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

     /*
      * 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. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 4. 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: releng/5.2/sys/kern/vfs_subr.c 123639 2003-12-18 16:22:16Z jeff $");
    
    #include "opt_ddb.h"
    #include "opt_mac.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/conf.h>
    #include <sys/eventhandler.h>
    #include <sys/extattr.h>
    #include <sys/fcntl.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/mac.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/namei.h>
    #include <sys/stat.h>
    #include <sys/sysctl.h>
    #include <sys/syslog.h>
    #include <sys/vmmeter.h>
    #include <sys/vnode.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>
    
    static MALLOC_DEFINE(M_NETADDR, "Export Host", "Export host address structure");
    
    static void     addalias(struct vnode *vp, dev_t nvp_rdev);
    static void     insmntque(struct vnode *vp, struct mount *mp);
    static void     vclean(struct vnode *vp, int flags, struct thread *td);
    static void     vlruvp(struct vnode *vp);
    static int      flushbuflist(struct buf *blist, int flags, struct vnode *vp,
                        int slpflag, int slptimeo, int *errorp);
    static int      vtryrecycle(struct vnode *vp);
    static void     vx_lock(struct vnode *vp);
    static void     vx_unlock(struct vnode *vp);
    static void     vgonechrl(struct vnode *vp, struct thread *td);
    
    
    /*
     * Number of vnodes in existence.  Increased whenever getnewvnode()
     * allocates a new vnode, never decreased.
     */
    static unsigned long    numvnodes;
    
   SYSCTL_LONG(_vfs, OID_AUTO, numvnodes, CTLFLAG_RD, &numvnodes, 0, "");
   
   /*
    * 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, VBAD,
   };
   int vttoif_tab[9] = {
           0, S_IFREG, S_IFDIR, S_IFBLK, S_IFCHR, S_IFLNK,
           S_IFSOCK, S_IFIFO, S_IFMT,
   };
   
   /*
    * List of vnodes that are ready for recycling.
    */
   static TAILQ_HEAD(freelst, vnode) vnode_free_list;
   
   /*
    * Minimum number of free vnodes.  If there are fewer than this free vnodes,
    * getnewvnode() will return a newly allocated vnode.
    */
   static u_long wantfreevnodes = 25;
   SYSCTL_LONG(_vfs, OID_AUTO, wantfreevnodes, CTLFLAG_RW, &wantfreevnodes, 0, "");
   /* Number of vnodes in the free list. */
   static u_long freevnodes;
   SYSCTL_LONG(_vfs, OID_AUTO, freevnodes, CTLFLAG_RD, &freevnodes, 0, "");
   
   /*
    * Various variables used for debugging the new implementation of
    * reassignbuf().
    * XXX these are probably of (very) limited utility now.
    */
   static int reassignbufcalls;
   SYSCTL_INT(_vfs, OID_AUTO, reassignbufcalls, CTLFLAG_RW, &reassignbufcalls, 0, "");
   static int nameileafonly;
   SYSCTL_INT(_vfs, OID_AUTO, nameileafonly, CTLFLAG_RW, &nameileafonly, 0, "");
   
   /*
    * Cache for the mount type id assigned to NFS.  This is used for
    * special checks in nfs/nfs_nqlease.c and vm/vnode_pager.c.
    */
   int     nfs_mount_type = -1;
   
   /* 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_free_list
    *      numvnodes
    *      freevnodes
    */
   static struct mtx vnode_free_list_mtx;
   
   /*
    * For any iteration/modification of dev->si_hlist (linked through
    * v_specnext)
    */
   static struct mtx spechash_mtx;
   
   /* Publicly exported FS */
   struct nfs_public nfs_pub;
   
   /* Zone for allocation of new vnodes - used exclusively by getnewvnode() */
   static uma_zone_t vnode_zone;
   static uma_zone_t vnodepoll_zone;
   
   /* Set to 1 to print out reclaim of active vnodes */
   int     prtactive;
   
   /*
    * 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, vnode);
   static struct synclist *syncer_workitem_pending;
   /*
    * The sync_mtx protects:
    *      vp->v_synclist
    *      syncer_delayno
    *      syncer_workitem_pending
    *      rushjob
    */
   static struct mtx sync_mtx;
   
   #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, "");
   static int dirdelay = 29;               /* time to delay syncing directories */
   SYSCTL_INT(_kern, OID_AUTO, dirdelay, CTLFLAG_RW, &dirdelay, 0, "");
   static int metadelay = 28;              /* time to delay syncing metadata */
   SYSCTL_INT(_kern, OID_AUTO, metadelay, CTLFLAG_RW, &metadelay, 0, "");
   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 vnodes we want to exist at any one time.  This is mostly used
    * to size hash tables in vnode-related code.  It is normally not used in
    * getnewvnode(), as wantfreevnodes is normally nonzero.)
    *
    * XXX desiredvnodes is historical cruft and should not exist.
    */
   int desiredvnodes;
   SYSCTL_INT(_kern, KERN_MAXVNODES, maxvnodes, CTLFLAG_RW,
       &desiredvnodes, 0, "Maximum number of vnodes");
   static int minvnodes;
   SYSCTL_INT(_kern, OID_AUTO, minvnodes, CTLFLAG_RW,
       &minvnodes, 0, "Minimum number of vnodes");
   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");
   
   /* Hook for calling soft updates */
   int (*softdep_process_worklist_hook)(struct mount *);
   
   /*
    * This only exists to supress warnings from unlocked specfs accesses.  It is
    * no longer ok to have an unlocked VFS.
    */
   #define IGNORE_LOCK(vp) ((vp)->v_type == VCHR || (vp)->v_type == VBAD)
   
   /* Print lock violations */
   int vfs_badlock_print = 1;
   
   /* Panic on violation */
   int vfs_badlock_panic = 1;
   
   /* Check for interlock across VOPs */
   int vfs_badlock_mutex = 1;
   
   static void
   vfs_badlock(const char *msg, const char *str, struct vnode *vp)
   {
           if (vfs_badlock_print)
                   printf("%s: %p %s\n", str, vp, msg);
           if (vfs_badlock_panic)
                   Debugger("Lock violation.\n");
   }
   
   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_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_vop_locked(struct vnode *vp, const char *str)
   {
           if (vp && !IGNORE_LOCK(vp) && !VOP_ISLOCKED(vp, NULL))
                   vfs_badlock("is not locked but should be", str, vp);
   }
   
   void
   assert_vop_unlocked(struct vnode *vp, const char *str)
   {
           if (vp && !IGNORE_LOCK(vp) &&
               VOP_ISLOCKED(vp, curthread) == LK_EXCLUSIVE)
                   vfs_badlock("is locked but should not be", str, vp);
   }
   
   void
   assert_vop_elocked(struct vnode *vp, const char *str)
   {
           if (vp && !IGNORE_LOCK(vp) &&
               VOP_ISLOCKED(vp, curthread) != LK_EXCLUSIVE)
                   vfs_badlock("is not exclusive locked but should be", str, vp);
   }
   
   void
   assert_vop_elocked_other(struct vnode *vp, const char *str)
   {
           if (vp && !IGNORE_LOCK(vp) &&
               VOP_ISLOCKED(vp, curthread) != LK_EXCLOTHER)
                   vfs_badlock("is not exclusive locked by another thread",
                       str, vp);
   }
   
   void
   assert_vop_slocked(struct vnode *vp, const char *str)
   {
           if (vp && !IGNORE_LOCK(vp) &&
               VOP_ISLOCKED(vp, curthread) != LK_SHARED)
                   vfs_badlock("is not locked shared but should be", str, vp);
   }
   
   void
   vop_rename_pre(void *ap)
   {
           struct vop_rename_args *a = ap;
   
           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 != a->a_fdvp)
                   ASSERT_VOP_UNLOCKED(a->a_fdvp, "vop_rename: fdvp locked.\n");
           if (a->a_tvp != a->a_fvp)
                   ASSERT_VOP_UNLOCKED(a->a_fvp, "vop_rename: tvp locked.\n");
   
           /* Check the target */
           if (a->a_tvp)
                   ASSERT_VOP_LOCKED(a->a_tvp, "vop_rename: tvp not locked.\n");
   
           ASSERT_VOP_LOCKED(a->a_tdvp, "vop_rename: tdvp not locked.\n");
   }
   
   void
   vop_strategy_pre(void *ap)
   {
           struct vop_strategy_args *a = ap;
           struct buf *bp;
   
           bp = a->a_bp;
   
           /*
            * Cluster ops lock their component buffers but not the IO container.
            */
           if ((bp->b_flags & B_CLUSTER) != 0)
                   return;
   
           if (BUF_REFCNT(bp) < 1) {
                   if (vfs_badlock_print)
                           printf("VOP_STRATEGY: bp is not locked but should be.\n");
                   if (vfs_badlock_panic)
                           Debugger("Lock violation.\n");
           }
   }
   
   void
   vop_lookup_pre(void *ap)
   {
           struct vop_lookup_args *a = ap;
           struct vnode *dvp;
   
           dvp = a->a_dvp;
   
           ASSERT_VI_UNLOCKED(dvp, "VOP_LOOKUP");
           ASSERT_VOP_LOCKED(dvp, "VOP_LOOKUP");
   }
   
   void
   vop_lookup_post(void *ap, int rc)
   {
           struct vop_lookup_args *a = ap;
           struct componentname *cnp;
           struct vnode *dvp;
           struct vnode *vp;
           int flags;
   
           dvp = a->a_dvp;
           cnp = a->a_cnp;
           vp = *(a->a_vpp);
           flags = cnp->cn_flags;
   
   
           ASSERT_VI_UNLOCKED(dvp, "VOP_LOOKUP");
           /*
            * If this is the last path component for this lookup and LOCPARENT
            * is set, OR if there is an error the directory has to be locked.
            */
           if ((flags & LOCKPARENT) && (flags & ISLASTCN))
                   ASSERT_VOP_LOCKED(dvp, "VOP_LOOKUP (LOCKPARENT)");
           else if (rc != 0)
                   ASSERT_VOP_LOCKED(dvp, "VOP_LOOKUP (error)");
           else if (dvp != vp)
                   ASSERT_VOP_UNLOCKED(dvp, "VOP_LOOKUP (dvp)");
   
           if (flags & PDIRUNLOCK)
                   ASSERT_VOP_UNLOCKED(dvp, "VOP_LOOKUP (PDIRUNLOCK)");
   }
   
   void
   vop_unlock_pre(void *ap)
   {
           struct vop_unlock_args *a = ap;
   
           if (a->a_flags & LK_INTERLOCK)
                   ASSERT_VI_LOCKED(a->a_vp, "VOP_UNLOCK");
   
           ASSERT_VOP_LOCKED(a->a_vp, "VOP_UNLOCK");
   }
   
   void
   vop_unlock_post(void *ap, int rc)
   {
           struct vop_unlock_args *a = ap;
   
           if (a->a_flags & LK_INTERLOCK)
                   ASSERT_VI_UNLOCKED(a->a_vp, "VOP_UNLOCK");
   }
   
   void
   vop_lock_pre(void *ap)
   {
           struct vop_lock_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_post(void *ap, int rc)
   {
           struct vop_lock_args *a;
   
           a = ap;
   
           ASSERT_VI_UNLOCKED(a->a_vp, "VOP_LOCK");
           if (rc == 0)
                   ASSERT_VOP_LOCKED(a->a_vp, "VOP_LOCK");
   }
   
   void
   v_addpollinfo(struct vnode *vp)
   {
           vp->v_pollinfo = uma_zalloc(vnodepoll_zone, M_WAITOK);
           mtx_init(&vp->v_pollinfo->vpi_lock, "vnode pollinfo", NULL, MTX_DEF);
   }
   
   /*
    * Initialize the vnode management data structures.
    */
   static void
   vntblinit(void *dummy __unused)
   {
   
           /*
            * Desiredvnodes is a function of the physical memory size and
            * the kernel's heap size.  Specifically, desiredvnodes scales
            * in proportion to the physical memory size until two fifths
            * of the kernel's heap size is consumed by vnodes and vm
            * objects.  
            */
           desiredvnodes = min(maxproc + cnt.v_page_count / 4, 2 * vm_kmem_size /
               (5 * (sizeof(struct vm_object) + sizeof(struct vnode))));
           minvnodes = desiredvnodes / 4;
           mtx_init(&mountlist_mtx, "mountlist", NULL, MTX_DEF);
           mtx_init(&mntid_mtx, "mntid", NULL, MTX_DEF);
           mtx_init(&spechash_mtx, "spechash", NULL, MTX_DEF);
           TAILQ_INIT(&vnode_free_list);
           mtx_init(&vnode_free_list_mtx, "vnode_free_list", NULL, MTX_DEF);
           vnode_zone = uma_zcreate("VNODE", sizeof (struct vnode), NULL, NULL,
               NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
           vnodepoll_zone = uma_zcreate("VNODEPOLL", sizeof (struct vpollinfo),
                 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
           /*
            * 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);
   }
   SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_FIRST, vntblinit, NULL)
   
   
   /*
    * Mark a mount point as busy. Used to synchronize access and to delay
    * unmounting. Interlock is not released on failure.
    */
   int
   vfs_busy(mp, flags, interlkp, td)
           struct mount *mp;
           int flags;
           struct mtx *interlkp;
           struct thread *td;
   {
           int lkflags;
   
           if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                   if (flags & LK_NOWAIT)
                           return (ENOENT);
                   mp->mnt_kern_flag |= MNTK_MWAIT;
                   /*
                    * Since all busy locks are shared except the exclusive
                    * lock granted when unmounting, the only place that a
                    * wakeup needs to be done is at the release of the
                    * exclusive lock at the end of dounmount.
                    */
                   msleep(mp, interlkp, PVFS, "vfs_busy", 0);
                   return (ENOENT);
           }
           lkflags = LK_SHARED | LK_NOPAUSE;
           if (interlkp)
                   lkflags |= LK_INTERLOCK;
           if (lockmgr(&mp->mnt_lock, lkflags, interlkp, td))
                   panic("vfs_busy: unexpected lock failure");
           return (0);
   }
   
   /*
    * Free a busy filesystem.
    */
   void
   vfs_unbusy(mp, td)
           struct mount *mp;
           struct thread *td;
   {
   
           lockmgr(&mp->mnt_lock, LK_RELEASE, NULL, td);
   }
   
   /*
    * Lookup a mount point by filesystem identifier.
    */
   struct mount *
   vfs_getvfs(fsid)
           fsid_t *fsid;
   {
           register struct mount *mp;
   
           mtx_lock(&mountlist_mtx);
           TAILQ_FOREACH(mp, &mountlist, mnt_list) {
                   if (mp->mnt_stat.f_fsid.val[0] == fsid->val[0] &&
                       mp->mnt_stat.f_fsid.val[1] == fsid->val[1]) {
                           mtx_unlock(&mountlist_mtx);
                           return (mp);
                   }
           }
           mtx_unlock(&mountlist_mtx);
           return ((struct mount *) 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(mp)
           struct mount *mp;
   {
           static u_int16_t mntid_base;
           fsid_t tfsid;
           int mtype;
   
           mtx_lock(&mntid_mtx);
           mtype = mp->mnt_vfc->vfc_typenum;
           tfsid.val[1] = mtype;
           mtype = (mtype & 0xFF) << 24;
           for (;;) {
                   tfsid.val[0] = makeudev(255,
                       mtype | ((mntid_base & 0xFF00) << 8) | (mntid_base & 0xFF));
                   mntid_base++;
                   if (vfs_getvfs(&tfsid) == NULL)
                           break;
           }
           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_SEC;
   SYSCTL_INT(_vfs, OID_AUTO, timestamp_precision, CTLFLAG_RW,
       &timestamp_precision, 0, "");
   
   /*
    * Get a current timestamp.
    */
   void
   vfs_timestamp(tsp)
           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(vap)
           register 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;
   }
   
   /*
    * 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
    * desireable 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.
    */
   static int
   vlrureclaim(struct mount *mp)
   {
           struct vnode *vp;
           int done;
           int trigger;
           int usevnodes;
           int count;
   
           /*
            * Calculate the trigger point, don't allow user
            * screwups to blow us up.   This prevents us from
            * recycling vnodes with lots of resident pages.  We
            * aren't trying to free memory, we are trying to
            * free vnodes.
            */
           usevnodes = desiredvnodes;
           if (usevnodes <= 0)
                   usevnodes = 1;
           trigger = cnt.v_page_count * 2 / usevnodes;
   
           done = 0;
           MNT_ILOCK(mp);
           count = mp->mnt_nvnodelistsize / 10 + 1;
           while (count && (vp = TAILQ_FIRST(&mp->mnt_nvnodelist)) != NULL) {
                   TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                   TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
   
                   if (vp->v_type != VNON &&
                       vp->v_type != VBAD &&
                       VI_TRYLOCK(vp)) {
                           if (VMIGHTFREE(vp) &&           /* critical path opt */
                               (vp->v_object == NULL ||
                               vp->v_object->resident_page_count < trigger)) {
                                   MNT_IUNLOCK(mp);
                                   vgonel(vp, curthread);
                                   done++;
                                   MNT_ILOCK(mp);
                           } else
                                   VI_UNLOCK(vp);
                   }
                   --count;
           }
           MNT_IUNLOCK(mp);
           return done;
   }
   
   /*
    * 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;
   
   static void
   vnlru_proc(void)
   {
           struct mount *mp, *nmp;
           int done;
           struct proc *p = vnlruproc;
           struct thread *td = FIRST_THREAD_IN_PROC(p);    /* XXXKSE */
   
           mtx_lock(&Giant);
   
           EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, p,
               SHUTDOWN_PRI_FIRST);
   
           for (;;) {
                   kthread_suspend_check(p);
                   mtx_lock(&vnode_free_list_mtx);
                   if (numvnodes - freevnodes <= desiredvnodes * 9 / 10) {
                           mtx_unlock(&vnode_free_list_mtx);
                           vnlruproc_sig = 0;
                           wakeup(&vnlruproc_sig);
                           tsleep(vnlruproc, PVFS, "vlruwt", hz);
                           continue;
                   }
                   mtx_unlock(&vnode_free_list_mtx);
                   done = 0;
                   mtx_lock(&mountlist_mtx);
                   for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                           if (vfs_busy(mp, LK_NOWAIT, &mountlist_mtx, td)) {
                                   nmp = TAILQ_NEXT(mp, mnt_list);
                                   continue;
                           }
                           done += vlrureclaim(mp);
                           mtx_lock(&mountlist_mtx);
                           nmp = TAILQ_NEXT(mp, mnt_list);
                           vfs_unbusy(mp, td);
                   }
                   mtx_unlock(&mountlist_mtx);
                   if (done == 0) {
   #if 0
                           /* These messages are temporary debugging aids */
                           if (vnlru_nowhere < 5)
                                   printf("vnlru process getting nowhere..\n");
                           else if (vnlru_nowhere == 5)
                                   printf("vnlru process messages stopped.\n");
   #endif
                           vnlru_nowhere++;
                           tsleep(vnlruproc, PPAUSE, "vlrup", hz * 3);
                   }
           }
   }
   
   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.
    */
   
   /*
    * Check to see if a free vnode can be recycled. If it can,
    * recycle it and return it with the vnode interlock held.
    */
   static int
   vtryrecycle(struct vnode *vp)
   {
           struct thread *td = curthread;
           vm_object_t object;
           struct mount *vnmp;
           int error;
   
           /* Don't recycle if we can't get the interlock */
           if (!VI_TRYLOCK(vp))
                   return (EWOULDBLOCK);
           /*
            * This vnode may found and locked via some other list, if so we
            * can't recycle it yet.
            */
           if (vn_lock(vp, LK_INTERLOCK | LK_EXCLUSIVE | LK_NOWAIT, td) != 0)
                   return (EWOULDBLOCK);
           /*
            * Don't recycle if its filesystem is being suspended.
            */
           if (vn_start_write(vp, &vnmp, V_NOWAIT) != 0) {
                   error = EBUSY;
                   goto done;
           }
   
           /*
            * Don't recycle if we still have cached pages.
            */
           if (VOP_GETVOBJECT(vp, &object) == 0) {
                   VM_OBJECT_LOCK(object);
                   if (object->resident_page_count ||
                       object->ref_count) {
                           VM_OBJECT_UNLOCK(object);
                           error = EBUSY;
                           goto done;
                   }
                   VM_OBJECT_UNLOCK(object);
           }
           if (LIST_FIRST(&vp->v_cache_src)) {
                   /*
                    * note: nameileafonly sysctl is temporary,
                    * for debugging only, and will eventually be
                    * removed.
                    */
                   if (nameileafonly > 0) {
                           /*
                            * Do not reuse namei-cached directory
                            * vnodes that have cached
                            * subdirectories.
                            */
                           if (cache_leaf_test(vp) < 0) {
                                   error = EISDIR;
                                   goto done;
                           }
                   } else if (nameileafonly < 0 ||
                               vmiodirenable == 0) {
                           /*
                            * Do not reuse namei-cached directory
                            * vnodes if nameileafonly is -1 or
                            * if VMIO backing for directories is
                            * turned off (otherwise we reuse them
                            * too quickly).
                            */
                           error = EBUSY;
                           goto done;
                   }
           }
           /*
            * 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 XLOCK via vgonel() so that anyone who does find it
            * will skip over it.
            */
           VI_LOCK(vp);
           if (VSHOULDBUSY(vp) && (vp->v_iflag & VI_XLOCK) == 0) {
                   VI_UNLOCK(vp);
                   error = EBUSY;
                   goto done;
           }
           mtx_lock(&vnode_free_list_mtx);
           TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
           vp->v_iflag &= ~VI_FREE;
           mtx_unlock(&vnode_free_list_mtx);
           vp->v_iflag |= VI_DOOMED;
           if (vp->v_type != VBAD) {
                   VOP_UNLOCK(vp, 0, td);
                   vgonel(vp, td);
                   VI_LOCK(vp);
           } else
                   VOP_UNLOCK(vp, 0, td);
           vn_finished_write(vnmp);
           return (0);
   done:
           VOP_UNLOCK(vp, 0, td);
           return (error);
   }
   
   /*
    * Return the next vnode from the free list.
    */
   int
   getnewvnode(tag, mp, vops, vpp)
           const char *tag;
           struct mount *mp;
           vop_t **vops;
           struct vnode **vpp;
   {
           struct vnode *vp = NULL;
           struct vpollinfo *pollinfo = NULL;
   
           mtx_lock(&vnode_free_list_mtx);
   
           /*
            * Try to reuse vnodes if we hit the max.  This situation only
            * occurs in certain large-memory (2G+) situations.  We cannot
            * attempt to directly reclaim vnodes due to nasty recursion
            * problems.
            */
           while (numvnodes - freevnodes > desiredvnodes) {
                   if (vnlruproc_sig == 0) {
                           vnlruproc_sig = 1;      /* avoid unnecessary wakeups */
                           wakeup(vnlruproc);
                   }
                   mtx_unlock(&vnode_free_list_mtx);
                   tsleep(&vnlruproc_sig, PVFS, "vlruwk", hz);
                   mtx_lock(&vnode_free_list_mtx);
           }
   
           /*
            * Attempt to reuse a vnode already on the free list, allocating
            * a new vnode if we can't find one or if we have not reached a
            * good minimum for good LRU performance.
            */
   
           if (freevnodes >= wantfreevnodes && numvnodes >= minvnodes) {
                   int error;
                   int count;
   
                   for (count = 0; count < freevnodes; count++) {
                           vp = TAILQ_FIRST(&vnode_free_list);
   
                           KASSERT(vp->v_usecount == 0 &&
                               (vp->v_iflag & VI_DOINGINACT) == 0,
                               ("getnewvnode: free vnode isn't"));
   
                           TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
                           TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
                           mtx_unlock(&vnode_free_list_mtx);
                           error = vtryrecycle(vp);
                           mtx_lock(&vnode_free_list_mtx);
                           if (error == 0)
                                   break;
                           vp = NULL;
                   }
           }
           if (vp) {
                   freevnodes--;
                   mtx_unlock(&vnode_free_list_mtx);
   
   #ifdef INVARIANTS
                   {
                           if (vp->v_data)
                                   panic("cleaned vnode isn't");
                           if (vp->v_numoutput)
                                   panic("Clean vnode has pending I/O's");
                           if (vp->v_writecount != 0)
                                   panic("Non-zero write count");
                   }
   #endif
                   if ((pollinfo = vp->v_pollinfo) != NULL) {
                           /*
                            * To avoid lock order reversals, the call to
                            * uma_zfree() must be delayed until the vnode
                            * interlock is released.   
                            */
                           vp->v_pollinfo = NULL;
                   }
   #ifdef MAC
                   mac_destroy_vnode(vp);
   #endif
                   vp->v_iflag = 0;
                   vp->v_vflag = 0;
                   vp->v_lastw = 0;
                   vp->v_lasta = 0;
                   vp->v_cstart = 0;
                   vp->v_clen = 0;
                   vp->v_socket = 0;
                   lockdestroy(vp->v_vnlock);
                  lockinit(vp->v_vnlock, PVFS, tag, VLKTIMEOUT, LK_NOPAUSE);
                  KASSERT(vp->v_cleanbufcnt == 0, ("cleanbufcnt not 0"));
                  KASSERT(vp->v_cleanblkroot == NULL, ("cleanblkroot not NULL"));
                  KASSERT(vp->v_dirtybufcnt == 0, ("dirtybufcnt not 0"));
                  KASSERT(vp->v_dirtyblkroot == NULL, ("dirtyblkroot not NULL"));
          } else {
                  numvnodes++;
                  mtx_unlock(&vnode_free_list_mtx);
  
                  vp = (struct vnode *) uma_zalloc(vnode_zone, M_WAITOK|M_ZERO);
                  mtx_init(&vp->v_interlock, "vnode interlock", NULL, MTX_DEF);
                  VI_LOCK(vp);
                  vp->v_dd = vp;
                  vp->v_vnlock = &vp->v_lock;
                  lockinit(vp->v_vnlock, PVFS, tag, VLKTIMEOUT, LK_NOPAUSE);
                  cache_purge(vp);                /* Sets up v_id. */
                  LIST_INIT(&vp->v_cache_src);
                  TAILQ_INIT(&vp->v_cache_dst);
          }
  
          TAILQ_INIT(&vp->v_cleanblkhd);
          TAILQ_INIT(&vp->v_dirtyblkhd);
          vp->v_type = VNON;
          vp->v_tag = tag;
          vp->v_op = vops;
          *vpp = vp;
          vp->v_usecount = 1;
          vp->v_data = 0;
          vp->v_cachedid = -1;
          VI_UNLOCK(vp);
          if (pollinfo != NULL) {
                  mtx_destroy(&pollinfo->vpi_lock);
                  uma_zfree(vnodepoll_zone, pollinfo);
          }
  #ifdef MAC
          mac_init_vnode(vp);
          if (mp != NULL && (mp->mnt_flag & MNT_MULTILABEL) == 0)
                  mac_associate_vnode_singlelabel(mp, vp);
  #endif
          insmntque(vp, mp);
  
          return (0);
  }
  
  /*
   * Move a vnode from one mount queue to another.
   */
  static void
  insmntque(vp, mp)
          register struct vnode *vp;
          register struct mount *mp;
  {
  
          /*
           * Delete from old mount point vnode list, if on one.
           */
          if (vp->v_mount != NULL) {
                  MNT_ILOCK(vp->v_mount);
                  KASSERT(vp->v_mount->mnt_nvnodelistsize > 0,
                          ("bad mount point vnode list size"));
                  TAILQ_REMOVE(&vp->v_mount->mnt_nvnodelist, vp, v_nmntvnodes);
                  vp->v_mount->mnt_nvnodelistsize--;
                  MNT_IUNLOCK(vp->v_mount);
          }
          /*
           * Insert into list of vnodes for the new mount point, if available.
           */
          if ((vp->v_mount = mp) != NULL) {
                  MNT_ILOCK(vp->v_mount);
                  TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                  mp->mnt_nvnodelistsize++;
                  MNT_IUNLOCK(vp->v_mount);
          }
  }
  
  /*
   * Update outstanding I/O count and do wakeup if requested.
   */
  void
  vwakeup(bp)
          register struct buf *bp;
  {
          register struct vnode *vp;
  
          bp->b_flags &= ~B_WRITEINPROG;
          if ((vp = bp->b_vp)) {
                  VI_LOCK(vp);
                  vp->v_numoutput--;
                  if (vp->v_numoutput < 0)
                          panic("vwakeup: neg numoutput");
                  if ((vp->v_numoutput == 0) && (vp->v_iflag & VI_BWAIT)) {
                          vp->v_iflag &= ~VI_BWAIT;
                          wakeup(&vp->v_numoutput);
                  }
                  VI_UNLOCK(vp);
          }
  }
  
  /*
   * Flush out and invalidate all buffers associated with a vnode.
   * Called with the underlying object locked.
   */
  int
  vinvalbuf(vp, flags, cred, td, slpflag, slptimeo)
          struct vnode *vp;
          int flags;
          struct ucred *cred;
          struct thread *td;
          int slpflag, slptimeo;
  {
          struct buf *blist;
          int error;
          vm_object_t object;
  
          GIANT_REQUIRED;
  
          ASSERT_VOP_LOCKED(vp, "vinvalbuf");
  
          VI_LOCK(vp);
          if (flags & V_SAVE) {
                  while (vp->v_numoutput) {
                          vp->v_iflag |= VI_BWAIT;
                          error = msleep(&vp->v_numoutput, VI_MTX(vp),
                              slpflag | (PRIBIO + 1), "vinvlbuf", slptimeo);
                          if (error) {
                                  VI_UNLOCK(vp);
                                  return (error);
                          }
                  }
                  if (!TAILQ_EMPTY(&vp->v_dirtyblkhd)) {
                          VI_UNLOCK(vp);
                          if ((error = VOP_FSYNC(vp, cred, MNT_WAIT, td)) != 0)
                                  return (error);
                          /*
                           * XXX We could save a lock/unlock if this was only
                           * enabled under INVARIANTS
                           */
                          VI_LOCK(vp);
                          if (vp->v_numoutput > 0 ||
                              !TAILQ_EMPTY(&vp->v_dirtyblkhd))
                                  panic("vinvalbuf: dirty bufs");
                  }
          }
          /*
           * 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.
           */
          for (error = 0;;) {
                  if ((blist = TAILQ_FIRST(&vp->v_cleanblkhd)) != 0 &&
                      flushbuflist(blist, flags, vp, slpflag, slptimeo, &error)) {
                          if (error)
                                  break;
                          continue;
                  }
                  if ((blist = TAILQ_FIRST(&vp->v_dirtyblkhd)) != 0 &&
                      flushbuflist(blist, flags, vp, slpflag, slptimeo, &error)) {
                          if (error)
                                  break;
                          continue;
                  }
                  break;
          }
          if (error) {
                  VI_UNLOCK(vp);
                  return (error);
          }
  
          /*
           * 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 {
                  while (vp->v_numoutput > 0) {
                          vp->v_iflag |= VI_BWAIT;
                          msleep(&vp->v_numoutput, VI_MTX(vp), PVM, "vnvlbv", 0);
                  }
                  VI_UNLOCK(vp);
                  if (VOP_GETVOBJECT(vp, &object) == 0) {
                          VM_OBJECT_LOCK(object);
                          vm_object_pip_wait(object, "vnvlbx");
                          VM_OBJECT_UNLOCK(object);
                  }
                  VI_LOCK(vp);
          } while (vp->v_numoutput > 0);
          VI_UNLOCK(vp);
  
          /*
           * Destroy the copy in the VM cache, too.
           */
          if (VOP_GETVOBJECT(vp, &object) == 0) {
                  VM_OBJECT_LOCK(object);
                  vm_object_page_remove(object, 0, 0,
                          (flags & V_SAVE) ? TRUE : FALSE);
                  VM_OBJECT_UNLOCK(object);
          }
  
  #ifdef INVARIANTS
          VI_LOCK(vp);
          if ((flags & (V_ALT | V_NORMAL)) == 0 &&
              (!TAILQ_EMPTY(&vp->v_dirtyblkhd) ||
               !TAILQ_EMPTY(&vp->v_cleanblkhd)))
                  panic("vinvalbuf: flush failed");
          VI_UNLOCK(vp);
  #endif
          return (0);
  }
  
  /*
   * Flush out buffers on the specified list.
   *
   */
  static int
  flushbuflist(blist, flags, vp, slpflag, slptimeo, errorp)
          struct buf *blist;
          int flags;
          struct vnode *vp;
          int slpflag, slptimeo;
          int *errorp;
  {
          struct buf *bp, *nbp;
          int found, error;
  
          ASSERT_VI_LOCKED(vp, "flushbuflist");
  
          for (found = 0, bp = blist; bp; bp = nbp) {
                  nbp = TAILQ_NEXT(bp, b_vnbufs);
                  if (((flags & V_NORMAL) && (bp->b_xflags & BX_ALTDATA)) ||
                      ((flags & V_ALT) && (bp->b_xflags & BX_ALTDATA) == 0)) {
                          continue;
                  }
                  found += 1;
                  error = BUF_TIMELOCK(bp,
                      LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK, VI_MTX(vp),
                      "flushbuf", slpflag, slptimeo);
                  if (error) {
                          if (error != ENOLCK)
                                  *errorp = error;
                          goto done;
                  }
                  /*
                   * 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.  Note that vfs_bio_awrite expects
                   * buffers to reside on a queue, while BUF_WRITE and
                   * brelse do not.
                   */
                  if (((bp->b_flags & (B_DELWRI | B_INVAL)) == B_DELWRI) &&
                          (flags & V_SAVE)) {
  
                          if (bp->b_vp == vp) {
                                  if (bp->b_flags & B_CLUSTEROK) {
                                          vfs_bio_awrite(bp);
                                  } else {
                                          bremfree(bp);
                                          bp->b_flags |= B_ASYNC;
                                          BUF_WRITE(bp);
                                  }
                          } else {
                                  bremfree(bp);
                                  (void) BUF_WRITE(bp);
                          }
                          goto done;
                  }
                  bremfree(bp);
                  bp->b_flags |= (B_INVAL | B_NOCACHE | B_RELBUF);
                  bp->b_flags &= ~B_ASYNC;
                  brelse(bp);
                  VI_LOCK(vp);
          }
          return (found);
  done:
          VI_LOCK(vp);
          return (found);
  }
  
  /*
   * 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(vp, cred, td, length, blksize)
          register struct vnode *vp;
          struct ucred *cred;
          struct thread *td;
          off_t length;
          int blksize;
  {
          register struct buf *bp;
          struct buf *nbp;
          int anyfreed;
          int trunclbn;
  
          /*
           * Round up to the *next* lbn.
           */
          trunclbn = (length + blksize - 1) / blksize;
  
          ASSERT_VOP_LOCKED(vp, "vtruncbuf");
  restart:
          VI_LOCK(vp);
          anyfreed = 1;
          for (;anyfreed;) {
                  anyfreed = 0;
                  for (bp = TAILQ_FIRST(&vp->v_cleanblkhd); bp; bp = nbp) {
                          nbp = TAILQ_NEXT(bp, b_vnbufs);
                          if (bp->b_lblkno >= trunclbn) {
                                  if (BUF_LOCK(bp,
                                      LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                                      VI_MTX(vp)) == ENOLCK)
                                          goto restart;
  
                                  bremfree(bp);
                                  bp->b_flags |= (B_INVAL | B_RELBUF);
                                  bp->b_flags &= ~B_ASYNC;
                                  brelse(bp);
                                  anyfreed = 1;
  
                                  if (nbp &&
                                      (((nbp->b_xflags & BX_VNCLEAN) == 0) ||
                                      (nbp->b_vp != vp) ||
                                      (nbp->b_flags & B_DELWRI))) {
                                          goto restart;
                                  }
                                  VI_LOCK(vp);
                          }
                  }
  
                  for (bp = TAILQ_FIRST(&vp->v_dirtyblkhd); bp; bp = nbp) {
                          nbp = TAILQ_NEXT(bp, b_vnbufs);
                          if (bp->b_lblkno >= trunclbn) {
                                  if (BUF_LOCK(bp,
                                      LK_EXCLUSIVE | LK_SLEEPFAIL | LK_INTERLOCK,
                                      VI_MTX(vp)) == ENOLCK)
                                          goto restart;
                                  bremfree(bp);
                                  bp->b_flags |= (B_INVAL | B_RELBUF);
                                  bp->b_flags &= ~B_ASYNC;
                                  brelse(bp);
                                  anyfreed = 1;
                                  if (nbp &&
                                      (((nbp->b_xflags & BX_VNDIRTY) == 0) ||
                                      (nbp->b_vp != vp) ||
                                      (nbp->b_flags & B_DELWRI) == 0)) {
                                          goto restart;
                                  }
                                  VI_LOCK(vp);
                          }
                  }
          }
  
          if (length > 0) {
  restartsync:
                  for (bp = TAILQ_FIRST(&vp->v_dirtyblkhd); bp; bp = nbp) {
                          nbp = TAILQ_NEXT(bp, b_vnbufs);
                          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,
                              VI_MTX(vp)) == ENOLCK) {
                                  goto restart;
                          }
                          KASSERT((bp->b_flags & B_DELWRI),
                              ("buf(%p) on dirty queue without DELWRI.", bp));
  
                          bremfree(bp);
                          bawrite(bp);
                          VI_LOCK(vp);
                          goto restartsync;
                  }
          }
          
          while (vp->v_numoutput > 0) {
                  vp->v_iflag |= VI_BWAIT;
                  msleep(&vp->v_numoutput, VI_MTX(vp), PVM, "vbtrunc", 0);
          }
          VI_UNLOCK(vp);
          vnode_pager_setsize(vp, length);
  
          return (0);
  }
  
  /*
   * buf_splay() - splay tree core for the clean/dirty list of buffers in
   *               a vnode.
   *
   *      NOTE: We have to deal with the special case of a background bitmap
   *      buffer, a situation where two buffers will have the same logical
   *      block offset.  We want (1) only the foreground buffer to be accessed
   *      in a lookup and (2) must differentiate between the foreground and
   *      background buffer in the splay tree algorithm because the splay
   *      tree cannot normally handle multiple entities with the same 'index'.
   *      We accomplish this by adding differentiating flags to the splay tree's
   *      numerical domain.
   */
  static
  struct buf *
  buf_splay(daddr_t lblkno, b_xflags_t xflags, struct buf *root)
  {
          struct buf dummy;
          struct buf *lefttreemax, *righttreemin, *y;
  
          if (root == NULL)
                  return (NULL);
          lefttreemax = righttreemin = &dummy;
          for (;;) {
                  if (lblkno < root->b_lblkno ||
                      (lblkno == root->b_lblkno &&
                      (xflags & BX_BKGRDMARKER) < (root->b_xflags & BX_BKGRDMARKER))) {
                          if ((y = root->b_left) == NULL)
                                  break;
                          if (lblkno < y->b_lblkno) {
                                  /* Rotate right. */
                                  root->b_left = y->b_right;
                                  y->b_right = root;
                                  root = y;
                                  if ((y = root->b_left) == NULL)
                                          break;
                          }
                          /* Link into the new root's right tree. */
                          righttreemin->b_left = root;
                          righttreemin = root;
                  } else if (lblkno > root->b_lblkno ||
                      (lblkno == root->b_lblkno &&
                      (xflags & BX_BKGRDMARKER) > (root->b_xflags & BX_BKGRDMARKER))) {
                          if ((y = root->b_right) == NULL)
                                  break;
                          if (lblkno > y->b_lblkno) {
                                  /* Rotate left. */
                                  root->b_right = y->b_left;
                                  y->b_left = root;
                                  root = y;
                                  if ((y = root->b_right) == NULL)
                                          break;
                          }
                          /* Link into the new root's left tree. */
                          lefttreemax->b_right = root;
                          lefttreemax = root;
                  } else {
                          break;
                  }
                  root = y;
          }
          /* Assemble the new root. */
          lefttreemax->b_right = root->b_left;
          righttreemin->b_left = root->b_right;
          root->b_left = dummy.b_right;
          root->b_right = dummy.b_left;
          return (root);
  }
  
  static
  void
  buf_vlist_remove(struct buf *bp)
  {
          struct vnode *vp = bp->b_vp;
          struct buf *root;
  
          ASSERT_VI_LOCKED(vp, "buf_vlist_remove");
          if (bp->b_xflags & BX_VNDIRTY) {
                  if (bp != vp->v_dirtyblkroot) {
                          root = buf_splay(bp->b_lblkno, bp->b_xflags, vp->v_dirtyblkroot);
                          KASSERT(root == bp, ("splay lookup failed during dirty remove"));
                  }
                  if (bp->b_left == NULL) {
                          root = bp->b_right;
                  } else {
                          root = buf_splay(bp->b_lblkno, bp->b_xflags, bp->b_left);
                          root->b_right = bp->b_right;
                  }
                  vp->v_dirtyblkroot = root;
                  TAILQ_REMOVE(&vp->v_dirtyblkhd, bp, b_vnbufs);
                  vp->v_dirtybufcnt--;
          } else {
                  /* KASSERT(bp->b_xflags & BX_VNCLEAN, ("bp wasn't clean")); */
                  if (bp != vp->v_cleanblkroot) {
                          root = buf_splay(bp->b_lblkno, bp->b_xflags, vp->v_cleanblkroot);
                          KASSERT(root == bp, ("splay lookup failed during clean remove"));
                  }
                  if (bp->b_left == NULL) {
                          root = bp->b_right;
                  } else {
                          root = buf_splay(bp->b_lblkno, bp->b_xflags, bp->b_left);
                          root->b_right = bp->b_right;
                  }
                  vp->v_cleanblkroot = root;
                  TAILQ_REMOVE(&vp->v_cleanblkhd, bp, b_vnbufs);
                  vp->v_cleanbufcnt--;
          }
          bp->b_xflags &= ~(BX_VNDIRTY | BX_VNCLEAN);
  }
  
  /*
   * Add the buffer to the sorted clean or dirty block list using a
   * splay tree algorithm.
   *
   * NOTE: xflags is passed as a constant, optimizing this inline function!
   */
  static 
  void
  buf_vlist_add(struct buf *bp, struct vnode *vp, b_xflags_t xflags)
  {
          struct buf *root;
  
          ASSERT_VI_LOCKED(vp, "buf_vlist_add");
          bp->b_xflags |= xflags;
          if (xflags & BX_VNDIRTY) {
                  root = buf_splay(bp->b_lblkno, bp->b_xflags, vp->v_dirtyblkroot);
                  if (root == NULL) {
                          bp->b_left = NULL;
                          bp->b_right = NULL;
                          TAILQ_INSERT_TAIL(&vp->v_dirtyblkhd, bp, b_vnbufs);
                  } else if (bp->b_lblkno < root->b_lblkno ||
                      (bp->b_lblkno == root->b_lblkno &&
                      (bp->b_xflags & BX_BKGRDMARKER) < (root->b_xflags & BX_BKGRDMARKER))) {
                          bp->b_left = root->b_left;
                          bp->b_right = root;
                          root->b_left = NULL;
                          TAILQ_INSERT_BEFORE(root, bp, b_vnbufs);
                  } else {
                          bp->b_right = root->b_right;
                          bp->b_left = root;
                          root->b_right = NULL;
                          TAILQ_INSERT_AFTER(&vp->v_dirtyblkhd, 
                              root, bp, b_vnbufs);
                  }
                  vp->v_dirtybufcnt++;
                  vp->v_dirtyblkroot = bp;
          } else {
                  /* KASSERT(xflags & BX_VNCLEAN, ("xflags not clean")); */
                  root = buf_splay(bp->b_lblkno, bp->b_xflags, vp->v_cleanblkroot);
                  if (root == NULL) {
                          bp->b_left = NULL;
                          bp->b_right = NULL;
                          TAILQ_INSERT_TAIL(&vp->v_cleanblkhd, bp, b_vnbufs);
                  } else if (bp->b_lblkno < root->b_lblkno ||
                      (bp->b_lblkno == root->b_lblkno &&
                      (bp->b_xflags & BX_BKGRDMARKER) < (root->b_xflags & BX_BKGRDMARKER))) {
                          bp->b_left = root->b_left;
                          bp->b_right = root;
                          root->b_left = NULL;
                          TAILQ_INSERT_BEFORE(root, bp, b_vnbufs);
                  } else {
                          bp->b_right = root->b_right;
                          bp->b_left = root;
                          root->b_right = NULL;
                          TAILQ_INSERT_AFTER(&vp->v_cleanblkhd, 
                              root, bp, b_vnbufs);
                  }
                  vp->v_cleanbufcnt++;
                  vp->v_cleanblkroot = bp;
          }
  }
  
  /*
   * Lookup a buffer using the splay tree.  Note that we specifically avoid
   * shadow buffers used in background bitmap writes.
   *
   * This code isn't quite efficient as it could be because we are maintaining
   * two sorted lists and do not know which list the block resides in.
   *
   * During a "make buildworld" the desired buffer is found at one of
   * the roots more than 60% of the time.  Thus, checking both roots
   * before performing either splay eliminates unnecessary splays on the
   * first tree splayed.
   */
  struct buf *
  gbincore(struct vnode *vp, daddr_t lblkno)
  {
          struct buf *bp;
  
          GIANT_REQUIRED;
  
          ASSERT_VI_LOCKED(vp, "gbincore");
          if ((bp = vp->v_cleanblkroot) != NULL &&
              bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                  return (bp);
          if ((bp = vp->v_dirtyblkroot) != NULL &&
              bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                  return (bp);
          if ((bp = vp->v_cleanblkroot) != NULL) {
                  vp->v_cleanblkroot = bp = buf_splay(lblkno, 0, bp);
                  if (bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                          return (bp);
          }
          if ((bp = vp->v_dirtyblkroot) != NULL) {
                  vp->v_dirtyblkroot = bp = buf_splay(lblkno, 0, bp);
                  if (bp->b_lblkno == lblkno && !(bp->b_xflags & BX_BKGRDMARKER))
                          return (bp);
          }
          return (NULL);
  }
  
  /*
   * Associate a buffer with a vnode.
   */
  void
  bgetvp(vp, bp)
          register struct vnode *vp;
          register struct buf *bp;
  {
          KASSERT(bp->b_vp == NULL, ("bgetvp: not free"));
  
          KASSERT((bp->b_xflags & (BX_VNDIRTY|BX_VNCLEAN)) == 0,
              ("bgetvp: bp already attached! %p", bp));
  
          ASSERT_VI_LOCKED(vp, "bgetvp");
          vholdl(vp);
          bp->b_vp = vp;
          bp->b_dev = vn_todev(vp);
          /*
           * Insert onto list for new vnode.
           */
          buf_vlist_add(bp, vp, BX_VNCLEAN);
  }
  
  /*
   * Disassociate a buffer from a vnode.
   */
  void
  brelvp(bp)
          register struct buf *bp;
  {
          struct vnode *vp;
  
          KASSERT(bp->b_vp != NULL, ("brelvp: NULL"));
  
          /*
           * Delete from old vnode list, if on one.
           */
          vp = bp->b_vp;
          VI_LOCK(vp);
          if (bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN))
                  buf_vlist_remove(bp);
          if ((vp->v_iflag & VI_ONWORKLST) && TAILQ_EMPTY(&vp->v_dirtyblkhd)) {
                  vp->v_iflag &= ~VI_ONWORKLST;
                  mtx_lock(&sync_mtx);
                  LIST_REMOVE(vp, v_synclist);
                  mtx_unlock(&sync_mtx);
          }
          vdropl(vp);
          bp->b_vp = (struct vnode *) 0;
          if (bp->b_object)
                  bp->b_object = NULL;
          VI_UNLOCK(vp);
  }
  
  /*
   * Add an item to the syncer work queue.
   */
  static void
  vn_syncer_add_to_worklist(struct vnode *vp, int delay)
  {
          int slot;
  
          ASSERT_VI_LOCKED(vp, "vn_syncer_add_to_worklist");
  
          mtx_lock(&sync_mtx);
          if (vp->v_iflag & VI_ONWORKLST)
                  LIST_REMOVE(vp, v_synclist);
          else
                  vp->v_iflag |= VI_ONWORKLST;
  
          if (delay > syncer_maxdelay - 2)
                  delay = syncer_maxdelay - 2;
          slot = (syncer_delayno + delay) & syncer_mask;
  
          LIST_INSERT_HEAD(&syncer_workitem_pending[slot], vp, v_synclist);
          mtx_unlock(&sync_mtx);
  }
  
  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)
  
  /*
   * System filesystem synchronizer daemon.
   */
  static void
  sched_sync(void)
  {
          struct synclist *next;
          struct synclist *slp;
          struct vnode *vp;
          struct mount *mp;
          long starttime;
          struct thread *td = FIRST_THREAD_IN_PROC(updateproc);  /* XXXKSE */
  
          mtx_lock(&Giant);
  
          EVENTHANDLER_REGISTER(shutdown_pre_sync, kproc_shutdown, td->td_proc,
              SHUTDOWN_PRI_LAST);
  
          for (;;) {
                  kthread_suspend_check(td->td_proc);
  
                  starttime = time_second;
  
                  /*
                   * Push files whose dirty time has expired.  Be careful
                   * of interrupt race on slp queue.
                   */
                  mtx_lock(&sync_mtx);
                  slp = &syncer_workitem_pending[syncer_delayno];
                  syncer_delayno += 1;
                  if (syncer_delayno == syncer_maxdelay)
                          syncer_delayno = 0;
                  next = &syncer_workitem_pending[syncer_delayno];
  
                  while ((vp = LIST_FIRST(slp)) != NULL) {
                          if (VOP_ISLOCKED(vp, NULL) != 0 || 
                              vn_start_write(vp, &mp, V_NOWAIT) != 0) {
                                  LIST_REMOVE(vp, v_synclist);
                                  LIST_INSERT_HEAD(next, vp, v_synclist);
                                  continue;
                          }
                          if (VI_TRYLOCK(vp) == 0) {
                                  LIST_REMOVE(vp, v_synclist);
                                  LIST_INSERT_HEAD(next, vp, v_synclist);
                                  vn_finished_write(mp);
                                  continue;
                          }
                          /*
                           * 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);
                          vn_lock(vp, LK_EXCLUSIVE | LK_RETRY | LK_INTERLOCK, td);
                          (void) VOP_FSYNC(vp, td->td_ucred, MNT_LAZY, td);
                          VOP_UNLOCK(vp, 0, td);
                          vn_finished_write(mp);
                          VI_LOCK(vp);
                          if ((vp->v_iflag & VI_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(vp, syncdelay);
                          }
                          vdropl(vp);
                          VI_UNLOCK(vp);
                          mtx_lock(&sync_mtx);
                  }
                  mtx_unlock(&sync_mtx);
  
                  /*
                   * Do soft update processing.
                   */
                  if (softdep_process_worklist_hook != NULL)
                          (*softdep_process_worklist_hook)(NULL);
  
                  /*
                   * 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.
                   */
                  mtx_lock(&sync_mtx);
                  if (rushjob > 0) {
                          rushjob -= 1;
                          mtx_unlock(&sync_mtx);
                          continue;
                  }
                  mtx_unlock(&sync_mtx);
                  /*
                   * 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 (time_second == starttime)
                          tsleep(&lbolt, PPAUSE, "syncer", 0);
          }
  }
  
  /*
   * 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.
   * XXXKSE  only one update?
   */
  int
  speedup_syncer()
  {
          struct thread *td;
          int ret = 0;
  
          td = FIRST_THREAD_IN_PROC(updateproc);
          mtx_lock_spin(&sched_lock);
          if (td->td_wchan == &lbolt) {
                  unsleep(td);
                  TD_CLR_SLEEPING(td);
                  setrunnable(td);
          }
          mtx_unlock_spin(&sched_lock);
          mtx_lock(&sync_mtx);
          if (rushjob < syncdelay / 2) {
                  rushjob += 1;
                  stat_rush_requests += 1;
                  ret = 1;
          }
          mtx_unlock(&sync_mtx);
          return (ret);
  }
  
  /*
   * Associate a p-buffer with a vnode.
   *
   * Also sets B_PAGING flag to indicate that vnode is not fully associated
   * with the buffer.  i.e. the bp has not been linked into the vnode or
   * ref-counted.
   */
  void
  pbgetvp(vp, bp)
          register struct vnode *vp;
          register struct buf *bp;
  {
  
          KASSERT(bp->b_vp == NULL, ("pbgetvp: not free"));
  
          bp->b_vp = vp;
          bp->b_object = vp->v_object;
          bp->b_flags |= B_PAGING;
          bp->b_dev = vn_todev(vp);
  }
  
  /*
   * Disassociate a p-buffer from a vnode.
   */
  void
  pbrelvp(bp)
          register struct buf *bp;
  {
  
          KASSERT(bp->b_vp != NULL, ("pbrelvp: NULL"));
  
          /* XXX REMOVE ME */
          VI_LOCK(bp->b_vp);
          if (TAILQ_NEXT(bp, b_vnbufs) != NULL) {
                  panic(
                      "relpbuf(): b_vp was probably reassignbuf()d %p %x",
                      bp,
                      (int)bp->b_flags
                  );
          }
          VI_UNLOCK(bp->b_vp);
          bp->b_vp = (struct vnode *) 0;
          bp->b_object = NULL;
          bp->b_flags &= ~B_PAGING;
  }
  
  /*
   * Reassign a buffer from one vnode to another.
   * Used to assign file specific control information
   * (indirect blocks) to the vnode to which they belong.
   */
  void
  reassignbuf(bp, newvp)
          register struct buf *bp;
          register struct vnode *newvp;
  {
          struct vnode *vp;
          int delay;
  
          if (newvp == NULL) {
                  printf("reassignbuf: NULL");
                  return;
          }
          vp = bp->b_vp;
          ++reassignbufcalls;
  
          /*
           * B_PAGING flagged buffers cannot be reassigned because their vp
           * is not fully linked in.
           */
          if (bp->b_flags & B_PAGING)
                  panic("cannot reassign paging buffer");
  
          /*
           * Delete from old vnode list, if on one.
           */
          VI_LOCK(vp);
          if (bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) {
                  buf_vlist_remove(bp);
                  if (vp != newvp) {
                          vdropl(bp->b_vp);
                          bp->b_vp = NULL;        /* for clarification */
                  }
          }
          if (vp != newvp) {
                  VI_UNLOCK(vp);
                  VI_LOCK(newvp);
          }
          /*
           * If dirty, put on list of dirty buffers; otherwise insert onto list
           * of clean buffers.
           */
          if (bp->b_flags & B_DELWRI) {
                  if ((newvp->v_iflag & VI_ONWORKLST) == 0) {
                          switch (newvp->v_type) {
                          case VDIR:
                                  delay = dirdelay;
                                  break;
                          case VCHR:
                                  if (newvp->v_rdev->si_mountpoint != NULL) {
                                          delay = metadelay;
                                          break;
                                  }
                                  /* FALLTHROUGH */
                          default:
                                  delay = filedelay;
                          }
                          vn_syncer_add_to_worklist(newvp, delay);
                  }
                  buf_vlist_add(bp, newvp, BX_VNDIRTY);
          } else {
                  buf_vlist_add(bp, newvp, BX_VNCLEAN);
  
                  if ((newvp->v_iflag & VI_ONWORKLST) &&
                      TAILQ_EMPTY(&newvp->v_dirtyblkhd)) {
                          mtx_lock(&sync_mtx);
                          LIST_REMOVE(newvp, v_synclist);
                          mtx_unlock(&sync_mtx);
                          newvp->v_iflag &= ~VI_ONWORKLST;
                  }
          }
          if (bp->b_vp != newvp) {
                  bp->b_vp = newvp;
                  vholdl(bp->b_vp);
          }
          VI_UNLOCK(newvp);
  }
  
  /*
   * Create a vnode for a device.
   * Used for mounting the root filesystem.
   */
  int
  bdevvp(dev, vpp)
          dev_t dev;
          struct vnode **vpp;
  {
          register struct vnode *vp;
          struct vnode *nvp;
          int error;
  
          if (dev == NODEV) {
                  *vpp = NULLVP;
                  return (ENXIO);
          }
          if (vfinddev(dev, VCHR, vpp))
                  return (0);
          error = getnewvnode("none", (struct mount *)0, spec_vnodeop_p, &nvp);
          if (error) {
                  *vpp = NULLVP;
                  return (error);
          }
          vp = nvp;
          vp->v_type = VCHR;
          addalias(vp, dev);
          *vpp = vp;
          return (0);
  }
  
  static void
  v_incr_usecount(struct vnode *vp, int delta)
  {
          vp->v_usecount += delta;
          if (vp->v_type == VCHR && vp->v_rdev != NULL) {
                  mtx_lock(&spechash_mtx);
                  vp->v_rdev->si_usecount += delta;
                  mtx_unlock(&spechash_mtx);
          }
  }
  
  /*
   * Add vnode to the alias list hung off the dev_t.
   *
   * The reason for this gunk is that multiple vnodes can reference
   * the same physical device, so checking vp->v_usecount to see
   * how many users there are is inadequate; the v_usecount for
   * the vnodes need to be accumulated.  vcount() does that.
   */
  struct vnode *
  addaliasu(nvp, nvp_rdev)
          struct vnode *nvp;
          udev_t nvp_rdev;
  {
          struct vnode *ovp;
          vop_t **ops;
          dev_t dev;
  
          if (nvp->v_type == VBLK)
                  return (nvp);
          if (nvp->v_type != VCHR)
                  panic("addaliasu on non-special vnode");
          dev = udev2dev(nvp_rdev, 0);
          /*
           * Check to see if we have a bdevvp vnode with no associated
           * filesystem. If so, we want to associate the filesystem of
           * the new newly instigated vnode with the bdevvp vnode and
           * discard the newly created vnode rather than leaving the
           * bdevvp vnode lying around with no associated filesystem.
           */
          if (vfinddev(dev, nvp->v_type, &ovp) == 0 || ovp->v_data != NULL) {
                  addalias(nvp, dev);
                  return (nvp);
          }
          /*
           * Discard unneeded vnode, but save its node specific data.
           * Note that if there is a lock, it is carried over in the
           * node specific data to the replacement vnode.
           */
          vref(ovp);
          ovp->v_data = nvp->v_data;
          ovp->v_tag = nvp->v_tag;
          nvp->v_data = NULL;
          lockdestroy(ovp->v_vnlock);
          lockinit(ovp->v_vnlock, PVFS, nvp->v_vnlock->lk_wmesg,
              nvp->v_vnlock->lk_timo, nvp->v_vnlock->lk_flags & LK_EXTFLG_MASK);
          ops = ovp->v_op;
          ovp->v_op = nvp->v_op;
          if (VOP_ISLOCKED(nvp, curthread)) {
                  VOP_UNLOCK(nvp, 0, curthread);
                  vn_lock(ovp, LK_EXCLUSIVE | LK_RETRY, curthread);
          }
          nvp->v_op = ops;
          insmntque(ovp, nvp->v_mount);
          vrele(nvp);
          vgone(nvp);
          return (ovp);
  }
  
  /* This is a local helper function that do the same as addaliasu, but for a
   * dev_t instead of an udev_t. */
  static void
  addalias(nvp, dev)
          struct vnode *nvp;
          dev_t dev;
  {
  
          KASSERT(nvp->v_type == VCHR, ("addalias on non-special vnode"));
          nvp->v_rdev = dev;
          VI_LOCK(nvp);
          mtx_lock(&spechash_mtx);
          SLIST_INSERT_HEAD(&dev->si_hlist, nvp, v_specnext);
          dev->si_usecount += nvp->v_usecount;
          mtx_unlock(&spechash_mtx);
          VI_UNLOCK(nvp);
  }
  
  /*
   * Grab a particular vnode from the free list, increment its
   * reference count and lock it. The vnode lock bit is set if the
   * vnode is being eliminated in vgone. The process is awakened
   * when the transition is completed, and an error returned to
   * indicate that the vnode is no longer usable (possibly having
   * been changed to a new filesystem type).
   */
  int
  vget(vp, flags, td)
          register struct vnode *vp;
          int flags;
          struct thread *td;
  {
          int error;
  
          /*
           * If the vnode is in the process of being cleaned out for
           * another use, we wait for the cleaning to finish and then
           * return failure. Cleaning is determined by checking that
           * the VI_XLOCK flag is set.
           */
          if ((flags & LK_INTERLOCK) == 0)
                  VI_LOCK(vp);
          if (vp->v_iflag & VI_XLOCK && vp->v_vxproc != curthread) {
                  if ((flags & LK_NOWAIT) == 0) {
                          vp->v_iflag |= VI_XWANT;
                          msleep(vp, VI_MTX(vp), PINOD | PDROP, "vget", 0);
                          return (ENOENT);
                  }
                  VI_UNLOCK(vp);
                  return (EBUSY);
          }
  
          v_incr_usecount(vp, 1);
  
          if (VSHOULDBUSY(vp))
                  vbusy(vp);
          if (flags & LK_TYPE_MASK) {
                  if ((error = vn_lock(vp, flags | LK_INTERLOCK, td)) != 0) {
                          /*
                           * must expand vrele here because we do not want
                           * to call VOP_INACTIVE if the reference count
                           * drops back to zero since it was never really
                           * active. We must remove it from the free list
                           * before sleeping so that multiple processes do
                           * not try to recycle it.
                           */
                          VI_LOCK(vp);
                          v_incr_usecount(vp, -1);
                          if (VSHOULDFREE(vp))
                                  vfree(vp);
                          else
                                  vlruvp(vp);
                          VI_UNLOCK(vp);
                  }
                  return (error);
          }
          VI_UNLOCK(vp);
          return (0);
  }
  
  /*
   * Increase the reference count of a vnode.
   */
  void
  vref(struct vnode *vp)
  {
          VI_LOCK(vp);
          v_incr_usecount(vp, 1);
          VI_UNLOCK(vp);
  }
  
  /*
   * Return reference count of a vnode.
   *
   * The results of this call are only guaranteed when some mechanism other
   * than the VI lock is used to stop other processes from gaining references
   * to the vnode.  This may be the case if the caller holds the only reference.
   * This is also useful when stale data is acceptable as race conditions may
   * be accounted for by some other means.
   */
  int
  vrefcnt(struct vnode *vp)
  {
          int usecnt;
  
          VI_LOCK(vp);
          usecnt = vp->v_usecount;
          VI_UNLOCK(vp);
  
          return (usecnt);
  }
  
  
  /*
   * Vnode put/release.
   * If count drops to zero, call inactive routine and return to freelist.
   */
  void
  vrele(vp)
          struct vnode *vp;
  {
          struct thread *td = curthread;  /* XXX */
  
          KASSERT(vp != NULL, ("vrele: null vp"));
  
          VI_LOCK(vp);
  
          /* Skip this v_writecount check if we're going to panic below. */
          KASSERT(vp->v_writecount < vp->v_usecount || vp->v_usecount < 1,
              ("vrele: missed vn_close"));
  
          if (vp->v_usecount > 1 || ((vp->v_iflag & VI_DOINGINACT) &&
              vp->v_usecount == 1)) {
                  v_incr_usecount(vp, -1);
                  VI_UNLOCK(vp);
  
                  return;
          }
  
          if (vp->v_usecount == 1) {
                  v_incr_usecount(vp, -1);
                  /*
                   * We must call VOP_INACTIVE with the node locked. Mark
                   * as VI_DOINGINACT to avoid recursion.
                   */
                  if (vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK, td) == 0) {
                          VI_LOCK(vp);
                          vp->v_iflag |= VI_DOINGINACT;
                          VI_UNLOCK(vp);
                          VOP_INACTIVE(vp, td);
                          VI_LOCK(vp);
                          KASSERT(vp->v_iflag & VI_DOINGINACT,
                              ("vrele: lost VI_DOINGINACT"));
                          vp->v_iflag &= ~VI_DOINGINACT;
                  } else
                          VI_LOCK(vp);
                  if (VSHOULDFREE(vp))
                          vfree(vp);
                  else
                          vlruvp(vp);
                  VI_UNLOCK(vp);
  
          } else {
  #ifdef DIAGNOSTIC
                  vprint("vrele: negative ref count", vp);
  #endif
                  VI_UNLOCK(vp);
                  panic("vrele: negative ref cnt");
          }
  }
  
  /*
   * Release an already locked vnode.  This give the same effects as
   * unlock+vrele(), but takes less time and avoids releasing and
   * re-aquiring the lock (as vrele() aquires the lock internally.)
   */
  void
  vput(vp)
          struct vnode *vp;
  {
          struct thread *td = curthread;  /* XXX */
  
          GIANT_REQUIRED;
  
          KASSERT(vp != NULL, ("vput: null vp"));
          VI_LOCK(vp);
          /* Skip this v_writecount check if we're going to panic below. */
          KASSERT(vp->v_writecount < vp->v_usecount || vp->v_usecount < 1,
              ("vput: missed vn_close"));
  
          if (vp->v_usecount > 1 || ((vp->v_iflag & VI_DOINGINACT) &&
              vp->v_usecount == 1)) {
                  v_incr_usecount(vp, -1);
                  VOP_UNLOCK(vp, LK_INTERLOCK, td);
                  return;
          }
  
          if (vp->v_usecount == 1) {
                  v_incr_usecount(vp, -1);
                  /*
                   * We must call VOP_INACTIVE with the node locked, so
                   * we just need to release the vnode mutex. Mark as
                   * as VI_DOINGINACT to avoid recursion.
                   */
                  vp->v_iflag |= VI_DOINGINACT;
                  VI_UNLOCK(vp);
                  VOP_INACTIVE(vp, td);
                  VI_LOCK(vp);
                  KASSERT(vp->v_iflag & VI_DOINGINACT,
                      ("vput: lost VI_DOINGINACT"));
                  vp->v_iflag &= ~VI_DOINGINACT;
                  if (VSHOULDFREE(vp))
                          vfree(vp);
                  else
                          vlruvp(vp);
                  VI_UNLOCK(vp);
  
          } else {
  #ifdef DIAGNOSTIC
                  vprint("vput: negative ref count", vp);
  #endif
                  panic("vput: negative ref cnt");
          }
  }
  
  /*
   * Somebody doesn't want the vnode recycled.
   */
  void
  vhold(struct vnode *vp)
  {
          VI_LOCK(vp);
          vholdl(vp);
          VI_UNLOCK(vp);
  }
  
  void
  vholdl(vp)
          register struct vnode *vp;
  {
          vp->v_holdcnt++;
          if (VSHOULDBUSY(vp))
                  vbusy(vp);
  }
  
  /*
   * Note that there is one less who cares about this vnode.  vdrop() is the
   * opposite of vhold().
   */
  void
  vdrop(struct vnode *vp)
  {
          VI_LOCK(vp);
          vdropl(vp);
          VI_UNLOCK(vp);
  }
          
  void
  vdropl(vp)
          register struct vnode *vp;
  {
          if (vp->v_holdcnt <= 0)
                  panic("vdrop: holdcnt");
          vp->v_holdcnt--;
          if (VSHOULDFREE(vp))
                  vfree(vp);
          else
                  vlruvp(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()
   * 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, "");
  #endif
  
  int
  vflush(mp, rootrefs, flags)
          struct mount *mp;
          int rootrefs;
          int flags;
  {
          struct thread *td = curthread;  /* XXX */
          struct vnode *vp, *nvp, *rootvp = NULL;
          struct vattr vattr;
          int busy = 0, error;
  
          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, &rootvp)) != 0)
                          return (error);
                  vput(rootvp);
  
          }
          MNT_ILOCK(mp);
  loop:
          for (vp = TAILQ_FIRST(&mp->mnt_nvnodelist); vp; vp = nvp) {
                  /*
                   * Make sure this vnode wasn't reclaimed in getnewvnode().
                   * Start over if it has (it won't be on the list anymore).
                   */
                  if (vp->v_mount != mp)
                          goto loop;
                  nvp = TAILQ_NEXT(vp, v_nmntvnodes);
  
                  VI_LOCK(vp);
                  MNT_IUNLOCK(mp);
                  error = vn_lock(vp, LK_INTERLOCK | LK_EXCLUSIVE, td);
                  if (error) {
                          MNT_ILOCK(mp);
                          goto loop;
                  }
                  /*
                   * Skip over a vnodes marked VV_SYSTEM.
                   */
                  if ((flags & SKIPSYSTEM) && (vp->v_vflag & VV_SYSTEM)) {
                          VOP_UNLOCK(vp, 0, td);
                          MNT_ILOCK(mp);
                          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) {
                          error = VOP_GETATTR(vp, &vattr, td->td_ucred, td);
                          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, LK_INTERLOCK, td);
                                  MNT_ILOCK(mp);
                                  continue;
                          }
                  } else
                          VI_LOCK(vp);
  
                  VOP_UNLOCK(vp, 0, td);
  
                  /*
                   * With v_usecount == 0, all we need to do is clear out the
                   * vnode data structures and we are done.
                   */
                  if (vp->v_usecount == 0) {
                          vgonel(vp, td);
                          MNT_ILOCK(mp);
                          continue;
                  }
  
                  /*
                   * If FORCECLOSE is set, forcibly close the vnode. For block
                   * or character devices, revert to an anonymous device. For
                   * all other files, just kill them.
                   */
                  if (flags & FORCECLOSE) {
                          if (vp->v_type != VCHR)
                                  vgonel(vp, td);
                          else
                                  vgonechrl(vp, td);
                          MNT_ILOCK(mp);
                          continue;
                  }
  #ifdef DIAGNOSTIC
                  if (busyprt)
                          vprint("vflush: busy vnode", vp);
  #endif
                  VI_UNLOCK(vp);
                  MNT_ILOCK(mp);
                  busy++;
          }
          MNT_IUNLOCK(mp);
          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"));
                  KASSERT(rootvp->v_usecount >= rootrefs, ("vflush: rootrefs"));
                  if (busy == 1 && rootvp->v_usecount == rootrefs) {
                          vgonel(rootvp, td);
                          busy = 0;
                  } else
                          VI_UNLOCK(rootvp);
          }
          if (busy)
                  return (EBUSY);
          for (; rootrefs > 0; rootrefs--)
                  vrele(rootvp);
          return (0);
  }
  
  /*
   * This moves a now (likely recyclable) vnode to the end of the
   * mountlist.  XXX However, it is temporarily disabled until we
   * can clean up ffs_sync() and friends, which have loop restart
   * conditions which this code causes to operate O(N^2).
   */
  static void
  vlruvp(struct vnode *vp)
  {
  #if 0
          struct mount *mp;
  
          if ((mp = vp->v_mount) != NULL) {
                  MNT_ILOCK(mp);
                  TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                  TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                  MNT_IUNLOCK(mp);
          }
  #endif
  }
  
  static void
  vx_lock(struct vnode *vp)
  {
          ASSERT_VI_LOCKED(vp, "vx_lock");
  
          /*
           * Prevent the vnode from being recycled or brought into use while we
           * clean it out.
           */
          if (vp->v_iflag & VI_XLOCK)
                  panic("vclean: deadlock");
          vp->v_iflag |= VI_XLOCK;
          vp->v_vxproc = curthread;
  }
  
  static void
  vx_unlock(struct vnode *vp)
  {
          ASSERT_VI_LOCKED(vp, "vx_unlock");
          vp->v_iflag &= ~VI_XLOCK;
          vp->v_vxproc = NULL;
          if (vp->v_iflag & VI_XWANT) {
                  vp->v_iflag &= ~VI_XWANT;
                  wakeup(vp);
          }
  }
  
  
  /*
   * Disassociate the underlying filesystem from a vnode.
   */
  static void
  vclean(vp, flags, td)
          struct vnode *vp;
          int flags;
          struct thread *td;
  {
          int active;
  
          ASSERT_VI_LOCKED(vp, "vclean");
          /*
           * Check to see if the vnode is in use. If so we have to reference it
           * before we clean it out so that its count cannot fall to zero and
           * generate a race against ourselves to recycle it.
           */
          if ((active = vp->v_usecount))
                  v_incr_usecount(vp, 1);
  
          /*
           * Even if the count is zero, the VOP_INACTIVE routine may still
           * have the object locked while it cleans it out. The VOP_LOCK
           * ensures that the VOP_INACTIVE routine is done with its work.
           * For active vnodes, it ensures that no other activity can
           * occur while the underlying object is being cleaned out.
           */
          VOP_LOCK(vp, LK_DRAIN | LK_INTERLOCK, td);
  
          /*
           * Clean out any buffers associated with the vnode.
           * If the flush fails, just toss the buffers.
           */
          if (flags & DOCLOSE) {
                  struct buf *bp;
                  bp = TAILQ_FIRST(&vp->v_dirtyblkhd);
                  if (bp != NULL)
                          (void) vn_write_suspend_wait(vp, NULL, V_WAIT);
                  if (vinvalbuf(vp, V_SAVE, NOCRED, td, 0, 0) != 0)
                          vinvalbuf(vp, 0, NOCRED, td, 0, 0);
          }
  
          VOP_DESTROYVOBJECT(vp);
  
          /*
           * Any other processes trying to obtain this lock must first
           * wait for VXLOCK to clear, then call the new lock operation.
           */
          VOP_UNLOCK(vp, 0, td);
  
          /*
           * If purging an active vnode, it must be closed and
           * deactivated before being reclaimed. Note that the
           * VOP_INACTIVE will unlock the vnode.
           */
          if (active) {
                  if (flags & DOCLOSE)
                          VOP_CLOSE(vp, FNONBLOCK, NOCRED, td);
                  VI_LOCK(vp);
                  if ((vp->v_iflag & VI_DOINGINACT) == 0) {
                          vp->v_iflag |= VI_DOINGINACT;
                          VI_UNLOCK(vp);
                          if (vn_lock(vp, LK_EXCLUSIVE | LK_NOWAIT, td) != 0)
                                  panic("vclean: cannot relock.");
                          VOP_INACTIVE(vp, td);
                          VI_LOCK(vp);
                          KASSERT(vp->v_iflag & VI_DOINGINACT,
                              ("vclean: lost VI_DOINGINACT"));
                          vp->v_iflag &= ~VI_DOINGINACT;
                  }
                  VI_UNLOCK(vp);
          }
          /*
           * Reclaim the vnode.
           */
          if (VOP_RECLAIM(vp, td))
                  panic("vclean: cannot reclaim");
  
          if (active) {
                  /*
                   * Inline copy of vrele() since VOP_INACTIVE
                   * has already been called.
                   */
                  VI_LOCK(vp);
                  v_incr_usecount(vp, -1);
                  if (vp->v_usecount <= 0) {
  #ifdef INVARIANTS
                          if (vp->v_usecount < 0 || vp->v_writecount != 0) {
                                  vprint("vclean: bad ref count", vp);
                                  panic("vclean: ref cnt");
                          }
  #endif
                          if (VSHOULDFREE(vp))
                                  vfree(vp);
                  }
                  VI_UNLOCK(vp);
          }
          /*
           * Delete from old mount point vnode list.
           */
          if (vp->v_mount != NULL)
                  insmntque(vp, (struct mount *)0);
          cache_purge(vp);
          VI_LOCK(vp);
          if (VSHOULDFREE(vp))
                  vfree(vp);
  
          /*
           * Done with purge, reset to the standard lock and
           * notify sleepers of the grim news.
           */
          vp->v_vnlock = &vp->v_lock;
          vp->v_op = dead_vnodeop_p;
          if (vp->v_pollinfo != NULL)
                  vn_pollgone(vp);
          vp->v_tag = "none";
  }
  
  /*
   * Eliminate all activity associated with the requested vnode
   * and with all vnodes aliased to the requested vnode.
   */
  int
  vop_revoke(ap)
          struct vop_revoke_args /* {
                  struct vnode *a_vp;
                  int a_flags;
          } */ *ap;
  {
          struct vnode *vp, *vq;
          dev_t dev;
  
          KASSERT((ap->a_flags & REVOKEALL) != 0, ("vop_revoke"));
          vp = ap->a_vp;
          KASSERT((vp->v_type == VCHR), ("vop_revoke: not VCHR"));
  
          VI_LOCK(vp);
          /*
           * If a vgone (or vclean) is already in progress,
           * wait until it is done and return.
           */
          if (vp->v_iflag & VI_XLOCK) {
                  vp->v_iflag |= VI_XWANT;
                  msleep(vp, VI_MTX(vp), PINOD | PDROP,
                      "vop_revokeall", 0);
                  return (0);
          }
          VI_UNLOCK(vp);
          dev = vp->v_rdev;
          for (;;) {
                  mtx_lock(&spechash_mtx);
                  vq = SLIST_FIRST(&dev->si_hlist);
                  mtx_unlock(&spechash_mtx);
                  if (!vq)
                          break;
                  vgone(vq);
          }
          return (0);
  }
  
  /*
   * Recycle an unused vnode to the front of the free list.
   * Release the passed interlock if the vnode will be recycled.
   */
  int
  vrecycle(vp, inter_lkp, td)
          struct vnode *vp;
          struct mtx *inter_lkp;
          struct thread *td;
  {
  
          VI_LOCK(vp);
          if (vp->v_usecount == 0) {
                  if (inter_lkp) {
                          mtx_unlock(inter_lkp);
                  }
                  vgonel(vp, td);
                  return (1);
          }
          VI_UNLOCK(vp);
          return (0);
  }
  
  /*
   * Eliminate all activity associated with a vnode
   * in preparation for reuse.
   */
  void
  vgone(vp)
          register struct vnode *vp;
  {
          struct thread *td = curthread;  /* XXX */
  
          VI_LOCK(vp);
          vgonel(vp, td);
  }
  
  /*
   * Disassociate a character device from the its underlying filesystem and
   * attach it to spec.  This is for use when the chr device is still active
   * and the filesystem is going away.
   */
  static void
  vgonechrl(struct vnode *vp, struct thread *td)
  {
          ASSERT_VI_LOCKED(vp, "vgonechrl");
          vx_lock(vp);
          /*
           * This is a custom version of vclean() which does not tearm down
           * the bufs or vm objects held by this vnode.  This allows filesystems
           * to continue using devices which were discovered via another
           * filesystem that has been unmounted.
           */
          if (vp->v_usecount != 0) {
                  v_incr_usecount(vp, 1);
                  /*
                   * Ensure that no other activity can occur while the
                   * underlying object is being cleaned out.
                   */
                  VOP_LOCK(vp, LK_DRAIN | LK_INTERLOCK, td);
                  /*
                   * Any other processes trying to obtain this lock must first
                   * wait for VXLOCK to clear, then call the new lock operation.
                   */
                  VOP_UNLOCK(vp, 0, td);
                  vp->v_vnlock = &vp->v_lock;
                  vp->v_tag = "orphanchr";
                  vp->v_op = spec_vnodeop_p;
                  if (vp->v_mount != NULL)
                          insmntque(vp, (struct mount *)0);
                  cache_purge(vp);
                  vrele(vp);
                  VI_LOCK(vp);
          } else
                  vclean(vp, 0, td);
          vp->v_op = spec_vnodeop_p;
          vx_unlock(vp);
          VI_UNLOCK(vp);
  }
  /*
   * vgone, with the vp interlock held.
   */
  void
  vgonel(vp, td)
          struct vnode *vp;
          struct thread *td;
  {
          /*
           * If a vgone (or vclean) is already in progress,
           * wait until it is done and return.
           */
          ASSERT_VI_LOCKED(vp, "vgonel");
          if (vp->v_iflag & VI_XLOCK) {
                  vp->v_iflag |= VI_XWANT;
                  msleep(vp, VI_MTX(vp), PINOD | PDROP, "vgone", 0);
                  return;
          }
          vx_lock(vp);
  
          /*
           * Clean out the filesystem specific data.
           */
          vclean(vp, DOCLOSE, td);
          VI_UNLOCK(vp);
  
          /*
           * If special device, remove it from special device alias list
           * if it is on one.
           */
          VI_LOCK(vp);
          if (vp->v_type == VCHR && vp->v_rdev != NULL && vp->v_rdev != NODEV) {
                  mtx_lock(&spechash_mtx);
                  SLIST_REMOVE(&vp->v_rdev->si_hlist, vp, vnode, v_specnext);
                  vp->v_rdev->si_usecount -= vp->v_usecount;
                  mtx_unlock(&spechash_mtx);
                  vp->v_rdev = NULL;
          }
  
          /*
           * If it is on the freelist and not already at the head,
           * move it to the head of the list. The test of the
           * VDOOMED flag and the reference count of zero is because
           * it will be removed from the free list by getnewvnode,
           * but will not have its reference count incremented until
           * after calling vgone. If the reference count were
           * incremented first, vgone would (incorrectly) try to
           * close the previous instance of the underlying object.
           */
          if (vp->v_usecount == 0 && !(vp->v_iflag & VI_DOOMED)) {
                  mtx_lock(&vnode_free_list_mtx);
                  if (vp->v_iflag & VI_FREE) {
                          TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
                  } else {
                          vp->v_iflag |= VI_FREE;
                          freevnodes++;
                  }
                  TAILQ_INSERT_HEAD(&vnode_free_list, vp, v_freelist);
                  mtx_unlock(&vnode_free_list_mtx);
          }
  
          vp->v_type = VBAD;
          vx_unlock(vp);
          VI_UNLOCK(vp);
  }
  
  /*
   * Lookup a vnode by device number.
   */
  int
  vfinddev(dev, type, vpp)
          dev_t dev;
          enum vtype type;
          struct vnode **vpp;
  {
          struct vnode *vp;
  
          mtx_lock(&spechash_mtx);
          SLIST_FOREACH(vp, &dev->si_hlist, v_specnext) {
                  if (type == vp->v_type) {
                          *vpp = vp;
                          mtx_unlock(&spechash_mtx);
                          return (1);
                  }
          }
          mtx_unlock(&spechash_mtx);
          return (0);
  }
  
  /*
   * Calculate the total number of references to a special device.
   */
  int
  vcount(vp)
          struct vnode *vp;
  {
          int count;
  
          mtx_lock(&spechash_mtx);
          count = vp->v_rdev->si_usecount;
          mtx_unlock(&spechash_mtx);
          return (count);
  }
  
  /*
   * Same as above, but using the dev_t as argument
   */
  int
  count_dev(dev)
          dev_t dev;
  {
          int count;
  
          mtx_lock(&spechash_mtx);
          count = dev->si_usecount;
          mtx_unlock(&spechash_mtx);
          return(count);
  }
  
  /*
   * Print out a description of a vnode.
   */
  static char *typename[] =
  {"VNON", "VREG", "VDIR", "VBLK", "VCHR", "VLNK", "VSOCK", "VFIFO", "VBAD"};
  
  void
  vprint(label, vp)
          char *label;
          struct vnode *vp;
  {
          char buf[96];
  
          if (label != NULL)
                  printf("%s: %p: ", label, (void *)vp);
          else
                  printf("%p: ", (void *)vp);
          printf("tag %s, type %s, usecount %d, writecount %d, refcount %d,",
              vp->v_tag, typename[vp->v_type], vp->v_usecount,
              vp->v_writecount, vp->v_holdcnt);
          buf[0] = '\0';
          if (vp->v_vflag & VV_ROOT)
                  strcat(buf, "|VV_ROOT");
          if (vp->v_vflag & VV_TEXT)
                  strcat(buf, "|VV_TEXT");
          if (vp->v_vflag & VV_SYSTEM)
                  strcat(buf, "|VV_SYSTEM");
          if (vp->v_iflag & VI_XLOCK)
                  strcat(buf, "|VI_XLOCK");
          if (vp->v_iflag & VI_XWANT)
                  strcat(buf, "|VI_XWANT");
          if (vp->v_iflag & VI_BWAIT)
                  strcat(buf, "|VI_BWAIT");
          if (vp->v_iflag & VI_DOOMED)
                  strcat(buf, "|VI_DOOMED");
          if (vp->v_iflag & VI_FREE)
                  strcat(buf, "|VI_FREE");
          if (vp->v_vflag & VV_OBJBUF)
                  strcat(buf, "|VV_OBJBUF");
          if (buf[0] != '\0')
                  printf(" flags (%s),", &buf[1]);
          lockmgr_printinfo(vp->v_vnlock);
          printf("\n");
          if (vp->v_data != NULL)
                  VOP_PRINT(vp);
  }
  
  #ifdef DDB
  #include <ddb/ddb.h>
  /*
   * List all of the locked vnodes in the system.
   * Called when debugging the kernel.
   */
  DB_SHOW_COMMAND(lockedvnods, lockedvnodes)
  {
          struct mount *mp, *nmp;
          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.
           */
          printf("Locked vnodes\n");
          for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                  nmp = TAILQ_NEXT(mp, mnt_list);
                  TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                          if (VOP_ISLOCKED(vp, NULL))
                                  vprint(NULL, vp);
                  }
                  nmp = TAILQ_NEXT(mp, mnt_list);
          }
  }
  #endif
  
  /*
   * Fill in a struct xvfsconf based on a struct vfsconf.
   */
  static void
  vfsconf2x(struct vfsconf *vfsp, struct xvfsconf *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;
  }
  
  static int
  sysctl_vfs_conflist(SYSCTL_HANDLER_ARGS)
  {
          struct vfsconf *vfsp;
          struct xvfsconf *xvfsp;
          int cnt, error, i;
  
          cnt = 0;
          for (vfsp = vfsconf; vfsp != NULL; vfsp = vfsp->vfc_next)
                  cnt++;
          xvfsp = malloc(sizeof(struct xvfsconf) * cnt, M_TEMP, M_WAITOK);
          /*
           * Handle the race that we will have here when struct vfsconf
           * will be locked down by using both cnt and checking vfc_next
           * against NULL to determine the end of the loop.  The race will
           * happen because we will have to unlock before calling malloc().
           * We are protected by Giant for now.
           */
          i = 0;
          for (vfsp = vfsconf; vfsp != NULL && i < cnt; vfsp = vfsp->vfc_next) {
                  vfsconf2x(vfsp, xvfsp + i);
                  i++;
          }
          error = SYSCTL_OUT(req, xvfsp, sizeof(struct xvfsconf) * i);
          free(xvfsp, M_TEMP);
          return (error);
  }
  
  SYSCTL_PROC(_vfs, OID_AUTO, conflist, CTLFLAG_RD, NULL, 0, sysctl_vfs_conflist,
      "S,xvfsconf", "List of all configured filesystems");
  
  /*
   * Top level filesystem related information gathering.
   */
  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;
          struct xvfsconf xvfsp;
  
          printf("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 */
                  for (vfsp = vfsconf; vfsp; vfsp = vfsp->vfc_next)
                          if (vfsp->vfc_typenum == name[2])
                                  break;
                  if (vfsp == NULL)
                          return (EOPNOTSUPP);
                  vfsconf2x(vfsp, &xvfsp);
                  return (SYSCTL_OUT(req, &xvfsp, sizeof(xvfsp)));
          }
          return (EOPNOTSUPP);
  }
  
  SYSCTL_NODE(_vfs, VFS_GENERIC, generic, CTLFLAG_RD | CTLFLAG_SKIP, 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;
  
          for (vfsp = vfsconf; vfsp; vfsp = vfsp->vfc_next) {
                  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)
                          return error;
          }
          return 0;
  }
  
  #endif /* 1 || COMPAT_PRELITE2 */
  
  #define KINFO_VNODESLOP         10
  #ifdef notyet
  /*
   * Dump vnode list (via sysctl).
   */
  /* ARGSUSED */
  static int
  sysctl_vnode(SYSCTL_HANDLER_ARGS)
  {
          struct xvnode *xvn;
          struct thread *td = req->td;
          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));
  
          sysctl_wire_old_buffer(req, 0);
          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, LK_NOWAIT, &mountlist_mtx, td))
                          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;
  #define XV_COPY(field) xvn[n].xv_##field = vp->v_##field
                          XV_COPY(usecount);
                          XV_COPY(writecount);
                          XV_COPY(holdcnt);
                          XV_COPY(id);
                          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:
                                  xvn[n].xv_dev = vp->v_cachedfs;
                                  xvn[n].xv_ino = vp->v_cachedid;
                                  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, td);
                  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,
          0, 0, sysctl_vnode, "S,xvnode", "");
  #endif
  
  /*
   * Check to see if a filesystem is mounted on a block device.
   */
  int
  vfs_mountedon(vp)
          struct vnode *vp;
  {
  
          if (vp->v_rdev->si_mountpoint != NULL)
                  return (EBUSY);
          return (0);
  }
  
  /*
   * Unmount all filesystems. The list is traversed in reverse order
   * of mounting to avoid dependencies.
   */
  void
  vfs_unmountall()
  {
          struct mount *mp;
          struct thread *td;
          int error;
  
          if (curthread != NULL)
                  td = curthread;
          else
                  td = FIRST_THREAD_IN_PROC(initproc); /* XXX XXX proc0? */
          /*
           * Since this only runs when rebooting, it is not interlocked.
           */
          while(!TAILQ_EMPTY(&mountlist)) {
                  mp = TAILQ_LAST(&mountlist, mntlist);
                  error = dounmount(mp, MNT_FORCE, td);
                  if (error) {
                          TAILQ_REMOVE(&mountlist, mp, mnt_list);
                          printf("unmount of %s failed (",
                              mp->mnt_stat.f_mntonname);
                          if (error == EBUSY)
                                  printf("BUSY)\n");
                          else
                                  printf("%d)\n", error);
                  } else {
                          /* The unmount has removed mp from the mountlist */
                  }
          }
  }
  
  /*
   * perform msync on all vnodes under a mount point
   * the mount point must be locked.
   */
  void
  vfs_msync(struct mount *mp, int flags)
  {
          struct vnode *vp, *nvp;
          struct vm_object *obj;
          int tries;
  
          GIANT_REQUIRED;
  
          tries = 5;
          MNT_ILOCK(mp);
  loop:
          for (vp = TAILQ_FIRST(&mp->mnt_nvnodelist); vp != NULL; vp = nvp) {
                  if (vp->v_mount != mp) {
                          if (--tries > 0)
                                  goto loop;
                          break;
                  }
                  nvp = TAILQ_NEXT(vp, v_nmntvnodes);
  
                  VI_LOCK(vp);
                  if (vp->v_iflag & VI_XLOCK) {
                          VI_UNLOCK(vp);
                          continue;
                  }
  
                  if ((vp->v_iflag & VI_OBJDIRTY) &&
                      (flags == MNT_WAIT || VOP_ISLOCKED(vp, NULL) == 0)) {
                          MNT_IUNLOCK(mp);
                          if (!vget(vp,
                              LK_EXCLUSIVE | LK_RETRY | LK_INTERLOCK,
                              curthread)) {
                                  if (vp->v_vflag & VV_NOSYNC) {  /* unlinked */
                                          vput(vp);
                                          MNT_ILOCK(mp);
                                          continue;
                                  }
  
                                  if (VOP_GETVOBJECT(vp, &obj) == 0) {
                                          VM_OBJECT_LOCK(obj);
                                          vm_object_page_clean(obj, 0, 0,
                                              flags == MNT_WAIT ?
                                              OBJPC_SYNC : OBJPC_NOSYNC);
                                          VM_OBJECT_UNLOCK(obj);
                                  }
                                  vput(vp);
                          }
                          MNT_ILOCK(mp);
                          if (TAILQ_NEXT(vp, v_nmntvnodes) != nvp) {
                                  if (--tries > 0)
                                          goto loop;
                                  break;
                          }
                  } else
                          VI_UNLOCK(vp);
          }
          MNT_IUNLOCK(mp);
  }
  
  /*
   * Create the VM object needed for VMIO and mmap support.  This
   * is done for all VREG files in the system.  Some filesystems might
   * afford the additional metadata buffering capability of the
   * VMIO code by making the device node be VMIO mode also.
   *
   * vp must be locked when vfs_object_create is called.
   */
  int
  vfs_object_create(vp, td, cred)
          struct vnode *vp;
          struct thread *td;
          struct ucred *cred;
  {
          GIANT_REQUIRED;
          return (VOP_CREATEVOBJECT(vp, cred, td));
  }
  
  /*
   * Mark a vnode as free, putting it up for recycling.
   */
  void
  vfree(vp)
          struct vnode *vp;
  {
          ASSERT_VI_LOCKED(vp, "vfree");
          mtx_lock(&vnode_free_list_mtx);
          KASSERT((vp->v_iflag & VI_FREE) == 0, ("vnode already free"));
          if (vp->v_iflag & VI_AGE) {
                  TAILQ_INSERT_HEAD(&vnode_free_list, vp, v_freelist);
          } else {
                  TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
          }
          freevnodes++;
          mtx_unlock(&vnode_free_list_mtx);
          vp->v_iflag &= ~VI_AGE;
          vp->v_iflag |= VI_FREE;
  }
  
  /*
   * Opposite of vfree() - mark a vnode as in use.
   */
  void
  vbusy(vp)
          struct vnode *vp;
  {
          ASSERT_VI_LOCKED(vp, "vbusy");
          KASSERT((vp->v_iflag & VI_FREE) != 0, ("vnode not free"));
  
          mtx_lock(&vnode_free_list_mtx);
          TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
          freevnodes--;
          mtx_unlock(&vnode_free_list_mtx);
  
          vp->v_iflag &= ~(VI_FREE|VI_AGE);
  }
  
  /*
   * 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(vp, td, events)
          struct vnode *vp;
          struct thread *td;
          short events;
  {
  
          if (vp->v_pollinfo == NULL)
                  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;
  }
  
  /*
   * Note the occurrence of an event.  If the VN_POLLEVENT macro is used,
   * it is possible for us to miss an event due to race conditions, but
   * that condition is expected to be rare, so for the moment it is the
   * preferred interface.
   */
  void
  vn_pollevent(vp, events)
          struct vnode *vp;
          short events;
  {
  
          if (vp->v_pollinfo == NULL)
                  v_addpollinfo(vp);
          mtx_lock(&vp->v_pollinfo->vpi_lock);
          if (vp->v_pollinfo->vpi_events & events) {
                  /*
                   * We clear vpi_events so that we don't
                   * call selwakeup() twice if two events are
                   * posted before the polling process(es) is
                   * awakened.  This also ensures that we take at
                   * most one selwakeup() if the polling process
                   * is no longer interested.  However, it does
                   * mean that only one event can be noticed at
                   * a time.  (Perhaps we should only clear those
                   * event bits which we note?) XXX
                   */
                  vp->v_pollinfo->vpi_events = 0; /* &= ~events ??? */
                  vp->v_pollinfo->vpi_revents |= events;
                  selwakeuppri(&vp->v_pollinfo->vpi_selinfo, PRIBIO);
          }
          mtx_unlock(&vp->v_pollinfo->vpi_lock);
  }
  
  /*
   * Wake up anyone polling on vp because it is being revoked.
   * This depends on dead_poll() returning POLLHUP for correct
   * behavior.
   */
  void
  vn_pollgone(vp)
          struct vnode *vp;
  {
  
          mtx_lock(&vp->v_pollinfo->vpi_lock);
          VN_KNOTE(vp, NOTE_REVOKE);
          if (vp->v_pollinfo->vpi_events) {
                  vp->v_pollinfo->vpi_events = 0;
                  selwakeuppri(&vp->v_pollinfo->vpi_selinfo, PRIBIO);
          }
          mtx_unlock(&vp->v_pollinfo->vpi_lock);
  }
  
  
  
  /*
   * 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 vop_t **sync_vnodeop_p;
  static struct vnodeopv_entry_desc sync_vnodeop_entries[] = {
          { &vop_default_desc,    (vop_t *) vop_eopnotsupp },
          { &vop_close_desc,      (vop_t *) sync_close },         /* close */
          { &vop_fsync_desc,      (vop_t *) sync_fsync },         /* fsync */
          { &vop_inactive_desc,   (vop_t *) sync_inactive },      /* inactive */
          { &vop_reclaim_desc,    (vop_t *) sync_reclaim },       /* reclaim */
          { &vop_lock_desc,       (vop_t *) vop_stdlock },        /* lock */
          { &vop_unlock_desc,     (vop_t *) vop_stdunlock },      /* unlock */
          { &vop_islocked_desc,   (vop_t *) vop_stdislocked },    /* islocked */
          { NULL, NULL }
  };
  static struct vnodeopv_desc sync_vnodeop_opv_desc =
          { &sync_vnodeop_p, sync_vnodeop_entries };
  
  VNODEOP_SET(sync_vnodeop_opv_desc);
  
  /*
   * Create a new filesystem syncer vnode for the specified mount point.
   */
  int
  vfs_allocate_syncvnode(mp)
          struct mount *mp;
  {
          struct vnode *vp;
          static long start, incr, next;
          int error;
  
          /* Allocate a new vnode */
          if ((error = getnewvnode("syncer", mp, sync_vnodeop_p, &vp)) != 0) {
                  mp->mnt_syncer = NULL;
                  return (error);
          }
          vp->v_type = VNON;
          /*
           * 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;
          }
          VI_LOCK(vp);
          vn_syncer_add_to_worklist(vp, syncdelay > 0 ? next % syncdelay : 0);
          VI_UNLOCK(vp);
          mp->mnt_syncer = vp;
          return (0);
  }
  
  /*
   * Do a lazy sync of the filesystem.
   */
  static int
  sync_fsync(ap)
          struct vop_fsync_args /* {
                  struct vnode *a_vp;
                  struct ucred *a_cred;
                  int a_waitfor;
                  struct thread *a_td;
          } */ *ap;
  {
          struct vnode *syncvp = ap->a_vp;
          struct mount *mp = syncvp->v_mount;
          struct thread *td = ap->a_td;
          int error, asyncflag;
  
          /*
           * 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.
           */
          VI_LOCK(syncvp);
          vn_syncer_add_to_worklist(syncvp, syncdelay);
          VI_UNLOCK(syncvp);
  
          /*
           * Walk the list of vnodes pushing all that are dirty and
           * not already on the sync list.
           */
          mtx_lock(&mountlist_mtx);
          if (vfs_busy(mp, LK_EXCLUSIVE | LK_NOWAIT, &mountlist_mtx, td) != 0) {
                  mtx_unlock(&mountlist_mtx);
                  return (0);
          }
          if (vn_start_write(NULL, &mp, V_NOWAIT) != 0) {
                  vfs_unbusy(mp, td);
                  return (0);
          }
          asyncflag = mp->mnt_flag & MNT_ASYNC;
          mp->mnt_flag &= ~MNT_ASYNC;
          vfs_msync(mp, MNT_NOWAIT);
          error = VFS_SYNC(mp, MNT_LAZY, ap->a_cred, td);
          if (asyncflag)
                  mp->mnt_flag |= MNT_ASYNC;
          vn_finished_write(mp);
          vfs_unbusy(mp, td);
          return (error);
  }
  
  /*
   * The syncer vnode is no referenced.
   */
  static int
  sync_inactive(ap)
          struct vop_inactive_args /* {
                  struct vnode *a_vp;
                  struct thread *a_td;
          } */ *ap;
  {
  
          VOP_UNLOCK(ap->a_vp, 0, ap->a_td);
          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(ap)
          struct vop_reclaim_args /* {
                  struct vnode *a_vp;
          } */ *ap;
  {
          struct vnode *vp = ap->a_vp;
  
          VI_LOCK(vp);
          vp->v_mount->mnt_syncer = NULL;
          if (vp->v_iflag & VI_ONWORKLST) {
                  mtx_lock(&sync_mtx);
                  LIST_REMOVE(vp, v_synclist);
                  mtx_unlock(&sync_mtx);
                  vp->v_iflag &= ~VI_ONWORKLST;
          }
          VI_UNLOCK(vp);
  
          return (0);
  }
  
  /*
   * extract the dev_t from a VCHR
   */
  dev_t
  vn_todev(vp)
          struct vnode *vp;
  {
          if (vp->v_type != VCHR)
                  return (NODEV);
          return (vp->v_rdev);
  }
  
  /*
   * Check if vnode represents a disk device
   */
  int
  vn_isdisk(vp, errp)
          struct vnode *vp;
          int *errp;
  {
          int error;
  
          error = 0;
          if (vp->v_type != VCHR)
                  error = ENOTBLK;
          else if (vp->v_rdev == NULL)
                  error = ENXIO;
          else if (!(devsw(vp->v_rdev)->d_flags & D_DISK))
                  error = ENOTBLK;
          if (errp != NULL)
                  *errp = error;
          return (error == 0);
  }
  
  /*
   * Free data allocated by namei(); see namei(9) for details.
   */
  void
  NDFREE(ndp, flags)
       struct nameidata *ndp;
       const u_int flags;
  {
          if (!(flags & NDF_NO_FREE_PNBUF) &&
              (ndp->ni_cnd.cn_flags & HASBUF)) {
                  uma_zfree(namei_zone, ndp->ni_cnd.cn_pnbuf);
                  ndp->ni_cnd.cn_flags &= ~HASBUF;
          }
          if (!(flags & NDF_NO_DVP_UNLOCK) &&
              (ndp->ni_cnd.cn_flags & LOCKPARENT) &&
              ndp->ni_dvp != ndp->ni_vp)
                  VOP_UNLOCK(ndp->ni_dvp, 0, ndp->ni_cnd.cn_thread);
          if (!(flags & NDF_NO_DVP_RELE) &&
              (ndp->ni_cnd.cn_flags & (LOCKPARENT|WANTPARENT))) {
                  vrele(ndp->ni_dvp);
                  ndp->ni_dvp = NULL;
          }
          if (!(flags & NDF_NO_VP_UNLOCK) &&
              (ndp->ni_cnd.cn_flags & LOCKLEAF) && ndp->ni_vp)
                  VOP_UNLOCK(ndp->ni_vp, 0, ndp->ni_cnd.cn_thread);
          if (!(flags & NDF_NO_VP_RELE) &&
              ndp->ni_vp) {
                  vrele(ndp->ni_vp);
                  ndp->ni_vp = NULL;
          }
          if (!(flags & NDF_NO_STARTDIR_RELE) &&
              (ndp->ni_cnd.cn_flags & SAVESTART)) {
                  vrele(ndp->ni_startdir);
                  ndp->ni_startdir = NULL;
          }
  }
  
  /*
   * Common filesystem object access control check routine.  Accepts a
   * vnode's type, "mode", uid and gid, requested access mode, credentials,
   * and optional call-by-reference privused argument allowing vaccess()
   * to indicate to the caller whether privilege was used to satisfy the
   * request (obsoleted).  Returns 0 on success, or an errno on failure.
   */
  int
  vaccess(type, file_mode, file_uid, file_gid, acc_mode, cred, privused)
          enum vtype type;
          mode_t file_mode;
          uid_t file_uid;
          gid_t file_gid;
          mode_t acc_mode;
          struct ucred *cred;
          int *privused;
  {
          mode_t dac_granted;
  #ifdef CAPABILITIES
          mode_t cap_granted;
  #endif
  
          /*
           * Look for a normal, non-privileged way to access the file/directory
           * as requested.  If it exists, go with that.
           */
  
          if (privused != NULL)
                  *privused = 0;
  
          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 ((acc_mode & dac_granted) == acc_mode)
                          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 ((acc_mode & dac_granted) == acc_mode)
                          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 ((acc_mode & dac_granted) == acc_mode)
                  return (0);
  
  privcheck:
          if (!suser_cred(cred, PRISON_ROOT)) {
                  /* XXX audit: privilege used */
                  if (privused != NULL)
                          *privused = 1;
                  return (0);
          }
  
  #ifdef CAPABILITIES
          /*
           * Build a capability mask to determine if the set of capabilities
           * satisfies the requirements when combined with the granted mask
           * from above.
           * For each capability, if the capability is required, bitwise
           * or the request type onto the cap_granted mask.
           */
          cap_granted = 0;
  
          if (type == VDIR) {
                  /*
                   * For directories, use CAP_DAC_READ_SEARCH to satisfy
                   * VEXEC requests, instead of CAP_DAC_EXECUTE.
                   */
                  if ((acc_mode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                      !cap_check(cred, NULL, CAP_DAC_READ_SEARCH, PRISON_ROOT))
                          cap_granted |= VEXEC;
          } else {
                  if ((acc_mode & VEXEC) && ((dac_granted & VEXEC) == 0) &&
                      !cap_check(cred, NULL, CAP_DAC_EXECUTE, PRISON_ROOT))
                          cap_granted |= VEXEC;
          }
  
          if ((acc_mode & VREAD) && ((dac_granted & VREAD) == 0) &&
              !cap_check(cred, NULL, CAP_DAC_READ_SEARCH, PRISON_ROOT))
                  cap_granted |= VREAD;
  
          if ((acc_mode & VWRITE) && ((dac_granted & VWRITE) == 0) &&
              !cap_check(cred, NULL, CAP_DAC_WRITE, PRISON_ROOT))
                  cap_granted |= (VWRITE | VAPPEND);
  
          if ((acc_mode & VADMIN) && ((dac_granted & VADMIN) == 0) &&
              !cap_check(cred, NULL, CAP_FOWNER, PRISON_ROOT))
                  cap_granted |= VADMIN;
  
          if ((acc_mode & (cap_granted | dac_granted)) == acc_mode) {
                  /* XXX audit: privilege used */
                  if (privused != NULL)
                          *privused = 1;
                  return (0);
          }
  #endif
  
          return ((acc_mode & 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, int access)
  {
  
          /*
           * Kernel-invoked always succeeds.
           */
          if (cred == NOCRED)
                  return (0);
  
          /*
           * Do not allow privileged processes in jail to directly
           * manipulate system attributes.
           *
           * XXX What capability should apply here?
           * Probably CAP_SYS_SETFFLAG.
           */
          switch (attrnamespace) {
          case EXTATTR_NAMESPACE_SYSTEM:
                  /* Potentially should be: return (EPERM); */
                  return (suser_cred(cred, 0));
          case EXTATTR_NAMESPACE_USER:
                  return (VOP_ACCESS(vp, access, cred, td));
          default:
                  return (EPERM);
          }
  }