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
     * $FreeBSD: stable/4/sys/kern/vfs_subr.c 145953 2005-05-06 02:50:00Z cperciva $
     */
    
    /*
     * External virtual filesystem routines
     */
    #include "opt_ddb.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/buf.h>
    #include <sys/conf.h>
    #include <sys/dirent.h>
    #include <sys/domain.h>
    #include <sys/eventhandler.h>
    #include <sys/fcntl.h>
    #include <sys/kernel.h>
    #include <sys/kthread.h>
    #include <sys/malloc.h>
    #include <sys/mbuf.h>
    #include <sys/mount.h>
    #include <sys/namei.h>
    #include <sys/proc.h>
    #include <sys/reboot.h>
    #include <sys/socket.h>
    #include <sys/stat.h>
    #include <sys/sysctl.h>
    #include <sys/syslog.h>
    #include <sys/vmmeter.h>
    #include <sys/vnode.h>
    
    #include <machine/limits.h>
    
    #include <vm/vm.h>
    #include <vm/vm_object.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_kern.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pager.h>
    #include <vm/vnode_pager.h>
    #include <vm/vm_zone.h>
    
    static MALLOC_DEFINE(M_NETADDR, "Export Host", "Export host address structure");
    
    static void     insmntque __P((struct vnode *vp, struct mount *mp));
    static void     vclean __P((struct vnode *vp, int flags, struct proc *p));
    static unsigned long    numvnodes;
    static void     vlruvp(struct vnode *vp);
    SYSCTL_INT(_debug, OID_AUTO, numvnodes, CTLFLAG_RD, &numvnodes, 0, "");
    
    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,
    };
    
   static TAILQ_HEAD(freelst, vnode) vnode_free_list;      /* vnode free list */
   
   static u_long wantfreevnodes = 25;
   SYSCTL_INT(_debug, OID_AUTO, wantfreevnodes, CTLFLAG_RW, &wantfreevnodes, 0, "");
   static u_long freevnodes = 0;
   SYSCTL_INT(_debug, OID_AUTO, freevnodes, CTLFLAG_RD, &freevnodes, 0, "");
   
   static int reassignbufcalls;
   SYSCTL_INT(_vfs, OID_AUTO, reassignbufcalls, CTLFLAG_RW, &reassignbufcalls, 0, "");
   static int reassignbufloops;
   SYSCTL_INT(_vfs, OID_AUTO, reassignbufloops, CTLFLAG_RW, &reassignbufloops, 0, "");
   static int reassignbufsortgood;
   SYSCTL_INT(_vfs, OID_AUTO, reassignbufsortgood, CTLFLAG_RW, &reassignbufsortgood, 0, "");
   static int reassignbufsortbad;
   SYSCTL_INT(_vfs, OID_AUTO, reassignbufsortbad, CTLFLAG_RW, &reassignbufsortbad, 0, "");
   static int reassignbufmethod = 1;
   SYSCTL_INT(_vfs, OID_AUTO, reassignbufmethod, CTLFLAG_RW, &reassignbufmethod, 0, "");
   static int nameileafonly = 0;
   SYSCTL_INT(_vfs, OID_AUTO, nameileafonly, CTLFLAG_RW, &nameileafonly, 0, "");
   
   #ifdef ENABLE_VFS_IOOPT
   int vfs_ioopt = 0;
   SYSCTL_INT(_vfs, OID_AUTO, ioopt, CTLFLAG_RW, &vfs_ioopt, 0, "");
   #endif
   
   struct mntlist mountlist = TAILQ_HEAD_INITIALIZER(mountlist); /* mounted fs */
   struct simplelock mountlist_slock;
   struct simplelock mntvnode_slock;
   int     nfs_mount_type = -1;
   #ifndef NULL_SIMPLELOCKS
   static struct simplelock mntid_slock;
   static struct simplelock vnode_free_list_slock;
   static struct simplelock spechash_slock;
   #endif
   struct nfs_public nfs_pub;      /* publicly exported FS */
   static vm_zone_t vnode_zone;
   
   /*
    * The workitem queue.
    */
   #define SYNCER_MAXDELAY         32
   static int syncer_maxdelay = SYNCER_MAXDELAY;   /* maximum delay time */
   time_t syncdelay = 30;          /* max time to delay syncing data */
   time_t filedelay = 30;          /* time to delay syncing files */
   SYSCTL_INT(_kern, OID_AUTO, filedelay, CTLFLAG_RW, &filedelay, 0, "");
   time_t dirdelay = 29;           /* time to delay syncing directories */
   SYSCTL_INT(_kern, OID_AUTO, dirdelay, CTLFLAG_RW, &dirdelay, 0, "");
   time_t 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, "");
   
   static int syncer_delayno = 0;
   static long syncer_mask; 
   LIST_HEAD(synclist, vnode);
   static struct synclist *syncer_workitem_pending;
   
   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 = 0;
   SYSCTL_INT(_debug, OID_AUTO, vnlru_nowhere, CTLFLAG_RW, &vnlru_nowhere, 0,
       "Number of times the vnlru process ran without success");
   
   static void     vfs_free_addrlist __P((struct netexport *nep));
   static int      vfs_free_netcred __P((struct radix_node *rn, void *w));
   static int      vfs_hang_addrlist __P((struct mount *mp, struct netexport *nep,
                                          struct export_args *argp));
   
   /*
    * Initialize the vnode management data structures.
    */
   void
   vntblinit()
   {
   
           /*
            * 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;
           simple_lock_init(&mntvnode_slock);
           simple_lock_init(&mntid_slock);
           simple_lock_init(&spechash_slock);
           TAILQ_INIT(&vnode_free_list);
           simple_lock_init(&vnode_free_list_slock);
           vnode_zone = zinit("VNODE", sizeof (struct vnode), 0, 0, 5);
           /*
            * Initialize the filesystem syncer.
            */     
           syncer_workitem_pending = hashinit(syncer_maxdelay, M_VNODE, 
                   &syncer_mask);
           syncer_maxdelay = syncer_mask + 1;
   }
   
   /*
    * 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, p)
           struct mount *mp;
           int flags;
           struct simplelock *interlkp;
           struct proc *p;
   {
           int lkflags;
   
           if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
                   if (flags & LK_NOWAIT)
                           return (ENOENT);
                   mp->mnt_kern_flag |= MNTK_MWAIT;
                   if (interlkp) {
                           simple_unlock(interlkp);
                   }
                   /*
                    * 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.
                    */
                   tsleep((caddr_t)mp, PVFS, "vfs_busy", 0);
                   if (interlkp) {
                           simple_lock(interlkp);
                   }
                   return (ENOENT);
           }
           lkflags = LK_SHARED | LK_NOPAUSE;
           if (interlkp)
                   lkflags |= LK_INTERLOCK;
           if (lockmgr(&mp->mnt_lock, lkflags, interlkp, p))
                   panic("vfs_busy: unexpected lock failure");
           return (0);
   }
   
   /*
    * Free a busy filesystem.
    */
   void
   vfs_unbusy(mp, p)
           struct mount *mp;
           struct proc *p;
   {
   
           lockmgr(&mp->mnt_lock, LK_RELEASE, NULL, p);
   }
   
   /*
    * Lookup a filesystem type, and if found allocate and initialize
    * a mount structure for it.
    *
    * Devname is usually updated by mount(8) after booting.
    */
   int
   vfs_rootmountalloc(fstypename, devname, mpp)
           char *fstypename;
           char *devname;
           struct mount **mpp;
   {
           struct proc *p = curproc;       /* XXX */
           struct vfsconf *vfsp;
           struct mount *mp;
   
           if (fstypename == NULL)
                   return (ENODEV);
           for (vfsp = vfsconf; vfsp; vfsp = vfsp->vfc_next)
                   if (!strcmp(vfsp->vfc_name, fstypename))
                           break;
           if (vfsp == NULL)
                   return (ENODEV);
           mp = malloc((u_long)sizeof(struct mount), M_MOUNT, M_WAITOK);
           bzero((char *)mp, (u_long)sizeof(struct mount));
           lockinit(&mp->mnt_lock, PVFS, "vfslock", VLKTIMEOUT, LK_NOPAUSE);
           (void)vfs_busy(mp, LK_NOWAIT, 0, p);
           TAILQ_INIT(&mp->mnt_nvnodelist);
           TAILQ_INIT(&mp->mnt_reservedvnlist);
           mp->mnt_nvnodelistsize = 0;
           mp->mnt_vfc = vfsp;
           mp->mnt_op = vfsp->vfc_vfsops;
           mp->mnt_flag = MNT_RDONLY;
           mp->mnt_vnodecovered = NULLVP;
           vfsp->vfc_refcount++;
           mp->mnt_iosize_max = DFLTPHYS;
           mp->mnt_stat.f_type = vfsp->vfc_typenum;
           mp->mnt_flag |= vfsp->vfc_flags & MNT_VISFLAGMASK;
           strncpy(mp->mnt_stat.f_fstypename, vfsp->vfc_name, MFSNAMELEN);
           mp->mnt_stat.f_mntonname[0] = '/';
           mp->mnt_stat.f_mntonname[1] = 0;
           (void) copystr(devname, mp->mnt_stat.f_mntfromname, MNAMELEN - 1, 0);
           *mpp = mp;
           return (0);
   }
   
   /*
    * Find an appropriate filesystem to use for the root. If a filesystem
    * has not been preselected, walk through the list of known filesystems
    * trying those that have mountroot routines, and try them until one
    * works or we have tried them all.
    */
   #ifdef notdef   /* XXX JH */
   int
   lite2_vfs_mountroot()
   {
           struct vfsconf *vfsp;
           extern int (*lite2_mountroot) __P((void));
           int error;
   
           if (lite2_mountroot != NULL)
                   return ((*lite2_mountroot)());
           for (vfsp = vfsconf; vfsp; vfsp = vfsp->vfc_next) {
                   if (vfsp->vfc_mountroot == NULL)
                           continue;
                   if ((error = (*vfsp->vfc_mountroot)()) == 0)
                           return (0);
                   printf("%s_mountroot failed: %d\n", vfsp->vfc_name, error);
           }
           return (ENODEV);
   }
   #endif
   
   /*
    * Lookup a mount point by filesystem identifier.
    */
   struct mount *
   vfs_getvfs(fsid)
           fsid_t *fsid;
   {
           register struct mount *mp;
   
           simple_lock(&mountlist_slock);
           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]) {
                           simple_unlock(&mountlist_slock);
                           return (mp);
               }
           }
           simple_unlock(&mountlist_slock);
           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;
   
           simple_lock(&mntid_slock);
           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];
           simple_unlock(&mntid_slock);
   }
   
   /*
    * 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_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;
           simple_lock(&mntvnode_slock);
           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 &&
                       VMIGHTFREE(vp) &&           /* critical path opt */
                       (vp->v_object == NULL || vp->v_object->resident_page_count < trigger) &&
                       simple_lock_try(&vp->v_interlock)
                   ) {
                           simple_unlock(&mntvnode_slock);
                           if (VMIGHTFREE(vp)) {
                                   vgonel(vp, curproc);
                                   done++;
                           } else {
                                   simple_unlock(&vp->v_interlock);
                           }
                           simple_lock(&mntvnode_slock);
                   }
                   --count;
           }
           simple_unlock(&mntvnode_slock);
           return done;
   }
   
   /*
    * Attempt to recycle vnodes in a context that is always safe to block.
    * Calling vlrurecycle() from the bowels of file system code has some
    * interesting deadlock problems.
    */
   static struct proc *vnlruproc;
   static int vnlruproc_sig;
   
   static void 
   vnlru_proc(void)
   {
           struct mount *mp, *nmp;
           int s;
           int done;
           struct proc *p = vnlruproc;
   
           EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_kproc, p,
               SHUTDOWN_PRI_FIRST);   
   
           s = splbio();
           for (;;) {
                   kproc_suspend_loop(p);
                   if (numvnodes - freevnodes <= desiredvnodes * 9 / 10) {
                           vnlruproc_sig = 0;
                           wakeup(&vnlruproc_sig);
                           tsleep(vnlruproc, PVFS, "vlruwt", hz);
                           continue;
                   }
                   done = 0;
                   simple_lock(&mountlist_slock);
                   for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                           if (vfs_busy(mp, LK_NOWAIT, &mountlist_slock, p)) {
                                   nmp = TAILQ_NEXT(mp, mnt_list);
                                   continue;
                           }
                           done += vlrureclaim(mp);
                           simple_lock(&mountlist_slock);
                           nmp = TAILQ_NEXT(mp, mnt_list);
                           vfs_unbusy(mp, p);
                   }
                   simple_unlock(&mountlist_slock);
                   if (done == 0) {
                           vnlru_nowhere++;
                           tsleep(vnlruproc, PPAUSE, "vlrup", hz * 3);
                   }
           }
           splx(s);
   }
   
   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.
    */
   extern vop_t **dead_vnodeop_p;
   
   /*
    * Return the next vnode from the free list.
    */
   int
   getnewvnode(tag, mp, vops, vpp)
           enum vtagtype tag;
           struct mount *mp;
           vop_t **vops;
           struct vnode **vpp;
   {
           int s;
           struct proc *p = curproc;       /* XXX */
           struct vnode *vp = NULL;
           vm_object_t object;
   
           s = splbio();
   
           /*
            * 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);
                   }
                   tsleep(&vnlruproc_sig, PVFS, "vlruwk", hz);
           }
   
   
           /*
            * 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.
            */
           simple_lock(&vnode_free_list_slock);
           if (freevnodes >= wantfreevnodes && numvnodes >= minvnodes) {
                   int count;
   
                   for (count = 0; count < freevnodes; count++) {
                           vp = TAILQ_FIRST(&vnode_free_list);
                           if (vp == NULL || vp->v_usecount)
                                   panic("getnewvnode: free vnode isn't");
   
                           TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
                           if ((VOP_GETVOBJECT(vp, &object) == 0 &&
                               (object->resident_page_count || object->ref_count)) ||
                               !simple_lock_try(&vp->v_interlock)) {
                                   TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
                                   vp = NULL;
                                   continue;
                           }
                           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) {
                                                   simple_unlock(&vp->v_interlock);
                                                   TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
                                                   vp = NULL;
                                                   continue;
                                           }
                                   } 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).
                                            */
                                           simple_unlock(&vp->v_interlock);
                                           TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
                                           vp = NULL;
                                           continue;
                                   }
                           }
                           break;
                   }
           }
   
           if (vp) {
                   vp->v_flag |= VDOOMED;
                   vp->v_flag &= ~VFREE;
                   freevnodes--;
                   simple_unlock(&vnode_free_list_slock);
                   cache_purge(vp);
                   vp->v_lease = NULL;
                   if (vp->v_type != VBAD) {
                           vgonel(vp, p);
                   } else {
                           simple_unlock(&vp->v_interlock);
                   }
   
   #ifdef INVARIANTS
                   {
                           int s;
   
                           if (vp->v_data)
                                   panic("cleaned vnode isn't");
                           s = splbio();
                           if (vp->v_numoutput)
                                   panic("Clean vnode has pending I/O's");
                           splx(s);
                   }
   #endif
                   vp->v_flag = 0;
                   vp->v_lastw = 0;
                   vp->v_lasta = 0;
                   vp->v_cstart = 0;
                   vp->v_clen = 0;
                   vp->v_socket = 0;
                   vp->v_writecount = 0;   /* XXX */
           } else {
                   simple_unlock(&vnode_free_list_slock);
                   vp = (struct vnode *) zalloc(vnode_zone);
                   bzero((char *) vp, sizeof *vp);
                   simple_lock_init(&vp->v_interlock);
                   vp->v_dd = vp;
                   cache_purge(vp);
                   LIST_INIT(&vp->v_cache_src);
                   TAILQ_INIT(&vp->v_cache_dst);
                   numvnodes++;
           }
   
           TAILQ_INIT(&vp->v_cleanblkhd);
           TAILQ_INIT(&vp->v_dirtyblkhd);
           vp->v_type = VNON;
           vp->v_tag = tag;
           vp->v_op = vops;
           insmntque(vp, mp);
           *vpp = vp;
           vp->v_usecount = 1;
           vp->v_data = 0;
           splx(s);
   
           vfs_object_create(vp, p, p->p_ucred);
           return (0);
   }
   
   /*
    * Move a vnode from one mount queue to another.
    */
   static void
   insmntque(vp, mp)
           register struct vnode *vp;
           register struct mount *mp;
   {
   
           simple_lock(&mntvnode_slock);
           /*
            * Delete from old mount point vnode list, if on one.
            */
           if (vp->v_mount != NULL) {
                   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--;
           }
           /*
            * Insert into list of vnodes for the new mount point, if available.
            */
           if ((vp->v_mount = mp) == NULL) {
                   simple_unlock(&mntvnode_slock);
                   return;
           }
           TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
           mp->mnt_nvnodelistsize++;
           simple_unlock(&mntvnode_slock);
   }
   
   /*
    * 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)) {
                   vp->v_numoutput--;
                   if (vp->v_numoutput < 0)
                           panic("vwakeup: neg numoutput");
                   if ((vp->v_numoutput == 0) && (vp->v_flag & VBWAIT)) {
                           vp->v_flag &= ~VBWAIT;
                           wakeup((caddr_t) &vp->v_numoutput);
                   }
           }
   }
   
   /*
    * Flush out and invalidate all buffers associated with a vnode.
    * Called with the underlying object locked.
    */
   int
   vinvalbuf(vp, flags, cred, p, slpflag, slptimeo)
           register struct vnode *vp;
           int flags;
           struct ucred *cred;
           struct proc *p;
           int slpflag, slptimeo;
   {
           register struct buf *bp;
           struct buf *nbp, *blist;
           int s, error;
           vm_object_t object;
   
           if (flags & V_SAVE) {
                   s = splbio();
                   while (vp->v_numoutput) {
                           vp->v_flag |= VBWAIT;
                           error = tsleep((caddr_t)&vp->v_numoutput,
                               slpflag | (PRIBIO + 1), "vinvlbuf", slptimeo);
                           if (error) {
                                   splx(s);
                                   return (error);
                           }
                   }
                   if (!TAILQ_EMPTY(&vp->v_dirtyblkhd)) {
                           splx(s);
                           if ((error = VOP_FSYNC(vp, cred, MNT_WAIT, p)) != 0)
                                   return (error);
                           s = splbio();
                           if (vp->v_numoutput > 0 ||
                               !TAILQ_EMPTY(&vp->v_dirtyblkhd))
                                   panic("vinvalbuf: dirty bufs");
                   }
                   splx(s);
           }
           s = splbio();
           for (;;) {
                   blist = TAILQ_FIRST(&vp->v_cleanblkhd);
                   if (!blist)
                           blist = TAILQ_FIRST(&vp->v_dirtyblkhd);
                   if (!blist)
                           break;
   
                   for (bp = blist; bp; bp = nbp) {
                           nbp = TAILQ_NEXT(bp, b_vnbufs);
                           if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT)) {
                                   error = BUF_TIMELOCK(bp,
                                       LK_EXCLUSIVE | LK_SLEEPFAIL,
                                       "vinvalbuf", slpflag, slptimeo);
                                   if (error == ENOLCK)
                                           break;
                                   splx(s);
                                   return (error);
                           }
                           /*
                            * 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 VOP_BWRITE 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) {
                                                   BUF_UNLOCK(bp);
                                                   vfs_bio_awrite(bp);
                                           } else {
                                                   bremfree(bp);
                                                   bp->b_flags |= B_ASYNC;
                                                   VOP_BWRITE(bp->b_vp, bp);
                                           }
                                   } else {
                                           bremfree(bp);
                                           (void) VOP_BWRITE(bp->b_vp, bp);
                                   }
                                   break;
                           }
                           bremfree(bp);
                           bp->b_flags |= (B_INVAL | B_NOCACHE | B_RELBUF);
                           bp->b_flags &= ~B_ASYNC;
                           brelse(bp);
                   }
           }
   
           /*
            * 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_flag |= VBWAIT;
                           tsleep(&vp->v_numoutput, PVM, "vnvlbv", 0);
                   }
                   if (VOP_GETVOBJECT(vp, &object) == 0) {
                           while (object->paging_in_progress)
                                   vm_object_pip_sleep(object, "vnvlbx");
                   }
           } while (vp->v_numoutput > 0);
   
           splx(s);
   
           /*
            * Destroy the copy in the VM cache, too.
            */
           simple_lock(&vp->v_interlock);
           if (VOP_GETVOBJECT(vp, &object) == 0) {
                   vm_object_page_remove(object, 0, 0,
                           (flags & V_SAVE) ? TRUE : FALSE);
           }
           simple_unlock(&vp->v_interlock);
   
           if (!TAILQ_EMPTY(&vp->v_dirtyblkhd) || !TAILQ_EMPTY(&vp->v_cleanblkhd))
                   panic("vinvalbuf: flush failed");
           return (0);
   }
   
   /*
    * Truncate a file's buffer and pages to a specified length.  This
    * is in lieu of the old vinvalbuf mechanism, which performed unneeded
    * sync activity.
    */
   int
   vtruncbuf(vp, cred, p, length, blksize)
           register struct vnode *vp;
           struct ucred *cred;
           struct proc *p;
           off_t length;
           int blksize;
   {
           register struct buf *bp;
           struct buf *nbp;
           int s, anyfreed;
           int trunclbn;
   
           /*
            * Round up to the *next* lbn.
            */
           trunclbn = (length + blksize - 1) / blksize;
   
           s = splbio();
   restart:
           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_NOWAIT)) {
                                           BUF_LOCK(bp, LK_EXCLUSIVE|LK_SLEEPFAIL);
                                           goto restart;
                                   } else {
                                           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;
                                   }
                           }
                   }
   
                   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_NOWAIT)) {
                                           BUF_LOCK(bp, LK_EXCLUSIVE|LK_SLEEPFAIL);
                                           goto restart;
                                   } else {
                                           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;
                                   }
                           }
                   }
           }
   
           if (length > 0) {
   restartsync:
                   for (bp = TAILQ_FIRST(&vp->v_dirtyblkhd); bp; bp = nbp) {
                           nbp = TAILQ_NEXT(bp, b_vnbufs);
                           if ((bp->b_flags & B_DELWRI) && (bp->b_lblkno < 0)) {
                                   if (BUF_LOCK(bp, LK_EXCLUSIVE | LK_NOWAIT)) {
                                           BUF_LOCK(bp, LK_EXCLUSIVE|LK_SLEEPFAIL);
                                           goto restart;
                                   } else {
                                           bremfree(bp);
                                           if (bp->b_vp == vp) {
                                                   bp->b_flags |= B_ASYNC;
                                           } else {
                                                   bp->b_flags &= ~B_ASYNC;
                                           }
                                           VOP_BWRITE(bp->b_vp, bp);
                                   }
                                   goto restartsync;
                          }
  
                  }
          }
  
          while (vp->v_numoutput > 0) {
                  vp->v_flag |= VBWAIT;
                  tsleep(&vp->v_numoutput, PVM, "vbtrunc", 0);
          }
  
          splx(s);
  
          vnode_pager_setsize(vp, length);
  
          return (0);
  }
  
  /*
   * Associate a buffer with a vnode.
   */
  void
  bgetvp(vp, bp)
          register struct vnode *vp;
          register struct buf *bp;
  {
          int s;
  
          KASSERT(bp->b_vp == NULL, ("bgetvp: not free"));
  
          vhold(vp);
          bp->b_vp = vp;
          bp->b_dev = vn_todev(vp);
          /*
           * Insert onto list for new vnode.
           */
          s = splbio();
          bp->b_xflags |= BX_VNCLEAN;
          bp->b_xflags &= ~BX_VNDIRTY;
          TAILQ_INSERT_TAIL(&vp->v_cleanblkhd, bp, b_vnbufs);
          splx(s);
  }
  
  /*
   * Disassociate a buffer from a vnode.
   */
  void
  brelvp(bp)
          register struct buf *bp;
  {
          struct vnode *vp;
          struct buflists *listheadp;
          int s;
  
          KASSERT(bp->b_vp != NULL, ("brelvp: NULL"));
  
          /*
           * Delete from old vnode list, if on one.
           */
          vp = bp->b_vp;
          s = splbio();
          if (bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) {
                  if (bp->b_xflags & BX_VNDIRTY)
                          listheadp = &vp->v_dirtyblkhd;
                  else 
                          listheadp = &vp->v_cleanblkhd;
                  TAILQ_REMOVE(listheadp, bp, b_vnbufs);
                  bp->b_xflags &= ~(BX_VNDIRTY | BX_VNCLEAN);
          }
          if ((vp->v_flag & VONWORKLST) && TAILQ_EMPTY(&vp->v_dirtyblkhd)) {
                  vp->v_flag &= ~VONWORKLST;
                  LIST_REMOVE(vp, v_synclist);
          }
          splx(s);
          bp->b_vp = (struct vnode *) 0;
          vdrop(vp);
  }
  
  /*
   * 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]
   *
   */
  
  /*
   * Add an item to the syncer work queue.
   */
  static void
  vn_syncer_add_to_worklist(struct vnode *vp, int delay)
  {
          int s, slot;
  
          s = splbio();
  
          if (vp->v_flag & VONWORKLST) {
                  LIST_REMOVE(vp, v_synclist);
          }
  
          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);
          vp->v_flag |= VONWORKLST;
          splx(s);
  }
  
  struct  proc *updateproc;
  static void sched_sync __P((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.
   */
  void 
  sched_sync(void)
  {
          struct synclist *slp;
          struct vnode *vp;
          long starttime;
          int s;
          struct proc *p = updateproc;
  
          EVENTHANDLER_REGISTER(shutdown_pre_sync, shutdown_kproc, p,
              SHUTDOWN_PRI_LAST);   
  
          for (;;) {
                  kproc_suspend_loop(p);
  
                  starttime = time_second;
  
                  /*
                   * Push files whose dirty time has expired.  Be careful
                   * of interrupt race on slp queue.
                   */
                  s = splbio();
                  slp = &syncer_workitem_pending[syncer_delayno];
                  syncer_delayno += 1;
                  if (syncer_delayno == syncer_maxdelay)
                          syncer_delayno = 0;
                  splx(s);
  
                  while ((vp = LIST_FIRST(slp)) != NULL) {
                          if (VOP_ISLOCKED(vp, NULL) == 0) {
                                  vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, p);
                                  (void) VOP_FSYNC(vp, p->p_ucred, MNT_LAZY, p);
                                  VOP_UNLOCK(vp, 0, p);
                          }
                          s = splbio();
                          if (LIST_FIRST(slp) == vp) {
                                  /*
                                   * Note: v_tag VT_VFS vps can remain on the
                                   * worklist too with no dirty blocks, but 
                                   * since sync_fsync() moves it to a different 
                                   * slot we are safe.
                                   */
                                  if (TAILQ_EMPTY(&vp->v_dirtyblkhd) &&
                                      !vn_isdisk(vp, NULL))
                                          panic("sched_sync: fsync failed vp %p tag %d", vp, vp->v_tag);
                                  /*
                                   * 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);
                          }
                          splx(s);
                  }
  
                  /*
                   * Do soft update processing.
                   */
                  if (bioops.io_sync)
                          (*bioops.io_sync)(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.
                   */
                  if (rushjob > 0) {
                          rushjob -= 1;
                          continue;
                  }
                  /*
                   * 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.
   */
  int
  speedup_syncer()
  {
          int s;
  
          s = splhigh();
          if (updateproc->p_wchan == &lbolt)
                  setrunnable(updateproc);
          splx(s);
          if (rushjob < syncdelay / 2) {
                  rushjob += 1;
                  stat_rush_requests += 1;
                  return (1);
          }
          return(0);
  }
  
  /*
   * 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_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 */
          if (TAILQ_NEXT(bp, b_vnbufs) != NULL) {
                  panic(
                      "relpbuf(): b_vp was probably reassignbuf()d %p %x", 
                      bp,
                      (int)bp->b_flags
                  );
          }
          bp->b_vp = (struct vnode *) 0;
          bp->b_flags &= ~B_PAGING;
  }
  
  void
  pbreassignbuf(bp, newvp)
          struct buf *bp;
          struct vnode *newvp;
  {
          if ((bp->b_flags & B_PAGING) == 0) {
                  panic(
                      "pbreassignbuf() on non phys bp %p", 
                      bp
                  );
          }
          bp->b_vp = newvp;
  }
  
  /*
   * 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 buflists *listheadp;
          int delay;
          int s;
  
          if (newvp == NULL) {
                  printf("reassignbuf: NULL");
                  return;
          }
          ++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");
  
          s = splbio();
          /*
           * Delete from old vnode list, if on one.
           */
          if (bp->b_xflags & (BX_VNDIRTY | BX_VNCLEAN)) {
                  if (bp->b_xflags & BX_VNDIRTY)
                          listheadp = &bp->b_vp->v_dirtyblkhd;
                  else 
                          listheadp = &bp->b_vp->v_cleanblkhd;
                  TAILQ_REMOVE(listheadp, bp, b_vnbufs);
                  bp->b_xflags &= ~(BX_VNDIRTY | BX_VNCLEAN);
                  if (bp->b_vp != newvp) {
                          vdrop(bp->b_vp);
                          bp->b_vp = NULL;        /* for clarification */
                  }
          }
          /*
           * If dirty, put on list of dirty buffers; otherwise insert onto list
           * of clean buffers.
           */
          if (bp->b_flags & B_DELWRI) {
                  struct buf *tbp;
  
                  listheadp = &newvp->v_dirtyblkhd;
                  if ((newvp->v_flag & VONWORKLST) == 0) {
                          switch (newvp->v_type) {
                          case VDIR:
                                  delay = dirdelay;
                                  break;
                          case VCHR:
                          case VBLK:
                                  if (newvp->v_specmountpoint != NULL) {
                                          delay = metadelay;
                                          break;
                                  }
                                  /* fall through */
                          default:
                                  delay = filedelay;
                          }
                          vn_syncer_add_to_worklist(newvp, delay);
                  }
                  bp->b_xflags |= BX_VNDIRTY;
                  tbp = TAILQ_FIRST(listheadp);
                  if (tbp == NULL ||
                      bp->b_lblkno == 0 ||
                      (bp->b_lblkno > 0 && tbp->b_lblkno < 0) ||
                      (bp->b_lblkno > 0 && bp->b_lblkno < tbp->b_lblkno)) {
                          TAILQ_INSERT_HEAD(listheadp, bp, b_vnbufs);
                          ++reassignbufsortgood;
                  } else if (bp->b_lblkno < 0) {
                          TAILQ_INSERT_TAIL(listheadp, bp, b_vnbufs);
                          ++reassignbufsortgood;
                  } else if (reassignbufmethod == 1) {
                          /*
                           * New sorting algorithm, only handle sequential case,
                           * otherwise append to end (but before metadata)
                           */
                          if ((tbp = gbincore(newvp, bp->b_lblkno - 1)) != NULL &&
                              (tbp->b_xflags & BX_VNDIRTY)) {
                                  /*
                                   * Found the best place to insert the buffer
                                   */
                                  TAILQ_INSERT_AFTER(listheadp, tbp, bp, b_vnbufs);
                                  ++reassignbufsortgood;
                          } else {
                                  /*
                                   * Missed, append to end, but before meta-data.
                                   * We know that the head buffer in the list is
                                   * not meta-data due to prior conditionals.
                                   *
                                   * Indirect effects:  NFS second stage write
                                   * tends to wind up here, giving maximum 
                                   * distance between the unstable write and the
                                   * commit rpc.
                                   */
                                  tbp = TAILQ_LAST(listheadp, buflists);
                                  while (tbp && tbp->b_lblkno < 0)
                                          tbp = TAILQ_PREV(tbp, buflists, b_vnbufs);
                                  TAILQ_INSERT_AFTER(listheadp, tbp, bp, b_vnbufs);
                                  ++reassignbufsortbad;
                          }
                  } else {
                          /*
                           * Old sorting algorithm, scan queue and insert
                           */
                          struct buf *ttbp;
                          while ((ttbp = TAILQ_NEXT(tbp, b_vnbufs)) &&
                              (ttbp->b_lblkno < bp->b_lblkno)) {
                                  ++reassignbufloops;
                                  tbp = ttbp;
                          }
                          TAILQ_INSERT_AFTER(listheadp, tbp, bp, b_vnbufs);
                  }
          } else {
                  bp->b_xflags |= BX_VNCLEAN;
                  TAILQ_INSERT_TAIL(&newvp->v_cleanblkhd, bp, b_vnbufs);
                  if ((newvp->v_flag & VONWORKLST) &&
                      TAILQ_EMPTY(&newvp->v_dirtyblkhd)) {
                          newvp->v_flag &= ~VONWORKLST;
                          LIST_REMOVE(newvp, v_synclist);
                  }
          }
          if (bp->b_vp != newvp) {
                  bp->b_vp = newvp;
                  vhold(bp->b_vp);
          }
          splx(s);
  }
  
  /*
   * Create a vnode for a block device.
   * Used for mounting the root file system.
   */
  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);
          }
          error = getnewvnode(VT_NON, (struct mount *)0, spec_vnodeop_p, &nvp);
          if (error) {
                  *vpp = NULLVP;
                  return (error);
          }
          vp = nvp;
          vp->v_type = VBLK;
          addalias(vp, dev);
          *vpp = vp;
          return (0);
  }
  
  /*
   * 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.
   */
  void
  addaliasu(nvp, nvp_rdev)
          struct vnode *nvp;
          udev_t nvp_rdev;
  {
  
          if (nvp->v_type != VBLK && nvp->v_type != VCHR)
                  panic("addaliasu on non-special vnode");
          addalias(nvp, udev2dev(nvp_rdev, nvp->v_type == VBLK ? 1 : 0));
  }
  
  void
  addalias(nvp, dev)
          struct vnode *nvp;
          dev_t dev;
  {
  
          if (nvp->v_type != VBLK && nvp->v_type != VCHR)
                  panic("addalias on non-special vnode");
  
          nvp->v_rdev = dev;
          simple_lock(&spechash_slock);
          SLIST_INSERT_HEAD(&dev->si_hlist, nvp, v_specnext);
          simple_unlock(&spechash_slock);
  }
  
  /*
   * 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 file system type).
   */
  int
  vget(vp, flags, p)
          register struct vnode *vp;
          int flags;
          struct proc *p;
  {
          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 VXLOCK flag is set.
           */
          if ((flags & LK_INTERLOCK) == 0) {
                  simple_lock(&vp->v_interlock);
          }
          if (vp->v_flag & VXLOCK) {
                  if (vp->v_vxproc == curproc) {
  #if 0
                          /* this can now occur in normal operation */
                          log(LOG_INFO, "VXLOCK interlock avoided\n");
  #endif
                  } else {
                          vp->v_flag |= VXWANT;
                          simple_unlock(&vp->v_interlock);
                          tsleep((caddr_t)vp, PINOD, "vget", 0);
                          return (ENOENT);
                  }
          }
  
          vp->v_usecount++;
  
          if (VSHOULDBUSY(vp))
                  vbusy(vp);
          if (flags & LK_TYPE_MASK) {
                  if ((error = vn_lock(vp, flags | LK_INTERLOCK, p)) != 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.
                           */
                          simple_lock(&vp->v_interlock);
                          vp->v_usecount--;
                          if (VSHOULDFREE(vp))
                                  vfree(vp);
                          else
                                  vlruvp(vp);
                          simple_unlock(&vp->v_interlock);
                  }
                  return (error);
          }
          simple_unlock(&vp->v_interlock);
          return (0);
  }
  
  void
  vref(struct vnode *vp)
  {
          simple_lock(&vp->v_interlock);
          vp->v_usecount++;
          simple_unlock(&vp->v_interlock);
  }
  
  /*
   * Vnode put/release.
   * If count drops to zero, call inactive routine and return to freelist.
   */
  void
  vrele(vp)
          struct vnode *vp;
  {
          struct proc *p = curproc;       /* XXX */
  
          KASSERT(vp != NULL, ("vrele: null vp"));
  
          simple_lock(&vp->v_interlock);
  
          if (vp->v_usecount > 1) {
  
                  vp->v_usecount--;
                  simple_unlock(&vp->v_interlock);
  
                  return;
          }
  
          if (vp->v_usecount == 1) {
                  vp->v_usecount--;
                  /*
                   * We must call VOP_INACTIVE with the node locked.
                   * If we are doing a vpu, the node is already locked,
                   * but, in the case of vrele, we must explicitly lock
                   * the vnode before calling VOP_INACTIVE
                   */
  
                  if (vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK, p) == 0)
                          VOP_INACTIVE(vp, p);
                  if (VSHOULDFREE(vp))
                          vfree(vp);
                  else
                          vlruvp(vp);
          } else {
  #ifdef DIAGNOSTIC
                  vprint("vrele: negative ref count", vp);
                  simple_unlock(&vp->v_interlock);
  #endif
                  panic("vrele: negative ref cnt");
          }
  }
  
  void
  vput(vp)
          struct vnode *vp;
  {
          struct proc *p = curproc;       /* XXX */
  
          KASSERT(vp != NULL, ("vput: null vp"));
  
          simple_lock(&vp->v_interlock);
  
          if (vp->v_usecount > 1) {
                  vp->v_usecount--;
                  VOP_UNLOCK(vp, LK_INTERLOCK, p);
                  return;
          }
  
          if (vp->v_usecount == 1) {
                  vp->v_usecount--;
                  /*
                   * We must call VOP_INACTIVE with the node locked.
                   * If we are doing a vpu, the node is already locked,
                   * so we just need to release the vnode mutex.
                   */
                  simple_unlock(&vp->v_interlock);
                  VOP_INACTIVE(vp, p);
                  if (VSHOULDFREE(vp))
                          vfree(vp);
                  else
                          vlruvp(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(vp)
          register struct vnode *vp;
  {
          int s;
  
          s = splbio();
          vp->v_holdcnt++;
          if (VSHOULDBUSY(vp))
                  vbusy(vp);
          splx(s);
  }
  
  /*
   * One less who cares about this vnode.
   */
  void
  vdrop(vp)
          register struct vnode *vp;
  {
          int s;
  
          s = splbio();
          if (vp->v_holdcnt <= 0)
                  panic("vdrop: holdcnt");
          vp->v_holdcnt--;
          if (VSHOULDFREE(vp))
                  vfree(vp);
          splx(s);
  }
  
  /*
   * 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 VSYSTEM 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 proc *p = curproc;       /* 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);
          }
          simple_lock(&mntvnode_slock);
  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);
  
                  simple_lock(&vp->v_interlock);
                  /*
                   * Skip over a vnodes marked VSYSTEM.
                   */
                  if ((flags & SKIPSYSTEM) && (vp->v_flag & VSYSTEM)) {
                          simple_unlock(&vp->v_interlock);
                          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) &&
                      (vp->v_type == VNON ||
                      (VOP_GETATTR(vp, &vattr, p->p_ucred, p) == 0 &&
                      vattr.va_nlink > 0)) &&
                      (vp->v_writecount == 0 || vp->v_type != VREG)) {
                          simple_unlock(&vp->v_interlock);
                          continue;
                  }
  
                  /*
                   * 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) {
                          simple_unlock(&mntvnode_slock);
                          vgonel(vp, p);
                          simple_lock(&mntvnode_slock);
                          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) {
                          simple_unlock(&mntvnode_slock);
                          if (vp->v_type != VBLK && vp->v_type != VCHR) {
                                  vgonel(vp, p);
                          } else {
                                  vclean(vp, 0, p);
                                  vp->v_op = spec_vnodeop_p;
                                  insmntque(vp, (struct mount *) 0);
                          }
                          simple_lock(&mntvnode_slock);
                          continue;
                  }
  #ifdef DIAGNOSTIC
                  if (busyprt)
                          vprint("vflush: busy vnode", vp);
  #endif
                  simple_unlock(&vp->v_interlock);
                  busy++;
          }
          simple_unlock(&mntvnode_slock);
          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.
                   */
                  simple_lock(&rootvp->v_interlock);
                  KASSERT(busy > 0, ("vflush: not busy"));
                  KASSERT(rootvp->v_usecount >= rootrefs, ("vflush: rootrefs"));
                  if (busy == 1 && rootvp->v_usecount == rootrefs) {
                          vgonel(rootvp, p);
                          busy = 0;
                  } else
                          simple_unlock(&rootvp->v_interlock);
          }
          if (busy)
                  return (EBUSY);
          for (; rootrefs > 0; rootrefs--)
                  vrele(rootvp);
          return (0);
  }
  
  /*
   * We do not want to recycle the vnode too quickly.
   *
   * XXX we can't move vp's around the nvnodelist without really screwing
   * up the efficiency of filesystem SYNC and friends.  This code is 
   * disabled until we fix the syncing code's scanning algorithm.
   */
  static void
  vlruvp(struct vnode *vp)
  {
  #if 0
          struct mount *mp;
  
          if ((mp = vp->v_mount) != NULL) {
                  simple_lock(&mntvnode_slock);
                  TAILQ_REMOVE(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                  TAILQ_INSERT_TAIL(&mp->mnt_nvnodelist, vp, v_nmntvnodes);
                  simple_unlock(&mntvnode_slock);
          }
  #endif
  }
  
  /*
   * Disassociate the underlying file system from a vnode.
   */
  static void
  vclean(vp, flags, p)
          struct vnode *vp;
          int flags;
          struct proc *p;
  {
          int active;
  
          /*
           * 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))
                  vp->v_usecount++;
  
          /*
           * Prevent the vnode from being recycled or brought into use while we
           * clean it out.
           */
          if (vp->v_flag & VXLOCK)
                  panic("vclean: deadlock");
          vp->v_flag |= VXLOCK;
          vp->v_vxproc = curproc;
          /*
           * 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, p);
  
          /*
           * Clean out any buffers associated with the vnode.
           */
          vinvalbuf(vp, V_SAVE, NOCRED, p, 0, 0);
  
          VOP_DESTROYVOBJECT(vp);
  
          /*
           * 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, p);
                  VOP_INACTIVE(vp, p);
          } else {
                  /*
                   * 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, p);
          }
          /*
           * Reclaim the vnode.
           */
          if (VOP_RECLAIM(vp, p))
                  panic("vclean: cannot reclaim");
  
          if (active) {
                  /*
                   * Inline copy of vrele() since VOP_INACTIVE
                   * has already been called.
                   */
                  simple_lock(&vp->v_interlock);
                  if (--vp->v_usecount <= 0) {
  #ifdef DIAGNOSTIC
                          if (vp->v_usecount < 0 || vp->v_writecount != 0) {
                                  vprint("vclean: bad ref count", vp);
                                  panic("vclean: ref cnt");
                          }
  #endif
                          vfree(vp);
                  }
                  simple_unlock(&vp->v_interlock);
          }
  
          cache_purge(vp);
          vp->v_vnlock = NULL;
  
          if (VSHOULDFREE(vp))
                  vfree(vp);
          
          /*
           * Done with purge, notify sleepers of the grim news.
           */
          vp->v_op = dead_vnodeop_p;
          vn_pollgone(vp);
          vp->v_tag = VT_NON;
          vp->v_flag &= ~VXLOCK;
          vp->v_vxproc = NULL;
          if (vp->v_flag & VXWANT) {
                  vp->v_flag &= ~VXWANT;
                  wakeup((caddr_t) vp);
          }
  }
  
  /*
   * 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;
          /*
           * If a vgone (or vclean) is already in progress,
           * wait until it is done and return.
           */
          if (vp->v_flag & VXLOCK) {
                  vp->v_flag |= VXWANT;
                  simple_unlock(&vp->v_interlock);
                  tsleep((caddr_t)vp, PINOD, "vop_revokeall", 0);
                  return (0);
          }
          dev = vp->v_rdev;
          for (;;) {
                  simple_lock(&spechash_slock);
                  vq = SLIST_FIRST(&dev->si_hlist);
                  simple_unlock(&spechash_slock);
                  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, p)
          struct vnode *vp;
          struct simplelock *inter_lkp;
          struct proc *p;
  {
  
          simple_lock(&vp->v_interlock);
          if (vp->v_usecount == 0) {
                  if (inter_lkp) {
                          simple_unlock(inter_lkp);
                  }
                  vgonel(vp, p);
                  return (1);
          }
          simple_unlock(&vp->v_interlock);
          return (0);
  }
  
  /*
   * Eliminate all activity associated with a vnode
   * in preparation for reuse.
   */
  void
  vgone(vp)
          register struct vnode *vp;
  {
          struct proc *p = curproc;       /* XXX */
  
          simple_lock(&vp->v_interlock);
          vgonel(vp, p);
  }
  
  /*
   * vgone, with the vp interlock held.
   */
  void
  vgonel(vp, p)
          struct vnode *vp;
          struct proc *p;
  {
          int s;
  
          /*
           * If a vgone (or vclean) is already in progress,
           * wait until it is done and return.
           */
          if (vp->v_flag & VXLOCK) {
                  vp->v_flag |= VXWANT;
                  simple_unlock(&vp->v_interlock);
                  tsleep((caddr_t)vp, PINOD, "vgone", 0);
                  return;
          }
  
          /*
           * Clean out the filesystem specific data.
           */
          vclean(vp, DOCLOSE, p);
          simple_lock(&vp->v_interlock);
  
          /*
           * Delete from old mount point vnode list, if on one.
           */
          if (vp->v_mount != NULL)
                  insmntque(vp, (struct mount *)0);
          /*
           * If special device, remove it from special device alias list
           * if it is on one.
           */
          if ((vp->v_type == VBLK || vp->v_type == VCHR) && vp->v_rdev != NULL) {
                  simple_lock(&spechash_slock);
                  SLIST_REMOVE(&vp->v_hashchain, vp, vnode, v_specnext);
                  freedev(vp->v_rdev);
                  simple_unlock(&spechash_slock);
                  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_flag & VDOOMED)) {
                  s = splbio();
                  simple_lock(&vnode_free_list_slock);
                  if (vp->v_flag & VFREE)
                          TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
                  else
                          freevnodes++;
                  vp->v_flag |= VFREE;
                  TAILQ_INSERT_HEAD(&vnode_free_list, vp, v_freelist);
                  simple_unlock(&vnode_free_list_slock);
                  splx(s);
          }
  
          vp->v_type = VBAD;
          simple_unlock(&vp->v_interlock);
  }
  
  /*
   * Lookup a vnode by device number.
   */
  int
  vfinddev(dev, type, vpp)
          dev_t dev;
          enum vtype type;
          struct vnode **vpp;
  {
          struct vnode *vp;
  
          simple_lock(&spechash_slock);
          SLIST_FOREACH(vp, &dev->si_hlist, v_specnext) {
                  if (type == vp->v_type) {
                          *vpp = vp;
                          simple_unlock(&spechash_slock);
                          return (1);
                  }
          }
          simple_unlock(&spechash_slock);
          return (0);
  }
  
  /*
   * Calculate the total number of references to a special device.
   */
  int
  vcount(vp)
          struct vnode *vp;
  {
          struct vnode *vq;
          int count;
  
          count = 0;
          simple_lock(&spechash_slock);
          SLIST_FOREACH(vq, &vp->v_hashchain, v_specnext)
                  count += vq->v_usecount;
          simple_unlock(&spechash_slock);
          return (count);
  }
  
  /*
   * Same as above, but using the dev_t as argument
   */
  
  int
  count_dev(dev)
          dev_t dev;
  {
          struct vnode *vp;
  
          vp = SLIST_FIRST(&dev->si_hlist);
          if (vp == NULL)
                  return (0);
          return(vcount(vp));
  }
  
  /*
   * 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("type %s, usecount %d, writecount %d, refcount %d,",
              typename[vp->v_type], vp->v_usecount, vp->v_writecount,
              vp->v_holdcnt);
          buf[0] = '\0';
          if (vp->v_flag & VROOT)
                  strcat(buf, "|VROOT");
          if (vp->v_flag & VTEXT)
                  strcat(buf, "|VTEXT");
          if (vp->v_flag & VSYSTEM)
                  strcat(buf, "|VSYSTEM");
          if (vp->v_flag & VXLOCK)
                  strcat(buf, "|VXLOCK");
          if (vp->v_flag & VXWANT)
                  strcat(buf, "|VXWANT");
          if (vp->v_flag & VBWAIT)
                  strcat(buf, "|VBWAIT");
          if (vp->v_flag & VDOOMED)
                  strcat(buf, "|VDOOMED");
          if (vp->v_flag & VFREE)
                  strcat(buf, "|VFREE");
          if (vp->v_flag & VOBJBUF)
                  strcat(buf, "|VOBJBUF");
          if (buf[0] != '\0')
                  printf(" flags (%s)", &buf[1]);
          if (vp->v_data == NULL) {
                  printf("\n");
          } else {
                  printf("\n\t");
                  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(lockedvnodes, lockedvnodes)
  {
          struct proc *p = curproc;       /* XXX */
          struct mount *mp, *nmp;
          struct vnode *vp;
  
          printf("Locked vnodes\n");
          simple_lock(&mountlist_slock);
          for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                  if (vfs_busy(mp, LK_NOWAIT, &mountlist_slock, p)) {
                          nmp = TAILQ_NEXT(mp, mnt_list);
                          continue;
                  }
                  TAILQ_FOREACH(vp, &mp->mnt_nvnodelist, v_nmntvnodes) {
                          if (VOP_ISLOCKED(vp, NULL))
                                  vprint((char *)0, vp);
                  }
                  simple_lock(&mountlist_slock);
                  nmp = TAILQ_NEXT(mp, mnt_list);
                  vfs_unbusy(mp, p);
          }
          simple_unlock(&mountlist_slock);
  }
  #endif
  
  /*
   * Top level filesystem related information gathering.
   */
  static int      sysctl_ovfs_conf __P((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;
  
  #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
  
  #ifdef notyet
          /* all sysctl names at this level are at least name and field */
          if (namelen < 2)
                  return (ENOTDIR);               /* overloaded */
          if (name[0] != VFS_GENERIC) {
                  for (vfsp = vfsconf; vfsp; vfsp = vfsp->vfc_next)
                          if (vfsp->vfc_typenum == name[0])
                                  break;
                  if (vfsp == NULL)
                          return (EOPNOTSUPP);
                  return ((*vfsp->vfc_vfsops->vfs_sysctl)(&name[1], namelen - 1,
                      oldp, oldlenp, newp, newlen, p));
          }
  #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);
                  return (SYSCTL_OUT(req, vfsp, sizeof *vfsp));
          }
          return (EOPNOTSUPP);
  }
  
  SYSCTL_NODE(_vfs, VFS_GENERIC, generic, CTLFLAG_RD, 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) {
                  bzero(&ovfs, sizeof(ovfs));
                  ovfs.vfc_vfsops = vfsp->vfc_vfsops;     /* XXX used as flag */
                  strcpy(ovfs.vfc_name, vfsp->vfc_name);
                  ovfs.vfc_index = vfsp->vfc_typenum;
                  ovfs.vfc_refcount = vfsp->vfc_refcount;
                  ovfs.vfc_flags = vfsp->vfc_flags;
                  error = SYSCTL_OUT(req, &ovfs, sizeof ovfs);
                  if (error)
                          return error;
          }
          return 0;
  }
  
  #endif /* 1 || COMPAT_PRELITE2 */
  
  #if 0
  #define KINFO_VNODESLOP 10
  /*
   * Dump vnode list (via sysctl).
   * Copyout address of vnode followed by vnode.
   */
  /* ARGSUSED */
  static int
  sysctl_vnode(SYSCTL_HANDLER_ARGS)
  {
          struct proc *p = curproc;       /* XXX */
          struct mount *mp, *nmp;
          struct vnode *nvp, *vp;
          int error;
  
  #define VPTRSZ  sizeof (struct vnode *)
  #define VNODESZ sizeof (struct vnode)
  
          req->lock = 0;
          if (!req->oldptr) /* Make an estimate */
                  return (SYSCTL_OUT(req, 0,
                          (numvnodes + KINFO_VNODESLOP) * (VPTRSZ + VNODESZ)));
  
          simple_lock(&mountlist_slock);
          for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
                  if (vfs_busy(mp, LK_NOWAIT, &mountlist_slock, p)) {
                          nmp = TAILQ_NEXT(mp, mnt_list);
                          continue;
                  }
  again:
                  simple_lock(&mntvnode_slock);
                  for (vp = TAILQ_FIRST(&mp->mnt_nvnodelist);
                       vp != NULL;
                       vp = nvp) {
                          /*
                           * Check that the vp is still associated with
                           * this filesystem.  RACE: could have been
                           * recycled onto the same filesystem.
                           */
                          if (vp->v_mount != mp) {
                                  simple_unlock(&mntvnode_slock);
                                  goto again;
                          }
                          nvp = TAILQ_NEXT(vp, v_nmntvnodes);
                          simple_unlock(&mntvnode_slock);
                          if ((error = SYSCTL_OUT(req, &vp, VPTRSZ)) ||
                              (error = SYSCTL_OUT(req, vp, VNODESZ)))
                                  return (error);
                          simple_lock(&mntvnode_slock);
                  }
                  simple_unlock(&mntvnode_slock);
                  simple_lock(&mountlist_slock);
                  nmp = TAILQ_NEXT(mp, mnt_list);
                  vfs_unbusy(mp, p);
          }
          simple_unlock(&mountlist_slock);
  
          return (0);
  }
  #endif
  
  /*
   * XXX
   * Exporting the vnode list on large systems causes them to crash.
   * Exporting the vnode list on medium systems causes sysctl to coredump.
   */
  #if 0
  SYSCTL_PROC(_kern, KERN_VNODE, vnode, CTLTYPE_OPAQUE|CTLFLAG_RD,
          0, 0, sysctl_vnode, "S,vnode", "");
  #endif
  
  /*
   * Check to see if a filesystem is mounted on a block device.
   */
  int
  vfs_mountedon(vp)
          struct vnode *vp;
  {
  
          if (vp->v_specmountpoint != 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 proc *p;
          int error;
  
          if (curproc != NULL)
                  p = curproc;
          else
                  p = initproc;   /* XXX XXX should this be 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, p);
                  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 */
                  }
          }
  }
  
  /*
   * Build hash lists of net addresses and hang them off the mount point.
   * Called by ufs_mount() to set up the lists of export addresses.
   */
  static int
  vfs_hang_addrlist(mp, nep, argp)
          struct mount *mp;
          struct netexport *nep;
          struct export_args *argp;
  {
          register struct netcred *np;
          register struct radix_node_head *rnh;
          register int i;
          struct radix_node *rn;
          struct sockaddr *saddr, *smask = 0;
          struct domain *dom;
          int error;
  
          if (argp->ex_addrlen == 0) {
                  if (mp->mnt_flag & MNT_DEFEXPORTED)
                          return (EPERM);
                  np = &nep->ne_defexported;
                  np->netc_exflags = argp->ex_flags;
                  np->netc_anon = argp->ex_anon;
                  np->netc_anon.cr_ref = 1;
                  mp->mnt_flag |= MNT_DEFEXPORTED;
                  return (0);
          }
  
          if (argp->ex_addrlen > MLEN)
                  return (EINVAL);
  
          i = sizeof(struct netcred) + argp->ex_addrlen + argp->ex_masklen;
          np = (struct netcred *) malloc(i, M_NETADDR, M_WAITOK);
          bzero((caddr_t) np, i);
          saddr = (struct sockaddr *) (np + 1);
          if ((error = copyin(argp->ex_addr, (caddr_t) saddr, argp->ex_addrlen)))
                  goto out;
          if (saddr->sa_len > argp->ex_addrlen)
                  saddr->sa_len = argp->ex_addrlen;
          if (argp->ex_masklen) {
                  smask = (struct sockaddr *) ((caddr_t) saddr + argp->ex_addrlen);
                  error = copyin(argp->ex_mask, (caddr_t) smask, argp->ex_masklen);
                  if (error)
                          goto out;
                  if (smask->sa_len > argp->ex_masklen)
                          smask->sa_len = argp->ex_masklen;
          }
          i = saddr->sa_family;
          if ((rnh = nep->ne_rtable[i]) == 0) {
                  /*
                   * Seems silly to initialize every AF when most are not used,
                   * do so on demand here
                   */
                  for (dom = domains; dom; dom = dom->dom_next)
                          if (dom->dom_family == i && dom->dom_rtattach) {
                                  dom->dom_rtattach((void **) &nep->ne_rtable[i],
                                      dom->dom_rtoffset);
                                  break;
                          }
                  if ((rnh = nep->ne_rtable[i]) == 0) {
                          error = ENOBUFS;
                          goto out;
                  }
          }
          rn = (*rnh->rnh_addaddr) ((caddr_t) saddr, (caddr_t) smask, rnh,
              np->netc_rnodes);
          if (rn == 0 || np != (struct netcred *) rn) {   /* already exists */
                  error = EPERM;
                  goto out;
          }
          np->netc_exflags = argp->ex_flags;
          np->netc_anon = argp->ex_anon;
          np->netc_anon.cr_ref = 1;
          return (0);
  out:
          free(np, M_NETADDR);
          return (error);
  }
  
  /* ARGSUSED */
  static int
  vfs_free_netcred(rn, w)
          struct radix_node *rn;
          void *w;
  {
          register struct radix_node_head *rnh = (struct radix_node_head *) w;
  
          (*rnh->rnh_deladdr) (rn->rn_key, rn->rn_mask, rnh);
          free((caddr_t) rn, M_NETADDR);
          return (0);
  }
  
  /*
   * Free the net address hash lists that are hanging off the mount points.
   */
  static void
  vfs_free_addrlist(nep)
          struct netexport *nep;
  {
          register int i;
          register struct radix_node_head *rnh;
  
          for (i = 0; i <= AF_MAX; i++)
                  if ((rnh = nep->ne_rtable[i])) {
                          (*rnh->rnh_walktree) (rnh, vfs_free_netcred,
                              (caddr_t) rnh);
                          free((caddr_t) rnh, M_RTABLE);
                          nep->ne_rtable[i] = 0;
                  }
  }
  
  int
  vfs_export(mp, nep, argp)
          struct mount *mp;
          struct netexport *nep;
          struct export_args *argp;
  {
          int error;
  
          if (argp->ex_flags & MNT_DELEXPORT) {
                  if (mp->mnt_flag & MNT_EXPUBLIC) {
                          vfs_setpublicfs(NULL, NULL, NULL);
                          mp->mnt_flag &= ~MNT_EXPUBLIC;
                  }
                  vfs_free_addrlist(nep);
                  mp->mnt_flag &= ~(MNT_EXPORTED | MNT_DEFEXPORTED);
          }
          if (argp->ex_flags & MNT_EXPORTED) {
                  if (argp->ex_flags & MNT_EXPUBLIC) {
                          if ((error = vfs_setpublicfs(mp, nep, argp)) != 0)
                                  return (error);
                          mp->mnt_flag |= MNT_EXPUBLIC;
                  }
                  if ((error = vfs_hang_addrlist(mp, nep, argp)))
                          return (error);
                  mp->mnt_flag |= MNT_EXPORTED;
          }
          return (0);
  }
  
  
  /*
   * Set the publicly exported filesystem (WebNFS). Currently, only
   * one public filesystem is possible in the spec (RFC 2054 and 2055)
   */
  int
  vfs_setpublicfs(mp, nep, argp)
          struct mount *mp;
          struct netexport *nep;
          struct export_args *argp;
  {
          int error;
          struct vnode *rvp;
          char *cp;
  
          /*
           * mp == NULL -> invalidate the current info, the FS is
           * no longer exported. May be called from either vfs_export
           * or unmount, so check if it hasn't already been done.
           */
          if (mp == NULL) {
                  if (nfs_pub.np_valid) {
                          nfs_pub.np_valid = 0;
                          if (nfs_pub.np_index != NULL) {
                                  FREE(nfs_pub.np_index, M_TEMP);
                                  nfs_pub.np_index = NULL;
                          }
                  }
                  return (0);
          }
  
          /*
           * Only one allowed at a time.
           */
          if (nfs_pub.np_valid != 0 && mp != nfs_pub.np_mount)
                  return (EBUSY);
  
          /*
           * Get real filehandle for root of exported FS.
           */
          bzero((caddr_t)&nfs_pub.np_handle, sizeof(nfs_pub.np_handle));
          nfs_pub.np_handle.fh_fsid = mp->mnt_stat.f_fsid;
  
          if ((error = VFS_ROOT(mp, &rvp)))
                  return (error);
  
          if ((error = VFS_VPTOFH(rvp, &nfs_pub.np_handle.fh_fid)))
                  return (error);
  
          vput(rvp);
  
          /*
           * If an indexfile was specified, pull it in.
           */
          if (argp->ex_indexfile != NULL) {
                  MALLOC(nfs_pub.np_index, char *, MAXNAMLEN + 1, M_TEMP,
                      M_WAITOK);
                  error = copyinstr(argp->ex_indexfile, nfs_pub.np_index,
                      MAXNAMLEN, (size_t *)0);
                  if (!error) {
                          /*
                           * Check for illegal filenames.
                           */
                          for (cp = nfs_pub.np_index; *cp; cp++) {
                                  if (*cp == '/') {
                                          error = EINVAL;
                                          break;
                                  }
                          }
                  }
                  if (error) {
                          FREE(nfs_pub.np_index, M_TEMP);
                          return (error);
                  }
          }
  
          nfs_pub.np_mount = mp;
          nfs_pub.np_valid = 1;
          return (0);
  }
  
  struct netcred *
  vfs_export_lookup(mp, nep, nam)
          register struct mount *mp;
          struct netexport *nep;
          struct sockaddr *nam;
  {
          register struct netcred *np;
          register struct radix_node_head *rnh;
          struct sockaddr *saddr;
  
          np = NULL;
          if (mp->mnt_flag & MNT_EXPORTED) {
                  /*
                   * Lookup in the export list first.
                   */
                  if (nam != NULL) {
                          saddr = nam;
                          rnh = nep->ne_rtable[saddr->sa_family];
                          if (rnh != NULL) {
                                  np = (struct netcred *)
                                          (*rnh->rnh_matchaddr)((caddr_t)saddr,
                                                                rnh);
                                  if (np && np->netc_rnodes->rn_flags & RNF_ROOT)
                                          np = NULL;
                          }
                  }
                  /*
                   * If no address match, use the default if it exists.
                   */
                  if (np == NULL && mp->mnt_flag & MNT_DEFEXPORTED)
                          np = &nep->ne_defexported;
          }
          return (np);
  }
  
  /*
   * 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;
  
          tries = 5;
          simple_lock(&mntvnode_slock);
  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);
  
                  if (vp->v_flag & VXLOCK)        /* XXX: what if MNT_WAIT? */
                          continue;
  
                  /*
                   * There could be hundreds of thousands of vnodes, we cannot
                   * afford to do anything heavy-weight until we have a fairly
                   * good indication that there is something to do.
                   */
                  if ((vp->v_flag & VOBJDIRTY) &&
                      (flags == MNT_WAIT || VOP_ISLOCKED(vp, NULL) == 0)) {
                          simple_unlock(&mntvnode_slock);
                          if (!vget(vp,
                              LK_EXCLUSIVE | LK_RETRY | LK_NOOBJ, curproc)) {
                                  if (VOP_GETVOBJECT(vp, &obj) == 0) {
                                          vm_object_page_clean(obj, 0, 0, flags == MNT_WAIT ? OBJPC_SYNC : OBJPC_NOSYNC);
                                  }
                                  vput(vp);
                          }
                          simple_lock(&mntvnode_slock);
                          if (TAILQ_NEXT(vp, v_nmntvnodes) != nvp) {
                                  if (--tries > 0)
                                          goto loop;
                                  break;
                          }
                  }
          }
          simple_unlock(&mntvnode_slock);
  }
  
  /*
   * 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, p, cred)
          struct vnode *vp;
          struct proc *p;
          struct ucred *cred;
  {
          return (VOP_CREATEVOBJECT(vp, cred, p));
  }
  
  void
  vfree(vp)
          struct vnode *vp;
  {
          int s;
  
          s = splbio();
          simple_lock(&vnode_free_list_slock);
          KASSERT((vp->v_flag & VFREE) == 0, ("vnode already free"));
          if (vp->v_flag & VAGE) {
                  TAILQ_INSERT_HEAD(&vnode_free_list, vp, v_freelist);
          } else {
                  TAILQ_INSERT_TAIL(&vnode_free_list, vp, v_freelist);
          }
          freevnodes++;
          simple_unlock(&vnode_free_list_slock);
          vp->v_flag &= ~VAGE;
          vp->v_flag |= VFREE;
          splx(s);
  }
  
  void
  vbusy(vp)
          struct vnode *vp;
  {
          int s;
  
          s = splbio();
          simple_lock(&vnode_free_list_slock);
          KASSERT((vp->v_flag & VFREE) != 0, ("vnode not free"));
          TAILQ_REMOVE(&vnode_free_list, vp, v_freelist);
          freevnodes--;
          simple_unlock(&vnode_free_list_slock);
          vp->v_flag &= ~(VFREE|VAGE);
          splx(s);
  }
  
  /*
   * 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, p, events)
          struct vnode *vp;
          struct proc *p;
          short events;
  {
          simple_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;
  
                  simple_unlock(&vp->v_pollinfo.vpi_lock);
                  return events;
          }
          vp->v_pollinfo.vpi_events |= events;
          selrecord(p, &vp->v_pollinfo.vpi_selinfo);
          simple_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;
  {
          simple_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;
                  selwakeup(&vp->v_pollinfo.vpi_selinfo);
          }
          simple_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;
  {
          simple_lock(&vp->v_pollinfo.vpi_lock);
          if (vp->v_pollinfo.vpi_events) {
                  vp->v_pollinfo.vpi_events = 0;
                  selwakeup(&vp->v_pollinfo.vpi_selinfo);
          }
          simple_unlock(&vp->v_pollinfo.vpi_lock);
  }
  
  
  
  /*
   * Routine to create and manage a filesystem syncer vnode.
   */
  #define sync_close ((int (*) __P((struct  vop_close_args *)))nullop)
  static int      sync_fsync __P((struct  vop_fsync_args *));
  static int      sync_inactive __P((struct  vop_inactive_args *));
  static int      sync_reclaim  __P((struct  vop_reclaim_args *));
  #define sync_lock ((int (*) __P((struct  vop_lock_args *)))vop_nolock)
  #define sync_unlock ((int (*) __P((struct  vop_unlock_args *)))vop_nounlock)
  static int      sync_print __P((struct vop_print_args *));
  #define sync_islocked ((int(*) __P((struct vop_islocked_args *)))vop_noislocked)
  
  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 *) sync_lock },          /* lock */
          { &vop_unlock_desc,     (vop_t *) sync_unlock },        /* unlock */
          { &vop_print_desc,      (vop_t *) sync_print },         /* print */
          { &vop_islocked_desc,   (vop_t *) sync_islocked },      /* 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(VT_VFS, 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;
          }
          vn_syncer_add_to_worklist(vp, syncdelay > 0 ? next % syncdelay : 0);
          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 proc *a_p;
          } */ *ap;
  {
          struct vnode *syncvp = ap->a_vp;
          struct mount *mp = syncvp->v_mount;
          struct proc *p = ap->a_p;
          int 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.
           */
          vn_syncer_add_to_worklist(syncvp, syncdelay);
  
          /*
           * Walk the list of vnodes pushing all that are dirty and
           * not already on the sync list.
           */
          simple_lock(&mountlist_slock);
          if (vfs_busy(mp, LK_EXCLUSIVE | LK_NOWAIT, &mountlist_slock, p) != 0) {
                  simple_unlock(&mountlist_slock);
                  return (0);
          }
          asyncflag = mp->mnt_flag & MNT_ASYNC;
          mp->mnt_flag &= ~MNT_ASYNC;
          vfs_msync(mp, MNT_NOWAIT);
          VFS_SYNC(mp, MNT_LAZY, ap->a_cred, p);
          if (asyncflag)
                  mp->mnt_flag |= MNT_ASYNC;
          vfs_unbusy(mp, p);
          return (0);
  }
  
  /*
   * The syncer vnode is no referenced.
   */
  static int
  sync_inactive(ap)
          struct vop_inactive_args /* {
                  struct vnode *a_vp;
                  struct proc *a_p;
          } */ *ap;
  {
  
          vgone(ap->a_vp);
          return (0);
  }
  
  /*
   * The syncer vnode is no longer needed and is being decommissioned.
   *
   * Modifications to the worklist must be protected at splbio().
   */
  static int
  sync_reclaim(ap)
          struct vop_reclaim_args /* {
                  struct vnode *a_vp;
          } */ *ap;
  {
          struct vnode *vp = ap->a_vp;
          int s;
  
          s = splbio();
          vp->v_mount->mnt_syncer = NULL;
          if (vp->v_flag & VONWORKLST) {
                  LIST_REMOVE(vp, v_synclist);
                  vp->v_flag &= ~VONWORKLST;
          }
          splx(s);
  
          return (0);
  }
  
  /*
   * Print out a syncer vnode.
   */
  static int
  sync_print(ap)
          struct vop_print_args /* {
                  struct vnode *a_vp;
          } */ *ap;
  {
          struct vnode *vp = ap->a_vp;
  
          printf("syncer vnode");
          if (vp->v_vnlock != NULL)
                  lockmgr_printinfo(vp->v_vnlock);
          printf("\n");
          return (0);
  }
  
  /*
   * extract the dev_t from a VBLK or VCHR
   */
  dev_t
  vn_todev(vp)
          struct vnode *vp;
  {
          if (vp->v_type != VBLK && 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;
  {
          if (vp->v_type != VBLK && vp->v_type != VCHR) {
                  if (errp != NULL)
                          *errp = ENOTBLK;
                  return (0);
          }
          if (vp->v_rdev == NULL) {
                  if (errp != NULL)
                          *errp = ENXIO;
                  return (0);
          }
          if (!devsw(vp->v_rdev)) {
                  if (errp != NULL)
                          *errp = ENXIO;
                  return (0);
          }
          if (!(devsw(vp->v_rdev)->d_flags & D_DISK)) {
                  if (errp != NULL)
                          *errp = ENOTBLK;
                  return (0);
          }
          if (errp != NULL)
                  *errp = 0;
          return (1);
  }
  
  void
  NDFREE(ndp, flags)
       struct nameidata *ndp;
       const uint flags;
  {
          if (!(flags & NDF_NO_FREE_PNBUF) &&
              (ndp->ni_cnd.cn_flags & HASBUF)) {
                  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_proc);
          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_proc);
          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;
          }
  }