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ffs_snapshot.c

/*-
 * Copyright 2000 Marshall Kirk McKusick. All Rights Reserved.
 *
 * Further information about snapshots can be obtained from:
 *
 *    Marshall Kirk McKusick        http://www.mckusick.com/softdep/
 *    1614 Oxford Street            mckusick@mckusick.com
 *    Berkeley, CA 94709-1608       +1-510-843-9542
 *    USA
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY MARSHALL KIRK MCKUSICK ``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 MARSHALL KIRK MCKUSICK 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.
 *
 *    @(#)ffs_snapshot.c      8.11 (McKusick) 7/23/00
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: src/sys/ufs/ffs/ffs_snapshot.c,v 1.136 2007/06/05 00:00:56 jeff Exp $");

#include "opt_quota.h"

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/systm.h>
#include <sys/conf.h>
#include <sys/bio.h>
#include <sys/buf.h>
#include <sys/proc.h>
#include <sys/namei.h>
#include <sys/sched.h>
#include <sys/stat.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/resource.h>
#include <sys/resourcevar.h>
#include <sys/vnode.h>

#include <geom/geom.h>

#include <ufs/ufs/extattr.h>
#include <ufs/ufs/quota.h>
#include <ufs/ufs/ufsmount.h>
#include <ufs/ufs/inode.h>
#include <ufs/ufs/ufs_extern.h>

#include <ufs/ffs/fs.h>
#include <ufs/ffs/ffs_extern.h>

#define KERNCRED thread0.td_ucred
#define DEBUG 1

#include "opt_ffs.h"

#ifdef NO_FFS_SNAPSHOT
int
ffs_snapshot(mp, snapfile)
      struct mount *mp;
      char *snapfile;
{
      return (EINVAL);
}

int
ffs_snapblkfree(fs, devvp, bno, size, inum)
      struct fs *fs;
      struct vnode *devvp;
      ufs2_daddr_t bno;
      long size;
      ino_t inum;
{
      return (EINVAL);
}

void
ffs_snapremove(vp)
      struct vnode *vp;
{
}

void
ffs_snapshot_mount(mp)
      struct mount *mp;
{
}

void
ffs_snapshot_unmount(mp)
      struct mount *mp;
{
}

void
ffs_snapgone(ip)
      struct inode *ip;
{
}

int
ffs_copyonwrite(devvp, bp)
      struct vnode *devvp;
      struct buf *bp;
{
      return (EINVAL);
}

#else

TAILQ_HEAD(snaphead, inode);

struct snapdata {
      struct snaphead sn_head;
      daddr_t sn_listsize;
      daddr_t *sn_blklist;
      struct lock sn_lock;
};

static int cgaccount(int, struct vnode *, struct buf *, int);
static int expunge_ufs1(struct vnode *, struct inode *, struct fs *,
    int (*)(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *, struct fs *,
    ufs_lbn_t, int), int);
static int indiracct_ufs1(struct vnode *, struct vnode *, int,
    ufs1_daddr_t, ufs_lbn_t, ufs_lbn_t, ufs_lbn_t, ufs_lbn_t, struct fs *,
    int (*)(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *, struct fs *,
    ufs_lbn_t, int), int);
static int fullacct_ufs1(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *,
    struct fs *, ufs_lbn_t, int);
static int snapacct_ufs1(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *,
    struct fs *, ufs_lbn_t, int);
static int mapacct_ufs1(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *,
    struct fs *, ufs_lbn_t, int);
static int expunge_ufs2(struct vnode *, struct inode *, struct fs *,
    int (*)(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *, struct fs *,
    ufs_lbn_t, int), int);
static int indiracct_ufs2(struct vnode *, struct vnode *, int,
    ufs2_daddr_t, ufs_lbn_t, ufs_lbn_t, ufs_lbn_t, ufs_lbn_t, struct fs *,
    int (*)(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *, struct fs *,
    ufs_lbn_t, int), int);
static int fullacct_ufs2(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *,
    struct fs *, ufs_lbn_t, int);
static int snapacct_ufs2(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *,
    struct fs *, ufs_lbn_t, int);
static int mapacct_ufs2(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *,
    struct fs *, ufs_lbn_t, int);
static int readblock(struct vnode *vp, struct buf *, ufs2_daddr_t);
static void process_deferred_inactive(struct mount *);
static void try_free_snapdata(struct vnode *devvp, struct thread *td);
static int ffs_bp_snapblk(struct vnode *, struct buf *);

/*
 * To ensure the consistency of snapshots across crashes, we must
 * synchronously write out copied blocks before allowing the
 * originals to be modified. Because of the rather severe speed
 * penalty that this imposes, the following flag allows this
 * crash persistence to be disabled.
 */
int dopersistence = 0;

#ifdef DEBUG
#include <sys/sysctl.h>
SYSCTL_INT(_debug, OID_AUTO, dopersistence, CTLFLAG_RW, &dopersistence, 0, "");
static int snapdebug = 0;
SYSCTL_INT(_debug, OID_AUTO, snapdebug, CTLFLAG_RW, &snapdebug, 0, "");
int collectsnapstats = 0;
SYSCTL_INT(_debug, OID_AUTO, collectsnapstats, CTLFLAG_RW, &collectsnapstats,
      0, "");
#endif /* DEBUG */

/*
 * Create a snapshot file and initialize it for the filesystem.
 */
int
ffs_snapshot(mp, snapfile)
      struct mount *mp;
      char *snapfile;
{
      ufs2_daddr_t numblks, blkno, *blkp, *snapblklist;
      int error, cg, snaploc;
      int i, size, len, loc;
      int flag;
      struct timespec starttime = {0, 0}, endtime;
      char saved_nice = 0;
      long redo = 0, snaplistsize = 0;
      int32_t *lp;
      void *space;
      struct fs *copy_fs = NULL, *fs;
      struct thread *td = curthread;
      struct inode *ip, *xp;
      struct buf *bp, *nbp, *ibp, *sbp = NULL;
      struct nameidata nd;
      struct mount *wrtmp;
      struct vattr vat;
      struct vnode *vp, *xvp, *mvp, *devvp;
      struct uio auio;
      struct iovec aiov;
      struct snapdata *sn;
      struct ufsmount *ump;

      ump = VFSTOUFS(mp);
      fs = ump->um_fs;
      sn = NULL;
      MNT_ILOCK(mp);
      flag = mp->mnt_flag;
      MNT_IUNLOCK(mp);

      /*
       * Need to serialize access to snapshot code per filesystem.
       */
      /*
       * Assign a snapshot slot in the superblock.
       */
      UFS_LOCK(ump);
      for (snaploc = 0; snaploc < FSMAXSNAP; snaploc++)
            if (fs->fs_snapinum[snaploc] == 0)
                  break;
      UFS_UNLOCK(ump);
      if (snaploc == FSMAXSNAP)
            return (ENOSPC);
      /*
       * Create the snapshot file.
       */
restart:
      NDINIT(&nd, CREATE, LOCKPARENT | LOCKLEAF, UIO_SYSSPACE, snapfile, td);
      if ((error = namei(&nd)) != 0)
            return (error);
      if (nd.ni_vp != NULL) {
            vput(nd.ni_vp);
            error = EEXIST;
      }
      if (nd.ni_dvp->v_mount != mp)
            error = EXDEV;
      if (error) {
            NDFREE(&nd, NDF_ONLY_PNBUF);
            if (nd.ni_dvp == nd.ni_vp)
                  vrele(nd.ni_dvp);
            else
                  vput(nd.ni_dvp);
            return (error);
      }
      VATTR_NULL(&vat);
      vat.va_type = VREG;
      vat.va_mode = S_IRUSR;
      vat.va_vaflags |= VA_EXCLUSIVE;
      if (VOP_GETWRITEMOUNT(nd.ni_dvp, &wrtmp))
            wrtmp = NULL;
      if (wrtmp != mp)
            panic("ffs_snapshot: mount mismatch");
      vfs_rel(wrtmp);
      if (vn_start_write(NULL, &wrtmp, V_NOWAIT) != 0) {
            NDFREE(&nd, NDF_ONLY_PNBUF);
            vput(nd.ni_dvp);
            if ((error = vn_start_write(NULL, &wrtmp,
                V_XSLEEP | PCATCH)) != 0)
                  return (error);
            goto restart;
      }
      VOP_LEASE(nd.ni_dvp, td, KERNCRED, LEASE_WRITE);
      error = VOP_CREATE(nd.ni_dvp, &nd.ni_vp, &nd.ni_cnd, &vat);
      VOP_UNLOCK(nd.ni_dvp, 0, td);
      if (error) {
            NDFREE(&nd, NDF_ONLY_PNBUF);
            vn_finished_write(wrtmp);
            vrele(nd.ni_dvp);
            return (error);
      }
      vp = nd.ni_vp;
      vp->v_vflag |= VV_SYSTEM;
      ip = VTOI(vp);
      devvp = ip->i_devvp;
      /*
       * Allocate and copy the last block contents so as to be able
       * to set size to that of the filesystem.
       */
      numblks = howmany(fs->fs_size, fs->fs_frag);
      error = UFS_BALLOC(vp, lblktosize(fs, (off_t)(numblks - 1)),
          fs->fs_bsize, KERNCRED, BA_CLRBUF, &bp);
      if (error)
            goto out;
      ip->i_size = lblktosize(fs, (off_t)numblks);
      DIP_SET(ip, i_size, ip->i_size);
      ip->i_flag |= IN_CHANGE | IN_UPDATE;
      error = readblock(vp, bp, numblks - 1);
      bawrite(bp);
      if (error != 0)
            goto out;
      /*
       * Preallocate critical data structures so that we can copy
       * them in without further allocation after we suspend all
       * operations on the filesystem. We would like to just release
       * the allocated buffers without writing them since they will
       * be filled in below once we are ready to go, but this upsets
       * the soft update code, so we go ahead and write the new buffers.
       *
       * Allocate all indirect blocks and mark all of them as not
       * needing to be copied.
       */
      for (blkno = NDADDR; blkno < numblks; blkno += NINDIR(fs)) {
            error = UFS_BALLOC(vp, lblktosize(fs, (off_t)blkno),
                fs->fs_bsize, td->td_ucred, BA_METAONLY, &ibp);
            if (error)
                  goto out;
            bawrite(ibp);
      }
      /*
       * Allocate copies for the superblock and its summary information.
       */
      error = UFS_BALLOC(vp, fs->fs_sblockloc, fs->fs_sbsize, KERNCRED,
          0, &nbp);
      if (error)
            goto out;
      bawrite(nbp);
      blkno = fragstoblks(fs, fs->fs_csaddr);
      len = howmany(fs->fs_cssize, fs->fs_bsize);
      for (loc = 0; loc < len; loc++) {
            error = UFS_BALLOC(vp, lblktosize(fs, (off_t)(blkno + loc)),
                fs->fs_bsize, KERNCRED, 0, &nbp);
            if (error)
                  goto out;
            bawrite(nbp);
      }
      /*
       * Allocate all cylinder group blocks.
       */
      for (cg = 0; cg < fs->fs_ncg; cg++) {
            error = UFS_BALLOC(vp, lfragtosize(fs, cgtod(fs, cg)),
                fs->fs_bsize, KERNCRED, 0, &nbp);
            if (error)
                  goto out;
            bawrite(nbp);
      }
      /*
       * Copy all the cylinder group maps. Although the
       * filesystem is still active, we hope that only a few
       * cylinder groups will change between now and when we
       * suspend operations. Thus, we will be able to quickly
       * touch up the few cylinder groups that changed during
       * the suspension period.
       */
      len = howmany(fs->fs_ncg, NBBY);
      MALLOC(space, void *, len, M_DEVBUF, M_WAITOK|M_ZERO);
      UFS_LOCK(ump);
      fs->fs_active = space;
      UFS_UNLOCK(ump);
      for (cg = 0; cg < fs->fs_ncg; cg++) {
            error = UFS_BALLOC(vp, lfragtosize(fs, cgtod(fs, cg)),
                fs->fs_bsize, KERNCRED, 0, &nbp);
            if (error)
                  goto out;
            error = cgaccount(cg, vp, nbp, 1);
            bawrite(nbp);
            if (error)
                  goto out;
      }
      /*
       * Change inode to snapshot type file.
       */
      ip->i_flags |= SF_SNAPSHOT;
      DIP_SET(ip, i_flags, ip->i_flags);
      ip->i_flag |= IN_CHANGE | IN_UPDATE;
      /*
       * Ensure that the snapshot is completely on disk.
       * Since we have marked it as a snapshot it is safe to
       * unlock it as no process will be allowed to write to it.
       */
      if ((error = ffs_syncvnode(vp, MNT_WAIT)) != 0)
            goto out;
      VOP_UNLOCK(vp, 0, td);
      /*
       * All allocations are done, so we can now snapshot the system.
       *
       * Recind nice scheduling while running with the filesystem suspended.
       */
      if (td->td_proc->p_nice > 0) {
            struct proc *p;

            p = td->td_proc;
            PROC_LOCK(p);
            PROC_SLOCK(p);
            saved_nice = p->p_nice;
            sched_nice(p, 0);
            PROC_SUNLOCK(p);
            PROC_UNLOCK(p);
      }
      /*
       * Suspend operation on filesystem.
       */
      for (;;) {
            vn_finished_write(wrtmp);
            if ((error = vfs_write_suspend(vp->v_mount)) != 0) {
                  vn_start_write(NULL, &wrtmp, V_WAIT);
                  vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
                  goto out;
            }
            if (mp->mnt_kern_flag & MNTK_SUSPENDED)
                  break;
            vn_start_write(NULL, &wrtmp, V_WAIT);
      }
      vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
      if (ip->i_effnlink == 0) {
            error = ENOENT;         /* Snapshot file unlinked */
            goto out1;
      }
      if (collectsnapstats)
            nanotime(&starttime);

      /* The last block might have changed.  Copy it again to be sure. */
      error = UFS_BALLOC(vp, lblktosize(fs, (off_t)(numblks - 1)),
          fs->fs_bsize, KERNCRED, BA_CLRBUF, &bp);
      if (error != 0)
            goto out1;
      error = readblock(vp, bp, numblks - 1);
      bp->b_flags |= B_VALIDSUSPWRT;
      bawrite(bp);
      if (error != 0)
            goto out1;
      /*
       * First, copy all the cylinder group maps that have changed.
       */
      for (cg = 0; cg < fs->fs_ncg; cg++) {
            if ((ACTIVECGNUM(fs, cg) & ACTIVECGOFF(cg)) != 0)
                  continue;
            redo++;
            error = UFS_BALLOC(vp, lfragtosize(fs, cgtod(fs, cg)),
                fs->fs_bsize, KERNCRED, 0, &nbp);
            if (error)
                  goto out1;
            error = cgaccount(cg, vp, nbp, 2);
            bawrite(nbp);
            if (error)
                  goto out1;
      }
      /*
       * Grab a copy of the superblock and its summary information.
       * We delay writing it until the suspension is released below.
       */
      error = bread(vp, lblkno(fs, fs->fs_sblockloc), fs->fs_bsize,
          KERNCRED, &sbp);
      if (error) {
            brelse(sbp);
            sbp = NULL;
            goto out1;
      }
      loc = blkoff(fs, fs->fs_sblockloc);
      copy_fs = (struct fs *)(sbp->b_data + loc);
      bcopy(fs, copy_fs, fs->fs_sbsize);
      if ((fs->fs_flags & (FS_UNCLEAN | FS_NEEDSFSCK)) == 0)
            copy_fs->fs_clean = 1;
      size = fs->fs_bsize < SBLOCKSIZE ? fs->fs_bsize : SBLOCKSIZE;
      if (fs->fs_sbsize < size)
            bzero(&sbp->b_data[loc + fs->fs_sbsize], size - fs->fs_sbsize);
      size = blkroundup(fs, fs->fs_cssize);
      if (fs->fs_contigsumsize > 0)
            size += fs->fs_ncg * sizeof(int32_t);
      space = malloc((u_long)size, M_UFSMNT, M_WAITOK);
      copy_fs->fs_csp = space;
      bcopy(fs->fs_csp, copy_fs->fs_csp, fs->fs_cssize);
      space = (char *)space + fs->fs_cssize;
      loc = howmany(fs->fs_cssize, fs->fs_fsize);
      i = fs->fs_frag - loc % fs->fs_frag;
      len = (i == fs->fs_frag) ? 0 : i * fs->fs_fsize;
      if (len > 0) {
            if ((error = bread(devvp, fsbtodb(fs, fs->fs_csaddr + loc),
                len, KERNCRED, &bp)) != 0) {
                  brelse(bp);
                  free(copy_fs->fs_csp, M_UFSMNT);
                  bawrite(sbp);
                  sbp = NULL;
                  goto out1;
            }
            bcopy(bp->b_data, space, (u_int)len);
            space = (char *)space + len;
            bp->b_flags |= B_INVAL | B_NOCACHE;
            brelse(bp);
      }
      if (fs->fs_contigsumsize > 0) {
            copy_fs->fs_maxcluster = lp = space;
            for (i = 0; i < fs->fs_ncg; i++)
                  *lp++ = fs->fs_contigsumsize;
      }
      /*
       * We must check for active files that have been unlinked
       * (e.g., with a zero link count). We have to expunge all
       * trace of these files from the snapshot so that they are
       * not reclaimed prematurely by fsck or unnecessarily dumped.
       * We turn off the MNTK_SUSPENDED flag to avoid a panic from
       * spec_strategy about writing on a suspended filesystem.
       * Note that we skip unlinked snapshot files as they will
       * be handled separately below.
       *
       * We also calculate the needed size for the snapshot list.
       */
      snaplistsize = fs->fs_ncg + howmany(fs->fs_cssize, fs->fs_bsize) +
          FSMAXSNAP + 1 /* superblock */ + 1 /* last block */ + 1 /* size */;
      MNT_ILOCK(mp);
      mp->mnt_kern_flag &= ~MNTK_SUSPENDED;
loop:
      MNT_VNODE_FOREACH(xvp, mp, mvp) {
            VI_LOCK(xvp);
            MNT_IUNLOCK(mp);
            if ((xvp->v_iflag & VI_DOOMED) ||
                (xvp->v_usecount == 0 &&
                 (xvp->v_iflag & (VI_OWEINACT | VI_DOINGINACT)) == 0) ||
                xvp->v_type == VNON ||
                (VTOI(xvp)->i_flags & SF_SNAPSHOT)) {
                  VI_UNLOCK(xvp);
                  MNT_ILOCK(mp);
                  continue;
            }
            /*
             * We can skip parent directory vnode because it must have
             * this snapshot file in it.
             */
            if (xvp == nd.ni_dvp) {
                  VI_UNLOCK(xvp);
                  MNT_ILOCK(mp);
                  continue;
            }
            vholdl(xvp);
            if (vn_lock(xvp, LK_EXCLUSIVE | LK_INTERLOCK, td) != 0) {
                  MNT_ILOCK(mp);
                  MNT_VNODE_FOREACH_ABORT_ILOCKED(mp, mvp);
                  vdrop(xvp);
                  goto loop;
            }
            VI_LOCK(xvp);
            if (xvp->v_usecount == 0 &&
                (xvp->v_iflag & (VI_OWEINACT | VI_DOINGINACT)) == 0) {
                  VI_UNLOCK(xvp);
                  VOP_UNLOCK(xvp, 0, td);
                  vdrop(xvp);
                  MNT_ILOCK(mp);
                  continue;
            }
            VI_UNLOCK(xvp);
            if (snapdebug)
                  vprint("ffs_snapshot: busy vnode", xvp);
            if (VOP_GETATTR(xvp, &vat, td->td_ucred, td) == 0 &&
                vat.va_nlink > 0) {
                  VOP_UNLOCK(xvp, 0, td);
                  vdrop(xvp);
                  MNT_ILOCK(mp);
                  continue;
            }
            xp = VTOI(xvp);
            if (ffs_checkfreefile(copy_fs, vp, xp->i_number)) {
                  VOP_UNLOCK(xvp, 0, td);
                  vdrop(xvp);
                  MNT_ILOCK(mp);
                  continue;
            }
            /*
             * If there is a fragment, clear it here.
             */
            blkno = 0;
            loc = howmany(xp->i_size, fs->fs_bsize) - 1;
            if (loc < NDADDR) {
                  len = fragroundup(fs, blkoff(fs, xp->i_size));
                  if (len != 0 && len < fs->fs_bsize) {
                        ffs_blkfree(ump, copy_fs, vp,
                            DIP(xp, i_db[loc]), len, xp->i_number);
                        blkno = DIP(xp, i_db[loc]);
                        DIP_SET(xp, i_db[loc], 0);
                  }
            }
            snaplistsize += 1;
            if (xp->i_ump->um_fstype == UFS1)
                  error = expunge_ufs1(vp, xp, copy_fs, fullacct_ufs1,
                      BLK_NOCOPY);
            else
                  error = expunge_ufs2(vp, xp, copy_fs, fullacct_ufs2,
                      BLK_NOCOPY);
            if (blkno)
                  DIP_SET(xp, i_db[loc], blkno);
            if (!error)
                  error = ffs_freefile(ump, copy_fs, vp, xp->i_number,
                      xp->i_mode);
            VOP_UNLOCK(xvp, 0, td);
            vdrop(xvp);
            if (error) {
                  free(copy_fs->fs_csp, M_UFSMNT);
                  bawrite(sbp);
                  sbp = NULL;
                  MNT_VNODE_FOREACH_ABORT(mp, mvp);
                  goto out1;
            }
            MNT_ILOCK(mp);
      }
      MNT_IUNLOCK(mp);
      /*
       * If there already exist snapshots on this filesystem, grab a
       * reference to their shared lock. If this is the first snapshot
       * on this filesystem, we need to allocate a lock for the snapshots
       * to share. In either case, acquire the snapshot lock and give
       * up our original private lock.
       */
      VI_LOCK(devvp);
      sn = devvp->v_rdev->si_snapdata;
      if (sn != NULL) {
            xp = TAILQ_FIRST(&sn->sn_head);
            VI_UNLOCK(devvp);
            VI_LOCK(vp);
            vp->v_vnlock = &sn->sn_lock;
      } else {
            VI_UNLOCK(devvp);
            sn = malloc(sizeof *sn, M_UFSMNT, M_WAITOK | M_ZERO);
            TAILQ_INIT(&sn->sn_head);
            lockinit(&sn->sn_lock, PVFS, "snaplk", VLKTIMEOUT,
                LK_CANRECURSE | LK_NOSHARE);
            VI_LOCK(vp);
            vp->v_vnlock = &sn->sn_lock;
            mp_fixme("si_snapdata setting is racey.");
            devvp->v_rdev->si_snapdata = sn;
            xp = NULL;
      }
      lockmgr(vp->v_vnlock, LK_INTERLOCK | LK_EXCLUSIVE | LK_RETRY,
          VI_MTX(vp), td);
      lockmgr(&vp->v_lock, LK_RELEASE, NULL, td);
      /*
       * If this is the first snapshot on this filesystem, then we need
       * to allocate the space for the list of preallocated snapshot blocks.
       * This list will be refined below, but this preliminary one will
       * keep us out of deadlock until the full one is ready.
       */
      if (xp == NULL) {
            MALLOC(snapblklist, daddr_t *, snaplistsize * sizeof(daddr_t),
                M_UFSMNT, M_WAITOK);
            blkp = &snapblklist[1];
            *blkp++ = lblkno(fs, fs->fs_sblockloc);
            blkno = fragstoblks(fs, fs->fs_csaddr);
            for (cg = 0; cg < fs->fs_ncg; cg++) {
                  if (fragstoblks(fs, cgtod(fs, cg) > blkno))
                        break;
                  *blkp++ = fragstoblks(fs, cgtod(fs, cg));
            }
            len = howmany(fs->fs_cssize, fs->fs_bsize);
            for (loc = 0; loc < len; loc++)
                  *blkp++ = blkno + loc;
            for (; cg < fs->fs_ncg; cg++)
                  *blkp++ = fragstoblks(fs, cgtod(fs, cg));
            snapblklist[0] = blkp - snapblklist;
            VI_LOCK(devvp);
            if (sn->sn_blklist != NULL)
                  panic("ffs_snapshot: non-empty list");
            sn->sn_blklist = snapblklist;
            sn->sn_listsize = blkp - snapblklist;
            VI_UNLOCK(devvp);
      }
      /*
       * Record snapshot inode. Since this is the newest snapshot,
       * it must be placed at the end of the list.
       */
      VI_LOCK(devvp);
      fs->fs_snapinum[snaploc] = ip->i_number;
      if (ip->i_nextsnap.tqe_prev != 0)
            panic("ffs_snapshot: %d already on list", ip->i_number);
      TAILQ_INSERT_TAIL(&sn->sn_head, ip, i_nextsnap);
      devvp->v_vflag |= VV_COPYONWRITE;
      VI_UNLOCK(devvp);
      ASSERT_VOP_LOCKED(vp, "ffs_snapshot vp");
out1:
      KASSERT((sn != NULL && sbp != NULL && error == 0) ||
            (sn == NULL && sbp == NULL && error != 0),
            ("email phk@ and mckusick@"));
      /*
       * Resume operation on filesystem.
       */
      vfs_write_resume(vp->v_mount);
      vn_start_write(NULL, &wrtmp, V_WAIT);
      if (collectsnapstats && starttime.tv_sec > 0) {
            nanotime(&endtime);
            timespecsub(&endtime, &starttime);
            printf("%s: suspended %ld.%03ld sec, redo %ld of %d\n",
                vp->v_mount->mnt_stat.f_mntonname, (long)endtime.tv_sec,
                endtime.tv_nsec / 1000000, redo, fs->fs_ncg);
      }
      if (sbp == NULL)
            goto out;
      /*
       * Copy allocation information from all the snapshots in
       * this snapshot and then expunge them from its view.
       */
      TAILQ_FOREACH(xp, &sn->sn_head, i_nextsnap) {
            if (xp == ip)
                  break;
            if (xp->i_ump->um_fstype == UFS1)
                  error = expunge_ufs1(vp, xp, fs, snapacct_ufs1,
                      BLK_SNAP);
            else
                  error = expunge_ufs2(vp, xp, fs, snapacct_ufs2,
                      BLK_SNAP);
            if (error == 0 && xp->i_effnlink == 0) {
                  error = ffs_freefile(ump,
                                   copy_fs,
                                   vp,
                                   xp->i_number,
                                   xp->i_mode);
            }
            if (error) {
                  fs->fs_snapinum[snaploc] = 0;
                  goto done;
            }
      }
      /*
       * Allocate space for the full list of preallocated snapshot blocks.
       */
      MALLOC(snapblklist, daddr_t *, snaplistsize * sizeof(daddr_t),
          M_UFSMNT, M_WAITOK);
      ip->i_snapblklist = &snapblklist[1];
      /*
       * Expunge the blocks used by the snapshots from the set of
       * blocks marked as used in the snapshot bitmaps. Also, collect
       * the list of allocated blocks in i_snapblklist.
       */
      if (ip->i_ump->um_fstype == UFS1)
            error = expunge_ufs1(vp, ip, copy_fs, mapacct_ufs1, BLK_SNAP);
      else
            error = expunge_ufs2(vp, ip, copy_fs, mapacct_ufs2, BLK_SNAP);
      if (error) {
            fs->fs_snapinum[snaploc] = 0;
            FREE(snapblklist, M_UFSMNT);
            goto done;
      }
      if (snaplistsize < ip->i_snapblklist - snapblklist)
            panic("ffs_snapshot: list too small");
      snaplistsize = ip->i_snapblklist - snapblklist;
      snapblklist[0] = snaplistsize;
      ip->i_snapblklist = 0;
      /*
       * Write out the list of allocated blocks to the end of the snapshot.
       */
      auio.uio_iov = &aiov;
      auio.uio_iovcnt = 1;
      aiov.iov_base = (void *)snapblklist;
      aiov.iov_len = snaplistsize * sizeof(daddr_t);
      auio.uio_resid = aiov.iov_len;;
      auio.uio_offset = ip->i_size;
      auio.uio_segflg = UIO_SYSSPACE;
      auio.uio_rw = UIO_WRITE;
      auio.uio_td = td;
      if ((error = VOP_WRITE(vp, &auio, IO_UNIT, td->td_ucred)) != 0) {
            fs->fs_snapinum[snaploc] = 0;
            FREE(snapblklist, M_UFSMNT);
            goto done;
      }
      /*
       * Write the superblock and its summary information
       * to the snapshot.
       */
      blkno = fragstoblks(fs, fs->fs_csaddr);
      len = howmany(fs->fs_cssize, fs->fs_bsize);
      space = copy_fs->fs_csp;
      for (loc = 0; loc < len; loc++) {
            error = bread(vp, blkno + loc, fs->fs_bsize, KERNCRED, &nbp);
            if (error) {
                  brelse(nbp);
                  fs->fs_snapinum[snaploc] = 0;
                  FREE(snapblklist, M_UFSMNT);
                  goto done;
            }
            bcopy(space, nbp->b_data, fs->fs_bsize);
            space = (char *)space + fs->fs_bsize;
            bawrite(nbp);
      }
      /*
       * As this is the newest list, it is the most inclusive, so
       * should replace the previous list.
       */
      VI_LOCK(devvp);
      space = sn->sn_blklist;
      sn->sn_blklist = snapblklist;
      sn->sn_listsize = snaplistsize;
      VI_UNLOCK(devvp);
      if (space != NULL)
            FREE(space, M_UFSMNT);
      /*
       * If another process is currently writing the buffer containing
       * the inode for this snapshot then a deadlock can occur. Drop
       * the snapshot lock until the buffer has been written.
       */
      VREF(vp);   /* Protect against ffs_snapgone() */
      VOP_UNLOCK(vp, 0, td);
      (void) bread(ip->i_devvp,
                 fsbtodb(fs, ino_to_fsba(fs, ip->i_number)),
                 (int) fs->fs_bsize, NOCRED, &nbp);
      brelse(nbp);
      vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
      if (ip->i_effnlink == 0)
            error = ENOENT;         /* Snapshot file unlinked */
      else
            vrele(vp);        /* Drop extra reference */
done:
      FREE(copy_fs->fs_csp, M_UFSMNT);
      bawrite(sbp);
out:
      NDFREE(&nd, NDF_ONLY_PNBUF);
      if (saved_nice > 0) {
            struct proc *p;

            p = td->td_proc;
            PROC_LOCK(p);
            PROC_SLOCK(p);
            sched_nice(td->td_proc, saved_nice);
            PROC_SUNLOCK(p);
            PROC_UNLOCK(td->td_proc);
      }
      UFS_LOCK(ump);
      if (fs->fs_active != 0) {
            FREE(fs->fs_active, M_DEVBUF);
            fs->fs_active = 0;
      }
      UFS_UNLOCK(ump);
      MNT_ILOCK(mp);
      mp->mnt_flag = (mp->mnt_flag & MNT_QUOTA) | (flag & ~MNT_QUOTA);
      MNT_IUNLOCK(mp);
      if (error)
            (void) ffs_truncate(vp, (off_t)0, 0, NOCRED, td);
      (void) ffs_syncvnode(vp, MNT_WAIT);
      if (error)
            vput(vp);
      else
            VOP_UNLOCK(vp, 0, td);
      vrele(nd.ni_dvp);
      vn_finished_write(wrtmp);
      process_deferred_inactive(mp);
      return (error);
}

/*
 * Copy a cylinder group map. All the unallocated blocks are marked
 * BLK_NOCOPY so that the snapshot knows that it need not copy them
 * if they are later written. If passno is one, then this is a first
 * pass, so only setting needs to be done. If passno is 2, then this
 * is a revision to a previous pass which must be undone as the
 * replacement pass is done.
 */
static int
cgaccount(cg, vp, nbp, passno)
      int cg;
      struct vnode *vp;
      struct buf *nbp;
      int passno;
{
      struct buf *bp, *ibp;
      struct inode *ip;
      struct cg *cgp;
      struct fs *fs;
      ufs2_daddr_t base, numblks;
      int error, len, loc, indiroff;

      ip = VTOI(vp);
      fs = ip->i_fs;
      error = bread(ip->i_devvp, fsbtodb(fs, cgtod(fs, cg)),
            (int)fs->fs_cgsize, KERNCRED, &bp);
      if (error) {
            brelse(bp);
            return (error);
      }
      cgp = (struct cg *)bp->b_data;
      if (!cg_chkmagic(cgp)) {
            brelse(bp);
            return (EIO);
      }
      UFS_LOCK(ip->i_ump);
      ACTIVESET(fs, cg);
      UFS_UNLOCK(ip->i_ump);
      bcopy(bp->b_data, nbp->b_data, fs->fs_cgsize);
      if (fs->fs_cgsize < fs->fs_bsize)
            bzero(&nbp->b_data[fs->fs_cgsize],
                fs->fs_bsize - fs->fs_cgsize);
      cgp = (struct cg *)nbp->b_data;
      bqrelse(bp);
      if (passno == 2)
            nbp->b_flags |= B_VALIDSUSPWRT;
      numblks = howmany(fs->fs_size, fs->fs_frag);
      len = howmany(fs->fs_fpg, fs->fs_frag);
      base = cgbase(fs, cg) / fs->fs_frag;
      if (base + len >= numblks)
            len = numblks - base - 1;
      loc = 0;
      if (base < NDADDR) {
            for ( ; loc < NDADDR; loc++) {
                  if (ffs_isblock(fs, cg_blksfree(cgp), loc))
                        DIP_SET(ip, i_db[loc], BLK_NOCOPY);
                  else if (passno == 2 && DIP(ip, i_db[loc])== BLK_NOCOPY)
                        DIP_SET(ip, i_db[loc], 0);
                  else if (passno == 1 && DIP(ip, i_db[loc])== BLK_NOCOPY)
                        panic("ffs_snapshot: lost direct block");
            }
      }
      error = UFS_BALLOC(vp, lblktosize(fs, (off_t)(base + loc)),
          fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
      if (error) {
            return (error);
      }
      indiroff = (base + loc - NDADDR) % NINDIR(fs);
      for ( ; loc < len; loc++, indiroff++) {
            if (indiroff >= NINDIR(fs)) {
                  if (passno == 2)
                        ibp->b_flags |= B_VALIDSUSPWRT;
                  bawrite(ibp);
                  error = UFS_BALLOC(vp,
                      lblktosize(fs, (off_t)(base + loc)),
                      fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
                  if (error) {
                        return (error);
                  }
                  indiroff = 0;
            }
            if (ip->i_ump->um_fstype == UFS1) {
                  if (ffs_isblock(fs, cg_blksfree(cgp), loc))
                        ((ufs1_daddr_t *)(ibp->b_data))[indiroff] =
                            BLK_NOCOPY;
                  else if (passno == 2 && ((ufs1_daddr_t *)(ibp->b_data))
                      [indiroff] == BLK_NOCOPY)
                        ((ufs1_daddr_t *)(ibp->b_data))[indiroff] = 0;
                  else if (passno == 1 && ((ufs1_daddr_t *)(ibp->b_data))
                      [indiroff] == BLK_NOCOPY)
                        panic("ffs_snapshot: lost indirect block");
                  continue;
            }
            if (ffs_isblock(fs, cg_blksfree(cgp), loc))
                  ((ufs2_daddr_t *)(ibp->b_data))[indiroff] = BLK_NOCOPY;
            else if (passno == 2 &&
                ((ufs2_daddr_t *)(ibp->b_data)) [indiroff] == BLK_NOCOPY)
                  ((ufs2_daddr_t *)(ibp->b_data))[indiroff] = 0;
            else if (passno == 1 &&
                ((ufs2_daddr_t *)(ibp->b_data)) [indiroff] == BLK_NOCOPY)
                  panic("ffs_snapshot: lost indirect block");
      }
      if (passno == 2)
            ibp->b_flags |= B_VALIDSUSPWRT;
      bdwrite(ibp);
      return (0);
}

/*
 * Before expunging a snapshot inode, note all the
 * blocks that it claims with BLK_SNAP so that fsck will
 * be able to account for those blocks properly and so
 * that this snapshot knows that it need not copy them
 * if the other snapshot holding them is freed. This code
 * is reproduced once each for UFS1 and UFS2.
 */
static int
expunge_ufs1(snapvp, cancelip, fs, acctfunc, expungetype)
      struct vnode *snapvp;
      struct inode *cancelip;
      struct fs *fs;
      int (*acctfunc)(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *,
          struct fs *, ufs_lbn_t, int);
      int expungetype;
{
      int i, error, indiroff;
      ufs_lbn_t lbn, rlbn;
      ufs2_daddr_t len, blkno, numblks, blksperindir;
      struct ufs1_dinode *dip;
      struct thread *td = curthread;
      struct buf *bp;

      /*
       * Prepare to expunge the inode. If its inode block has not
       * yet been copied, then allocate and fill the copy.
       */
      lbn = fragstoblks(fs, ino_to_fsba(fs, cancelip->i_number));
      blkno = 0;
      if (lbn < NDADDR) {
            blkno = VTOI(snapvp)->i_din1->di_db[lbn];
      } else {
            td->td_pflags |= TDP_COWINPROGRESS;
            error = ffs_balloc_ufs1(snapvp, lblktosize(fs, (off_t)lbn),
               fs->fs_bsize, KERNCRED, BA_METAONLY, &bp);
            td->td_pflags &= ~TDP_COWINPROGRESS;
            if (error)
                  return (error);
            indiroff = (lbn - NDADDR) % NINDIR(fs);
            blkno = ((ufs1_daddr_t *)(bp->b_data))[indiroff];
            bqrelse(bp);
      }
      if (blkno != 0) {
            if ((error = bread(snapvp, lbn, fs->fs_bsize, KERNCRED, &bp)))
                  return (error);
      } else {
            error = ffs_balloc_ufs1(snapvp, lblktosize(fs, (off_t)lbn),
                fs->fs_bsize, KERNCRED, 0, &bp);
            if (error)
                  return (error);
            if ((error = readblock(snapvp, bp, lbn)) != 0)
                  return (error);
      }
      /*
       * Set a snapshot inode to be a zero length file, regular files
       * or unlinked snapshots to be completely unallocated.
       */
      dip = (struct ufs1_dinode *)bp->b_data +
          ino_to_fsbo(fs, cancelip->i_number);
      if (expungetype == BLK_NOCOPY || cancelip->i_effnlink == 0)
            dip->di_mode = 0;
      dip->di_size = 0;
      dip->di_blocks = 0;
      dip->di_flags &= ~SF_SNAPSHOT;
      bzero(&dip->di_db[0], (NDADDR + NIADDR) * sizeof(ufs1_daddr_t));
      bdwrite(bp);
      /*
       * Now go through and expunge all the blocks in the file
       * using the function requested.
       */
      numblks = howmany(cancelip->i_size, fs->fs_bsize);
      if ((error = (*acctfunc)(snapvp, &cancelip->i_din1->di_db[0],
          &cancelip->i_din1->di_db[NDADDR], fs, 0, expungetype)))
            return (error);
      if ((error = (*acctfunc)(snapvp, &cancelip->i_din1->di_ib[0],
          &cancelip->i_din1->di_ib[NIADDR], fs, -1, expungetype)))
            return (error);
      blksperindir = 1;
      lbn = -NDADDR;
      len = numblks - NDADDR;
      rlbn = NDADDR;
      for (i = 0; len > 0 && i < NIADDR; i++) {
            error = indiracct_ufs1(snapvp, ITOV(cancelip), i,
                cancelip->i_din1->di_ib[i], lbn, rlbn, len,
                blksperindir, fs, acctfunc, expungetype);
            if (error)
                  return (error);
            blksperindir *= NINDIR(fs);
            lbn -= blksperindir + 1;
            len -= blksperindir;
            rlbn += blksperindir;
      }
      return (0);
}

/*
 * Descend an indirect block chain for vnode cancelvp accounting for all
 * its indirect blocks in snapvp.
 */ 
static int
indiracct_ufs1(snapvp, cancelvp, level, blkno, lbn, rlbn, remblks,
          blksperindir, fs, acctfunc, expungetype)
      struct vnode *snapvp;
      struct vnode *cancelvp;
      int level;
      ufs1_daddr_t blkno;
      ufs_lbn_t lbn;
      ufs_lbn_t rlbn;
      ufs_lbn_t remblks;
      ufs_lbn_t blksperindir;
      struct fs *fs;
      int (*acctfunc)(struct vnode *, ufs1_daddr_t *, ufs1_daddr_t *,
          struct fs *, ufs_lbn_t, int);
      int expungetype;
{
      int error, num, i;
      ufs_lbn_t subblksperindir;
      struct indir indirs[NIADDR + 2];
      ufs1_daddr_t last, *bap;
      struct buf *bp;

      if (blkno == 0) {
            if (expungetype == BLK_NOCOPY)
                  return (0);
            panic("indiracct_ufs1: missing indir");
      }
      if ((error = ufs_getlbns(cancelvp, rlbn, indirs, &num)) != 0)
            return (error);
      if (lbn != indirs[num - 1 - level].in_lbn || num < 2)
            panic("indiracct_ufs1: botched params");
      /*
       * We have to expand bread here since it will deadlock looking
       * up the block number for any blocks that are not in the cache.
       */
      bp = getblk(cancelvp, lbn, fs->fs_bsize, 0, 0, 0);
      bp->b_blkno = fsbtodb(fs, blkno);
      if ((bp->b_flags & (B_DONE | B_DELWRI)) == 0 &&
          (error = readblock(cancelvp, bp, fragstoblks(fs, blkno)))) {
            brelse(bp);
            return (error);
      }
      /*
       * Account for the block pointers in this indirect block.
       */
      last = howmany(remblks, blksperindir);
      if (last > NINDIR(fs))
            last = NINDIR(fs);
      MALLOC(bap, ufs1_daddr_t *, fs->fs_bsize, M_DEVBUF, M_WAITOK);
      bcopy(bp->b_data, (caddr_t)bap, fs->fs_bsize);
      bqrelse(bp);
      error = (*acctfunc)(snapvp, &bap[0], &bap[last], fs,
          level == 0 ? rlbn : -1, expungetype);
      if (error || level == 0)
            goto out;
      /*
       * Account for the block pointers in each of the indirect blocks
       * in the levels below us.
       */
      subblksperindir = blksperindir / NINDIR(fs);
      for (lbn++, level--, i = 0; i < last; i++) {
            error = indiracct_ufs1(snapvp, cancelvp, level, bap[i], lbn,
                rlbn, remblks, subblksperindir, fs, acctfunc, expungetype);
            if (error)
                  goto out;
            rlbn += blksperindir;
            lbn -= blksperindir;
            remblks -= blksperindir;
      }
out:
      FREE(bap, M_DEVBUF);
      return (error);
}

/*
 * Do both snap accounting and map accounting.
 */
static int
fullacct_ufs1(vp, oldblkp, lastblkp, fs, lblkno, exptype)
      struct vnode *vp;
      ufs1_daddr_t *oldblkp, *lastblkp;
      struct fs *fs;
      ufs_lbn_t lblkno;
      int exptype;      /* BLK_SNAP or BLK_NOCOPY */
{
      int error;

      if ((error = snapacct_ufs1(vp, oldblkp, lastblkp, fs, lblkno, exptype)))
            return (error);
      return (mapacct_ufs1(vp, oldblkp, lastblkp, fs, lblkno, exptype));
}

/*
 * Identify a set of blocks allocated in a snapshot inode.
 */
static int
snapacct_ufs1(vp, oldblkp, lastblkp, fs, lblkno, expungetype)
      struct vnode *vp;
      ufs1_daddr_t *oldblkp, *lastblkp;
      struct fs *fs;
      ufs_lbn_t lblkno;
      int expungetype;  /* BLK_SNAP or BLK_NOCOPY */
{
      struct inode *ip = VTOI(vp);
      ufs1_daddr_t blkno, *blkp;
      ufs_lbn_t lbn;
      struct buf *ibp;
      int error;

      for ( ; oldblkp < lastblkp; oldblkp++) {
            blkno = *oldblkp;
            if (blkno == 0 || blkno == BLK_NOCOPY || blkno == BLK_SNAP)
                  continue;
            lbn = fragstoblks(fs, blkno);
            if (lbn < NDADDR) {
                  blkp = &ip->i_din1->di_db[lbn];
                  ip->i_flag |= IN_CHANGE | IN_UPDATE;
            } else {
                  error = ffs_balloc_ufs1(vp, lblktosize(fs, (off_t)lbn),
                      fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
                  if (error)
                        return (error);
                  blkp = &((ufs1_daddr_t *)(ibp->b_data))
                      [(lbn - NDADDR) % NINDIR(fs)];
            }
            /*
             * If we are expunging a snapshot vnode and we
             * find a block marked BLK_NOCOPY, then it is
             * one that has been allocated to this snapshot after
             * we took our current snapshot and can be ignored.
             */
            if (expungetype == BLK_SNAP && *blkp == BLK_NOCOPY) {
                  if (lbn >= NDADDR)
                        brelse(ibp);
            } else {
                  if (*blkp != 0)
                        panic("snapacct_ufs1: bad block");
                  *blkp = expungetype;
                  if (lbn >= NDADDR)
                        bdwrite(ibp);
            }
      }
      return (0);
}

/*
 * Account for a set of blocks allocated in a snapshot inode.
 */
static int
mapacct_ufs1(vp, oldblkp, lastblkp, fs, lblkno, expungetype)
      struct vnode *vp;
      ufs1_daddr_t *oldblkp, *lastblkp;
      struct fs *fs;
      ufs_lbn_t lblkno;
      int expungetype;
{
      ufs1_daddr_t blkno;
      struct inode *ip;
      ino_t inum;
      int acctit;

      ip = VTOI(vp);
      inum = ip->i_number;
      if (lblkno == -1)
            acctit = 0;
      else
            acctit = 1;
      for ( ; oldblkp < lastblkp; oldblkp++, lblkno++) {
            blkno = *oldblkp;
            if (blkno == 0 || blkno == BLK_NOCOPY)
                  continue;
            if (acctit && expungetype == BLK_SNAP && blkno != BLK_SNAP)
                  *ip->i_snapblklist++ = lblkno;
            if (blkno == BLK_SNAP)
                  blkno = blkstofrags(fs, lblkno);
            ffs_blkfree(ip->i_ump, fs, vp, blkno, fs->fs_bsize, inum);
      }
      return (0);
}

/*
 * Before expunging a snapshot inode, note all the
 * blocks that it claims with BLK_SNAP so that fsck will
 * be able to account for those blocks properly and so
 * that this snapshot knows that it need not copy them
 * if the other snapshot holding them is freed. This code
 * is reproduced once each for UFS1 and UFS2.
 */
static int
expunge_ufs2(snapvp, cancelip, fs, acctfunc, expungetype)
      struct vnode *snapvp;
      struct inode *cancelip;
      struct fs *fs;
      int (*acctfunc)(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *,
          struct fs *, ufs_lbn_t, int);
      int expungetype;
{
      int i, error, indiroff;
      ufs_lbn_t lbn, rlbn;
      ufs2_daddr_t len, blkno, numblks, blksperindir;
      struct ufs2_dinode *dip;
      struct thread *td = curthread;
      struct buf *bp;

      /*
       * Prepare to expunge the inode. If its inode block has not
       * yet been copied, then allocate and fill the copy.
       */
      lbn = fragstoblks(fs, ino_to_fsba(fs, cancelip->i_number));
      blkno = 0;
      if (lbn < NDADDR) {
            blkno = VTOI(snapvp)->i_din2->di_db[lbn];
      } else {
            td->td_pflags |= TDP_COWINPROGRESS;
            error = ffs_balloc_ufs2(snapvp, lblktosize(fs, (off_t)lbn),
               fs->fs_bsize, KERNCRED, BA_METAONLY, &bp);
            td->td_pflags &= ~TDP_COWINPROGRESS;
            if (error)
                  return (error);
            indiroff = (lbn - NDADDR) % NINDIR(fs);
            blkno = ((ufs2_daddr_t *)(bp->b_data))[indiroff];
            bqrelse(bp);
      }
      if (blkno != 0) {
            if ((error = bread(snapvp, lbn, fs->fs_bsize, KERNCRED, &bp)))
                  return (error);
      } else {
            error = ffs_balloc_ufs2(snapvp, lblktosize(fs, (off_t)lbn),
                fs->fs_bsize, KERNCRED, 0, &bp);
            if (error)
                  return (error);
            if ((error = readblock(snapvp, bp, lbn)) != 0)
                  return (error);
      }
      /*
       * Set a snapshot inode to be a zero length file, regular files
       * to be completely unallocated.
       */
      dip = (struct ufs2_dinode *)bp->b_data +
          ino_to_fsbo(fs, cancelip->i_number);
      if (expungetype == BLK_NOCOPY)
            dip->di_mode = 0;
      dip->di_size = 0;
      dip->di_blocks = 0;
      dip->di_flags &= ~SF_SNAPSHOT;
      bzero(&dip->di_db[0], (NDADDR + NIADDR) * sizeof(ufs2_daddr_t));
      bdwrite(bp);
      /*
       * Now go through and expunge all the blocks in the file
       * using the function requested.
       */
      numblks = howmany(cancelip->i_size, fs->fs_bsize);
      if ((error = (*acctfunc)(snapvp, &cancelip->i_din2->di_db[0],
          &cancelip->i_din2->di_db[NDADDR], fs, 0, expungetype)))
            return (error);
      if ((error = (*acctfunc)(snapvp, &cancelip->i_din2->di_ib[0],
          &cancelip->i_din2->di_ib[NIADDR], fs, -1, expungetype)))
            return (error);
      blksperindir = 1;
      lbn = -NDADDR;
      len = numblks - NDADDR;
      rlbn = NDADDR;
      for (i = 0; len > 0 && i < NIADDR; i++) {
            error = indiracct_ufs2(snapvp, ITOV(cancelip), i,
                cancelip->i_din2->di_ib[i], lbn, rlbn, len,
                blksperindir, fs, acctfunc, expungetype);
            if (error)
                  return (error);
            blksperindir *= NINDIR(fs);
            lbn -= blksperindir + 1;
            len -= blksperindir;
            rlbn += blksperindir;
      }
      return (0);
}

/*
 * Descend an indirect block chain for vnode cancelvp accounting for all
 * its indirect blocks in snapvp.
 */ 
static int
indiracct_ufs2(snapvp, cancelvp, level, blkno, lbn, rlbn, remblks,
          blksperindir, fs, acctfunc, expungetype)
      struct vnode *snapvp;
      struct vnode *cancelvp;
      int level;
      ufs2_daddr_t blkno;
      ufs_lbn_t lbn;
      ufs_lbn_t rlbn;
      ufs_lbn_t remblks;
      ufs_lbn_t blksperindir;
      struct fs *fs;
      int (*acctfunc)(struct vnode *, ufs2_daddr_t *, ufs2_daddr_t *,
          struct fs *, ufs_lbn_t, int);
      int expungetype;
{
      int error, num, i;
      ufs_lbn_t subblksperindir;
      struct indir indirs[NIADDR + 2];
      ufs2_daddr_t last, *bap;
      struct buf *bp;

      if (blkno == 0) {
            if (expungetype == BLK_NOCOPY)
                  return (0);
            panic("indiracct_ufs2: missing indir");
      }
      if ((error = ufs_getlbns(cancelvp, rlbn, indirs, &num)) != 0)
            return (error);
      if (lbn != indirs[num - 1 - level].in_lbn || num < 2)
            panic("indiracct_ufs2: botched params");
      /*
       * We have to expand bread here since it will deadlock looking
       * up the block number for any blocks that are not in the cache.
       */
      bp = getblk(cancelvp, lbn, fs->fs_bsize, 0, 0, 0);
      bp->b_blkno = fsbtodb(fs, blkno);
      if ((bp->b_flags & (B_DONE | B_DELWRI)) == 0 &&
          (error = readblock(cancelvp, bp, fragstoblks(fs, blkno)))) {
            brelse(bp);
            return (error);
      }
      /*
       * Account for the block pointers in this indirect block.
       */
      last = howmany(remblks, blksperindir);
      if (last > NINDIR(fs))
            last = NINDIR(fs);
      MALLOC(bap, ufs2_daddr_t *, fs->fs_bsize, M_DEVBUF, M_WAITOK);
      bcopy(bp->b_data, (caddr_t)bap, fs->fs_bsize);
      bqrelse(bp);
      error = (*acctfunc)(snapvp, &bap[0], &bap[last], fs,
          level == 0 ? rlbn : -1, expungetype);
      if (error || level == 0)
            goto out;
      /*
       * Account for the block pointers in each of the indirect blocks
       * in the levels below us.
       */
      subblksperindir = blksperindir / NINDIR(fs);
      for (lbn++, level--, i = 0; i < last; i++) {
            error = indiracct_ufs2(snapvp, cancelvp, level, bap[i], lbn,
                rlbn, remblks, subblksperindir, fs, acctfunc, expungetype);
            if (error)
                  goto out;
            rlbn += blksperindir;
            lbn -= blksperindir;
            remblks -= blksperindir;
      }
out:
      FREE(bap, M_DEVBUF);
      return (error);
}

/*
 * Do both snap accounting and map accounting.
 */
static int
fullacct_ufs2(vp, oldblkp, lastblkp, fs, lblkno, exptype)
      struct vnode *vp;
      ufs2_daddr_t *oldblkp, *lastblkp;
      struct fs *fs;
      ufs_lbn_t lblkno;
      int exptype;      /* BLK_SNAP or BLK_NOCOPY */
{
      int error;

      if ((error = snapacct_ufs2(vp, oldblkp, lastblkp, fs, lblkno, exptype)))
            return (error);
      return (mapacct_ufs2(vp, oldblkp, lastblkp, fs, lblkno, exptype));
}

/*
 * Identify a set of blocks allocated in a snapshot inode.
 */
static int
snapacct_ufs2(vp, oldblkp, lastblkp, fs, lblkno, expungetype)
      struct vnode *vp;
      ufs2_daddr_t *oldblkp, *lastblkp;
      struct fs *fs;
      ufs_lbn_t lblkno;
      int expungetype;  /* BLK_SNAP or BLK_NOCOPY */
{
      struct inode *ip = VTOI(vp);
      ufs2_daddr_t blkno, *blkp;
      ufs_lbn_t lbn;
      struct buf *ibp;
      int error;

      for ( ; oldblkp < lastblkp; oldblkp++) {
            blkno = *oldblkp;
            if (blkno == 0 || blkno == BLK_NOCOPY || blkno == BLK_SNAP)
                  continue;
            lbn = fragstoblks(fs, blkno);
            if (lbn < NDADDR) {
                  blkp = &ip->i_din2->di_db[lbn];
                  ip->i_flag |= IN_CHANGE | IN_UPDATE;
            } else {
                  error = ffs_balloc_ufs2(vp, lblktosize(fs, (off_t)lbn),
                      fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
                  if (error)
                        return (error);
                  blkp = &((ufs2_daddr_t *)(ibp->b_data))
                      [(lbn - NDADDR) % NINDIR(fs)];
            }
            /*
             * If we are expunging a snapshot vnode and we
             * find a block marked BLK_NOCOPY, then it is
             * one that has been allocated to this snapshot after
             * we took our current snapshot and can be ignored.
             */
            if (expungetype == BLK_SNAP && *blkp == BLK_NOCOPY) {
                  if (lbn >= NDADDR)
                        brelse(ibp);
            } else {
                  if (*blkp != 0)
                        panic("snapacct_ufs2: bad block");
                  *blkp = expungetype;
                  if (lbn >= NDADDR)
                        bdwrite(ibp);
            }
      }
      return (0);
}

/*
 * Account for a set of blocks allocated in a snapshot inode.
 */
static int
mapacct_ufs2(vp, oldblkp, lastblkp, fs, lblkno, expungetype)
      struct vnode *vp;
      ufs2_daddr_t *oldblkp, *lastblkp;
      struct fs *fs;
      ufs_lbn_t lblkno;
      int expungetype;
{
      ufs2_daddr_t blkno;
      struct inode *ip;
      ino_t inum;
      int acctit;

      ip = VTOI(vp);
      inum = ip->i_number;
      if (lblkno == -1)
            acctit = 0;
      else
            acctit = 1;
      for ( ; oldblkp < lastblkp; oldblkp++, lblkno++) {
            blkno = *oldblkp;
            if (blkno == 0 || blkno == BLK_NOCOPY)
                  continue;
            if (acctit && expungetype == BLK_SNAP && blkno != BLK_SNAP)
                  *ip->i_snapblklist++ = lblkno;
            if (blkno == BLK_SNAP)
                  blkno = blkstofrags(fs, lblkno);
            ffs_blkfree(ip->i_ump, fs, vp, blkno, fs->fs_bsize, inum);
      }
      return (0);
}

/*
 * Decrement extra reference on snapshot when last name is removed.
 * It will not be freed until the last open reference goes away.
 */
void
ffs_snapgone(ip)
      struct inode *ip;
{
      struct inode *xp;
      struct fs *fs;
      int snaploc;
      struct snapdata *sn;
      struct ufsmount *ump;

      /*
       * Find snapshot in incore list.
       */
      xp = NULL;
      sn = ip->i_devvp->v_rdev->si_snapdata;
      if (sn != NULL)
            TAILQ_FOREACH(xp, &sn->sn_head, i_nextsnap)
                  if (xp == ip)
                        break;
      if (xp != NULL)
            vrele(ITOV(ip));
      else if (snapdebug)
            printf("ffs_snapgone: lost snapshot vnode %d\n",
                ip->i_number);
      /*
       * Delete snapshot inode from superblock. Keep list dense.
       */
      fs = ip->i_fs;
      ump = ip->i_ump;
      UFS_LOCK(ump);
      for (snaploc = 0; snaploc < FSMAXSNAP; snaploc++)
            if (fs->fs_snapinum[snaploc] == ip->i_number)
                  break;
      if (snaploc < FSMAXSNAP) {
            for (snaploc++; snaploc < FSMAXSNAP; snaploc++) {
                  if (fs->fs_snapinum[snaploc] == 0)
                        break;
                  fs->fs_snapinum[snaploc - 1] = fs->fs_snapinum[snaploc];
            }
            fs->fs_snapinum[snaploc - 1] = 0;
      }
      UFS_UNLOCK(ump);
}

/*
 * Prepare a snapshot file for being removed.
 */
void
ffs_snapremove(vp)
      struct vnode *vp;
{
      struct inode *ip;
      struct vnode *devvp;
      struct buf *ibp;
      struct fs *fs;
      struct thread *td = curthread;
      ufs2_daddr_t numblks, blkno, dblk;
      int error, loc, last;
      struct snapdata *sn;

      ip = VTOI(vp);
      fs = ip->i_fs;
      devvp = ip->i_devvp;
      /*
       * If active, delete from incore list (this snapshot may
       * already have been in the process of being deleted, so
       * would not have been active).
       *
       * Clear copy-on-write flag if last snapshot.
       */
      VI_LOCK(devvp);
      if (ip->i_nextsnap.tqe_prev != 0) {
            sn = devvp->v_rdev->si_snapdata;
            TAILQ_REMOVE(&sn->sn_head, ip, i_nextsnap);
            ip->i_nextsnap.tqe_prev = 0;
            VI_UNLOCK(devvp);
            lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL, td);
            VI_LOCK(vp);
            KASSERT(vp->v_vnlock == &sn->sn_lock,
                  ("ffs_snapremove: lost lock mutation")); 
            vp->v_vnlock = &vp->v_lock;
            VI_UNLOCK(vp);
            VI_LOCK(devvp);
            lockmgr(&sn->sn_lock, LK_RELEASE, NULL, td);
            try_free_snapdata(devvp, td);
      } else
            VI_UNLOCK(devvp);
      /*
       * Clear all BLK_NOCOPY fields. Pass any block claims to other
       * snapshots that want them (see ffs_snapblkfree below).
       */
      for (blkno = 1; blkno < NDADDR; blkno++) {
            dblk = DIP(ip, i_db[blkno]);
            if (dblk == 0)
                  continue;
            if (dblk == BLK_NOCOPY || dblk == BLK_SNAP)
                  DIP_SET(ip, i_db[blkno], 0);
            else if ((dblk == blkstofrags(fs, blkno) &&
                 ffs_snapblkfree(fs, ip->i_devvp, dblk, fs->fs_bsize,
                 ip->i_number))) {
                  DIP_SET(ip, i_blocks, DIP(ip, i_blocks) -
                      btodb(fs->fs_bsize));
                  DIP_SET(ip, i_db[blkno], 0);
            }
      }
      numblks = howmany(ip->i_size, fs->fs_bsize);
      for (blkno = NDADDR; blkno < numblks; blkno += NINDIR(fs)) {
            error = UFS_BALLOC(vp, lblktosize(fs, (off_t)blkno),
                fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
            if (error)
                  continue;
            if (fs->fs_size - blkno > NINDIR(fs))
                  last = NINDIR(fs);
            else
                  last = fs->fs_size - blkno;
            for (loc = 0; loc < last; loc++) {
                  if (ip->i_ump->um_fstype == UFS1) {
                        dblk = ((ufs1_daddr_t *)(ibp->b_data))[loc];
                        if (dblk == 0)
                              continue;
                        if (dblk == BLK_NOCOPY || dblk == BLK_SNAP)
                              ((ufs1_daddr_t *)(ibp->b_data))[loc]= 0;
                        else if ((dblk == blkstofrags(fs, blkno) &&
                             ffs_snapblkfree(fs, ip->i_devvp, dblk,
                             fs->fs_bsize, ip->i_number))) {
                              ip->i_din1->di_blocks -=
                                  btodb(fs->fs_bsize);
                              ((ufs1_daddr_t *)(ibp->b_data))[loc]= 0;
                        }
                        continue;
                  }
                  dblk = ((ufs2_daddr_t *)(ibp->b_data))[loc];
                  if (dblk == 0)
                        continue;
                  if (dblk == BLK_NOCOPY || dblk == BLK_SNAP)
                        ((ufs2_daddr_t *)(ibp->b_data))[loc] = 0;
                  else if ((dblk == blkstofrags(fs, blkno) &&
                       ffs_snapblkfree(fs, ip->i_devvp, dblk,
                       fs->fs_bsize, ip->i_number))) {
                        ip->i_din2->di_blocks -= btodb(fs->fs_bsize);
                        ((ufs2_daddr_t *)(ibp->b_data))[loc] = 0;
                  }
            }
            bawrite(ibp);
      }
      /*
       * Clear snapshot flag and drop reference.
       */
      ip->i_flags &= ~SF_SNAPSHOT;
      DIP_SET(ip, i_flags, ip->i_flags);
      ip->i_flag |= IN_CHANGE | IN_UPDATE;
#ifdef QUOTA
      /*
       * Reenable disk quotas for ex-snapshot file.
       */
      if (!getinoquota(ip))
            (void) chkdq(ip, DIP(ip, i_blocks), KERNCRED, FORCE);
#endif
}

/*
 * Notification that a block is being freed. Return zero if the free
 * should be allowed to proceed. Return non-zero if the snapshot file
 * wants to claim the block. The block will be claimed if it is an
 * uncopied part of one of the snapshots. It will be freed if it is
 * either a BLK_NOCOPY or has already been copied in all of the snapshots.
 * If a fragment is being freed, then all snapshots that care about
 * it must make a copy since a snapshot file can only claim full sized
 * blocks. Note that if more than one snapshot file maps the block,
 * we can pick one at random to claim it. Since none of the snapshots
 * can change, we are assurred that they will all see the same unmodified
 * image. When deleting a snapshot file (see ffs_snapremove above), we
 * must push any of these claimed blocks to one of the other snapshots
 * that maps it. These claimed blocks are easily identified as they will
 * have a block number equal to their logical block number within the
 * snapshot. A copied block can never have this property because they
 * must always have been allocated from a BLK_NOCOPY location.
 */
int
ffs_snapblkfree(fs, devvp, bno, size, inum)
      struct fs *fs;
      struct vnode *devvp;
      ufs2_daddr_t bno;
      long size;
      ino_t inum;
{
      struct buf *ibp, *cbp, *savedcbp = 0;
      struct thread *td = curthread;
      struct inode *ip;
      struct vnode *vp = NULL;
      ufs_lbn_t lbn;
      ufs2_daddr_t blkno;
      int indiroff = 0, error = 0, claimedblk = 0;
      struct snapdata *sn;

      lbn = fragstoblks(fs, bno);
retry:
      VI_LOCK(devvp);
      sn = devvp->v_rdev->si_snapdata;
      if (sn == NULL) {
            VI_UNLOCK(devvp);
            return (0);
      }
      if (lockmgr(&sn->sn_lock,
                LK_INTERLOCK | LK_EXCLUSIVE | LK_SLEEPFAIL,
                VI_MTX(devvp), td) != 0)
            goto retry;
      TAILQ_FOREACH(ip, &sn->sn_head, i_nextsnap) {
            vp = ITOV(ip);
            /*
             * Lookup block being written.
             */
            if (lbn < NDADDR) {
                  blkno = DIP(ip, i_db[lbn]);
            } else {
                  td->td_pflags |= TDP_COWINPROGRESS;
                  error = UFS_BALLOC(vp, lblktosize(fs, (off_t)lbn),
                      fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
                  td->td_pflags &= ~TDP_COWINPROGRESS;
                  if (error)
                        break;
                  indiroff = (lbn - NDADDR) % NINDIR(fs);
                  if (ip->i_ump->um_fstype == UFS1)
                        blkno=((ufs1_daddr_t *)(ibp->b_data))[indiroff];
                  else
                        blkno=((ufs2_daddr_t *)(ibp->b_data))[indiroff];
            }
            /*
             * Check to see if block needs to be copied.
             */
            if (blkno == 0) {
                  /*
                   * A block that we map is being freed. If it has not
                   * been claimed yet, we will claim or copy it (below).
                   */
                  claimedblk = 1;
            } else if (blkno == BLK_SNAP) {
                  /*
                   * No previous snapshot claimed the block,
                   * so it will be freed and become a BLK_NOCOPY
                   * (don't care) for us.
                   */
                  if (claimedblk)
                        panic("snapblkfree: inconsistent block type");
                  if (lbn < NDADDR) {
                        DIP_SET(ip, i_db[lbn], BLK_NOCOPY);
                        ip->i_flag |= IN_CHANGE | IN_UPDATE;
                  } else if (ip->i_ump->um_fstype == UFS1) {
                        ((ufs1_daddr_t *)(ibp->b_data))[indiroff] =
                            BLK_NOCOPY;
                        bdwrite(ibp);
                  } else {
                        ((ufs2_daddr_t *)(ibp->b_data))[indiroff] =
                            BLK_NOCOPY;
                        bdwrite(ibp);
                  }
                  continue;
            } else /* BLK_NOCOPY or default */ {
                  /*
                   * If the snapshot has already copied the block
                   * (default), or does not care about the block,
                   * it is not needed.
                   */
                  if (lbn >= NDADDR)
                        bqrelse(ibp);
                  continue;
            }
            /*
             * If this is a full size block, we will just grab it
             * and assign it to the snapshot inode. Otherwise we
             * will proceed to copy it. See explanation for this
             * routine as to why only a single snapshot needs to
             * claim this block.
             */
            if (size == fs->fs_bsize) {
#ifdef DEBUG
                  if (snapdebug)
                        printf("%s %d lbn %jd from inum %d\n",
                            "Grabonremove: snapino", ip->i_number,
                            (intmax_t)lbn, inum);
#endif
                  if (lbn < NDADDR) {
                        DIP_SET(ip, i_db[lbn], bno);
                  } else if (ip->i_ump->um_fstype == UFS1) {
                        ((ufs1_daddr_t *)(ibp->b_data))[indiroff] = bno;
                        bdwrite(ibp);
                  } else {
                        ((ufs2_daddr_t *)(ibp->b_data))[indiroff] = bno;
                        bdwrite(ibp);
                  }
                  DIP_SET(ip, i_blocks, DIP(ip, i_blocks) + btodb(size));
                  ip->i_flag |= IN_CHANGE | IN_UPDATE;
                  lockmgr(vp->v_vnlock, LK_RELEASE, NULL, td);
                  return (1);
            }
            if (lbn >= NDADDR)
                  bqrelse(ibp);
            /*
             * Allocate the block into which to do the copy. Note that this
             * allocation will never require any additional allocations for
             * the snapshot inode.
             */
            td->td_pflags |= TDP_COWINPROGRESS;
            error = UFS_BALLOC(vp, lblktosize(fs, (off_t)lbn),
                fs->fs_bsize, KERNCRED, 0, &cbp);
            td->td_pflags &= ~TDP_COWINPROGRESS;
            if (error)
                  break;
#ifdef DEBUG
            if (snapdebug)
                  printf("%s%d lbn %jd %s %d size %ld to blkno %jd\n",
                      "Copyonremove: snapino ", ip->i_number,
                      (intmax_t)lbn, "for inum", inum, size,
                      (intmax_t)cbp->b_blkno);
#endif
            /*
             * If we have already read the old block contents, then
             * simply copy them to the new block. Note that we need
             * to synchronously write snapshots that have not been
             * unlinked, and hence will be visible after a crash,
             * to ensure their integrity.
             */
            if (savedcbp != 0) {
                  bcopy(savedcbp->b_data, cbp->b_data, fs->fs_bsize);
                  bawrite(cbp);
                  if (dopersistence && ip->i_effnlink > 0)
                        (void) ffs_syncvnode(vp, MNT_WAIT);
                  continue;
            }
            /*
             * Otherwise, read the old block contents into the buffer.
             */
            if ((error = readblock(vp, cbp, lbn)) != 0) {
                  bzero(cbp->b_data, fs->fs_bsize);
                  bawrite(cbp);
                  if (dopersistence && ip->i_effnlink > 0)
                        (void) ffs_syncvnode(vp, MNT_WAIT);
                  break;
            }
            savedcbp = cbp;
      }
      /*
       * Note that we need to synchronously write snapshots that
       * have not been unlinked, and hence will be visible after
       * a crash, to ensure their integrity.
       */
      if (savedcbp) {
            vp = savedcbp->b_vp;
            bawrite(savedcbp);
            if (dopersistence && VTOI(vp)->i_effnlink > 0)
                  (void) ffs_syncvnode(vp, MNT_WAIT);
      }
      /*
       * If we have been unable to allocate a block in which to do
       * the copy, then return non-zero so that the fragment will
       * not be freed. Although space will be lost, the snapshot
       * will stay consistent.
       */
      lockmgr(vp->v_vnlock, LK_RELEASE, NULL, td);
      return (error);
}

/*
 * Associate snapshot files when mounting.
 */
void
ffs_snapshot_mount(mp)
      struct mount *mp;
{
      struct ufsmount *ump = VFSTOUFS(mp);
      struct vnode *devvp = ump->um_devvp;
      struct fs *fs = ump->um_fs;
      struct thread *td = curthread;
      struct snapdata *sn;
      struct vnode *vp;
      struct vnode *lastvp;
      struct inode *ip;
      struct uio auio;
      struct iovec aiov;
      void *snapblklist;
      char *reason;
      daddr_t snaplistsize;
      int error, snaploc, loc;

      /*
       * XXX The following needs to be set before ffs_truncate or
       * VOP_READ can be called.
       */
      mp->mnt_stat.f_iosize = fs->fs_bsize;
      /*
       * Process each snapshot listed in the superblock.
       */
      vp = NULL;
      lastvp = NULL;
      sn = devvp->v_rdev->si_snapdata;
      for (snaploc = 0; snaploc < FSMAXSNAP; snaploc++) {
            if (fs->fs_snapinum[snaploc] == 0)
                  break;
            if ((error = ffs_vget(mp, fs->fs_snapinum[snaploc],
                LK_EXCLUSIVE, &vp)) != 0){
                  printf("ffs_snapshot_mount: vget failed %d\n", error);
                  continue;
            }
            ip = VTOI(vp);
            if ((ip->i_flags & SF_SNAPSHOT) == 0 || ip->i_size ==
                lblktosize(fs, howmany(fs->fs_size, fs->fs_frag))) {
                  if ((ip->i_flags & SF_SNAPSHOT) == 0) {
                        reason = "non-snapshot";
                  } else {
                        reason = "old format snapshot";
                        (void)ffs_truncate(vp, (off_t)0, 0, NOCRED, td);
                        (void)ffs_syncvnode(vp, MNT_WAIT);
                  }
                  printf("ffs_snapshot_mount: %s inode %d\n",
                      reason, fs->fs_snapinum[snaploc]);
                  vput(vp);
                  vp = NULL;
                  for (loc = snaploc + 1; loc < FSMAXSNAP; loc++) {
                        if (fs->fs_snapinum[loc] == 0)
                              break;
                        fs->fs_snapinum[loc - 1] = fs->fs_snapinum[loc];
                  }
                  fs->fs_snapinum[loc - 1] = 0;
                  snaploc--;
                  continue;
            }
            /*
             * If there already exist snapshots on this filesystem, grab a
             * reference to their shared lock. If this is the first snapshot
             * on this filesystem, we need to allocate a lock for the
             * snapshots to share. In either case, acquire the snapshot
             * lock and give up our original private lock.
             */
            VI_LOCK(devvp);
            if (sn != NULL) {

                  VI_UNLOCK(devvp);
                  VI_LOCK(vp);
                  vp->v_vnlock = &sn->sn_lock;
            } else {
                  VI_UNLOCK(devvp);
                  sn = malloc(sizeof *sn, M_UFSMNT, M_WAITOK | M_ZERO);
                  TAILQ_INIT(&sn->sn_head);
                  lockinit(&sn->sn_lock, PVFS, "snaplk", VLKTIMEOUT,
                      LK_CANRECURSE | LK_NOSHARE);
                  VI_LOCK(vp);
                  vp->v_vnlock = &sn->sn_lock;
                  devvp->v_rdev->si_snapdata = sn;
            }
            lockmgr(vp->v_vnlock, LK_INTERLOCK | LK_EXCLUSIVE | LK_RETRY,
                VI_MTX(vp), td);
            lockmgr(&vp->v_lock, LK_RELEASE, NULL, td);
            /*
             * Link it onto the active snapshot list.
             */
            VI_LOCK(devvp);
            if (ip->i_nextsnap.tqe_prev != 0)
                  panic("ffs_snapshot_mount: %d already on list",
                      ip->i_number);
            else
                  TAILQ_INSERT_TAIL(&sn->sn_head, ip, i_nextsnap);
            vp->v_vflag |= VV_SYSTEM;
            VI_UNLOCK(devvp);
            VOP_UNLOCK(vp, 0, td);
            lastvp = vp;
      }
      vp = lastvp;
      /*
       * No usable snapshots found.
       */
      if (vp == NULL)
            return;
      /*
       * Allocate the space for the block hints list. We always want to
       * use the list from the newest snapshot.
       */
      auio.uio_iov = &aiov;
      auio.uio_iovcnt = 1;
      aiov.iov_base = (void *)&snaplistsize;
      aiov.iov_len = sizeof(snaplistsize);
      auio.uio_resid = aiov.iov_len;
      auio.uio_offset =
          lblktosize(fs, howmany(fs->fs_size, fs->fs_frag));
      auio.uio_segflg = UIO_SYSSPACE;
      auio.uio_rw = UIO_READ;
      auio.uio_td = td;
      vn_lock(vp, LK_EXCLUSIVE | LK_RETRY, td);
      if ((error = VOP_READ(vp, &auio, IO_UNIT, td->td_ucred)) != 0) {
            printf("ffs_snapshot_mount: read_1 failed %d\n", error);
            VOP_UNLOCK(vp, 0, td);
            return;
      }
      MALLOC(snapblklist, void *, snaplistsize * sizeof(daddr_t),
          M_UFSMNT, M_WAITOK);
      auio.uio_iovcnt = 1;
      aiov.iov_base = snapblklist;
      aiov.iov_len = snaplistsize * sizeof (daddr_t);
      auio.uio_resid = aiov.iov_len;
      auio.uio_offset -= sizeof(snaplistsize);
      if ((error = VOP_READ(vp, &auio, IO_UNIT, td->td_ucred)) != 0) {
            printf("ffs_snapshot_mount: read_2 failed %d\n", error);
            VOP_UNLOCK(vp, 0, td);
            FREE(snapblklist, M_UFSMNT);
            return;
      }
      VOP_UNLOCK(vp, 0, td);
      VI_LOCK(devvp);
      ASSERT_VOP_LOCKED(devvp, "ffs_snapshot_mount");
      sn->sn_listsize = snaplistsize;
      sn->sn_blklist = (daddr_t *)snapblklist;
      devvp->v_vflag |= VV_COPYONWRITE;
      VI_UNLOCK(devvp);
}

/*
 * Disassociate snapshot files when unmounting.
 */
void
ffs_snapshot_unmount(mp)
      struct mount *mp;
{
      struct vnode *devvp = VFSTOUFS(mp)->um_devvp;
      struct snapdata *sn;
      struct inode *xp;
      struct vnode *vp;
      struct thread *td = curthread;

      VI_LOCK(devvp);
      sn = devvp->v_rdev->si_snapdata;
      while (sn != NULL && (xp = TAILQ_FIRST(&sn->sn_head)) != NULL) {
            vp = ITOV(xp);
            TAILQ_REMOVE(&sn->sn_head, xp, i_nextsnap);
            xp->i_nextsnap.tqe_prev = 0;
            lockmgr(&sn->sn_lock, 
                  LK_INTERLOCK | LK_EXCLUSIVE,
                  VI_MTX(devvp),
                  td);
            VI_LOCK(vp);
            lockmgr(&vp->v_lock,
                  LK_INTERLOCK | LK_EXCLUSIVE,
                  VI_MTX(vp), td);
            VI_LOCK(vp);
            KASSERT(vp->v_vnlock == &sn->sn_lock,
            ("ffs_snapshot_unmount: lost lock mutation")); 
            vp->v_vnlock = &vp->v_lock;
            VI_UNLOCK(vp);
            lockmgr(&vp->v_lock, LK_RELEASE, NULL, td);
            lockmgr(&sn->sn_lock, LK_RELEASE, NULL, td);
            if (xp->i_effnlink > 0)
                  vrele(vp);
            VI_LOCK(devvp);
            sn = devvp->v_rdev->si_snapdata;
      }
      try_free_snapdata(devvp, td);
      ASSERT_VOP_LOCKED(devvp, "ffs_snapshot_unmount");
}

/*
 * Check the buffer block to be belong to device buffer that shall be
 * locked after snaplk. devvp shall be locked on entry, and will be
 * leaved locked upon exit.
 */
static int
ffs_bp_snapblk(devvp, bp)
      struct vnode *devvp;
      struct buf *bp;
{
      struct snapdata *sn;
      struct fs *fs;
      ufs2_daddr_t lbn, *snapblklist;
      int lower, upper, mid;

      ASSERT_VI_LOCKED(devvp, "ffs_bp_snapblk");
      KASSERT(devvp->v_type == VCHR, ("Not a device %p", devvp));
      sn = devvp->v_rdev->si_snapdata;
      if (sn == NULL || TAILQ_FIRST(&sn->sn_head) == NULL)
            return (0);
      fs = TAILQ_FIRST(&sn->sn_head)->i_fs;
      lbn = fragstoblks(fs, dbtofsb(fs, bp->b_blkno));
      snapblklist = sn->sn_blklist;
      upper = sn->sn_listsize - 1;
      lower = 1;
      while (lower <= upper) {
            mid = (lower + upper) / 2;
            if (snapblklist[mid] == lbn)
                  break;
            if (snapblklist[mid] < lbn)
                  lower = mid + 1;
            else
                  upper = mid - 1;
      }
      if (lower <= upper)
            return (1);
      return (0);
}

void
ffs_bdflush(bo, bp)
      struct bufobj *bo;
      struct buf *bp;
{
      struct thread *td;
      struct vnode *vp, *devvp;
      struct buf *nbp;
      int bp_bdskip;

      if (bo->bo_dirty.bv_cnt <= dirtybufthresh)
            return;

      td = curthread;
      vp = bp->b_vp;
      devvp = bo->__bo_vnode;
      KASSERT(vp == devvp, ("devvp != vp %p %p", bo, bp));

      VI_LOCK(devvp);
      bp_bdskip = ffs_bp_snapblk(devvp, bp);
      if (bp_bdskip)
            bdwriteskip++;
      VI_UNLOCK(devvp);
      if (bo->bo_dirty.bv_cnt > dirtybufthresh + 10 && !bp_bdskip) {
            (void) VOP_FSYNC(vp, MNT_NOWAIT, td);
            altbufferflushes++;
      } else {
            BO_LOCK(bo);
            /*
             * Try to find a buffer to flush.
             */
            TAILQ_FOREACH(nbp, &bo->bo_dirty.bv_hd, b_bobufs) {
                  if ((nbp->b_vflags & BV_BKGRDINPROG) ||
                      BUF_LOCK(nbp,
                             LK_EXCLUSIVE | LK_NOWAIT, NULL))
                        continue;
                  if (bp == nbp)
                        panic("bdwrite: found ourselves");
                  BO_UNLOCK(bo);
                  /*
                   * Don't countdeps with the bo lock
                   * held.
                   */
                  if (buf_countdeps(nbp, 0)) {
                        BO_LOCK(bo);
                        BUF_UNLOCK(nbp);
                        continue;
                  }
                  if (bp_bdskip) {
                        VI_LOCK(devvp);
                        if (!ffs_bp_snapblk(vp, nbp)) {
                              if (BO_MTX(bo) != VI_MTX(vp)) {
                                    VI_UNLOCK(devvp);
                                    BO_LOCK(bo);
                              }
                              BUF_UNLOCK(nbp);
                              continue;
                        }
                        VI_UNLOCK(devvp);
                  }
                  if (nbp->b_flags & B_CLUSTEROK) {
                        vfs_bio_awrite(nbp);
                  } else {
                        bremfree(nbp);
                        bawrite(nbp);
                  }
                  dirtybufferflushes++;
                  break;
            }
            if (nbp == NULL)
                  BO_UNLOCK(bo);
      }
}

/*
 * Check for need to copy block that is about to be written,
 * copying the block if necessary.
 */
int
ffs_copyonwrite(devvp, bp)
      struct vnode *devvp;
      struct buf *bp;
{
      struct snapdata *sn;
      struct buf *ibp, *cbp, *savedcbp = 0;
      struct thread *td = curthread;
      struct fs *fs;
      struct inode *ip;
      struct vnode *vp = 0;
      ufs2_daddr_t lbn, blkno, *snapblklist;
      int lower, upper, mid, indiroff, error = 0;
      int launched_async_io, prev_norunningbuf;
      long saved_runningbufspace;

      if (devvp != bp->b_vp && (VTOI(bp->b_vp)->i_flags & SF_SNAPSHOT) != 0)
            return (0);       /* Update on a snapshot file */
      if (td->td_pflags & TDP_COWINPROGRESS)
            panic("ffs_copyonwrite: recursive call");
      /*
       * First check to see if it is in the preallocated list.
       * By doing this check we avoid several potential deadlocks.
       */
      VI_LOCK(devvp);
      sn = devvp->v_rdev->si_snapdata;
      if (sn == NULL ||
          TAILQ_EMPTY(&sn->sn_head)) {
            VI_UNLOCK(devvp);
            return (0);       /* No snapshot */
      }
      ip = TAILQ_FIRST(&sn->sn_head);
      fs = ip->i_fs;
      lbn = fragstoblks(fs, dbtofsb(fs, bp->b_blkno));
      snapblklist = sn->sn_blklist;
      upper = sn->sn_listsize - 1;
      lower = 1;
      while (lower <= upper) {
            mid = (lower + upper) / 2;
            if (snapblklist[mid] == lbn)
                  break;
            if (snapblklist[mid] < lbn)
                  lower = mid + 1;
            else
                  upper = mid - 1;
      }
      if (lower <= upper) {
            VI_UNLOCK(devvp);
            return (0);
      }
      launched_async_io = 0;
      prev_norunningbuf = td->td_pflags & TDP_NORUNNINGBUF;
      /*
       * Since I/O on bp isn't yet in progress and it may be blocked
       * for a long time waiting on snaplk, back it out of
       * runningbufspace, possibly waking other threads waiting for space.
       */
      saved_runningbufspace = bp->b_runningbufspace;
      if (saved_runningbufspace != 0)
            runningbufwakeup(bp);
      /*
       * Not in the precomputed list, so check the snapshots.
       */
      while (lockmgr(&sn->sn_lock,
                   LK_INTERLOCK | LK_EXCLUSIVE | LK_SLEEPFAIL,
                   VI_MTX(devvp), td) != 0) {
            VI_LOCK(devvp);
            sn = devvp->v_rdev->si_snapdata;
            if (sn == NULL ||
                TAILQ_EMPTY(&sn->sn_head)) {
                  VI_UNLOCK(devvp);
                  if (saved_runningbufspace != 0) {
                        bp->b_runningbufspace = saved_runningbufspace;
                        atomic_add_int(&runningbufspace,
                                     bp->b_runningbufspace);
                  }
                  return (0);       /* Snapshot gone */
            }
      }
      TAILQ_FOREACH(ip, &sn->sn_head, i_nextsnap) {
            vp = ITOV(ip);
            /*
             * We ensure that everything of our own that needs to be
             * copied will be done at the time that ffs_snapshot is
             * called. Thus we can skip the check here which can
             * deadlock in doing the lookup in UFS_BALLOC.
             */
            if (bp->b_vp == vp)
                  continue;
            /*
             * Check to see if block needs to be copied. We do not have
             * to hold the snapshot lock while doing this lookup as it
             * will never require any additional allocations for the
             * snapshot inode.
             */
            if (lbn < NDADDR) {
                  blkno = DIP(ip, i_db[lbn]);
            } else {
                  td->td_pflags |= TDP_COWINPROGRESS | TDP_NORUNNINGBUF;
                  error = UFS_BALLOC(vp, lblktosize(fs, (off_t)lbn),
                     fs->fs_bsize, KERNCRED, BA_METAONLY, &ibp);
                  td->td_pflags &= ~TDP_COWINPROGRESS;
                  if (error)
                        break;
                  indiroff = (lbn - NDADDR) % NINDIR(fs);
                  if (ip->i_ump->um_fstype == UFS1)
                        blkno=((ufs1_daddr_t *)(ibp->b_data))[indiroff];
                  else
                        blkno=((ufs2_daddr_t *)(ibp->b_data))[indiroff];
                  bqrelse(ibp);
            }
#ifdef DIAGNOSTIC
            if (blkno == BLK_SNAP && bp->b_lblkno >= 0)
                  panic("ffs_copyonwrite: bad copy block");
#endif
            if (blkno != 0)
                  continue;
            /*
             * Allocate the block into which to do the copy. Since
             * multiple processes may all try to copy the same block,
             * we have to recheck our need to do a copy if we sleep
             * waiting for the lock.
             *
             * Because all snapshots on a filesystem share a single
             * lock, we ensure that we will never be in competition
             * with another process to allocate a block.
             */
            td->td_pflags |= TDP_COWINPROGRESS | TDP_NORUNNINGBUF;
            error = UFS_BALLOC(vp, lblktosize(fs, (off_t)lbn),
                fs->fs_bsize, KERNCRED, 0, &cbp);
            td->td_pflags &= ~TDP_COWINPROGRESS;
            if (error)
                  break;
#ifdef DEBUG
            if (snapdebug) {
                  printf("Copyonwrite: snapino %d lbn %jd for ",
                      ip->i_number, (intmax_t)lbn);
                  if (bp->b_vp == devvp)
                        printf("fs metadata");
                  else
                        printf("inum %d", VTOI(bp->b_vp)->i_number);
                  printf(" lblkno %jd to blkno %jd\n",
                      (intmax_t)bp->b_lblkno, (intmax_t)cbp->b_blkno);
            }
#endif
            /*
             * If we have already read the old block contents, then
             * simply copy them to the new block. Note that we need
             * to synchronously write snapshots that have not been
             * unlinked, and hence will be visible after a crash,
             * to ensure their integrity.
             */
            if (savedcbp != 0) {
                  bcopy(savedcbp->b_data, cbp->b_data, fs->fs_bsize);
                  bawrite(cbp);
                  if (dopersistence && ip->i_effnlink > 0)
                        (void) ffs_syncvnode(vp, MNT_WAIT);
                  else
                        launched_async_io = 1;
                  continue;
            }
            /*
             * Otherwise, read the old block contents into the buffer.
             */
            if ((error = readblock(vp, cbp, lbn)) != 0) {
                  bzero(cbp->b_data, fs->fs_bsize);
                  bawrite(cbp);
                  if (dopersistence && ip->i_effnlink > 0)
                        (void) ffs_syncvnode(vp, MNT_WAIT);
                  else
                        launched_async_io = 1;
                  break;
            }
            savedcbp = cbp;
      }
      /*
       * Note that we need to synchronously write snapshots that
       * have not been unlinked, and hence will be visible after
       * a crash, to ensure their integrity.
       */
      if (savedcbp) {
            vp = savedcbp->b_vp;
            bawrite(savedcbp);
            if (dopersistence && VTOI(vp)->i_effnlink > 0)
                  (void) ffs_syncvnode(vp, MNT_WAIT);
            else
                  launched_async_io = 1;
      }
      lockmgr(vp->v_vnlock, LK_RELEASE, NULL, td);
      td->td_pflags = (td->td_pflags & ~TDP_NORUNNINGBUF) |
            prev_norunningbuf;
      if (launched_async_io && (td->td_pflags & TDP_NORUNNINGBUF) == 0)
            waitrunningbufspace();
      /*
       * I/O on bp will now be started, so count it in runningbufspace.
       */
      if (saved_runningbufspace != 0) {
            bp->b_runningbufspace = saved_runningbufspace;
            atomic_add_int(&runningbufspace, bp->b_runningbufspace);
      }
      return (error);
}

/*
 * Read the specified block into the given buffer.
 * Much of this boiler-plate comes from bwrite().
 */
static int
readblock(vp, bp, lbn)
      struct vnode *vp;
      struct buf *bp;
      ufs2_daddr_t lbn;
{
      struct inode *ip = VTOI(vp);
      struct bio *bip;

      bip = g_alloc_bio();
      bip->bio_cmd = BIO_READ;
      bip->bio_offset = dbtob(fsbtodb(ip->i_fs, blkstofrags(ip->i_fs, lbn)));
      bip->bio_data = bp->b_data;
      bip->bio_length = bp->b_bcount;
      bip->bio_done = NULL;

      g_io_request(bip, ip->i_devvp->v_bufobj.bo_private);
      bp->b_error = biowait(bip, "snaprdb");
      g_destroy_bio(bip);
      return (bp->b_error);
}

/*
 * Process file deletes that were deferred by ufs_inactive() due to
 * the file system being suspended. Transfer IN_LAZYACCESS into
 * IN_MODIFIED for vnodes that were accessed during suspension.
 */
static void
process_deferred_inactive(struct mount *mp)
{
      struct vnode *vp, *mvp;
      struct inode *ip;
      struct thread *td;
      int error;

      td = curthread;
      (void) vn_start_secondary_write(NULL, &mp, V_WAIT);
      MNT_ILOCK(mp);
 loop:
      MNT_VNODE_FOREACH(vp, mp, mvp) {
            VI_LOCK(vp);
            /*
             * IN_LAZYACCESS is checked here without holding any
             * vnode lock, but this flag is set only while holding
             * vnode interlock.
             */
            if (vp->v_type == VNON || (vp->v_iflag & VI_DOOMED) != 0 ||
                ((VTOI(vp)->i_flag & IN_LAZYACCESS) == 0 &&
                  ((vp->v_iflag & VI_OWEINACT) == 0 ||
                  vp->v_usecount > 0))) {
                  VI_UNLOCK(vp);
                  continue;
            }
            MNT_IUNLOCK(mp);
            vholdl(vp);
            error = vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK, td);
            if (error != 0) {
                  vdrop(vp);
                  MNT_ILOCK(mp);
                  if (error == ENOENT)
                        continue;   /* vnode recycled */
                  MNT_VNODE_FOREACH_ABORT_ILOCKED(mp, mvp);
                  goto loop;
            }
            ip = VTOI(vp);
            if ((ip->i_flag & IN_LAZYACCESS) != 0) {
                  ip->i_flag &= ~IN_LAZYACCESS;
                  ip->i_flag |= IN_MODIFIED;
            }
            VI_LOCK(vp);
            if ((vp->v_iflag & VI_OWEINACT) == 0 || vp->v_usecount > 0) {
                  VI_UNLOCK(vp);
                  VOP_UNLOCK(vp, 0, td);
                  vdrop(vp);
                  MNT_ILOCK(mp);
                  continue;
            }
            
            VNASSERT((vp->v_iflag & VI_DOINGINACT) == 0, vp,
                   ("process_deferred_inactive: "
                    "recursed on VI_DOINGINACT"));
            vp->v_iflag |= VI_DOINGINACT;
            vp->v_iflag &= ~VI_OWEINACT;
            VI_UNLOCK(vp);
            (void) VOP_INACTIVE(vp, td);
            VI_LOCK(vp);
            VNASSERT(vp->v_iflag & VI_DOINGINACT, vp,
                   ("process_deferred_inactive: lost VI_DOINGINACT"));
            VNASSERT((vp->v_iflag & VI_OWEINACT) == 0, vp,
                   ("process_deferred_inactive: got VI_OWEINACT"));
            vp->v_iflag &= ~VI_DOINGINACT;
            VI_UNLOCK(vp);
            VOP_UNLOCK(vp, 0, td);
            vdrop(vp);
            MNT_ILOCK(mp);
      }
      MNT_IUNLOCK(mp);
      vn_finished_secondary_write(mp);
}

/* Try to free snapdata associated with devvp */
static void
try_free_snapdata(struct vnode *devvp,
              struct thread *td)
{
      struct snapdata *sn;
      ufs2_daddr_t *snapblklist;

      sn = devvp->v_rdev->si_snapdata;

      if (sn == NULL || TAILQ_FIRST(&sn->sn_head) != NULL ||
          (devvp->v_vflag & VV_COPYONWRITE) == 0) {
            VI_UNLOCK(devvp);
            return;
      }

      devvp->v_rdev->si_snapdata = NULL;
      devvp->v_vflag &= ~VV_COPYONWRITE;
      snapblklist = sn->sn_blklist;
      sn->sn_blklist = NULL;
      sn->sn_listsize = 0;
      lockmgr(&sn->sn_lock, LK_DRAIN|LK_INTERLOCK, VI_MTX(devvp), td);
      lockmgr(&sn->sn_lock, LK_RELEASE, NULL, td);
      lockdestroy(&sn->sn_lock);
      free(sn, M_UFSMNT);
      if (snapblklist != NULL)
            FREE(snapblklist, M_UFSMNT);
}
#endif

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