Copy stable/9 to releng/9.0 as part of the FreeBSD 9.0-RELEASE release

[FreeBSD/releng/9.0.git] / sys / ufs / ffs / 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("$FreeBSD$");

#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/fcntl.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, vtype, wkhd)
        struct fs *fs;
        struct vnode *devvp;
        ufs2_daddr_t bno;
        long size;
        ino_t inum;
        enum vtype vtype;
        struct workhead *wkhd;
{
        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);
}

void
ffs_sync_snap(mp, waitfor)
        struct mount *mp;
        int waitfor;
{
}

#else
FEATURE(ffs_snapshot, "FFS snapshot support");

LIST_HEAD(, snapdata) snapfree;
static struct mtx snapfree_lock;
MTX_SYSINIT(ffs_snapfree, &snapfree_lock, "snapdata free list", MTX_DEF);

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, 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, 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 try_free_snapdata(struct vnode *devvp);
static struct snapdata *ffs_snapdata_acquire(struct vnode *devvp);
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 code normally only ensures
 * persistence for the filesystem metadata contained within a
 * snapshot. Setting the following flag allows this crash
 * persistence to be enabled for file contents.
 */
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;
        uint64_t 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;
        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;
        }
        error = VOP_CREATE(nd.ni_dvp, &nd.ni_vp, &nd.ni_cnd, &vat);
        VOP_UNLOCK(nd.ni_dvp, 0);
        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);
                if (cg % 10 == 0)
                        ffs_syncvnode(vp, MNT_WAIT);
        }
        /*
         * 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);
        space = malloc(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 (cg % 10 == 0)
                        ffs_syncvnode(vp, MNT_WAIT);
                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);
        /*
         * 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);
                saved_nice = p->p_nice;
                sched_nice(p, 0);
                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);
                        goto out;
                }
                if (mp->mnt_kern_flag & MNTK_SUSPENDED)
                        break;
                vn_start_write(NULL, &wrtmp, V_WAIT);
        }
        vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
        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.
         */
        copy_fs = malloc((u_long)fs->fs_bsize, M_UFSMNT, M_WAITOK);
        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(&((char *)copy_fs)[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);
                        free(copy_fs, M_UFSMNT);
                        copy_fs = 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) != 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);
                        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) == 0 &&
                    vat.va_nlink > 0) {
                        VOP_UNLOCK(xvp, 0);
                        vdrop(xvp);
                        MNT_ILOCK(mp);
                        continue;
                }
                xp = VTOI(xvp);
                if (ffs_checkfreefile(copy_fs, vp, xp->i_number)) {
                        VOP_UNLOCK(xvp, 0);
                        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,
                                    xvp->v_type, NULL);
                                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, 1);
                else
                        error = expunge_ufs2(vp, xp, copy_fs, fullacct_ufs2,
                            BLK_NOCOPY, 1);
                if (blkno)
                        DIP_SET(xp, i_db[loc], blkno);
                if (!error)
                        error = ffs_freefile(ump, copy_fs, vp, xp->i_number,
                            xp->i_mode, NULL);
                VOP_UNLOCK(xvp, 0);
                vdrop(xvp);
                if (error) {
                        free(copy_fs->fs_csp, M_UFSMNT);
                        free(copy_fs, M_UFSMNT);
                        copy_fs = NULL;
                        MNT_VNODE_FOREACH_ABORT(mp, mvp);
                        goto out1;
                }
                MNT_ILOCK(mp);
        }
        MNT_IUNLOCK(mp);
        /*
         * Erase the journal file from the snapshot.
         */
        if (fs->fs_flags & FS_SUJ) {
                error = softdep_journal_lookup(mp, &xvp);
                if (error) {
                        free(copy_fs->fs_csp, M_UFSMNT);
                        free(copy_fs, M_UFSMNT);
                        copy_fs = NULL;
                        goto out1;
                }
                xp = VTOI(xvp);
                if (xp->i_ump->um_fstype == UFS1)
                        error = expunge_ufs1(vp, xp, copy_fs, fullacct_ufs1,
                            BLK_NOCOPY, 0);
                else
                        error = expunge_ufs2(vp, xp, copy_fs, fullacct_ufs2,
                            BLK_NOCOPY, 0);
                vput(xvp);
        }
        /*
         * Acquire a lock on the snapdata structure, creating it if necessary.
         */
        sn = ffs_snapdata_acquire(devvp);
        /* 
         * Change vnode to use shared snapshot lock instead of the original
         * private lock.
         */
        vp->v_vnlock = &sn->sn_lock;
        lockmgr(&vp->v_lock, LK_RELEASE, NULL);
        xp = TAILQ_FIRST(&sn->sn_head);
        /*
         * 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) {
                snapblklist = malloc(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 && copy_fs != NULL && error == 0) ||
                (sn == NULL && copy_fs == 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 (copy_fs == 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, 0);
                else
                        error = expunge_ufs2(vp, xp, fs, snapacct_ufs2,
                            BLK_SNAP, 0);
                if (error == 0 && xp->i_effnlink == 0) {
                        error = ffs_freefile(ump,
                                             copy_fs,
                                             vp,
                                             xp->i_number,
                                             xp->i_mode, NULL);
                }
                if (error) {
                        fs->fs_snapinum[snaploc] = 0;
                        goto done;
                }
        }
        /*
         * Allocate space for the full list of preallocated snapshot blocks.
         */
        snapblklist = malloc(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, 0);
        else
                error = expunge_ufs2(vp, ip, copy_fs, mapacct_ufs2,
                    BLK_SNAP, 0);
        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);
        }
        error = bread(vp, lblkno(fs, fs->fs_sblockloc), fs->fs_bsize,
            KERNCRED, &nbp);
        if (error) {
                brelse(nbp);
        } else {
                loc = blkoff(fs, fs->fs_sblockloc);
                bcopy((char *)copy_fs, &nbp->b_data[loc], 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);
        (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);
        if (ip->i_effnlink == 0)
                error = ENOENT;         /* Snapshot file unlinked */
        else
                vrele(vp);              /* Drop extra reference */
done:
        free(copy_fs->fs_csp, M_UFSMNT);
        free(copy_fs, M_UFSMNT);
        copy_fs = NULL;
out:
        NDFREE(&nd, NDF_ONLY_PNBUF);
        if (saved_nice > 0) {
                struct proc *p;

                p = td->td_proc;
                PROC_LOCK(p);
                sched_nice(td->td_proc, saved_nice);
                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);
        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);
        /*
         * Recomputation of summary information might not have been performed
         * at mount time.  Sync up summary information for current cylinder
         * group while data is in memory to ensure that result of background
         * fsck is slightly more consistent.
         */
        fs->fs_cs(fs, cg) = cgp->cg_cs;
        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, clearmode)
        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 clearmode;
{
        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 {
                if (DOINGSOFTDEP(snapvp))
                        softdep_prealloc(snapvp, MNT_WAIT);
                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 (clearmode || 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);
        bap = malloc(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,
                    vp->v_type, NULL);
        }
        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, clearmode)
        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 clearmode;
{
        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 {
                if (DOINGSOFTDEP(snapvp))
                        softdep_prealloc(snapvp, MNT_WAIT);
                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 (clearmode || 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(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);
        bap = malloc(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,
                    vp->v_type, NULL);
        }
        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;
        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);
                KASSERT(vp->v_vnlock == &sn->sn_lock,
                        ("ffs_snapremove: lost lock mutation")); 
                vp->v_vnlock = &vp->v_lock;
                VI_LOCK(devvp);
                lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
                try_free_snapdata(devvp);
        } 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, vp->v_type, NULL))) {
                        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, vp->v_type,
                                     NULL))) {
                                        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, vp->v_type, NULL))) {
                                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;
        /*
         * The dirtied indirects must be written out before
         * softdep_setup_freeblocks() is called.  Otherwise indir_trunc()
         * may find indirect pointers using the magic BLK_* values.
         */
        if (DOINGSOFTDEP(vp))
                ffs_syncvnode(vp, MNT_WAIT);
#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, vtype, wkhd)
        struct fs *fs;
        struct vnode *devvp;
        ufs2_daddr_t bno;
        long size;
        ino_t inum;
        enum vtype vtype;
        struct workhead *wkhd;
{
        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)) != 0)
                goto retry;
        TAILQ_FOREACH(ip, &sn->sn_head, i_nextsnap) {
                vp = ITOV(ip);
                if (DOINGSOFTDEP(vp))
                        softdep_prealloc(vp, MNT_WAIT);
                /*
                 * 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 journaling is tracking this write we must add
                         * the work to the inode or indirect being written.
                         */
                        if (wkhd != NULL) {
                                if (lbn < NDADDR)
                                        softdep_inode_append(ip,
                                            curthread->td_ucred, wkhd);
                                else
                                        softdep_buf_append(ibp, wkhd);
                        }
                        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);
                        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. At a minimum we ensure the
                 * integrity of the filesystem metadata, but use the
                 * dopersistence sysctl-setable flag to decide on the
                 * persistence needed for file content data.
                 */
                if (savedcbp != 0) {
                        bcopy(savedcbp->b_data, cbp->b_data, fs->fs_bsize);
                        bawrite(cbp);
                        if ((vtype == VDIR || 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 ((vtype == VDIR || 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. At a minimum we
         * ensure the integrity of the filesystem metadata, but
         * use the dopersistence sysctl-setable flag to decide on
         * the persistence needed for file content data.
         */
        if (savedcbp) {
                vp = savedcbp->b_vp;
                bawrite(savedcbp);
                if ((vtype == VDIR || 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.
         */
        if (error != 0 && wkhd != NULL)
                softdep_freework(wkhd);
        lockmgr(vp->v_vnlock, LK_RELEASE, NULL);
        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 = NULL;
        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;
                }
                /*
                 * Acquire a lock on the snapdata structure, creating it if
                 * necessary.
                 */
                sn = ffs_snapdata_acquire(devvp);
                /* 
                 * Change vnode to use shared snapshot lock instead of the
                 * original private lock.
                 */
                vp->v_vnlock = &sn->sn_lock;
                lockmgr(&vp->v_lock, LK_RELEASE, NULL);
                /*
                 * 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);
                lastvp = vp;
        }
        vp = lastvp;
        /*
         * No usable snapshots found.
         */
        if (sn == NULL || 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);
        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);
                return;
        }
        snapblklist = malloc(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);
                free(snapblklist, M_UFSMNT);
                return;
        }
        VOP_UNLOCK(vp, 0);
        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;

        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));
                lockmgr(&vp->v_lock, LK_EXCLUSIVE, NULL);
                KASSERT(vp->v_vnlock == &sn->sn_lock,
                ("ffs_snapshot_unmount: lost lock mutation")); 
                vp->v_vnlock = &vp->v_lock;
                lockmgr(&vp->v_lock, LK_RELEASE, NULL);
                lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
                if (xp->i_effnlink > 0)
                        vrele(vp);
                VI_LOCK(devvp);
                sn = devvp->v_rdev->si_snapdata;
        }
        try_free_snapdata(devvp);
        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)) != 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_long(&runningbufspace,
                                               bp->b_runningbufspace);
                        }
                        return (0);             /* Snapshot gone */
                }
        }
        TAILQ_FOREACH(ip, &sn->sn_head, i_nextsnap) {
                vp = ITOV(ip);
                if (DOINGSOFTDEP(vp))
                        softdep_prealloc(vp, MNT_WAIT);
                /*
                 * 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 INVARIANTS
                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. At a minimum we ensure the
                 * integrity of the filesystem metadata, but use the
                 * dopersistence sysctl-setable flag to decide on the
                 * persistence needed for file content data.
                 */
                if (savedcbp != 0) {
                        bcopy(savedcbp->b_data, cbp->b_data, fs->fs_bsize);
                        bawrite(cbp);
                        if ((devvp == bp->b_vp || bp->b_vp->v_type == VDIR ||
                            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 ((devvp == bp->b_vp || bp->b_vp->v_type == VDIR ||
                            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. At a minimum we
         * ensure the integrity of the filesystem metadata, but
         * use the dopersistence sysctl-setable flag to decide on
         * the persistence needed for file content data.
         */
        if (savedcbp) {
                vp = savedcbp->b_vp;
                bawrite(savedcbp);
                if ((devvp == bp->b_vp || bp->b_vp->v_type == VDIR ||
                    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_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_long(&runningbufspace, bp->b_runningbufspace);
        }
        return (error);
}

/*
 * sync snapshots to force freework records waiting on snapshots to claim
 * blocks to free.
 */
void
ffs_sync_snap(mp, waitfor)
        struct mount *mp;
        int waitfor;
{
        struct snapdata *sn;
        struct vnode *devvp;
        struct vnode *vp;
        struct inode *ip;

        devvp = VFSTOUFS(mp)->um_devvp;
        if ((devvp->v_vflag & VV_COPYONWRITE) == 0)
                return;
        for (;;) {
                VI_LOCK(devvp);
                sn = devvp->v_rdev->si_snapdata;
                if (sn == NULL) {
                        VI_UNLOCK(devvp);
                        return;
                }
                if (lockmgr(&sn->sn_lock,
                    LK_INTERLOCK | LK_EXCLUSIVE | LK_SLEEPFAIL,
                    VI_MTX(devvp)) == 0)
                        break;
        }
        TAILQ_FOREACH(ip, &sn->sn_head, i_nextsnap) {
                vp = ITOV(ip);
                ffs_syncvnode(vp, waitfor);
        }
        lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
}

/*
 * 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);
}

#endif

/*
 * 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.
 */
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);
                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);
                        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);
                vdrop(vp);
                MNT_ILOCK(mp);
        }
        MNT_IUNLOCK(mp);
        vn_finished_secondary_write(mp);
}

#ifndef NO_FFS_SNAPSHOT

static struct snapdata *
ffs_snapdata_alloc(void)
{
        struct snapdata *sn;

        /*
         * Fetch a snapdata from the free list if there is one available.
         */
        mtx_lock(&snapfree_lock);
        sn = LIST_FIRST(&snapfree);
        if (sn != NULL)
                LIST_REMOVE(sn, sn_link);
        mtx_unlock(&snapfree_lock);
        if (sn != NULL)
                return (sn);
        /*
         * If there were no free snapdatas allocate one.
         */
        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);
        return (sn);
}

/*
 * The snapdata is never freed because we can not be certain that
 * there are no threads sleeping on the snap lock.  Persisting
 * them permanently avoids costly synchronization in ffs_lock().
 */
static void
ffs_snapdata_free(struct snapdata *sn)
{
        mtx_lock(&snapfree_lock);
        LIST_INSERT_HEAD(&snapfree, sn, sn_link);
        mtx_unlock(&snapfree_lock);
}

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

        ASSERT_VI_LOCKED(devvp, "try_free_snapdata");
        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;
        lockmgr(&sn->sn_lock, LK_DRAIN|LK_INTERLOCK, VI_MTX(devvp));
        snapblklist = sn->sn_blklist;
        sn->sn_blklist = NULL;
        sn->sn_listsize = 0;
        lockmgr(&sn->sn_lock, LK_RELEASE, NULL);
        if (snapblklist != NULL)
                free(snapblklist, M_UFSMNT);
        ffs_snapdata_free(sn);
}

static struct snapdata *
ffs_snapdata_acquire(struct vnode *devvp)
{
        struct snapdata *nsn;
        struct snapdata *sn;

        /*
         * Allocate a free snapdata.  This is done before acquiring the
         * devvp lock to avoid allocation while the devvp interlock is
         * held.
         */
        nsn = ffs_snapdata_alloc();
        /*
         * If there snapshots already exist on this filesystem grab a
         * reference to the shared lock.  Otherwise this is the first
         * snapshot on this filesystem and we need to use our
         * pre-allocated snapdata.
         */
        VI_LOCK(devvp);
        if (devvp->v_rdev->si_snapdata == NULL) {
                devvp->v_rdev->si_snapdata = nsn;
                nsn = NULL;
        }
        sn = devvp->v_rdev->si_snapdata;
        /*
         * Acquire the snapshot lock.
         */
        lockmgr(&sn->sn_lock,
            LK_INTERLOCK | LK_EXCLUSIVE | LK_RETRY, VI_MTX(devvp));
        /*
         * Free any unused snapdata.
         */
        if (nsn != NULL)
                ffs_snapdata_free(nsn);

        return (sn);
}

#endif