zfs_ctldir.c

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/*
 * 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) 2011 Pawel Jakub Dawidek <pawel@dawidek.net>.
 * All rights reserved.
 */

#include <sys/zfs_context.h>
#include <sys/zfs_ctldir.h>
#include <sys/zfs_ioctl.h>
#include <sys/zfs_vfsops.h>
#include <sys/namei.h>
#include <sys/gfs.h>
#include <sys/stat.h>
#include <sys/dmu.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;      
} 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);
}

#ifdef sun
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[];
#else   /* !sun */
static struct vop_vector zfsctl_ops_root;
static struct vop_vector zfsctl_ops_snapdir;
static struct vop_vector zfsctl_ops_snapshot;
static struct vop_vector zfsctl_ops_shares;
static struct vop_vector zfsctl_ops_shares_dir;
#endif  /* !sun */

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 *);

#ifdef sun
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 }
};
#endif  /* sun */

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)


void
zfsctl_init(void)
{
#ifdef sun
        VERIFY(gfs_make_opsvec(zfsctl_opsvec) == 0);
#endif
}

void
zfsctl_fini(void)
{
#ifdef sun
        /*
         * 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;
#endif  /* sun */
}

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));

}

/* 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);
}

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, LK_EXCLUSIVE, &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_URELE(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_vflag &= ~VV_ROOT;

        zfsvfs->z_ctldir = vp;

        VOP_UNLOCK(vp, 0);
}

void
zfsctl_destroy(zfsvfs_t *zfsvfs)
{
        VN_RELE(zfsvfs->z_ctldir);
        zfsvfs->z_ctldir = NULL;
}

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);
}

/* ARGSUSED */
static int
zfsctl_common_open(struct vop_open_args *ap)
{
        int flags = ap->a_mode;

        if (flags & FWRITE)
                return (EACCES);

        return (0);
}

/* ARGSUSED */
static int
zfsctl_common_close(struct vop_close_args *ap)
{
        return (0);
}

/* ARGSUSED */
static int
zfsctl_common_access(ap)
        struct vop_access_args /* {
                struct vnode *a_vp;
                accmode_t a_accmode;
                struct ucred *a_cred;
                struct thread *a_td;
        } */ *ap;
{
        accmode_t accmode = ap->a_accmode;

#ifdef TODO
        if (flags & V_ACE_MASK) {
                if (accmode & ACE_ALL_WRITE_PERMS)
                        return (EACCES);
        } else {
#endif
                if (accmode & VWRITE)
                        return (EACCES);
#ifdef TODO
        }
#endif

        return (0);
}

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_mount->mnt_stat.f_fsid.val[0];
        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;
        /* FreeBSD: Reset chflags(2) flags. */
        vap->va_flags = 0;
}

/*ARGSUSED*/
static int
zfsctl_common_fid(ap)
        struct vop_fid_args /* {
                struct vnode *a_vp;
                struct fid *a_fid;
        } */ *ap;
{
        vnode_t         *vp = ap->a_vp;
        fid_t           *fidp = (void *)ap->a_fid;
        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);

        fidp->fid_len = SHORT_FID_LEN;

        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(ap)
        struct vop_fid_args /* {
                struct vnode *a_vp;
                struct fid *a_fid;
        } */ *ap;
{
        vnode_t         *vp = ap->a_vp;
        fid_t           *fidp = (void *)ap->a_fid;
        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 (ENOTSUP);
        }

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

        ZFS_EXIT(zfsvfs);
        return (error);
}

static int
zfsctl_common_reclaim(ap)
        struct vop_reclaim_args /* {
                struct vnode *a_vp;
                struct thread *a_td;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;

        /*
         * Destroy the vm object and flush associated pages.
         */
        vnode_destroy_vobject(vp);
        VI_LOCK(vp);
        vp->v_data = NULL;
        VI_UNLOCK(vp);
        return (0);
}

#define ZFSCTL_INO_SNAP(id)     (id)

/* ARGSUSED */
static int
zfsctl_root_getattr(ap)
        struct vop_getattr_args /* {
                struct vnode *a_vp;
                struct vattr *a_vap;
                struct ucred *a_cred;
        } */ *ap;
{
        struct vnode *vp = ap->a_vp;
        struct vattr *vap = ap->a_vap;
        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;
        vap->va_birthtime = vap->va_ctime;

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

        return (0);
}

/* 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 (EINVAL);

        ZFS_ENTER(zfsvfs);

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

        ZFS_EXIT(zfsvfs);

        return (err);
}

#ifdef sun
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));
}
#endif  /* sun */

#ifdef sun
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 }
};
#endif  /* sun */

/* ARGSUSED */
int
zfsctl_freebsd_root_lookup(ap)
        struct vop_lookup_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
        } */ *ap;
{
        vnode_t *dvp = ap->a_dvp;
        vnode_t **vpp = ap->a_vpp;
        cred_t *cr = ap->a_cnp->cn_cred;
        int flags = ap->a_cnp->cn_flags;
        int nameiop = ap->a_cnp->cn_nameiop;
        char nm[NAME_MAX + 1];
        int err;

        if ((flags & ISLASTCN) && (nameiop == RENAME || nameiop == CREATE))
                return (EOPNOTSUPP);

        ASSERT(ap->a_cnp->cn_namelen < sizeof(nm));
        strlcpy(nm, ap->a_cnp->cn_nameptr, ap->a_cnp->cn_namelen + 1);

        err = zfsctl_root_lookup(dvp, nm, vpp, NULL, 0, NULL, cr, NULL, NULL, NULL);
        if (err == 0 && (nm[0] != '.' || nm[1] != '\0'))
                vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
        return (err);
}

static struct vop_vector zfsctl_ops_root = {
        .vop_default =  &default_vnodeops,
        .vop_open =     zfsctl_common_open,
        .vop_close =    zfsctl_common_close,
        .vop_ioctl =    VOP_EINVAL,
        .vop_getattr =  zfsctl_root_getattr,
        .vop_access =   zfsctl_common_access,
        .vop_readdir =  gfs_vop_readdir,
        .vop_lookup =   zfsctl_freebsd_root_lookup,
        .vop_inactive = gfs_vop_inactive,
        .vop_reclaim =  zfsctl_common_reclaim,
#ifdef TODO
        .vop_pathconf = zfsctl_pathconf,
#endif
        .vop_fid =      zfsctl_common_fid,
};

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 (snapshot_namecheck(name, NULL, NULL) != 0)
                return (EILSEQ);
        dmu_objset_name(os, zname);
        if (strlen(zname) + 1 + strlen(name) >= len)
                return (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);

#ifdef sun
        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);
#else   /* !sun */
        return (dounmount(vn_mountedvfs(svp), fflags, curthread));
#endif  /* !sun */
}

#ifdef sun
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);
}
#endif  /* sun */

#ifdef sun
/*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[MAXNAMELEN], to[MAXNAMELEN];
        char real[MAXNAMELEN];
        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,
                    MAXNAMELEN, NULL);
                if (err == 0) {
                        snm = real;
                } else if (err != ENOTSUP) {
                        ZFS_EXIT(zfsvfs);
                        return (err);
                }
        }

        ZFS_EXIT(zfsvfs);

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

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

        err = dmu_objset_rename(from, to, 0);
        if (err == 0)
                zfsctl_rename_snap(sdp, sep, tnm);

        mutex_exit(&sdp->sd_lock);

        return (err);
}
#endif  /* sun */

#ifdef sun
/* 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[MAXNAMELEN];
        char real[MAXNAMELEN];
        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,
                    MAXNAMELEN, NULL);
                if (err == 0) {
                        name = real;
                } else if (err != ENOTSUP) {
                        ZFS_EXIT(zfsvfs);
                        return (err);
                }
        }

        ZFS_EXIT(zfsvfs);

        err = zfsctl_snapshot_zname(dvp, name, MAXNAMELEN, snapname);
        if (!err)
                err = zfs_secpolicy_destroy_perms(snapname, cr);
        if (err)
                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) {
                        avl_index_t where;

                        if (avl_find(&sdp->sd_snaps, sep, &where) == NULL)
                                avl_insert(&sdp->sd_snaps, sep, where);
                } else
                        err = dmu_objset_destroy(snapname, B_FALSE);
        } else {
                err = ENOENT;
        }

        mutex_exit(&sdp->sd_lock);

        return (err);
}
#endif  /* sun */

/* 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[MAXNAMELEN];
        int err;
        static enum symfollow follow = NO_FOLLOW;
        static enum uio_seg seg = UIO_SYSSPACE;

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

        dmu_objset_name(zfsvfs->z_os, name);

        *vpp = NULL;

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

        if (err == 0) {
                err = dmu_objset_snapshot(name, dirname, NULL, NULL,
                    B_FALSE, B_FALSE, -1);
                if (err)
                        return (err);
                err = lookupnameat(dirname, seg, follow, NULL, vpp, dvp);
        }

        return (err);
}

static int
zfsctl_freebsd_snapdir_mkdir(ap)
        struct vop_mkdir_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
                struct vattr *a_vap;
        } */ *ap;
{

        ASSERT(ap->a_cnp->cn_flags & SAVENAME);

        return (zfsctl_snapdir_mkdir(ap->a_dvp, ap->a_cnp->cn_nameptr, NULL,
            ap->a_vpp, ap->a_cnp->cn_cred, NULL, 0, NULL));
}

/* ARGSUSED */
int
zfsctl_snapdir_lookup(ap)
        struct vop_lookup_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
        } */ *ap;
{
        vnode_t *dvp = ap->a_dvp;
        vnode_t **vpp = ap->a_vpp;
        struct componentname *cnp = ap->a_cnp;
        char nm[NAME_MAX + 1];
        zfsctl_snapdir_t *sdp = dvp->v_data;
        objset_t *snap;
        char snapname[MAXNAMELEN];
        char real[MAXNAMELEN];
        char *mountpoint;
        zfs_snapentry_t *sep, search;
        size_t mountpoint_len;
        avl_index_t where;
        zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
        int err;
        int flags = 0;

        /*
         * No extended attributes allowed under .zfs
         */
        if (flags & LOOKUP_XATTR)
                return (EINVAL);
        ASSERT(ap->a_cnp->cn_namelen < sizeof(nm));
        strlcpy(nm, ap->a_cnp->cn_nameptr, ap->a_cnp->cn_namelen + 1);

        ASSERT(dvp->v_type == VDIR);

        *vpp = NULL;

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

        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, LK_EXCLUSIVE | LK_RETRY);
                if (err) {
                        VN_RELE(*vpp);
                        *vpp = NULL;
                } else if (*vpp == sep->se_root) {
                        /*
                         * The snapshot was unmounted behind our backs,
                         * try to remount it.
                         */
                        VERIFY(zfsctl_snapshot_zname(dvp, nm, MAXNAMELEN, snapname) == 0);
                        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, MAXNAMELEN, snapname);
        if (err) {
                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);
                /* Translate errors and add SAVENAME when needed. */
                if ((cnp->cn_flags & ISLASTCN) && cnp->cn_nameiop == CREATE) {
                        err = EJUSTRETURN;
                        cnp->cn_flags |= SAVENAME;
                } else {
                        err = ENOENT;
                }
                ZFS_EXIT(zfsvfs);
                return (err);
        }

        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));
        VN_HOLD(*vpp);
        avl_insert(&sdp->sd_snaps, sep, where);

        dmu_objset_rele(snap, FTAG);
domount:
        mountpoint_len = strlen(dvp->v_vfsp->mnt_stat.f_mntonname) +
            strlen("/" ZFS_CTLDIR_NAME "/snapshot/") + strlen(nm) + 1;
        mountpoint = kmem_alloc(mountpoint_len, KM_SLEEP);
        (void) snprintf(mountpoint, mountpoint_len,
            "%s/" ZFS_CTLDIR_NAME "/snapshot/%s",
            dvp->v_vfsp->mnt_stat.f_mntonname, nm);
        err = mount_snapshot(curthread, vpp, "zfs", mountpoint, snapname, 0);
        kmem_free(mountpoint, mountpoint_len);
        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;
        }
        mutex_exit(&sdp->sd_lock);
        ZFS_EXIT(zfsvfs);
        if (err != 0)
                *vpp = NULL;
        return (err);
}

/* ARGSUSED */
int
zfsctl_shares_lookup(ap)
        struct vop_lookup_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
        } */ *ap;
{
        vnode_t *dvp = ap->a_dvp;
        vnode_t **vpp = ap->a_vpp;
        struct componentname *cnp = ap->a_cnp;
        zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
        char nm[NAME_MAX + 1];
        znode_t *dzp;
        int error;

        ZFS_ENTER(zfsvfs);

        ASSERT(cnp->cn_namelen < sizeof(nm));
        strlcpy(nm, cnp->cn_nameptr, cnp->cn_namelen + 1);

        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 (ENOTSUP);
        }
        if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0)
                error = VOP_LOOKUP(ZTOV(dzp), vpp, cnp);

        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[MAXNAMELEN];
        uint64_t id, cookie;
        boolean_t case_conflict;
        int error;

        ZFS_ENTER(zfsvfs);

        cookie = *offp;
        error = dmu_snapshot_list_next(zfsvfs->z_os, MAXNAMELEN, snapname, &id,
            &cookie, &case_conflict);
        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(ap)
        struct vop_readdir_args /* {
                struct vnode *a_vp;
                struct uio *a_uio;
                struct ucred *a_cred;
                int *a_eofflag;
                int *a_ncookies;
                u_long **a_cookies;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        uio_t *uiop = ap->a_uio;
        cred_t *cr = ap->a_cred;
        int *eofp = ap->a_eofflag;
        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 (ENOTSUP);
        }
        if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0) {
                vn_lock(ZTOV(dzp), LK_SHARED | LK_RETRY);
                error = VOP_READDIR(ZTOV(dzp), uiop, cr, eofp, ap->a_ncookies, ap->a_cookies);
                VN_URELE(ZTOV(dzp));
        } else {
                *eofp = 1;
                error = ENOENT;
        }

        ZFS_EXIT(zfsvfs);
        return (error);
}

vnode_t *
zfsctl_mknode_snapdir(vnode_t *pvp)
{
        vnode_t *vp;
        zfsctl_snapdir_t *sdp;

        vp = gfs_dir_create(sizeof (zfsctl_snapdir_t), pvp, pvp->v_vfsp,
            &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));
        VOP_UNLOCK(vp, 0);
        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, pvp->v_vfsp,
            &zfsctl_ops_shares, NULL, NULL, MAXNAMELEN,
            NULL, NULL);
        sdp = vp->v_data;
        sdp->zc_cmtime = ((zfsctl_node_t *)pvp->v_data)->zc_cmtime;
        VOP_UNLOCK(vp, 0);
        return (vp);

}

/* ARGSUSED */
static int
zfsctl_shares_getattr(ap)
        struct vop_getattr_args /* {
                struct vnode *a_vp;
                struct vattr *a_vap;
                struct ucred *a_cred;
                struct thread *a_td;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        vattr_t *vap = ap->a_vap;
        cred_t *cr = ap->a_cred;
        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 (ENOTSUP);
        }
        if ((error = zfs_zget(zfsvfs, zfsvfs->z_shares_dir, &dzp)) == 0) {
                vn_lock(ZTOV(dzp), LK_SHARED | LK_RETRY);
                error = VOP_GETATTR(ZTOV(dzp), vap, cr);
                VN_URELE(ZTOV(dzp));
        }
        ZFS_EXIT(zfsvfs);
        return (error);


}

/* ARGSUSED */
static int
zfsctl_snapdir_getattr(ap)
        struct vop_getattr_args /* {
                struct vnode *a_vp;
                struct vattr *a_vap;
                struct ucred *a_cred;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        vattr_t *vap = ap->a_vap;
        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);
        vap->va_birthtime = vap->va_ctime;
        ZFS_EXIT(zfsvfs);

        return (0);
}

/* ARGSUSED */
static int
zfsctl_snapdir_inactive(ap)
        struct vop_inactive_args /* {
                struct vnode *a_vp;
                struct thread *a_td;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        zfsctl_snapdir_t *sdp = vp->v_data;
        zfs_snapentry_t *sep;

        /*
         * On forced unmount we have to free snapshots from here.
         */
        mutex_enter(&sdp->sd_lock);
        while ((sep = avl_first(&sdp->sd_snaps)) != NULL) {
                avl_remove(&sdp->sd_snaps, sep);
                kmem_free(sep->se_name, strlen(sep->se_name) + 1);
                kmem_free(sep, sizeof (zfs_snapentry_t));
        }
        mutex_exit(&sdp->sd_lock);
        gfs_dir_inactive(vp);
        ASSERT(avl_numnodes(&sdp->sd_snaps) == 0);
        mutex_destroy(&sdp->sd_lock);
        avl_destroy(&sdp->sd_snaps);
        kmem_free(sdp, sizeof (zfsctl_snapdir_t));

        return (0);
}

#ifdef sun
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 }
};
#else   /* !sun */
static struct vop_vector zfsctl_ops_snapdir = {
        .vop_default =  &default_vnodeops,
        .vop_open =     zfsctl_common_open,
        .vop_close =    zfsctl_common_close,
        .vop_ioctl =    VOP_EINVAL,
        .vop_getattr =  zfsctl_snapdir_getattr,
        .vop_access =   zfsctl_common_access,
        .vop_mkdir =    zfsctl_freebsd_snapdir_mkdir,
        .vop_readdir =  gfs_vop_readdir,
        .vop_lookup =   zfsctl_snapdir_lookup,
        .vop_inactive = zfsctl_snapdir_inactive,
        .vop_reclaim =  zfsctl_common_reclaim,
        .vop_fid =      zfsctl_common_fid,
};

static struct vop_vector zfsctl_ops_shares = {
        .vop_default =  &default_vnodeops,
        .vop_open =     zfsctl_common_open,
        .vop_close =    zfsctl_common_close,
        .vop_ioctl =    VOP_EINVAL,
        .vop_getattr =  zfsctl_shares_getattr,
        .vop_access =   zfsctl_common_access,
        .vop_readdir =  zfsctl_shares_readdir,
        .vop_lookup =   zfsctl_shares_lookup,
        .vop_inactive = gfs_vop_inactive,
        .vop_reclaim =  zfsctl_common_reclaim,
        .vop_fid =      zfsctl_shares_fid,
};
#endif  /* !sun */

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, pvp->v_vfsp,
            &zfsctl_ops_snapshot, NULL, NULL, MAXNAMELEN, NULL, NULL);
        VN_HOLD(vp);
        zcp = vp->v_data;
        zcp->zc_id = objset;
        VOP_UNLOCK(vp, 0);

        return (vp);
}

static int
zfsctl_snapshot_inactive(ap)
        struct vop_inactive_args /* {
                struct vnode *a_vp;
                struct thread *a_td;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        cred_t *cr = ap->a_td->td_ucred;
        struct vop_inactive_args iap;
        zfsctl_snapdir_t *sdp;
        zfs_snapentry_t *sep, *next;
        int locked;
        vnode_t *dvp;

        if (vp->v_count > 0)
                goto end;

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

        if (!(locked = MUTEX_HELD(&sdp->sd_lock)))
                mutex_enter(&sdp->sd_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);

        if (!locked)
                mutex_exit(&sdp->sd_lock);
        VN_RELE(dvp);

end:
        /*
         * 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.
         */
        iap.a_vp = vp;
        return (gfs_vop_inactive(&iap));
}

static int
zfsctl_traverse_begin(vnode_t **vpp, int lktype)
{

        VN_HOLD(*vpp);
        /* Snapshot should be already mounted, but just in case. */
        if (vn_mountedvfs(*vpp) == NULL)
                return (ENOENT);
        return (traverse(vpp, lktype));
}

static void
zfsctl_traverse_end(vnode_t *vp, int err)
{

        if (err == 0)
                vput(vp);
        else
                VN_RELE(vp);
}

static int
zfsctl_snapshot_getattr(ap)
        struct vop_getattr_args /* {
                struct vnode *a_vp;
                struct vattr *a_vap;
                struct ucred *a_cred;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        int err;

        err = zfsctl_traverse_begin(&vp, LK_SHARED | LK_RETRY);
        if (err == 0)
                err = VOP_GETATTR(vp, ap->a_vap, ap->a_cred);
        zfsctl_traverse_end(vp, err);
        return (err);
}

static int
zfsctl_snapshot_fid(ap)
        struct vop_fid_args /* {
                struct vnode *a_vp;
                struct fid *a_fid;
        } */ *ap;
{
        vnode_t *vp = ap->a_vp;
        int err;

        err = zfsctl_traverse_begin(&vp, LK_SHARED | LK_RETRY);
        if (err == 0)
                err = VOP_VPTOFH(vp, (void *)ap->a_fid);
        zfsctl_traverse_end(vp, err);
        return (err);
}

static int
zfsctl_snapshot_lookup(ap)
        struct vop_lookup_args /* {
                struct vnode *a_dvp;
                struct vnode **a_vpp;
                struct componentname *a_cnp;
        } */ *ap;
{
        vnode_t *dvp = ap->a_dvp;
        vnode_t **vpp = ap->a_vpp;
        struct componentname *cnp = ap->a_cnp;
        cred_t *cr = ap->a_cnp->cn_cred;
        zfsvfs_t *zfsvfs = dvp->v_vfsp->vfs_data;
        int error;

        if (cnp->cn_namelen != 2 || cnp->cn_nameptr[0] != '.' ||
            cnp->cn_nameptr[1] != '.') {
                return (ENOENT);
        }

        ASSERT(dvp->v_type == VDIR);
        ASSERT(zfsvfs->z_ctldir != NULL);

        error = zfsctl_root_lookup(zfsvfs->z_ctldir, "snapshot", vpp,
            NULL, 0, NULL, cr, NULL, NULL, NULL);
        if (error == 0)
                vn_lock(*vpp, LK_EXCLUSIVE | LK_RETRY);
        return (error);
}

static int
zfsctl_snapshot_vptocnp(struct vop_vptocnp_args *ap)
{
        zfsvfs_t *zfsvfs = ap->a_vp->v_vfsp->vfs_data;
        vnode_t *dvp, *vp;
        zfsctl_snapdir_t *sdp;
        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;
                if (vp == ap->a_vp)
                        break;
                sep = AVL_NEXT(&sdp->sd_snaps, sep);
        }
        if (sep == NULL) {
                mutex_exit(&sdp->sd_lock);
                error = ENOENT;
        } else {
                size_t len;

                len = strlen(sep->se_name);
                *ap->a_buflen -= len;
                bcopy(sep->se_name, ap->a_buf + *ap->a_buflen, len);
                mutex_exit(&sdp->sd_lock);
                vref(dvp);
                *ap->a_vpp = dvp;
        }
        VN_RELE(dvp);

        return (error);
}

static struct vop_vector zfsctl_ops_snapshot = {
        .vop_default =  &default_vnodeops,
        .vop_inactive = zfsctl_snapshot_inactive,
        .vop_lookup =   zfsctl_snapshot_lookup,
        .vop_reclaim =  zfsctl_common_reclaim,
        .vop_getattr =  zfsctl_snapshot_getattr,
        .vop_fid =      zfsctl_snapshot_fid,
        .vop_vptocnp =  zfsctl_snapshot_vptocnp,
};

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, LK_SHARED | LK_RETRY);
                if (error == 0) {
                        if (vp == sep->se_root)
                                error = EINVAL;
                        else
                                *zfsvfsp = VTOZ(vp)->z_zfsvfs;
                }
                mutex_exit(&sdp->sd_lock);
                if (error == 0)
                        VN_URELE(vp);
                else
                        VN_RELE(vp);
        } else {
                error = EINVAL;
                mutex_exit(&sdp->sd_lock);
        }

        VN_RELE(dvp);

        return (error);
}

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)) {
                        error = zfsctl_unmount_snap(sep, fflags, cr);
                        if (error) {
                                avl_index_t where;

                                /*
                                 * Before reinserting snapshot to the tree,
                                 * check if it was actually removed. For example
                                 * when snapshot mount point is busy, we will
                                 * have an error here, but there will be no need
                                 * to reinsert snapshot.
                                 */
                                if (avl_find(&sdp->sd_snaps, sep, &where) == NULL)
                                        avl_insert(&sdp->sd_snaps, sep, where);
                                break;
                        }
                }
                sep = next;
        }

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

        return (error);
}