fs/zfs/zfs_ctldir.c

	zfs_ctldir.c revision 9adfa60d484ce2435f5af77cc99dcd4e692b6660
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
 * Copyright 2015, OmniTI Computer Consulting, Inc. All rights reserved.
 */

/*
 * ZFS control directory (a.k.a. ".zfs")
 *
 * This directory provides a common location for all ZFS meta-objects.
 * Currently, this is only the 'snapshot' directory, but this may expand in the
 * future.  The elements are built using the GFS primitives, as the hierarchy
 * does not actually exist on disk.
 *
 * For 'snapshot', we don't want to have all snapshots always mounted, because
 * this would take up a huge amount of space in /etc/mnttab.  We have three
 * types of objects:
 *
 *  ctldir ------> snapshotdir -------> snapshot
 *                                             |
 *                                             |
 *                                             V
 *                                         mounted fs
 *
 * The 'snapshot' node contains just enough information to lookup '..' and act
 * as a mountpoint for the snapshot.  Whenever we lookup a specific snapshot, we
 * perform an automount of the underlying filesystem and return the
 * corresponding vnode.
 *
 * All mounts are handled automatically by the kernel, but unmounts are
 * (currently) handled from user land.  The main reason is that there is no
 * reliable way to auto-unmount the filesystem when it's "no longer in use".
 * When the user unmounts a filesystem, we call zfsctl_unmount(), which
 * unmounts any snapshots within the snapshot directory.
 *
 * The '.zfs', '.zfs/snapshot', and all directories created under
 * '.zfs/snapshot' (ie: '.zfs/snapshot/<snapname>') are all GFS nodes and
 * share the same vfs_t as the head filesystem (what '.zfs' lives under).
 *
 * File systems mounted ontop of the GFS nodes '.zfs/snapshot/<snapname>'
 * (ie: snapshots) are ZFS nodes and have their own unique vfs_t.
 * However, vnodes within these mounted on file systems have their v_vfsp
 * fields set to the head filesystem to make NFS happy (see
 * zfsctl_snapdir_lookup()). We VFS_HOLD the head filesystem's vfs_t
 * so that it cannot be freed until all snapshots have been unmounted.
 */

#include <fs/fs_subr.h>
#include <sys/zfs_ctldir.h>
#include <sys/zfs_ioctl.h>
#include <sys/zfs_vfsops.h>
#include <sys/vfs_opreg.h>
#include <sys/gfs.h>
#include <sys/stat.h>
#include <sys/dmu.h>
#include <sys/dsl_destroy.h>
#include <sys/dsl_deleg.h>
#include <sys/mount.h>
#include <sys/sunddi.h>

#include "zfs_namecheck.h"

typedef struct zfsctl_node {
    gfs_dir_t   zc_gfs_private;
    uint64_t    zc_id;
    timestruc_t zc_cmtime;  /* ctime and mtime, always the same */
} zfsctl_node_t;

typedef struct zfsctl_snapdir {
    zfsctl_node_t   sd_node;
    kmutex_t    sd_lock;
    avl_tree_t  sd_snaps;
} zfsctl_snapdir_t;

typedef struct {
    char        *se_name;
    vnode_t     *se_root;
    avl_node_t  se_node;
} zfs_snapentry_t;

static int
snapentry_compare(const void *a, const void *b)
{
    const zfs_snapentry_t *sa = a;
    const zfs_snapentry_t *sb = b;
    int ret = strcmp(sa->se_name, sb->se_name);

    if (ret < 0)
        return (-1);
    else if (ret > 0)
        return (1);
    else
        return (0);
}

vnodeops_t *zfsctl_ops_root;
vnodeops_t *zfsctl_ops_snapdir;
vnodeops_t *zfsctl_ops_snapshot;
vnodeops_t *zfsctl_ops_shares;
vnodeops_t *zfsctl_ops_shares_dir;

static const fs_operation_def_t zfsctl_tops_root[];
static const fs_operation_def_t zfsctl_tops_snapdir[];
static const fs_operation_def_t zfsctl_tops_snapshot[];
static const fs_operation_def_t zfsctl_tops_shares[];

static vnode_t *zfsctl_mknode_snapdir(vnode_t *);
static vnode_t *zfsctl_mknode_shares(vnode_t *);
static vnode_t *zfsctl_snapshot_mknode(vnode_t *, uint64_t objset);
static int zfsctl_unmount_snap(zfs_snapentry_t *, int, cred_t *);

static gfs_opsvec_t zfsctl_opsvec[] = {
    { ".zfs", zfsctl_tops_root, &zfsctl_ops_root },
    { ".zfs/snapshot", zfsctl_tops_snapdir, &zfsctl_ops_snapdir },
    { ".zfs/snapshot/vnode", zfsctl_tops_snapshot, &zfsctl_ops_snapshot },
    { ".zfs/shares", zfsctl_tops_shares, &zfsctl_ops_shares_dir },
    { ".zfs/shares/vnode", zfsctl_tops_shares, &zfsctl_ops_shares },
    { NULL }
};

/*
 * Root directory elements.  We only have two entries
 * snapshot and shares.
 */
static gfs_dirent_t zfsctl_root_entries[] = {
    { "snapshot", zfsctl_mknode_snapdir, GFS_CACHE_VNODE },
    { "shares", zfsctl_mknode_shares, GFS_CACHE_VNODE },
    { NULL }
};

/* include . and .. in the calculation */
#define NROOT_ENTRIES   ((sizeof (zfsctl_root_entries) / \
    sizeof (gfs_dirent_t)) + 1)


/*
 * Initialize the various GFS pieces we'll need to create and manipulate .zfs
 * directories.  This is called from the ZFS init routine, and initializes the
 * vnode ops vectors that we'll be using.
 */
void
zfsctl_init(void)
{
    VERIFY(gfs_make_opsvec(zfsctl_opsvec) == 0);
}

void
zfsctl_fini(void)
{
    /*
     * Remove vfsctl vnode ops
     */
    if (zfsctl_ops_root)
        vn_freevnodeops(zfsctl_ops_root);
    if (zfsctl_ops_snapdir)
        vn_freevnodeops(zfsctl_ops_snapdir);
    if (zfsctl_ops_snapshot)
        vn_freevnodeops(zfsctl_ops_snapshot);
    if (zfsctl_ops_shares)
        vn_freevnodeops(zfsctl_ops_shares);
    if (zfsctl_ops_shares_dir)
        vn_freevnodeops(zfsctl_ops_shares_dir);

    zfsctl_ops_root = NULL;
    zfsctl_ops_snapdir = NULL;
    zfsctl_ops_snapshot = NULL;
    zfsctl_ops_shares = NULL;
    zfsctl_ops_shares_dir = NULL;
}

boolean_t
zfsctl_is_node(vnode_t *vp)
{
    return (vn_matchops(vp, zfsctl_ops_root) ||
        vn_matchops(vp, zfsctl_ops_snapdir) ||
        vn_matchops(vp, zfsctl_ops_snapshot) ||
        vn_matchops(vp, zfsctl_ops_shares) ||
        vn_matchops(vp, zfsctl_ops_shares_dir));

}

/*
 * Return the inode number associated with the 'snapshot' or
 * 'shares' directory.
 */
/* ARGSUSED */
static ino64_t
zfsctl_root_inode_cb(vnode_t *vp, int index)
{
    zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;

    ASSERT(index <= 2);

    if (index == 0)
        return (ZFSCTL_INO_SNAPDIR);

    return (zfsvfs->z_shares_dir);
}

/*
 * Create the '.zfs' directory.  This directory is cached as part of the VFS
 * structure.  This results in a hold on the vfs_t.  The code in zfs_umount()
 * therefore checks against a vfs_count of 2 instead of 1.  This reference
 * is removed when the ctldir is destroyed in the unmount.
 */
void
zfsctl_create(zfsvfs_t *zfsvfs)
{
    vnode_t *vp, *rvp;
    zfsctl_node_t *zcp;
    uint64_t crtime[2];

    ASSERT(zfsvfs->z_ctldir == NULL);

    vp = gfs_root_create(sizeof (zfsctl_node_t), zfsvfs->z_vfs,
        zfsctl_ops_root, ZFSCTL_INO_ROOT, zfsctl_root_entries,
        zfsctl_root_inode_cb, MAXNAMELEN, NULL, NULL);
    zcp = vp->v_data;
    zcp->zc_id = ZFSCTL_INO_ROOT;

    VERIFY(VFS_ROOT(zfsvfs->z_vfs, &rvp) == 0);
    VERIFY(0 == sa_lookup(VTOZ(rvp)->z_sa_hdl, SA_ZPL_CRTIME(zfsvfs),
        &crtime, sizeof (crtime)));
    ZFS_TIME_DECODE(&zcp->zc_cmtime, crtime);
    VN_RELE(rvp);

    /*
     * We're only faking the fact that we have a root of a filesystem for
     * the sake of the GFS interfaces.  Undo the flag manipulation it did
     * for us.
     */
    vp->v_flag &= ~(VROOT | VNOCACHE | VNOMAP | VNOSWAP | VNOMOUNT);

    zfsvfs->z_ctldir = vp;
}

/*
 * Destroy the '.zfs' directory.  Only called when the filesystem is unmounted.
 * There might still be more references if we were force unmounted, but only
 * new zfs_inactive() calls can occur and they don't reference .zfs
 */
void
zfsctl_destroy(zfsvfs_t *zfsvfs)
{
    VN_RELE(zfsvfs->z_ctldir);
    zfsvfs->z_ctldir = NULL;
}

/*
 * Given a root znode, retrieve the associated .zfs directory.
 * Add a hold to the vnode and return it.
 */
vnode_t *
zfsctl_root(znode_t *zp)
{
    ASSERT(zfs_has_ctldir(zp));
    VN_HOLD(zp->z_zfsvfs->z_ctldir);
    return (zp->z_zfsvfs->z_ctldir);
}

/*
 * Common open routine.  Disallow any write access.
 */
/* ARGSUSED */
static int
zfsctl_common_open(vnode_t **vpp, int flags, cred_t *cr, caller_context_t *ct)
{
    if (flags & FWRITE)
        return (SET_ERROR(EACCES));

    return (0);
}

/*
 * Common close routine.  Nothing to do here.
 */
/* ARGSUSED */
static int
zfsctl_common_close(vnode_t *vpp, int flags, int count, offset_t off,
    cred_t *cr, caller_context_t *ct)
{
    return (0);
}

/*
 * Common access routine.  Disallow writes.
 */
/* ARGSUSED */
static int
zfsctl_common_access(vnode_t *vp, int mode, int flags, cred_t *cr,
    caller_context_t *ct)
{
    if (flags & V_ACE_MASK) {
        if (mode & ACE_ALL_WRITE_PERMS)
            return (SET_ERROR(EACCES));
    } else {
        if (mode & VWRITE)
            return (SET_ERROR(EACCES));
    }

    return (0);
}

/*
 * Common getattr function.  Fill in basic information.
 */
static void
zfsctl_common_getattr(vnode_t *vp, vattr_t *vap)
{
    timestruc_t now;

    vap->va_uid = 0;
    vap->va_gid = 0;
    vap->va_rdev = 0;
    /*
     * We are a purely virtual object, so we have no
     * blocksize or allocated blocks.
     */
    vap->va_blksize = 0;
    vap->va_nblocks = 0;
    vap->va_seq = 0;
    vap->va_fsid = vp->v_vfsp->vfs_dev;
    vap->va_mode = S_IRUSR | S_IXUSR | S_IRGRP | S_IXGRP |
        S_IROTH | S_IXOTH;
    vap->va_type = VDIR;
    /*
     * We live in the now (for atime).
     */
    gethrestime(&now);
    vap->va_atime = now;
}

/*ARGSUSED*/
static int
zfsctl_common_fid(vnode_t *vp, fid_t *fidp, caller_context_t *ct)
{
    zfsvfs_t    *zfsvfs = vp->v_vfsp->vfs_data;
    zfsctl_node_t   *zcp = vp->v_data;
    uint64_t    object = zcp->zc_id;
    zfid_short_t    *zfid;
    int     i;

    ZFS_ENTER(zfsvfs);

    if (fidp->fid_len < SHORT_FID_LEN) {
        fidp->fid_len = SHORT_FID_LEN;
        ZFS_EXIT(zfsvfs);
        return (SET_ERROR(ENOSPC));
    }

    zfid = (zfid_short_t *)fidp;

    zfid->zf_len = SHORT_FID_LEN;

    for (i = 0; i < sizeof (zfid->zf_object); i++)
        zfid->zf_object[i] = (uint8_t)(object >> (8 * i));

    /* .zfs znodes always have a generation number of 0 */
    for (i = 0; i < sizeof (zfid->zf_gen); i++)
        zfid->zf_gen[i] = 0;

    ZFS_EXIT(zfsvfs);
    return (0);
}


/*ARGSUSED*/
static int
zfsctl_shares_fid(vnode_t *vp, fid_t *fidp, caller_context_t *ct)
{
    zfsvfs_t    *zfsvfs = vp->v_vfsp->vfs_data;
    znode_t     *dzp;
    int     error;

    ZFS_ENTER(zfsvfs);

    if (zfsvfs->z_shares_dir == 0) {
        ZFS_EXIT(zfsvfs);
        return (SET_ERROR(ENOTSUP));
    }

    if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0) {
        error = VOP_FID(ZTOV(dzp), fidp, ct);
        VN_RELE(ZTOV(dzp));
    }

    ZFS_EXIT(zfsvfs);
    return (error);
}
/*
 * .zfs inode namespace
 *
 * We need to generate unique inode numbers for all files and directories
 * within the .zfs pseudo-filesystem.  We use the following scheme:
 *
 *  ENTRY           ZFSCTL_INODE
 *  .zfs            1
 *  .zfs/snapshot       2
 *  .zfs/snapshot/<snap>    objectid(snap)
 */

#define ZFSCTL_INO_SNAP(id) (id)

/*
 * Get root directory attributes.
 */
/* ARGSUSED */
static int
zfsctl_root_getattr(vnode_t *vp, vattr_t *vap, int flags, cred_t *cr,
    caller_context_t *ct)
{
    zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;
    zfsctl_node_t *zcp = vp->v_data;

    ZFS_ENTER(zfsvfs);
    vap->va_nodeid = ZFSCTL_INO_ROOT;
    vap->va_nlink = vap->va_size = NROOT_ENTRIES;
    vap->va_mtime = vap->va_ctime = zcp->zc_cmtime;

    zfsctl_common_getattr(vp, vap);
    ZFS_EXIT(zfsvfs);

    return (0);
}

/*
 * Special case the handling of "..".
 */
/* ARGSUSED */
int
zfsctl_root_lookup(vnode_t *dvp, char *nm, vnode_t **vpp, pathname_t *pnp,
    int flags, vnode_t *rdir, cred_t *cr, caller_context_t *ct,
    int *direntflags, pathname_t *realpnp)
{
    zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
    int err;

    /*
     * No extended attributes allowed under .zfs
     */
    if (flags & LOOKUP_XATTR)
        return (SET_ERROR(EINVAL));

    ZFS_ENTER(zfsvfs);

    if (strcmp(nm, "..") == 0) {
        err = VFS_ROOT(dvp->v_vfsp, vpp);
    } else {
        err = gfs_vop_lookup(dvp, nm, vpp, pnp, flags, rdir,
            cr, ct, direntflags, realpnp);
    }

    ZFS_EXIT(zfsvfs);

    return (err);
}

static int
zfsctl_pathconf(vnode_t *vp, int cmd, ulong_t *valp, cred_t *cr,
    caller_context_t *ct)
{
    /*
     * We only care about ACL_ENABLED so that libsec can
     * display ACL correctly and not default to POSIX draft.
     */
    if (cmd == _PC_ACL_ENABLED) {
        *valp = _ACL_ACE_ENABLED;
        return (0);
    }

    return (fs_pathconf(vp, cmd, valp, cr, ct));
}

static const fs_operation_def_t zfsctl_tops_root[] = {
    { VOPNAME_OPEN,     { .vop_open = zfsctl_common_open }  },
    { VOPNAME_CLOSE,    { .vop_close = zfsctl_common_close }    },
    { VOPNAME_IOCTL,    { .error = fs_inval }           },
    { VOPNAME_GETATTR,  { .vop_getattr = zfsctl_root_getattr }  },
    { VOPNAME_ACCESS,   { .vop_access = zfsctl_common_access }  },
    { VOPNAME_READDIR,  { .vop_readdir = gfs_vop_readdir }  },
    { VOPNAME_LOOKUP,   { .vop_lookup = zfsctl_root_lookup }    },
    { VOPNAME_SEEK,     { .vop_seek = fs_seek }         },
    { VOPNAME_INACTIVE, { .vop_inactive = gfs_vop_inactive }    },
    { VOPNAME_PATHCONF, { .vop_pathconf = zfsctl_pathconf } },
    { VOPNAME_FID,      { .vop_fid = zfsctl_common_fid  }   },
    { NULL }
};

/*
 * Gets the full dataset name that corresponds to the given snapshot name
 * Example:
 *  zfsctl_snapshot_zname("snap1") -> "mypool/myfs@snap1"
 */
static int
zfsctl_snapshot_zname(vnode_t *vp, const char *name, int len, char *zname)
{
    objset_t *os = ((zfsvfs_t *)((vp)->v_vfsp->vfs_data))->z_os;

    if (zfs_component_namecheck(name, NULL, NULL) != 0)
        return (SET_ERROR(EILSEQ));
    dmu_objset_name(os, zname);
    if (strlen(zname) + 1 + strlen(name) >= len)
        return (SET_ERROR(ENAMETOOLONG));
    (void) strcat(zname, "@");
    (void) strcat(zname, name);
    return (0);
}

static int
zfsctl_unmount_snap(zfs_snapentry_t *sep, int fflags, cred_t *cr)
{
    vnode_t *svp = sep->se_root;
    int error;

    ASSERT(vn_ismntpt(svp));

    /* this will be dropped by dounmount() */
    if ((error = vn_vfswlock(svp)) != 0)
        return (error);

    VN_HOLD(svp);
    error = dounmount(vn_mountedvfs(svp), fflags, cr);
    if (error) {
        VN_RELE(svp);
        return (error);
    }

    /*
     * We can't use VN_RELE(), as that will try to invoke
     * zfsctl_snapdir_inactive(), which would cause us to destroy
     * the sd_lock mutex held by our caller.
     */
    ASSERT(svp->v_count == 1);
    gfs_vop_inactive(svp, cr, NULL);

    kmem_free(sep->se_name, strlen(sep->se_name) + 1);
    kmem_free(sep, sizeof (zfs_snapentry_t));

    return (0);
}

static void
zfsctl_rename_snap(zfsctl_snapdir_t *sdp, zfs_snapentry_t *sep, const char *nm)
{
    avl_index_t where;
    vfs_t *vfsp;
    refstr_t *pathref;
    char newpath[MAXNAMELEN];
    char *tail;

    ASSERT(MUTEX_HELD(&sdp->sd_lock));
    ASSERT(sep != NULL);

    vfsp = vn_mountedvfs(sep->se_root);
    ASSERT(vfsp != NULL);

    vfs_lock_wait(vfsp);

    /*
     * Change the name in the AVL tree.
     */
    avl_remove(&sdp->sd_snaps, sep);
    kmem_free(sep->se_name, strlen(sep->se_name) + 1);
    sep->se_name = kmem_alloc(strlen(nm) + 1, KM_SLEEP);
    (void) strcpy(sep->se_name, nm);
    VERIFY(avl_find(&sdp->sd_snaps, sep, &where) == NULL);
    avl_insert(&sdp->sd_snaps, sep, where);

    /*
     * Change the current mountpoint info:
     *  - update the tail of the mntpoint path
     *  - update the tail of the resource path
     */
    pathref = vfs_getmntpoint(vfsp);
    (void) strncpy(newpath, refstr_value(pathref), sizeof (newpath));
    VERIFY((tail = strrchr(newpath, '/')) != NULL);
    *(tail+1) = '\0';
    ASSERT3U(strlen(newpath) + strlen(nm), <, sizeof (newpath));
    (void) strcat(newpath, nm);
    refstr_rele(pathref);
    vfs_setmntpoint(vfsp, newpath, 0);

    pathref = vfs_getresource(vfsp);
    (void) strncpy(newpath, refstr_value(pathref), sizeof (newpath));
    VERIFY((tail = strrchr(newpath, '@')) != NULL);
    *(tail+1) = '\0';
    ASSERT3U(strlen(newpath) + strlen(nm), <, sizeof (newpath));
    (void) strcat(newpath, nm);
    refstr_rele(pathref);
    vfs_setresource(vfsp, newpath, 0);

    vfs_unlock(vfsp);
}

/*ARGSUSED*/
static int
zfsctl_snapdir_rename(vnode_t *sdvp, char *snm, vnode_t *tdvp, char *tnm,
    cred_t *cr, caller_context_t *ct, int flags)
{
    zfsctl_snapdir_t *sdp = sdvp->v_data;
    zfs_snapentry_t search, *sep;
    zfsvfs_t *zfsvfs;
    avl_index_t where;
    char from[ZFS_MAX_DATASET_NAME_LEN], to[ZFS_MAX_DATASET_NAME_LEN];
    char real[ZFS_MAX_DATASET_NAME_LEN], fsname[ZFS_MAX_DATASET_NAME_LEN];
    int err;

    zfsvfs = sdvp->v_vfsp->vfs_data;
    ZFS_ENTER(zfsvfs);

    if ((flags & FIGNORECASE) || zfsvfs->z_case == ZFS_CASE_INSENSITIVE) {
        err = dmu_snapshot_realname(zfsvfs->z_os, snm, real,
            sizeof (real), NULL);
        if (err == 0) {
            snm = real;
        } else if (err != ENOTSUP) {
            ZFS_EXIT(zfsvfs);
            return (err);
        }
    }

    ZFS_EXIT(zfsvfs);

    dmu_objset_name(zfsvfs->z_os, fsname);

    err = zfsctl_snapshot_zname(sdvp, snm, sizeof (from), from);
    if (err == 0)
        err = zfsctl_snapshot_zname(tdvp, tnm, sizeof (to), to);
    if (err == 0)
        err = zfs_secpolicy_rename_perms(from, to, cr);
    if (err != 0)
        return (err);

    /*
     * Cannot move snapshots out of the snapdir.
     */
    if (sdvp != tdvp)
        return (SET_ERROR(EINVAL));

    if (strcmp(snm, tnm) == 0)
        return (0);

    mutex_enter(&sdp->sd_lock);

    search.se_name = (char *)snm;
    if ((sep = avl_find(&sdp->sd_snaps, &search, &where)) == NULL) {
        mutex_exit(&sdp->sd_lock);
        return (SET_ERROR(ENOENT));
    }

    err = dsl_dataset_rename_snapshot(fsname, snm, tnm, B_FALSE);
    if (err == 0)
        zfsctl_rename_snap(sdp, sep, tnm);

    mutex_exit(&sdp->sd_lock);

    return (err);
}

/* ARGSUSED */
static int
zfsctl_snapdir_remove(vnode_t *dvp, char *name, vnode_t *cwd, cred_t *cr,
    caller_context_t *ct, int flags)
{
    zfsctl_snapdir_t *sdp = dvp->v_data;
    zfs_snapentry_t *sep;
    zfs_snapentry_t search;
    zfsvfs_t *zfsvfs;
    char snapname[ZFS_MAX_DATASET_NAME_LEN];
    char real[ZFS_MAX_DATASET_NAME_LEN];
    int err;

    zfsvfs = dvp->v_vfsp->vfs_data;
    ZFS_ENTER(zfsvfs);

    if ((flags & FIGNORECASE) || zfsvfs->z_case == ZFS_CASE_INSENSITIVE) {

        err = dmu_snapshot_realname(zfsvfs->z_os, name, real,
            sizeof (real), NULL);
        if (err == 0) {
            name = real;
        } else if (err != ENOTSUP) {
            ZFS_EXIT(zfsvfs);
            return (err);
        }
    }

    ZFS_EXIT(zfsvfs);

    err = zfsctl_snapshot_zname(dvp, name, sizeof (snapname), snapname);
    if (err == 0)
        err = zfs_secpolicy_destroy_perms(snapname, cr);
    if (err != 0)
        return (err);

    mutex_enter(&sdp->sd_lock);

    search.se_name = name;
    sep = avl_find(&sdp->sd_snaps, &search, NULL);
    if (sep) {
        avl_remove(&sdp->sd_snaps, sep);
        err = zfsctl_unmount_snap(sep, MS_FORCE, cr);
        if (err != 0)
            avl_add(&sdp->sd_snaps, sep);
        else
            err = dsl_destroy_snapshot(snapname, B_FALSE);
    } else {
        err = SET_ERROR(ENOENT);
    }

    mutex_exit(&sdp->sd_lock);

    return (err);
}

/*
 * This creates a snapshot under '.zfs/snapshot'.
 */
/* ARGSUSED */
static int
zfsctl_snapdir_mkdir(vnode_t *dvp, char *dirname, vattr_t *vap, vnode_t  **vpp,
    cred_t *cr, caller_context_t *cc, int flags, vsecattr_t *vsecp)
{
    zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
    char name[ZFS_MAX_DATASET_NAME_LEN];
    int err;
    static enum symfollow follow = NO_FOLLOW;
    static enum uio_seg seg = UIO_SYSSPACE;

    if (zfs_component_namecheck(dirname, NULL, NULL) != 0)
        return (SET_ERROR(EILSEQ));

    dmu_objset_name(zfsvfs->z_os, name);

    *vpp = NULL;

    err = zfs_secpolicy_snapshot_perms(name, cr);
    if (err != 0)
        return (err);

    if (err == 0) {
        err = dmu_objset_snapshot_one(name, dirname);
        if (err != 0)
            return (err);
        err = lookupnameat(dirname, seg, follow, NULL, vpp, dvp);
    }

    return (err);
}

/*
 * Lookup entry point for the 'snapshot' directory.  Try to open the
 * snapshot if it exist, creating the pseudo filesystem vnode as necessary.
 * Perform a mount of the associated dataset on top of the vnode.
 */
/* ARGSUSED */
static int
zfsctl_snapdir_lookup(vnode_t *dvp, char *nm, vnode_t **vpp, pathname_t *pnp,
    int flags, vnode_t *rdir, cred_t *cr, caller_context_t *ct,
    int *direntflags, pathname_t *realpnp)
{
    zfsctl_snapdir_t *sdp = dvp->v_data;
    objset_t *snap;
    char snapname[ZFS_MAX_DATASET_NAME_LEN];
    char real[ZFS_MAX_DATASET_NAME_LEN];
    char *mountpoint;
    zfs_snapentry_t *sep, search;
    struct mounta margs;
    vfs_t *vfsp;
    size_t mountpoint_len;
    avl_index_t where;
    zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
    int err;

    /*
     * No extended attributes allowed under .zfs
     */
    if (flags & LOOKUP_XATTR)
        return (SET_ERROR(EINVAL));

    ASSERT(dvp->v_type == VDIR);

    /*
     * If we get a recursive call, that means we got called
     * from the domount() code while it was trying to look up the
     * spec (which looks like a local path for zfs).  We need to
     * add some flag to domount() to tell it not to do this lookup.
     */
    if (MUTEX_HELD(&sdp->sd_lock))
        return (SET_ERROR(ENOENT));

    ZFS_ENTER(zfsvfs);

    if (gfs_lookup_dot(vpp, dvp, zfsvfs->z_ctldir, nm) == 0) {
        ZFS_EXIT(zfsvfs);
        return (0);
    }

    if (flags & FIGNORECASE) {
        boolean_t conflict = B_FALSE;

        err = dmu_snapshot_realname(zfsvfs->z_os, nm, real,
            sizeof (real), &conflict);
        if (err == 0) {
            nm = real;
        } else if (err != ENOTSUP) {
            ZFS_EXIT(zfsvfs);
            return (err);
        }
        if (realpnp)
            (void) strlcpy(realpnp->pn_buf, nm,
                realpnp->pn_bufsize);
        if (conflict && direntflags)
            *direntflags = ED_CASE_CONFLICT;
    }

    mutex_enter(&sdp->sd_lock);
    search.se_name = (char *)nm;
    if ((sep = avl_find(&sdp->sd_snaps, &search, &where)) != NULL) {
        *vpp = sep->se_root;
        VN_HOLD(*vpp);
        err = traverse(vpp);
        if (err != 0) {
            VN_RELE(*vpp);
            *vpp = NULL;
        } else if (*vpp == sep->se_root) {
            /*
             * The snapshot was unmounted behind our backs,
             * try to remount it.
             */
            goto domount;
        } else {
            /*
             * VROOT was set during the traverse call.  We need
             * to clear it since we're pretending to be part
             * of our parent's vfs.
             */
            (*vpp)->v_flag &= ~VROOT;
        }
        mutex_exit(&sdp->sd_lock);
        ZFS_EXIT(zfsvfs);
        return (err);
    }

    /*
     * The requested snapshot is not currently mounted, look it up.
     */
    err = zfsctl_snapshot_zname(dvp, nm, sizeof (snapname), snapname);
    if (err != 0) {
        mutex_exit(&sdp->sd_lock);
        ZFS_EXIT(zfsvfs);
        /*
         * handle "ls *" or "?" in a graceful manner,
         * forcing EILSEQ to ENOENT.
         * Since shell ultimately passes "*" or "?" as name to lookup
         */
        return (err == EILSEQ ? ENOENT : err);
    }
    if (dmu_objset_hold(snapname, FTAG, &snap) != 0) {
        mutex_exit(&sdp->sd_lock);
        ZFS_EXIT(zfsvfs);
        return (SET_ERROR(ENOENT));
    }

    sep = kmem_alloc(sizeof (zfs_snapentry_t), KM_SLEEP);
    sep->se_name = kmem_alloc(strlen(nm) + 1, KM_SLEEP);
    (void) strcpy(sep->se_name, nm);
    *vpp = sep->se_root = zfsctl_snapshot_mknode(dvp, dmu_objset_id(snap));
    avl_insert(&sdp->sd_snaps, sep, where);

    dmu_objset_rele(snap, FTAG);
domount:
    mountpoint_len = strlen(refstr_value(dvp->v_vfsp->vfs_mntpt)) +
        strlen("/.zfs/snapshot/") + strlen(nm) + 1;
    mountpoint = kmem_alloc(mountpoint_len, KM_SLEEP);
    (void) snprintf(mountpoint, mountpoint_len, "%s/.zfs/snapshot/%s",
        refstr_value(dvp->v_vfsp->vfs_mntpt), nm);

    margs.spec = snapname;
    margs.dir = mountpoint;
    margs.flags = MS_SYSSPACE | MS_NOMNTTAB;
    margs.fstype = "zfs";
    margs.dataptr = NULL;
    margs.datalen = 0;
    margs.optptr = NULL;
    margs.optlen = 0;

    err = domount("zfs", &margs, *vpp, kcred, &vfsp);
    kmem_free(mountpoint, mountpoint_len);

    if (err == 0) {
        /*
         * Return the mounted root rather than the covered mount point.
         * Takes the GFS vnode at .zfs/snapshot/<snapname> and returns
         * the ZFS vnode mounted on top of the GFS node.  This ZFS
         * vnode is the root of the newly created vfsp.
         */
        VFS_RELE(vfsp);
        err = traverse(vpp);
    }

    if (err == 0) {
        /*
         * Fix up the root vnode mounted on .zfs/snapshot/<snapname>.
         *
         * This is where we lie about our v_vfsp in order to
         * make .zfs/snapshot/<snapname> accessible over NFS
         * without requiring manual mounts of <snapname>.
         */
        ASSERT(VTOZ(*vpp)->z_zfsvfs != zfsvfs);
        VTOZ(*vpp)->z_zfsvfs->z_parent = zfsvfs;
        (*vpp)->v_vfsp = zfsvfs->z_vfs;
        (*vpp)->v_flag &= ~VROOT;
    }
    mutex_exit(&sdp->sd_lock);
    ZFS_EXIT(zfsvfs);

    /*
     * If we had an error, drop our hold on the vnode and
     * zfsctl_snapshot_inactive() will clean up.
     */
    if (err != 0) {
        VN_RELE(*vpp);
        *vpp = NULL;
    }
    return (err);
}

/* ARGSUSED */
static int
zfsctl_shares_lookup(vnode_t *dvp, char *nm, vnode_t **vpp, pathname_t *pnp,
    int flags, vnode_t *rdir, cred_t *cr, caller_context_t *ct,
    int *direntflags, pathname_t *realpnp)
{
    zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
    znode_t *dzp;
    int error;

    ZFS_ENTER(zfsvfs);

    if (gfs_lookup_dot(vpp, dvp, zfsvfs->z_ctldir, nm) == 0) {
        ZFS_EXIT(zfsvfs);
        return (0);
    }

    if (zfsvfs->z_shares_dir == 0) {
        ZFS_EXIT(zfsvfs);
        return (SET_ERROR(ENOTSUP));
    }
    if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0) {
        error = VOP_LOOKUP(ZTOV(dzp), nm, vpp, pnp,
            flags, rdir, cr, ct, direntflags, realpnp);
        VN_RELE(ZTOV(dzp));
    }

    ZFS_EXIT(zfsvfs);

    return (error);
}

/* ARGSUSED */
static int
zfsctl_snapdir_readdir_cb(vnode_t *vp, void *dp, int *eofp,
    offset_t *offp, offset_t *nextp, void *data, int flags)
{
    zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;
    char snapname[ZFS_MAX_DATASET_NAME_LEN];
    uint64_t id, cookie;
    boolean_t case_conflict;
    int error;

    ZFS_ENTER(zfsvfs);

    cookie = *offp;
    dsl_pool_config_enter(dmu_objset_pool(zfsvfs->z_os), FTAG);
    error = dmu_snapshot_list_next(zfsvfs->z_os,
        sizeof (snapname), snapname, &id, &cookie, &case_conflict);
    dsl_pool_config_exit(dmu_objset_pool(zfsvfs->z_os), FTAG);
    if (error) {
        ZFS_EXIT(zfsvfs);
        if (error == ENOENT) {
            *eofp = 1;
            return (0);
        }
        return (error);
    }

    if (flags & V_RDDIR_ENTFLAGS) {
        edirent_t *eodp = dp;

        (void) strcpy(eodp->ed_name, snapname);
        eodp->ed_ino = ZFSCTL_INO_SNAP(id);
        eodp->ed_eflags = case_conflict ? ED_CASE_CONFLICT : 0;
    } else {
        struct dirent64 *odp = dp;

        (void) strcpy(odp->d_name, snapname);
        odp->d_ino = ZFSCTL_INO_SNAP(id);
    }
    *nextp = cookie;

    ZFS_EXIT(zfsvfs);

    return (0);
}

/* ARGSUSED */
static int
zfsctl_shares_readdir(vnode_t *vp, uio_t *uiop, cred_t *cr, int *eofp,
    caller_context_t *ct, int flags)
{
    zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;
    znode_t *dzp;
    int error;

    ZFS_ENTER(zfsvfs);

    if (zfsvfs->z_shares_dir == 0) {
        ZFS_EXIT(zfsvfs);
        return (SET_ERROR(ENOTSUP));
    }
    if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0) {
        error = VOP_READDIR(ZTOV(dzp), uiop, cr, eofp, ct, flags);
        VN_RELE(ZTOV(dzp));
    } else {
        *eofp = 1;
        error = SET_ERROR(ENOENT);
    }

    ZFS_EXIT(zfsvfs);
    return (error);
}

/*
 * pvp is the '.zfs' directory (zfsctl_node_t).
 *
 * Creates vp, which is '.zfs/snapshot' (zfsctl_snapdir_t).
 *
 * This function is the callback to create a GFS vnode for '.zfs/snapshot'
 * when a lookup is performed on .zfs for "snapshot".
 */
vnode_t *
zfsctl_mknode_snapdir(vnode_t *pvp)
{
    vnode_t *vp;
    zfsctl_snapdir_t *sdp;

    vp = gfs_dir_create(sizeof (zfsctl_snapdir_t), pvp,
        zfsctl_ops_snapdir, NULL, NULL, MAXNAMELEN,
        zfsctl_snapdir_readdir_cb, NULL);
    sdp = vp->v_data;
    sdp->sd_node.zc_id = ZFSCTL_INO_SNAPDIR;
    sdp->sd_node.zc_cmtime = ((zfsctl_node_t *)pvp->v_data)->zc_cmtime;
    mutex_init(&sdp->sd_lock, NULL, MUTEX_DEFAULT, NULL);
    avl_create(&sdp->sd_snaps, snapentry_compare,
        sizeof (zfs_snapentry_t), offsetof(zfs_snapentry_t, se_node));
    return (vp);
}

vnode_t *
zfsctl_mknode_shares(vnode_t *pvp)
{
    vnode_t *vp;
    zfsctl_node_t *sdp;

    vp = gfs_dir_create(sizeof (zfsctl_node_t), pvp,
        zfsctl_ops_shares, NULL, NULL, MAXNAMELEN,
        NULL, NULL);
    sdp = vp->v_data;
    sdp->zc_cmtime = ((zfsctl_node_t *)pvp->v_data)->zc_cmtime;
    return (vp);

}

/* ARGSUSED */
static int
zfsctl_shares_getattr(vnode_t *vp, vattr_t *vap, int flags, cred_t *cr,
    caller_context_t *ct)
{
    zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;
    znode_t *dzp;
    int error;

    ZFS_ENTER(zfsvfs);
    if (zfsvfs->z_shares_dir == 0) {
        ZFS_EXIT(zfsvfs);
        return (SET_ERROR(ENOTSUP));
    }
    if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0) {
        error = VOP_GETATTR(ZTOV(dzp), vap, flags, cr, ct);
        VN_RELE(ZTOV(dzp));
    }
    ZFS_EXIT(zfsvfs);
    return (error);


}

/* ARGSUSED */
static int
zfsctl_snapdir_getattr(vnode_t *vp, vattr_t *vap, int flags, cred_t *cr,
    caller_context_t *ct)
{
    zfsvfs_t *zfsvfs = vp->v_vfsp->vfs_data;
    zfsctl_snapdir_t *sdp = vp->v_data;

    ZFS_ENTER(zfsvfs);
    zfsctl_common_getattr(vp, vap);
    vap->va_nodeid = gfs_file_inode(vp);
    vap->va_nlink = vap->va_size = avl_numnodes(&sdp->sd_snaps) + 2;
    vap->va_ctime = vap->va_mtime = dmu_objset_snap_cmtime(zfsvfs->z_os);
    ZFS_EXIT(zfsvfs);

    return (0);
}

/* ARGSUSED */
static void
zfsctl_snapdir_inactive(vnode_t *vp, cred_t *cr, caller_context_t *ct)
{
    zfsctl_snapdir_t *sdp = vp->v_data;
    void *private;

    private = gfs_dir_inactive(vp);
    if (private != NULL) {
        ASSERT(avl_numnodes(&sdp->sd_snaps) == 0);
        mutex_destroy(&sdp->sd_lock);
        avl_destroy(&sdp->sd_snaps);
        kmem_free(private, sizeof (zfsctl_snapdir_t));
    }
}

static const fs_operation_def_t zfsctl_tops_snapdir[] = {
    { VOPNAME_OPEN,     { .vop_open = zfsctl_common_open }  },
    { VOPNAME_CLOSE,    { .vop_close = zfsctl_common_close }    },
    { VOPNAME_IOCTL,    { .error = fs_inval }           },
    { VOPNAME_GETATTR,  { .vop_getattr = zfsctl_snapdir_getattr } },
    { VOPNAME_ACCESS,   { .vop_access = zfsctl_common_access }  },
    { VOPNAME_RENAME,   { .vop_rename = zfsctl_snapdir_rename } },
    { VOPNAME_RMDIR,    { .vop_rmdir = zfsctl_snapdir_remove }  },
    { VOPNAME_MKDIR,    { .vop_mkdir = zfsctl_snapdir_mkdir }   },
    { VOPNAME_READDIR,  { .vop_readdir = gfs_vop_readdir }  },
    { VOPNAME_LOOKUP,   { .vop_lookup = zfsctl_snapdir_lookup } },
    { VOPNAME_SEEK,     { .vop_seek = fs_seek }         },
    { VOPNAME_INACTIVE, { .vop_inactive = zfsctl_snapdir_inactive } },
    { VOPNAME_FID,      { .vop_fid = zfsctl_common_fid }    },
    { NULL }
};

static const fs_operation_def_t zfsctl_tops_shares[] = {
    { VOPNAME_OPEN,     { .vop_open = zfsctl_common_open }  },
    { VOPNAME_CLOSE,    { .vop_close = zfsctl_common_close }    },
    { VOPNAME_IOCTL,    { .error = fs_inval }           },
    { VOPNAME_GETATTR,  { .vop_getattr = zfsctl_shares_getattr } },
    { VOPNAME_ACCESS,   { .vop_access = zfsctl_common_access }  },
    { VOPNAME_READDIR,  { .vop_readdir = zfsctl_shares_readdir } },
    { VOPNAME_LOOKUP,   { .vop_lookup = zfsctl_shares_lookup }  },
    { VOPNAME_SEEK,     { .vop_seek = fs_seek }         },
    { VOPNAME_INACTIVE, { .vop_inactive = gfs_vop_inactive } },
    { VOPNAME_FID,      { .vop_fid = zfsctl_shares_fid } },
    { NULL }
};

/*
 * pvp is the GFS vnode '.zfs/snapshot'.
 *
 * This creates a GFS node under '.zfs/snapshot' representing each
 * snapshot.  This newly created GFS node is what we mount snapshot
 * vfs_t's ontop of.
 */
static vnode_t *
zfsctl_snapshot_mknode(vnode_t *pvp, uint64_t objset)
{
    vnode_t *vp;
    zfsctl_node_t *zcp;

    vp = gfs_dir_create(sizeof (zfsctl_node_t), pvp,
        zfsctl_ops_snapshot, NULL, NULL, MAXNAMELEN, NULL, NULL);
    zcp = vp->v_data;
    zcp->zc_id = objset;

    return (vp);
}

static void
zfsctl_snapshot_inactive(vnode_t *vp, cred_t *cr, caller_context_t *ct)
{
    zfsctl_snapdir_t *sdp;
    zfs_snapentry_t *sep, *next;
    vnode_t *dvp;

    VERIFY(gfs_dir_lookup(vp, "..", &dvp, cr, 0, NULL, NULL) == 0);
    sdp = dvp->v_data;

    mutex_enter(&sdp->sd_lock);

    mutex_enter(&vp->v_lock);
    if (vp->v_count > 1) {
        vp->v_count--;
        mutex_exit(&vp->v_lock);
        mutex_exit(&sdp->sd_lock);
        VN_RELE(dvp);
        return;
    }
    mutex_exit(&vp->v_lock);
    ASSERT(!vn_ismntpt(vp));

    sep = avl_first(&sdp->sd_snaps);
    while (sep != NULL) {
        next = AVL_NEXT(&sdp->sd_snaps, sep);

        if (sep->se_root == vp) {
            avl_remove(&sdp->sd_snaps, sep);
            kmem_free(sep->se_name, strlen(sep->se_name) + 1);
            kmem_free(sep, sizeof (zfs_snapentry_t));
            break;
        }
        sep = next;
    }
    ASSERT(sep != NULL);

    mutex_exit(&sdp->sd_lock);
    VN_RELE(dvp);

    /*
     * Dispose of the vnode for the snapshot mount point.
     * This is safe to do because once this entry has been removed
     * from the AVL tree, it can't be found again, so cannot become
     * "active".  If we lookup the same name again we will end up
     * creating a new vnode.
     */
    gfs_vop_inactive(vp, cr, ct);
}


/*
 * These VP's should never see the light of day.  They should always
 * be covered.
 */
static const fs_operation_def_t zfsctl_tops_snapshot[] = {
    VOPNAME_INACTIVE, { .vop_inactive =  zfsctl_snapshot_inactive },
    NULL, NULL
};

int
zfsctl_lookup_objset(vfs_t *vfsp, uint64_t objsetid, zfsvfs_t **zfsvfsp)
{
    zfsvfs_t *zfsvfs = vfsp->vfs_data;
    vnode_t *dvp, *vp;
    zfsctl_snapdir_t *sdp;
    zfsctl_node_t *zcp;
    zfs_snapentry_t *sep;
    int error;

    ASSERT(zfsvfs->z_ctldir != NULL);
    error = zfsctl_root_lookup(zfsvfs->z_ctldir, "snapshot", &dvp,
        NULL, 0, NULL, kcred, NULL, NULL, NULL);
    if (error != 0)
        return (error);
    sdp = dvp->v_data;

    mutex_enter(&sdp->sd_lock);
    sep = avl_first(&sdp->sd_snaps);
    while (sep != NULL) {
        vp = sep->se_root;
        zcp = vp->v_data;
        if (zcp->zc_id == objsetid)
            break;

        sep = AVL_NEXT(&sdp->sd_snaps, sep);
    }

    if (sep != NULL) {
        VN_HOLD(vp);
        /*
         * Return the mounted root rather than the covered mount point.
         * Takes the GFS vnode at .zfs/snapshot/<snapshot objsetid>
         * and returns the ZFS vnode mounted on top of the GFS node.
         * This ZFS vnode is the root of the vfs for objset 'objsetid'.
         */
        error = traverse(&vp);
        if (error == 0) {
            if (vp == sep->se_root)
                error = SET_ERROR(EINVAL);
            else
                *zfsvfsp = VTOZ(vp)->z_zfsvfs;
        }
        mutex_exit(&sdp->sd_lock);
        VN_RELE(vp);
    } else {
        error = SET_ERROR(EINVAL);
        mutex_exit(&sdp->sd_lock);
    }

    VN_RELE(dvp);

    return (error);
}

/*
 * Unmount any snapshots for the given filesystem.  This is called from
 * zfs_umount() - if we have a ctldir, then go through and unmount all the
 * snapshots.
 */
int
zfsctl_umount_snapshots(vfs_t *vfsp, int fflags, cred_t *cr)
{
    zfsvfs_t *zfsvfs = vfsp->vfs_data;
    vnode_t *dvp;
    zfsctl_snapdir_t *sdp;
    zfs_snapentry_t *sep, *next;
    int error;

    ASSERT(zfsvfs->z_ctldir != NULL);
    error = zfsctl_root_lookup(zfsvfs->z_ctldir, "snapshot", &dvp,
        NULL, 0, NULL, cr, NULL, NULL, NULL);
    if (error != 0)
        return (error);
    sdp = dvp->v_data;

    mutex_enter(&sdp->sd_lock);

    sep = avl_first(&sdp->sd_snaps);
    while (sep != NULL) {
        next = AVL_NEXT(&sdp->sd_snaps, sep);

        /*
         * If this snapshot is not mounted, then it must
         * have just been unmounted by somebody else, and
         * will be cleaned up by zfsctl_snapdir_inactive().
         */
        if (vn_ismntpt(sep->se_root)) {
            avl_remove(&sdp->sd_snaps, sep);
            error = zfsctl_unmount_snap(sep, fflags, cr);
            if (error) {
                avl_add(&sdp->sd_snaps, sep);
                break;
            }
        }
        sep = next;
    }

    mutex_exit(&sdp->sd_lock);
    VN_RELE(dvp);

    return (error);
}