          VFS_KNOTE_UNLOCKED(a->a_tdvp, hint);
                  }
  
                  VFS_KNOTE_UNLOCKED(a->a_fvp, NOTE_RENAME);
                  if (a->a_tvp)
                          VFS_KNOTE_UNLOCKED(a->a_tvp, NOTE_DELETE);
          }
          if (a->a_tdvp != a->a_fdvp)
                  vdrop(a->a_fdvp);
          if (a->a_tvp != a->a_fvp)
                  vdrop(a->a_fvp);
          vdrop(a->a_tdvp);
          if (a->a_tvp)
                  vdrop(a->a_tvp);
  }
  
  void
  vop_rmdir_pre(void *ap)
  {
          struct vop_rmdir_args *a;
          struct vnode *dvp, *vp;
  
          a = ap;
          dvp = a->a_dvp;
          vp = a->a_vp;
          vn_seqc_write_begin(dvp);
          vn_seqc_write_begin(vp);
  }
  
  void
  vop_rmdir_post(void *ap, int rc)
  {
          struct vop_rmdir_args *a;
          struct vnode *dvp, *vp;
  
          a = ap;
          dvp = a->a_dvp;
          vp = a->a_vp;
          vn_seqc_write_end(dvp);
          vn_seqc_write_end(vp);
          if (!rc) {
                  vp->v_vflag |= VV_UNLINKED;
                  VFS_KNOTE_LOCKED(dvp, NOTE_WRITE | NOTE_LINK);
                  VFS_KNOTE_LOCKED(vp, NOTE_DELETE);
          }
  }
  
  void
  vop_setattr_pre(void *ap)
  {
          struct vop_setattr_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_begin(vp);
  }
  
  void
  vop_setattr_post(void *ap, int rc)
  {
          struct vop_setattr_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_end(vp);
          if (!rc)
                  VFS_KNOTE_LOCKED(vp, NOTE_ATTRIB);
  }
  
  void
  vop_setacl_pre(void *ap)
  {
          struct vop_setacl_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_begin(vp);
  }
  
  void
  vop_setacl_post(void *ap, int rc __unused)
  {
          struct vop_setacl_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_end(vp);
  }
  
  void
  vop_setextattr_pre(void *ap)
  {
          struct vop_setextattr_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_begin(vp);
  }
  
  void
  vop_setextattr_post(void *ap, int rc)
  {
          struct vop_setextattr_args *a;
          struct vnode *vp;
  
          a = ap;
          vp = a->a_vp;
          vn_seqc_write_end(vp);
          if (!rc)
                  VFS_KNOTE_LOCKED(vp, NOTE_ATTRIB);
  }
  
  void
  vop_symlink_pre(void *ap)
  {
          struct vop_symlink_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_begin(dvp);
  }
  
  void
  vop_symlink_post(void *ap, int rc)
  {
          struct vop_symlink_args *a;
          struct vnode *dvp;
  
          a = ap;
          dvp = a->a_dvp;
          vn_seqc_write_end(dvp);
          if (!rc)
                  VFS_KNOTE_LOCKED(dvp, NOTE_WRITE);
  }
  
  void
  vop_open_post(void *ap, int rc)
  {
          struct vop_open_args *a = ap;
  
          if (!rc)
                  VFS_KNOTE_LOCKED(a->a_vp, NOTE_OPEN);
  }
  
  void
  vop_close_post(void *ap, int rc)
  {
          struct vop_close_args *a = ap;
  
          if (!rc && (a->a_cred != NOCRED || /* filter out revokes */
              !VN_IS_DOOMED(a->a_vp))) {
                  VFS_KNOTE_LOCKED(a->a_vp, (a->a_fflag & FWRITE) != 0 ?
                      NOTE_CLOSE_WRITE : NOTE_CLOSE);
          }
  }
  
  void
  vop_read_post(void *ap, int rc)
  {
          struct vop_read_args *a = ap;
  
          if (!rc)
                  VFS_KNOTE_LOCKED(a->a_vp, NOTE_READ);
  }
  
  void
  vop_read_pgcache_post(void *ap, int rc)
  {
          struct vop_read_pgcache_args *a = ap;
  
          if (!rc)
                  VFS_KNOTE_UNLOCKED(a->a_vp, NOTE_READ);
  }
  
  void
  vop_readdir_post(void *ap, int rc)
  {
          struct vop_readdir_args *a = ap;
  
          if (!rc)
                  VFS_KNOTE_LOCKED(a->a_vp, NOTE_READ);
  }
  
  static struct knlist fs_knlist;
  
  static void
  vfs_event_init(void *arg)
  {
          knlist_init_mtx(&fs_knlist, NULL);
  }
  /* XXX - correct order? */
  SYSINIT(vfs_knlist, SI_SUB_VFS, SI_ORDER_ANY, vfs_event_init, NULL);
  
  void
  vfs_event_signal(fsid_t *fsid, uint32_t event, intptr_t data __unused)
  {
  
          KNOTE_UNLOCKED(&fs_knlist, event);
  }
  
  static int      filt_fsattach(struct knote *kn);
  static void     filt_fsdetach(struct knote *kn);
  static int      filt_fsevent(struct knote *kn, long hint);
  
  struct filterops fs_filtops = {
          .f_isfd = 0,
          .f_attach = filt_fsattach,
          .f_detach = filt_fsdetach,
          .f_event = filt_fsevent
  };
  
  static int
  filt_fsattach(struct knote *kn)
  {
  
          kn->kn_flags |= EV_CLEAR;
          knlist_add(&fs_knlist, kn, 0);
          return (0);
  }
  
  static void
  filt_fsdetach(struct knote *kn)
  {
  
          knlist_remove(&fs_knlist, kn, 0);
  }
  
  static int
  filt_fsevent(struct knote *kn, long hint)
  {
  
          kn->kn_fflags |= hint;
          return (kn->kn_fflags != 0);
  }
  
  static int
  sysctl_vfs_ctl(SYSCTL_HANDLER_ARGS)
  {
          struct vfsidctl vc;
          int error;
          struct mount *mp;
  
          error = SYSCTL_IN(req, &vc, sizeof(vc));
          if (error)
                  return (error);
          if (vc.vc_vers != VFS_CTL_VERS1)
                  return (EINVAL);
          mp = vfs_getvfs(&vc.vc_fsid);
          if (mp == NULL)
                  return (ENOENT);
          /* ensure that a specific sysctl goes to the right filesystem. */
          if (strcmp(vc.vc_fstypename, "*") != 0 &&
              strcmp(vc.vc_fstypename, mp->mnt_vfc->vfc_name) != 0) {
                  vfs_rel(mp);
                  return (EINVAL);
          }
          VCTLTOREQ(&vc, req);
          error = VFS_SYSCTL(mp, vc.vc_op, req);
          vfs_rel(mp);
          return (error);
  }
  
  SYSCTL_PROC(_vfs, OID_AUTO, ctl, CTLTYPE_OPAQUE | CTLFLAG_MPSAFE | CTLFLAG_WR,
      NULL, 0, sysctl_vfs_ctl, "",
      "Sysctl by fsid");
  
  /*
   * Function to initialize a va_filerev field sensibly.
   * XXX: Wouldn't a random number make a lot more sense ??
   */
  u_quad_t
  init_va_filerev(void)
  {
          struct bintime bt;
  
          getbinuptime(&bt);
          return (((u_quad_t)bt.sec << 32LL) | (bt.frac >> 32LL));
  }
  
  static int      filt_vfsread(struct knote *kn, long hint);
  static int      filt_vfswrite(struct knote *kn, long hint);
  static int      filt_vfsvnode(struct knote *kn, long hint);
  static void     filt_vfsdetach(struct knote *kn);
  static struct filterops vfsread_filtops = {
          .f_isfd = 1,
          .f_detach = filt_vfsdetach,
          .f_event = filt_vfsread
  };
  static struct filterops vfswrite_filtops = {
          .f_isfd = 1,
          .f_detach = filt_vfsdetach,
          .f_event = filt_vfswrite
  };
  static struct filterops vfsvnode_filtops = {
          .f_isfd = 1,
          .f_detach = filt_vfsdetach,
          .f_event = filt_vfsvnode
  };
  
  static void
  vfs_knllock(void *arg)
  {
          struct vnode *vp = arg;
  
          vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
  }
  
  static void
  vfs_knlunlock(void *arg)
  {
          struct vnode *vp = arg;
  
          VOP_UNLOCK(vp);
  }
  
  static void
  vfs_knl_assert_lock(void *arg, int what)
  {
  #ifdef DEBUG_VFS_LOCKS
          struct vnode *vp = arg;
  
          if (what == LA_LOCKED)
                  ASSERT_VOP_LOCKED(vp, "vfs_knl_assert_locked");
          else
                  ASSERT_VOP_UNLOCKED(vp, "vfs_knl_assert_unlocked");
  #endif
  }
  
  int
  vfs_kqfilter(struct vop_kqfilter_args *ap)
  {
          struct vnode *vp = ap->a_vp;
          struct knote *kn = ap->a_kn;
          struct knlist *knl;
  
          switch (kn->kn_filter) {
          case EVFILT_READ:
                  kn->kn_fop = &vfsread_filtops;
                  break;
          case EVFILT_WRITE:
                  kn->kn_fop = &vfswrite_filtops;
                  break;
          case EVFILT_VNODE:
                  kn->kn_fop = &vfsvnode_filtops;
                  break;
          default:
                  return (EINVAL);
          }
  
          kn->kn_hook = (caddr_t)vp;
  
          v_addpollinfo(vp);
          if (vp->v_pollinfo == NULL)
                  return (ENOMEM);
          knl = &vp->v_pollinfo->vpi_selinfo.si_note;
          vhold(vp);
          knlist_add(knl, kn, 0);
  
          return (0);
  }
  
  /*
   * Detach knote from vnode
   */
  static void
  filt_vfsdetach(struct knote *kn)
  {
          struct vnode *vp = (struct vnode *)kn->kn_hook;
  
          KASSERT(vp->v_pollinfo != NULL, ("Missing v_pollinfo"));
          knlist_remove(&vp->v_pollinfo->vpi_selinfo.si_note, kn, 0);
          vdrop(vp);
  }
  
  /*ARGSUSED*/
  static int
  filt_vfsread(struct knote *kn, long hint)
  {
          struct vnode *vp = (struct vnode *)kn->kn_hook;
          struct vattr va;
          int res;
  
          /*
           * filesystem is gone, so set the EOF flag and schedule
           * the knote for deletion.
           */
          if (hint == NOTE_REVOKE || (hint == 0 && vp->v_type == VBAD)) {
                  VI_LOCK(vp);
                  kn->kn_flags |= (EV_EOF | EV_ONESHOT);
                  VI_UNLOCK(vp);
                  return (1);
          }
  
          if (VOP_GETATTR(vp, &va, curthread->td_ucred))
                  return (0);
  
          VI_LOCK(vp);
          kn->kn_data = va.va_size - kn->kn_fp->f_offset;
          res = (kn->kn_sfflags & NOTE_FILE_POLL) != 0 || kn->kn_data != 0;
          VI_UNLOCK(vp);
          return (res);
  }
  
  /*ARGSUSED*/
  static int
  filt_vfswrite(struct knote *kn, long hint)
  {
          struct vnode *vp = (struct vnode *)kn->kn_hook;
  
          VI_LOCK(vp);
  
          /*
           * filesystem is gone, so set the EOF flag and schedule
           * the knote for deletion.
           */
          if (hint == NOTE_REVOKE || (hint == 0 && vp->v_type == VBAD))
                  kn->kn_flags |= (EV_EOF | EV_ONESHOT);
  
          kn->kn_data = 0;
          VI_UNLOCK(vp);
          return (1);
  }
  
  static int
  filt_vfsvnode(struct knote *kn, long hint)
  {
          struct vnode *vp = (struct vnode *)kn->kn_hook;
          int res;
  
          VI_LOCK(vp);
          if (kn->kn_sfflags & hint)
                  kn->kn_fflags |= hint;
          if (hint == NOTE_REVOKE || (hint == 0 && vp->v_type == VBAD)) {
                  kn->kn_flags |= EV_EOF;
                  VI_UNLOCK(vp);
                  return (1);
          }
          res = (kn->kn_fflags != 0);
          VI_UNLOCK(vp);
          return (res);
  }
  
  /*
   * Returns whether the directory is empty or not.
   * If it is empty, the return value is 0; otherwise
   * the return value is an error value (which may
   * be ENOTEMPTY).
   */
  int
  vfs_emptydir(struct vnode *vp)
  {
          struct uio uio;
          struct iovec iov;
          struct dirent *dirent, *dp, *endp;
          int error, eof;
  
          error = 0;
          eof = 0;
  
          ASSERT_VOP_LOCKED(vp, "vfs_emptydir");
          VNASSERT(vp->v_type == VDIR, vp, ("vp is not a directory"));
  
          dirent = malloc(sizeof(struct dirent), M_TEMP, M_WAITOK);
          iov.iov_base = dirent;
          iov.iov_len = sizeof(struct dirent);
  
          uio.uio_iov = &iov;
          uio.uio_iovcnt = 1;
          uio.uio_offset = 0;
          uio.uio_resid = sizeof(struct dirent);
          uio.uio_segflg = UIO_SYSSPACE;
          uio.uio_rw = UIO_READ;
          uio.uio_td = curthread;
  
          while (eof == 0 && error == 0) {
                  error = VOP_READDIR(vp, &uio, curthread->td_ucred, &eof,
                      NULL, NULL);
                  if (error != 0)
                          break;
                  endp = (void *)((uint8_t *)dirent +
                      sizeof(struct dirent) - uio.uio_resid);
                  for (dp = dirent; dp < endp;
                       dp = (void *)((uint8_t *)dp + GENERIC_DIRSIZ(dp))) {
                          if (dp->d_type == DT_WHT)
                                  continue;
                          if (dp->d_namlen == 0)
                                  continue;
                          if (dp->d_type != DT_DIR &&
                              dp->d_type != DT_UNKNOWN) {
                                  error = ENOTEMPTY;
                                  break;
                          }
                          if (dp->d_namlen > 2) {
                                  error = ENOTEMPTY;
                                  break;
                          }
                          if (dp->d_namlen == 1 &&
                              dp->d_name[0] != '.') {
                                  error = ENOTEMPTY;
                                  break;
                          }
                          if (dp->d_namlen == 2 &&
                              dp->d_name[1] != '.') {
                                  error = ENOTEMPTY;
                                  break;
                          }
                          uio.uio_resid = sizeof(struct dirent);
                  }
          }
          free(dirent, M_TEMP);
          return (error);
  }
  
  int
  vfs_read_dirent(struct vop_readdir_args *ap, struct dirent *dp, off_t off)
  {
          int error;
  
          if (dp->d_reclen > ap->a_uio->uio_resid)
                  return (ENAMETOOLONG);
          error = uiomove(dp, dp->d_reclen, ap->a_uio);
          if (error) {
                  if (ap->a_ncookies != NULL) {
                          if (ap->a_cookies != NULL)
                                  free(ap->a_cookies, M_TEMP);
                          ap->a_cookies = NULL;
                          *ap->a_ncookies = 0;
                  }
                  return (error);
          }
          if (ap->a_ncookies == NULL)
                  return (0);
  
          KASSERT(ap->a_cookies,
              ("NULL ap->a_cookies value with non-NULL ap->a_ncookies!"));
  
          *ap->a_cookies = realloc(*ap->a_cookies,
              (*ap->a_ncookies + 1) * sizeof(u_long), M_TEMP, M_WAITOK | M_ZERO);
          (*ap->a_cookies)[*ap->a_ncookies] = off;
          *ap->a_ncookies += 1;
          return (0);
  }
  
  /*
   * The purpose of this routine is to remove granularity from accmode_t,
   * reducing it into standard unix access bits - VEXEC, VREAD, VWRITE,
   * VADMIN and VAPPEND.
   *
   * If it returns 0, the caller is supposed to continue with the usual
   * access checks using 'accmode' as modified by this routine.  If it
   * returns nonzero value, the caller is supposed to return that value
   * as errno.
   *
   * Note that after this routine runs, accmode may be zero.
   */
  int
  vfs_unixify_accmode(accmode_t *accmode)
  {
          /*
           * There is no way to specify explicit "deny" rule using
           * file mode or POSIX.1e ACLs.
           */
          if (*accmode & VEXPLICIT_DENY) {
                  *accmode = 0;
                  return (0);
          }
  
          /*
           * None of these can be translated into usual access bits.
           * Also, the common case for NFSv4 ACLs is to not contain
           * either of these bits. Caller should check for VWRITE
           * on the containing directory instead.
           */
          if (*accmode & (VDELETE_CHILD | VDELETE))
                  return (EPERM);
  
          if (*accmode & VADMIN_PERMS) {
                  *accmode &= ~VADMIN_PERMS;
                  *accmode |= VADMIN;
          }
  
          /*
           * There is no way to deny VREAD_ATTRIBUTES, VREAD_ACL
           * or VSYNCHRONIZE using file mode or POSIX.1e ACL.
           */
          *accmode &= ~(VSTAT_PERMS | VSYNCHRONIZE);
  
          return (0);
  }
  
  /*
   * Clear out a doomed vnode (if any) and replace it with a new one as long
   * as the fs is not being unmounted. Return the root vnode to the caller.
   */
  static int __noinline
  vfs_cache_root_fallback(struct mount *mp, int flags, struct vnode **vpp)
  {
          struct vnode *vp;
          int error;
  
  restart:
          if (mp->mnt_rootvnode != NULL) {
                  MNT_ILOCK(mp);
                  vp = mp->mnt_rootvnode;
                  if (vp != NULL) {
                          if (!VN_IS_DOOMED(vp)) {
                                  vrefact(vp);
                                  MNT_IUNLOCK(mp);
                                  error = vn_lock(vp, flags);
                                  if (error == 0) {
                                          *vpp = vp;
                                          return (0);
                                  }
                                  vrele(vp);
                                  goto restart;
                          }
                          /*
                           * Clear the old one.
                           */
                          mp->mnt_rootvnode = NULL;
                  }
                  MNT_IUNLOCK(mp);
                  if (vp != NULL) {
                          vfs_op_barrier_wait(mp);
                          vrele(vp);
                  }
          }
          error = VFS_CACHEDROOT(mp, flags, vpp);
          if (error != 0)
                  return (error);
          if (mp->mnt_vfs_ops == 0) {
                  MNT_ILOCK(mp);
                  if (mp->mnt_vfs_ops != 0) {
                          MNT_IUNLOCK(mp);
                          return (0);
                  }
                  if (mp->mnt_rootvnode == NULL) {
                          vrefact(*vpp);
                          mp->mnt_rootvnode = *vpp;
                  } else {
                          if (mp->mnt_rootvnode != *vpp) {
                                  if (!VN_IS_DOOMED(mp->mnt_rootvnode)) {
                                          panic("%s: mismatch between vnode returned "
                                              " by VFS_CACHEDROOT and the one cached "
                                              " (%p != %p)",
                                              __func__, *vpp, mp->mnt_rootvnode);
                                  }
                          }
                  }
                  MNT_IUNLOCK(mp);
          }
          return (0);
  }
  
  int
  vfs_cache_root(struct mount *mp, int flags, struct vnode **vpp)
  {
          struct mount_pcpu *mpcpu;
          struct vnode *vp;
          int error;
  
          if (!vfs_op_thread_enter(mp, mpcpu))
                  return (vfs_cache_root_fallback(mp, flags, vpp));
          vp = atomic_load_ptr(&mp->mnt_rootvnode);
          if (vp == NULL || VN_IS_DOOMED(vp)) {
                  vfs_op_thread_exit(mp, mpcpu);
                  return (vfs_cache_root_fallback(mp, flags, vpp));
          }
          vrefact(vp);
          vfs_op_thread_exit(mp, mpcpu);
          error = vn_lock(vp, flags);
          if (error != 0) {
                  vrele(vp);
                  return (vfs_cache_root_fallback(mp, flags, vpp));
          }
          *vpp = vp;
          return (0);
  }
  
  struct vnode *
  vfs_cache_root_clear(struct mount *mp)
  {
          struct vnode *vp;
  
          /*
           * ops > 0 guarantees there is nobody who can see this vnode
           */
          MPASS(mp->mnt_vfs_ops > 0);
          vp = mp->mnt_rootvnode;
          if (vp != NULL)
                  vn_seqc_write_begin(vp);
          mp->mnt_rootvnode = NULL;
          return (vp);
  }
  
  void
  vfs_cache_root_set(struct mount *mp, struct vnode *vp)
  {
  
          MPASS(mp->mnt_vfs_ops > 0);
          vrefact(vp);
          mp->mnt_rootvnode = vp;
  }
  
  /*
   * These are helper functions for filesystems to traverse all
   * their vnodes.  See MNT_VNODE_FOREACH_ALL() in sys/mount.h.
   *
   * This interface replaces MNT_VNODE_FOREACH.
   */
  
  struct vnode *
  __mnt_vnode_next_all(struct vnode **mvp, struct mount *mp)
  {
          struct vnode *vp;
  
          if (should_yield())
                  kern_yield(PRI_USER);
          MNT_ILOCK(mp);
          KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
          for (vp = TAILQ_NEXT(*mvp, v_nmntvnodes); vp != NULL;
              vp = TAILQ_NEXT(vp, v_nmntvnodes)) {
                  /* Allow a racy peek at VIRF_DOOMED to save a lock acquisition. */
                  if (vp->v_type == VMARKER || VN_IS_DOOMED(vp))
                          continue;
                  VI_LOCK(vp);
                  if (VN_IS_DOOMED(vp)) {
                          VI_UNLOCK(vp);
                          continue;
                  }
                  break;
          }
          if (vp == NULL) {
                  __mnt_vnode_markerfree_all(mvp, mp);
                  /* MNT_IUNLOCK(mp); -- done in above function */
                  mtx_assert(MNT_MTX(mp), MA_NOTOWNED);
                  return (NULL);
          }
          TAILQ_REMOVE(&mp->mnt_nvnodelist, *mvp, v_nmntvnodes);
          TAILQ_INSERT_AFTER(&mp->mnt_nvnodelist, vp, *mvp, v_nmntvnodes);
          MNT_IUNLOCK(mp);
          return (vp);
  }
  
  struct vnode *
  __mnt_vnode_first_all(struct vnode **mvp, struct mount *mp)
  {
          struct vnode *vp;
  
          *mvp = vn_alloc_marker(mp);
          MNT_ILOCK(mp);
          MNT_REF(mp);
  
          TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                  /* Allow a racy peek at VIRF_DOOMED to save a lock acquisition. */
                  if (vp->v_type == VMARKER || VN_IS_DOOMED(vp))
                          continue;
                  VI_LOCK(vp);
                  if (VN_IS_DOOMED(vp)) {
                          VI_UNLOCK(vp);
                          continue;
                  }
                  break;
          }
          if (vp == NULL) {
                  MNT_REL(mp);
                  MNT_IUNLOCK(mp);
                  vn_free_marker(*mvp);
                  *mvp = NULL;
                  return (NULL);
          }
          TAILQ_INSERT_AFTER(&mp->mnt_nvnodelist, vp, *mvp, v_nmntvnodes);
          MNT_IUNLOCK(mp);
          return (vp);
  }
  
  void
  __mnt_vnode_markerfree_all(struct vnode **mvp, struct mount *mp)
  {
  
          if (*mvp == NULL) {
                  MNT_IUNLOCK(mp);
                  return;
          }
  
          mtx_assert(MNT_MTX(mp), MA_OWNED);
  
          KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
          TAILQ_REMOVE(&mp->mnt_nvnodelist, *mvp, v_nmntvnodes);
          MNT_REL(mp);
          MNT_IUNLOCK(mp);
          vn_free_marker(*mvp);
          *mvp = NULL;
  }
  
  /*
   * These are helper functions for filesystems to traverse their
   * lazy vnodes.  See MNT_VNODE_FOREACH_LAZY() in sys/mount.h
   */
  static void
  mnt_vnode_markerfree_lazy(struct vnode **mvp, struct mount *mp)
  {
  
          KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
  
          MNT_ILOCK(mp);
          MNT_REL(mp);
          MNT_IUNLOCK(mp);
          vn_free_marker(*mvp);
          *mvp = NULL;
  }
  
  /*
   * Relock the mp mount vnode list lock with the vp vnode interlock in the
   * conventional lock order during mnt_vnode_next_lazy iteration.
   *
   * On entry, the mount vnode list lock is held and the vnode interlock is not.
   * The list lock is dropped and reacquired.  On success, both locks are held.
   * On failure, the mount vnode list lock is held but the vnode interlock is
   * not, and the procedure may have yielded.
   */
  static bool
  mnt_vnode_next_lazy_relock(struct vnode *mvp, struct mount *mp,
      struct vnode *vp)
  {
  
          VNASSERT(mvp->v_mount == mp && mvp->v_type == VMARKER &&
              TAILQ_NEXT(mvp, v_lazylist) != NULL, mvp,
              ("%s: bad marker", __func__));
          VNASSERT(vp->v_mount == mp && vp->v_type != VMARKER, vp,
              ("%s: inappropriate vnode", __func__));
          ASSERT_VI_UNLOCKED(vp, __func__);
          mtx_assert(&mp->mnt_listmtx, MA_OWNED);
  
          TAILQ_REMOVE(&mp->mnt_lazyvnodelist, mvp, v_lazylist);
          TAILQ_INSERT_BEFORE(vp, mvp, v_lazylist);
  
          /*
           * Note we may be racing against vdrop which transitioned the hold
           * count to 0 and now waits for the ->mnt_listmtx lock. This is fine,
           * if we are the only user after we get the interlock we will just
           * vdrop.
           */
          vhold(vp);
          mtx_unlock(&mp->mnt_listmtx);
          VI_LOCK(vp);
          if (VN_IS_DOOMED(vp)) {
                  VNPASS((vp->v_mflag & VMP_LAZYLIST) == 0, vp);
                  goto out_lost;
          }
          VNPASS(vp->v_mflag & VMP_LAZYLIST, vp);
          /*
           * There is nothing to do if we are the last user.
           */
          if (!refcount_release_if_not_last(&vp->v_holdcnt))
                  goto out_lost;
          mtx_lock(&mp->mnt_listmtx);
          return (true);
  out_lost:
          vdropl(vp);
          maybe_yield();
          mtx_lock(&mp->mnt_listmtx);
          return (false);
  }
  
  static struct vnode *
  mnt_vnode_next_lazy(struct vnode **mvp, struct mount *mp, mnt_lazy_cb_t *cb,
      void *cbarg)
  {
          struct vnode *vp;
  
          mtx_assert(&mp->mnt_listmtx, MA_OWNED);
          KASSERT((*mvp)->v_mount == mp, ("marker vnode mount list mismatch"));
  restart:
          vp = TAILQ_NEXT(*mvp, v_lazylist);
          while (vp != NULL) {
                  if (vp->v_type == VMARKER) {
                          vp = TAILQ_NEXT(vp, v_lazylist);
                          continue;
                  }
                  /*
                   * See if we want to process the vnode. Note we may encounter a
                   * long string of vnodes we don't care about and hog the list
                   * as a result. Check for it and requeue the marker.
                   */
                  VNPASS(!VN_IS_DOOMED(vp), vp);
                  if (!cb(vp, cbarg)) {
                          if (!should_yield()) {
                                  vp = TAILQ_NEXT(vp, v_lazylist);
                                  continue;
                          }
                          TAILQ_REMOVE(&mp->mnt_lazyvnodelist, *mvp,
                              v_lazylist);
                          TAILQ_INSERT_AFTER(&mp->mnt_lazyvnodelist, vp, *mvp,
                              v_lazylist);
                          mtx_unlock(&mp->mnt_listmtx);
                          kern_yield(PRI_USER);
                          mtx_lock(&mp->mnt_listmtx);
                          goto restart;
                  }
                  /*
                   * Try-lock because this is the wrong lock order.
                   */
                  if (!VI_TRYLOCK(vp) &&
                      !mnt_vnode_next_lazy_relock(*mvp, mp, vp))
                          goto restart;
                  KASSERT(vp->v_type != VMARKER, ("locked marker %p", vp));
                  KASSERT(vp->v_mount == mp || vp->v_mount == NULL,
                      ("alien vnode on the lazy list %p %p", vp, mp));
                  VNPASS(vp->v_mount == mp, vp);
                  VNPASS(!VN_IS_DOOMED(vp), vp);
                  break;
          }
          TAILQ_REMOVE(&mp->mnt_lazyvnodelist, *mvp, v_lazylist);
  
          /* Check if we are done */
          if (vp == NULL) {
                  mtx_unlock(&mp->mnt_listmtx);
                  mnt_vnode_markerfree_lazy(mvp, mp);
                  return (NULL);
          }
          TAILQ_INSERT_AFTER(&mp->mnt_lazyvnodelist, vp, *mvp, v_lazylist);
          mtx_unlock(&mp->mnt_listmtx);
          ASSERT_VI_LOCKED(vp, "lazy iter");
          return (vp);
  }
  
  struct vnode *
  __mnt_vnode_next_lazy(struct vnode **mvp, struct mount *mp, mnt_lazy_cb_t *cb,
      void *cbarg)
  {
  
          if (should_yield())
                  kern_yield(PRI_USER);
          mtx_lock(&mp->mnt_listmtx);
          return (mnt_vnode_next_lazy(mvp, mp, cb, cbarg));
  }
  
  struct vnode *
  __mnt_vnode_first_lazy(struct vnode **mvp, struct mount *mp, mnt_lazy_cb_t *cb,
      void *cbarg)
  {
          struct vnode *vp;
  
          if (TAILQ_EMPTY(&mp->mnt_lazyvnodelist))
                  return (NULL);
  
          *mvp = vn_alloc_marker(mp);
          MNT_ILOCK(mp);
          MNT_REF(mp);
          MNT_IUNLOCK(mp);
  
          mtx_lock(&mp->mnt_listmtx);
          vp = TAILQ_FIRST(&mp->mnt_lazyvnodelist);
          if (vp == NULL) {
                  mtx_unlock(&mp->mnt_listmtx);
                  mnt_vnode_markerfree_lazy(mvp, mp);
                  return (NULL);
          }
          TAILQ_INSERT_BEFORE(vp, *mvp, v_lazylist);
          return (mnt_vnode_next_lazy(mvp, mp, cb, cbarg));
  }
  
  void
  __mnt_vnode_markerfree_lazy(struct vnode **mvp, struct mount *mp)
  {
  
          if (*mvp == NULL)
                  return;
  
          mtx_lock(&mp->mnt_listmtx);
          TAILQ_REMOVE(&mp->mnt_lazyvnodelist, *mvp, v_lazylist);
          mtx_unlock(&mp->mnt_listmtx);
          mnt_vnode_markerfree_lazy(mvp, mp);
  }
  
  int
  vn_dir_check_exec(struct vnode *vp, struct componentname *cnp)
  {
  
          if ((cnp->cn_flags & NOEXECCHECK) != 0) {
                  cnp->cn_flags &= ~NOEXECCHECK;
                  return (0);
          }
  
          return (VOP_ACCESS(vp, VEXEC, cnp->cn_cred, cnp->cn_thread));
  }
  
  /*
   * Do not use this variant unless you have means other than the hold count
   * to prevent the vnode from getting freed.
   */
  void
  vn_seqc_write_begin_locked(struct vnode *vp)
  {
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNPASS(vp->v_holdcnt > 0, vp);
          VNPASS(vp->v_seqc_users >= 0, vp);
          vp->v_seqc_users++;
          if (vp->v_seqc_users == 1)
                  seqc_sleepable_write_begin(&vp->v_seqc);
  }
  
  void
  vn_seqc_write_begin(struct vnode *vp)
  {
  
          VI_LOCK(vp);
          vn_seqc_write_begin_locked(vp);
          VI_UNLOCK(vp);
  }
  
  void
  vn_seqc_write_end_locked(struct vnode *vp)
  {
  
          ASSERT_VI_LOCKED(vp, __func__);
          VNPASS(vp->v_seqc_users > 0, vp);
          vp->v_seqc_users--;
          if (vp->v_seqc_users == 0)
                  seqc_sleepable_write_end(&vp->v_seqc);
  }
  
  void
  vn_seqc_write_end(struct vnode *vp)
  {
  
          VI_LOCK(vp);
          vn_seqc_write_end_locked(vp);
          VI_UNLOCK(vp);
  }
  
  /*
   * Special case handling for allocating and freeing vnodes.
   *
   * The counter remains unchanged on free so that a doomed vnode will
   * keep testing as in modify as long as it is accessible with SMR.
   */
  static void
  vn_seqc_init(struct vnode *vp)
  {
  
          vp->v_seqc = 0;
          vp->v_seqc_users = 0;
  }
  
  static void
  vn_seqc_write_end_free(struct vnode *vp)
  {
  
          VNPASS(seqc_in_modify(vp->v_seqc), vp);
          VNPASS(vp->v_seqc_users == 1, vp);
  }
  
  void
  vn_irflag_set_locked(struct vnode *vp, short toset)
  {
          short flags;
  
          ASSERT_VI_LOCKED(vp, __func__);
          flags = vn_irflag_read(vp);
          VNASSERT((flags & toset) == 0, vp,
              ("%s: some of the passed flags already set (have %d, passed %d)\n",
              __func__, flags, toset));
          atomic_store_short(&vp->v_irflag, flags | toset);
  }
  
  void
  vn_irflag_set(struct vnode *vp, short toset)
  {
  
          VI_LOCK(vp);
          vn_irflag_set_locked(vp, toset);
          VI_UNLOCK(vp);
  }
  
  void
  vn_irflag_set_cond_locked(struct vnode *vp, short toset)
  {
          short flags;
  
          ASSERT_VI_LOCKED(vp, __func__);
          flags = vn_irflag_read(vp);
          atomic_store_short(&vp->v_irflag, flags | toset);
  }
  
  void
  vn_irflag_set_cond(struct vnode *vp, short toset)
  {
  
          VI_LOCK(vp);
          vn_irflag_set_cond_locked(vp, toset);
          VI_UNLOCK(vp);
  }
  
  void
  vn_irflag_unset_locked(struct vnode *vp, short tounset)
  {
          short flags;
  
          ASSERT_VI_LOCKED(vp, __func__);
          flags = vn_irflag_read(vp);
          VNASSERT((flags & tounset) == tounset, vp,
              ("%s: some of the passed flags not set (have %d, passed %d)\n",
              __func__, flags, tounset));
          atomic_store_short(&vp->v_irflag, flags & ~tounset);
  }
  
  void
  vn_irflag_unset(struct vnode *vp, short tounset)
  {
  
          VI_LOCK(vp);
          vn_irflag_unset_locked(vp, tounset);
          VI_UNLOCK(vp);
  }