[zfs.git] / module / zfs / zfs_dir.c

/*
 * 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 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/systm.h>
#include <sys/sysmacros.h>
#include <sys/resource.h>
#include <sys/vfs.h>
#include <sys/vnode.h>
#include <sys/file.h>
#include <sys/mode.h>
#include <sys/kmem.h>
#include <sys/uio.h>
#include <sys/pathname.h>
#include <sys/cmn_err.h>
#include <sys/errno.h>
#include <sys/stat.h>
#include <sys/unistd.h>
#include <sys/sunddi.h>
#include <sys/random.h>
#include <sys/policy.h>
#include <sys/zfs_dir.h>
#include <sys/zfs_acl.h>
#include <sys/fs/zfs.h>
#include "fs/fs_subr.h"
#include <sys/zap.h>
#include <sys/dmu.h>
#include <sys/atomic.h>
#include <sys/zfs_ctldir.h>
#include <sys/zfs_fuid.h>
#include <sys/dnlc.h>
#include <sys/extdirent.h>

/*
 * zfs_match_find() is used by zfs_dirent_lock() to peform zap lookups
 * of names after deciding which is the appropriate lookup interface.
 */
static int
zfs_match_find(zfsvfs_t *zfsvfs, znode_t *dzp, char *name, boolean_t exact,
    boolean_t update, int *deflags, pathname_t *rpnp, uint64_t *zoid)
{
        int error;

        if (zfsvfs->z_norm) {
                matchtype_t mt = MT_FIRST;
                boolean_t conflict = B_FALSE;
                size_t bufsz = 0;
                char *buf = NULL;

                if (rpnp) {
                        buf = rpnp->pn_buf;
                        bufsz = rpnp->pn_bufsize;
                }
                if (exact)
                        mt = MT_EXACT;
                /*
                 * In the non-mixed case we only expect there would ever
                 * be one match, but we need to use the normalizing lookup.
                 */
                error = zap_lookup_norm(zfsvfs->z_os, dzp->z_id, name, 8, 1,
                    zoid, mt, buf, bufsz, &conflict);
                if (!error && deflags)
                        *deflags = conflict ? ED_CASE_CONFLICT : 0;
        } else {
                error = zap_lookup(zfsvfs->z_os, dzp->z_id, name, 8, 1, zoid);
        }
        *zoid = ZFS_DIRENT_OBJ(*zoid);

        if (error == ENOENT && update)
                dnlc_update(ZTOV(dzp), name, DNLC_NO_VNODE);

        return (error);
}

/*
 * Lock a directory entry.  A dirlock on <dzp, name> protects that name
 * in dzp's directory zap object.  As long as you hold a dirlock, you can
 * assume two things: (1) dzp cannot be reaped, and (2) no other thread
 * can change the zap entry for (i.e. link or unlink) this name.
 *
 * Input arguments:
 *      dzp     - znode for directory
 *      name    - name of entry to lock
 *      flag    - ZNEW: if the entry already exists, fail with EEXIST.
 *                ZEXISTS: if the entry does not exist, fail with ENOENT.
 *                ZSHARED: allow concurrent access with other ZSHARED callers.
 *                ZXATTR: we want dzp's xattr directory
 *                ZCILOOK: On a mixed sensitivity file system,
 *                         this lookup should be case-insensitive.
 *                ZCIEXACT: On a purely case-insensitive file system,
 *                          this lookup should be case-sensitive.
 *                ZRENAMING: we are locking for renaming, force narrow locks
 *
 * Output arguments:
 *      zpp     - pointer to the znode for the entry (NULL if there isn't one)
 *      dlpp    - pointer to the dirlock for this entry (NULL on error)
 *      direntflags - (case-insensitive lookup only)
 *              flags if multiple case-sensitive matches exist in directory
 *      realpnp     - (case-insensitive lookup only)
 *              actual name matched within the directory
 *
 * Return value: 0 on success or errno on failure.
 *
 * NOTE: Always checks for, and rejects, '.' and '..'.
 * NOTE: For case-insensitive file systems we take wide locks (see below),
 *       but return znode pointers to a single match.
 */
int
zfs_dirent_lock(zfs_dirlock_t **dlpp, znode_t *dzp, char *name, znode_t **zpp,
    int flag, int *direntflags, pathname_t *realpnp)
{
        zfsvfs_t        *zfsvfs = dzp->z_zfsvfs;
        zfs_dirlock_t   *dl;
        boolean_t       update;
        boolean_t       exact;
        uint64_t        zoid;
        vnode_t         *vp = NULL;
        int             error = 0;
        int             cmpflags;

        *zpp = NULL;
        *dlpp = NULL;

        /*
         * Verify that we are not trying to lock '.', '..', or '.zfs'
         */
        if (name[0] == '.' &&
            (name[1] == '\0' || (name[1] == '.' && name[2] == '\0')) ||
            zfs_has_ctldir(dzp) && strcmp(name, ZFS_CTLDIR_NAME) == 0)
                return (EEXIST);

        /*
         * Case sensitivity and normalization preferences are set when
         * the file system is created.  These are stored in the
         * zfsvfs->z_case and zfsvfs->z_norm fields.  These choices
         * affect what vnodes can be cached in the DNLC, how we
         * perform zap lookups, and the "width" of our dirlocks.
         *
         * A normal dirlock locks a single name.  Note that with
         * normalization a name can be composed multiple ways, but
         * when normalized, these names all compare equal.  A wide
         * dirlock locks multiple names.  We need these when the file
         * system is supporting mixed-mode access.  It is sometimes
         * necessary to lock all case permutations of file name at
         * once so that simultaneous case-insensitive/case-sensitive
         * behaves as rationally as possible.
         */

        /*
         * Decide if exact matches should be requested when performing
         * a zap lookup on file systems supporting case-insensitive
         * access.
         */
        exact =
            ((zfsvfs->z_case == ZFS_CASE_INSENSITIVE) && (flag & ZCIEXACT)) ||
            ((zfsvfs->z_case == ZFS_CASE_MIXED) && !(flag & ZCILOOK));

        /*
         * Only look in or update the DNLC if we are looking for the
         * name on a file system that does not require normalization
         * or case folding.  We can also look there if we happen to be
         * on a non-normalizing, mixed sensitivity file system IF we
         * are looking for the exact name.
         *
         * Maybe can add TO-UPPERed version of name to dnlc in ci-only
         * case for performance improvement?
         */
        update = !zfsvfs->z_norm ||
            ((zfsvfs->z_case == ZFS_CASE_MIXED) &&
            !(zfsvfs->z_norm & ~U8_TEXTPREP_TOUPPER) && !(flag & ZCILOOK));

        /*
         * ZRENAMING indicates we are in a situation where we should
         * take narrow locks regardless of the file system's
         * preferences for normalizing and case folding.  This will
         * prevent us deadlocking trying to grab the same wide lock
         * twice if the two names happen to be case-insensitive
         * matches.
         */
        if (flag & ZRENAMING)
                cmpflags = 0;
        else
                cmpflags = zfsvfs->z_norm;

        /*
         * Wait until there are no locks on this name.
         */
        rw_enter(&dzp->z_name_lock, RW_READER);
        mutex_enter(&dzp->z_lock);
        for (;;) {
                if (dzp->z_unlinked) {
                        mutex_exit(&dzp->z_lock);
                        rw_exit(&dzp->z_name_lock);
                        return (ENOENT);
                }
                for (dl = dzp->z_dirlocks; dl != NULL; dl = dl->dl_next) {
                        if ((u8_strcmp(name, dl->dl_name, 0, cmpflags,
                            U8_UNICODE_LATEST, &error) == 0) || error != 0)
                                break;
                }
                if (error != 0) {
                        mutex_exit(&dzp->z_lock);
                        rw_exit(&dzp->z_name_lock);
                        return (ENOENT);
                }
                if (dl == NULL) {
                        /*
                         * Allocate a new dirlock and add it to the list.
                         */
                        dl = kmem_alloc(sizeof (zfs_dirlock_t), KM_SLEEP);
                        cv_init(&dl->dl_cv, NULL, CV_DEFAULT, NULL);
                        dl->dl_name = name;
                        dl->dl_sharecnt = 0;
                        dl->dl_namesize = 0;
                        dl->dl_dzp = dzp;
                        dl->dl_next = dzp->z_dirlocks;
                        dzp->z_dirlocks = dl;
                        break;
                }
                if ((flag & ZSHARED) && dl->dl_sharecnt != 0)
                        break;
                cv_wait(&dl->dl_cv, &dzp->z_lock);
        }

        if ((flag & ZSHARED) && ++dl->dl_sharecnt > 1 && dl->dl_namesize == 0) {
                /*
                 * We're the second shared reference to dl.  Make a copy of
                 * dl_name in case the first thread goes away before we do.
                 * Note that we initialize the new name before storing its
                 * pointer into dl_name, because the first thread may load
                 * dl->dl_name at any time.  He'll either see the old value,
                 * which is his, or the new shared copy; either is OK.
                 */
                dl->dl_namesize = strlen(dl->dl_name) + 1;
                name = kmem_alloc(dl->dl_namesize, KM_SLEEP);
                bcopy(dl->dl_name, name, dl->dl_namesize);
                dl->dl_name = name;
        }

        mutex_exit(&dzp->z_lock);

        /*
         * We have a dirlock on the name.  (Note that it is the dirlock,
         * not the dzp's z_lock, that protects the name in the zap object.)
         * See if there's an object by this name; if so, put a hold on it.
         */
        if (flag & ZXATTR) {
                zoid = dzp->z_phys->zp_xattr;
                error = (zoid == 0 ? ENOENT : 0);
        } else {
                if (update)
                        vp = dnlc_lookup(ZTOV(dzp), name);
                if (vp == DNLC_NO_VNODE) {
                        VN_RELE(vp);
                        error = ENOENT;
                } else if (vp) {
                        if (flag & ZNEW) {
                                zfs_dirent_unlock(dl);
                                VN_RELE(vp);
                                return (EEXIST);
                        }
                        *dlpp = dl;
                        *zpp = VTOZ(vp);
                        return (0);
                } else {
                        error = zfs_match_find(zfsvfs, dzp, name, exact,
                            update, direntflags, realpnp, &zoid);
                }
        }
        if (error) {
                if (error != ENOENT || (flag & ZEXISTS)) {
                        zfs_dirent_unlock(dl);
                        return (error);
                }
        } else {
                if (flag & ZNEW) {
                        zfs_dirent_unlock(dl);
                        return (EEXIST);
                }
                error = zfs_zget(zfsvfs, zoid, zpp);
                if (error) {
                        zfs_dirent_unlock(dl);
                        return (error);
                }
                if (!(flag & ZXATTR) && update)
                        dnlc_update(ZTOV(dzp), name, ZTOV(*zpp));
        }

        *dlpp = dl;

        return (0);
}

/*
 * Unlock this directory entry and wake anyone who was waiting for it.
 */
void
zfs_dirent_unlock(zfs_dirlock_t *dl)
{
        znode_t *dzp = dl->dl_dzp;
        zfs_dirlock_t **prev_dl, *cur_dl;

        mutex_enter(&dzp->z_lock);
        rw_exit(&dzp->z_name_lock);
        if (dl->dl_sharecnt > 1) {
                dl->dl_sharecnt--;
                mutex_exit(&dzp->z_lock);
                return;
        }
        prev_dl = &dzp->z_dirlocks;
        while ((cur_dl = *prev_dl) != dl)
                prev_dl = &cur_dl->dl_next;
        *prev_dl = dl->dl_next;
        cv_broadcast(&dl->dl_cv);
        mutex_exit(&dzp->z_lock);

        if (dl->dl_namesize != 0)
                kmem_free(dl->dl_name, dl->dl_namesize);
        cv_destroy(&dl->dl_cv);
        kmem_free(dl, sizeof (*dl));
}

/*
 * Look up an entry in a directory.
 *
 * NOTE: '.' and '..' are handled as special cases because
 *      no directory entries are actually stored for them.  If this is
 *      the root of a filesystem, then '.zfs' is also treated as a
 *      special pseudo-directory.
 */
int
zfs_dirlook(znode_t *dzp, char *name, vnode_t **vpp, int flags,
    int *deflg, pathname_t *rpnp)
{
        zfs_dirlock_t *dl;
        znode_t *zp;
        int error = 0;

        if (name[0] == 0 || (name[0] == '.' && name[1] == 0)) {
                *vpp = ZTOV(dzp);
                VN_HOLD(*vpp);
        } else if (name[0] == '.' && name[1] == '.' && name[2] == 0) {
                zfsvfs_t *zfsvfs = dzp->z_zfsvfs;
                /*
                 * If we are a snapshot mounted under .zfs, return
                 * the vp for the snapshot directory.
                 */
                if (dzp->z_phys->zp_parent == dzp->z_id &&
                    zfsvfs->z_parent != zfsvfs) {
                        error = zfsctl_root_lookup(zfsvfs->z_parent->z_ctldir,
                            "snapshot", vpp, NULL, 0, NULL, kcred,
                            NULL, NULL, NULL);
                        return (error);
                }
                rw_enter(&dzp->z_parent_lock, RW_READER);
                error = zfs_zget(zfsvfs, dzp->z_phys->zp_parent, &zp);
                if (error == 0)
                        *vpp = ZTOV(zp);
                rw_exit(&dzp->z_parent_lock);
        } else if (zfs_has_ctldir(dzp) && strcmp(name, ZFS_CTLDIR_NAME) == 0) {
                *vpp = zfsctl_root(dzp);
        } else {
                int zf;

                zf = ZEXISTS | ZSHARED;
                if (flags & FIGNORECASE)
                        zf |= ZCILOOK;

                error = zfs_dirent_lock(&dl, dzp, name, &zp, zf, deflg, rpnp);
                if (error == 0) {
                        *vpp = ZTOV(zp);
                        zfs_dirent_unlock(dl);
                        dzp->z_zn_prefetch = B_TRUE; /* enable prefetching */
                }
                rpnp = NULL;
        }

        if ((flags & FIGNORECASE) && rpnp && !error)
                (void) strlcpy(rpnp->pn_buf, name, rpnp->pn_bufsize);

        return (error);
}

/*
 * unlinked Set (formerly known as the "delete queue") Error Handling
 *
 * When dealing with the unlinked set, we dmu_tx_hold_zap(), but we
 * don't specify the name of the entry that we will be manipulating.  We
 * also fib and say that we won't be adding any new entries to the
 * unlinked set, even though we might (this is to lower the minimum file
 * size that can be deleted in a full filesystem).  So on the small
 * chance that the nlink list is using a fat zap (ie. has more than
 * 2000 entries), we *may* not pre-read a block that's needed.
 * Therefore it is remotely possible for some of the assertions
 * regarding the unlinked set below to fail due to i/o error.  On a
 * nondebug system, this will result in the space being leaked.
 */
void
zfs_unlinked_add(znode_t *zp, dmu_tx_t *tx)
{
        zfsvfs_t *zfsvfs = zp->z_zfsvfs;

        ASSERT(zp->z_unlinked);
        ASSERT3U(zp->z_phys->zp_links, ==, 0);

        VERIFY3U(0, ==,
            zap_add_int(zfsvfs->z_os, zfsvfs->z_unlinkedobj, zp->z_id, tx));
}

/*
 * Clean up any znodes that had no links when we either crashed or
 * (force) umounted the file system.
 */
void
zfs_unlinked_drain(zfsvfs_t *zfsvfs)
{
        zap_cursor_t    zc;
        zap_attribute_t zap;
        dmu_object_info_t doi;
        znode_t         *zp;
        int             error;

        /*
         * Interate over the contents of the unlinked set.
         */
        for (zap_cursor_init(&zc, zfsvfs->z_os, zfsvfs->z_unlinkedobj);
            zap_cursor_retrieve(&zc, &zap) == 0;
            zap_cursor_advance(&zc)) {

                /*
                 * See what kind of object we have in list
                 */

                error = dmu_object_info(zfsvfs->z_os,
                    zap.za_first_integer, &doi);
                if (error != 0)
                        continue;

                ASSERT((doi.doi_type == DMU_OT_PLAIN_FILE_CONTENTS) ||
                    (doi.doi_type == DMU_OT_DIRECTORY_CONTENTS));
                /*
                 * We need to re-mark these list entries for deletion,
                 * so we pull them back into core and set zp->z_unlinked.
                 */
                error = zfs_zget(zfsvfs, zap.za_first_integer, &zp);

                /*
                 * We may pick up znodes that are already marked for deletion.
                 * This could happen during the purge of an extended attribute
                 * directory.  All we need to do is skip over them, since they
                 * are already in the system marked z_unlinked.
                 */
                if (error != 0)
                        continue;

                zp->z_unlinked = B_TRUE;
                VN_RELE(ZTOV(zp));
        }
        zap_cursor_fini(&zc);
}

/*
 * Delete the entire contents of a directory.  Return a count
 * of the number of entries that could not be deleted. If we encounter
 * an error, return a count of at least one so that the directory stays
 * in the unlinked set.
 *
 * NOTE: this function assumes that the directory is inactive,
 *      so there is no need to lock its entries before deletion.
 *      Also, it assumes the directory contents is *only* regular
 *      files.
 */
static int
zfs_purgedir(znode_t *dzp)
{
        zap_cursor_t    zc;
        zap_attribute_t zap;
        znode_t         *xzp;
        dmu_tx_t        *tx;
        zfsvfs_t        *zfsvfs = dzp->z_zfsvfs;
        zfs_dirlock_t   dl;
        int skipped = 0;
        int error;

        for (zap_cursor_init(&zc, zfsvfs->z_os, dzp->z_id);
            (error = zap_cursor_retrieve(&zc, &zap)) == 0;
            zap_cursor_advance(&zc)) {
                error = zfs_zget(zfsvfs,
                    ZFS_DIRENT_OBJ(zap.za_first_integer), &xzp);
                if (error) {
                        skipped += 1;
                        continue;
                }

                ASSERT((ZTOV(xzp)->v_type == VREG) ||
                    (ZTOV(xzp)->v_type == VLNK));

                tx = dmu_tx_create(zfsvfs->z_os);
                dmu_tx_hold_bonus(tx, dzp->z_id);
                dmu_tx_hold_zap(tx, dzp->z_id, FALSE, zap.za_name);
                dmu_tx_hold_bonus(tx, xzp->z_id);
                dmu_tx_hold_zap(tx, zfsvfs->z_unlinkedobj, FALSE, NULL);
                error = dmu_tx_assign(tx, TXG_WAIT);
                if (error) {
                        dmu_tx_abort(tx);
                        VN_RELE(ZTOV(xzp));
                        skipped += 1;
                        continue;
                }
                bzero(&dl, sizeof (dl));
                dl.dl_dzp = dzp;
                dl.dl_name = zap.za_name;

                error = zfs_link_destroy(&dl, xzp, tx, 0, NULL);
                if (error)
                        skipped += 1;
                dmu_tx_commit(tx);

                VN_RELE(ZTOV(xzp));
        }
        zap_cursor_fini(&zc);
        if (error != ENOENT)
                skipped += 1;
        return (skipped);
}

void
zfs_rmnode(znode_t *zp)
{
        zfsvfs_t        *zfsvfs = zp->z_zfsvfs;
        objset_t        *os = zfsvfs->z_os;
        znode_t         *xzp = NULL;
        dmu_tx_t        *tx;
        uint64_t        acl_obj;
        int             error;

        ASSERT(ZTOV(zp)->v_count == 0);
        ASSERT(zp->z_phys->zp_links == 0);

        /*
         * If this is an attribute directory, purge its contents.
         */
        if (ZTOV(zp)->v_type == VDIR && (zp->z_phys->zp_flags & ZFS_XATTR)) {
                if (zfs_purgedir(zp) != 0) {
                        /*
                         * Not enough space to delete some xattrs.
                         * Leave it in the unlinked set.
                         */
                        zfs_znode_dmu_fini(zp);
                        zfs_znode_free(zp);
                        return;
                }
        }

        /*
         * Free up all the data in the file.
         */
        error = dmu_free_long_range(os, zp->z_id, 0, DMU_OBJECT_END);
        if (error) {
                /*
                 * Not enough space.  Leave the file in the unlinked set.
                 */
                zfs_znode_dmu_fini(zp);
                zfs_znode_free(zp);
                return;
        }

        /*
         * If the file has extended attributes, we're going to unlink
         * the xattr dir.
         */
        if (zp->z_phys->zp_xattr) {
                error = zfs_zget(zfsvfs, zp->z_phys->zp_xattr, &xzp);
                ASSERT(error == 0);
        }

        acl_obj = zp->z_phys->zp_acl.z_acl_extern_obj;

        /*
         * Set up the final transaction.
         */
        tx = dmu_tx_create(os);
        dmu_tx_hold_free(tx, zp->z_id, 0, DMU_OBJECT_END);
        dmu_tx_hold_zap(tx, zfsvfs->z_unlinkedobj, FALSE, NULL);
        if (xzp) {
                dmu_tx_hold_bonus(tx, xzp->z_id);
                dmu_tx_hold_zap(tx, zfsvfs->z_unlinkedobj, TRUE, NULL);
        }
        if (acl_obj)
                dmu_tx_hold_free(tx, acl_obj, 0, DMU_OBJECT_END);
        error = dmu_tx_assign(tx, TXG_WAIT);
        if (error) {
                /*
                 * Not enough space to delete the file.  Leave it in the
                 * unlinked set, leaking it until the fs is remounted (at
                 * which point we'll call zfs_unlinked_drain() to process it).
                 */
                dmu_tx_abort(tx);
                zfs_znode_dmu_fini(zp);
                zfs_znode_free(zp);
                goto out;
        }

        if (xzp) {
                dmu_buf_will_dirty(xzp->z_dbuf, tx);
                mutex_enter(&xzp->z_lock);
                xzp->z_unlinked = B_TRUE;       /* mark xzp for deletion */
                xzp->z_phys->zp_links = 0;      /* no more links to it */
                mutex_exit(&xzp->z_lock);
                zfs_unlinked_add(xzp, tx);
        }

        /* Remove this znode from the unlinked set */
        VERIFY3U(0, ==,
            zap_remove_int(zfsvfs->z_os, zfsvfs->z_unlinkedobj, zp->z_id, tx));

        zfs_znode_delete(zp, tx);

        dmu_tx_commit(tx);
out:
        if (xzp)
                VN_RELE(ZTOV(xzp));
}

static uint64_t
zfs_dirent(znode_t *zp)
{
        uint64_t de = zp->z_id;
        if (zp->z_zfsvfs->z_version >= ZPL_VERSION_DIRENT_TYPE)
                de |= IFTODT((zp)->z_phys->zp_mode) << 60;
        return (de);
}

/*
 * Link zp into dl.  Can only fail if zp has been unlinked.
 */
int
zfs_link_create(zfs_dirlock_t *dl, znode_t *zp, dmu_tx_t *tx, int flag)
{
        znode_t *dzp = dl->dl_dzp;
        vnode_t *vp = ZTOV(zp);
        uint64_t value;
        int zp_is_dir = (vp->v_type == VDIR);
        int error;

        dmu_buf_will_dirty(zp->z_dbuf, tx);
        mutex_enter(&zp->z_lock);

        if (!(flag & ZRENAMING)) {
                if (zp->z_unlinked) {   /* no new links to unlinked zp */
                        ASSERT(!(flag & (ZNEW | ZEXISTS)));
                        mutex_exit(&zp->z_lock);
                        return (ENOENT);
                }
                zp->z_phys->zp_links++;
        }
        zp->z_phys->zp_parent = dzp->z_id;      /* dzp is now zp's parent */

        if (!(flag & ZNEW))
                zfs_time_stamper_locked(zp, STATE_CHANGED, tx);
        mutex_exit(&zp->z_lock);

        dmu_buf_will_dirty(dzp->z_dbuf, tx);
        mutex_enter(&dzp->z_lock);
        dzp->z_phys->zp_size++;                 /* one dirent added */
        dzp->z_phys->zp_links += zp_is_dir;     /* ".." link from zp */
        zfs_time_stamper_locked(dzp, CONTENT_MODIFIED, tx);
        mutex_exit(&dzp->z_lock);

        value = zfs_dirent(zp);
        error = zap_add(zp->z_zfsvfs->z_os, dzp->z_id, dl->dl_name,
            8, 1, &value, tx);
        ASSERT(error == 0);

        dnlc_update(ZTOV(dzp), dl->dl_name, vp);

        return (0);
}

/*
 * Unlink zp from dl, and mark zp for deletion if this was the last link.
 * Can fail if zp is a mount point (EBUSY) or a non-empty directory (EEXIST).
 * If 'unlinkedp' is NULL, we put unlinked znodes on the unlinked list.
 * If it's non-NULL, we use it to indicate whether the znode needs deletion,
 * and it's the caller's job to do it.
 */
int
zfs_link_destroy(zfs_dirlock_t *dl, znode_t *zp, dmu_tx_t *tx, int flag,
        boolean_t *unlinkedp)
{
        znode_t *dzp = dl->dl_dzp;
        vnode_t *vp = ZTOV(zp);
        int zp_is_dir = (vp->v_type == VDIR);
        boolean_t unlinked = B_FALSE;
        int error;

        dnlc_remove(ZTOV(dzp), dl->dl_name);

        if (!(flag & ZRENAMING)) {
                dmu_buf_will_dirty(zp->z_dbuf, tx);

                if (vn_vfswlock(vp))            /* prevent new mounts on zp */
                        return (EBUSY);

                if (vn_ismntpt(vp)) {           /* don't remove mount point */
                        vn_vfsunlock(vp);
                        return (EBUSY);
                }

                mutex_enter(&zp->z_lock);
                if (zp_is_dir && !zfs_dirempty(zp)) {   /* dir not empty */
                        mutex_exit(&zp->z_lock);
                        vn_vfsunlock(vp);
                        return (EEXIST);
                }
                if (zp->z_phys->zp_links <= zp_is_dir) {
                        zfs_panic_recover("zfs: link count on %s is %u, "
                            "should be at least %u",
                            zp->z_vnode->v_path ? zp->z_vnode->v_path :
                            "<unknown>", (int)zp->z_phys->zp_links,
                            zp_is_dir + 1);
                        zp->z_phys->zp_links = zp_is_dir + 1;
                }
                if (--zp->z_phys->zp_links == zp_is_dir) {
                        zp->z_unlinked = B_TRUE;
                        zp->z_phys->zp_links = 0;
                        unlinked = B_TRUE;
                } else {
                        zfs_time_stamper_locked(zp, STATE_CHANGED, tx);
                }
                mutex_exit(&zp->z_lock);
                vn_vfsunlock(vp);
        }

        dmu_buf_will_dirty(dzp->z_dbuf, tx);
        mutex_enter(&dzp->z_lock);
        dzp->z_phys->zp_size--;                 /* one dirent removed */
        dzp->z_phys->zp_links -= zp_is_dir;     /* ".." link from zp */
        zfs_time_stamper_locked(dzp, CONTENT_MODIFIED, tx);
        mutex_exit(&dzp->z_lock);

        if (zp->z_zfsvfs->z_norm) {
                if (((zp->z_zfsvfs->z_case == ZFS_CASE_INSENSITIVE) &&
                    (flag & ZCIEXACT)) ||
                    ((zp->z_zfsvfs->z_case == ZFS_CASE_MIXED) &&
                    !(flag & ZCILOOK)))
                        error = zap_remove_norm(zp->z_zfsvfs->z_os,
                            dzp->z_id, dl->dl_name, MT_EXACT, tx);
                else
                        error = zap_remove_norm(zp->z_zfsvfs->z_os,
                            dzp->z_id, dl->dl_name, MT_FIRST, tx);
        } else {
                error = zap_remove(zp->z_zfsvfs->z_os,
                    dzp->z_id, dl->dl_name, tx);
        }
        ASSERT(error == 0);

        if (unlinkedp != NULL)
                *unlinkedp = unlinked;
        else if (unlinked)
                zfs_unlinked_add(zp, tx);

        return (0);
}

/*
 * Indicate whether the directory is empty.  Works with or without z_lock
 * held, but can only be consider a hint in the latter case.  Returns true
 * if only "." and ".." remain and there's no work in progress.
 */
boolean_t
zfs_dirempty(znode_t *dzp)
{
        return (dzp->z_phys->zp_size == 2 && dzp->z_dirlocks == 0);
}

int
zfs_make_xattrdir(znode_t *zp, vattr_t *vap, vnode_t **xvpp, cred_t *cr)
{
        zfsvfs_t *zfsvfs = zp->z_zfsvfs;
        znode_t *xzp;
        dmu_tx_t *tx;
        int error;
        zfs_acl_ids_t acl_ids;
        boolean_t fuid_dirtied;

        *xvpp = NULL;

        if (error = zfs_zaccess(zp, ACE_WRITE_NAMED_ATTRS, 0, B_FALSE, cr))
                return (error);

        if ((error = zfs_acl_ids_create(zp, IS_XATTR, vap, cr, NULL,
            &acl_ids)) != 0)
                return (error);
        if (zfs_acl_ids_overquota(zfsvfs, &acl_ids)) {
                zfs_acl_ids_free(&acl_ids);
                return (EDQUOT);
        }

        tx = dmu_tx_create(zfsvfs->z_os);
        dmu_tx_hold_bonus(tx, zp->z_id);
        dmu_tx_hold_zap(tx, DMU_NEW_OBJECT, FALSE, NULL);
        fuid_dirtied = zfsvfs->z_fuid_dirty;
        if (fuid_dirtied)
                zfs_fuid_txhold(zfsvfs, tx);
        error = dmu_tx_assign(tx, TXG_NOWAIT);
        if (error) {
                zfs_acl_ids_free(&acl_ids);
                if (error == ERESTART)
                        dmu_tx_wait(tx);
                dmu_tx_abort(tx);
                return (error);
        }
        zfs_mknode(zp, vap, tx, cr, IS_XATTR, &xzp, 0, &acl_ids);

        if (fuid_dirtied)
                zfs_fuid_sync(zfsvfs, tx);

        ASSERT(xzp->z_phys->zp_parent == zp->z_id);
        dmu_buf_will_dirty(zp->z_dbuf, tx);
        zp->z_phys->zp_xattr = xzp->z_id;

        (void) zfs_log_create(zfsvfs->z_log, tx, TX_MKXATTR, zp,
            xzp, "", NULL, acl_ids.z_fuidp, vap);

        zfs_acl_ids_free(&acl_ids);
        dmu_tx_commit(tx);

        *xvpp = ZTOV(xzp);

        return (0);
}

/*
 * Return a znode for the extended attribute directory for zp.
 * ** If the directory does not already exist, it is created **
 *
 *      IN:     zp      - znode to obtain attribute directory from
 *              cr      - credentials of caller
 *              flags   - flags from the VOP_LOOKUP call
 *
 *      OUT:    xzpp    - pointer to extended attribute znode
 *
 *      RETURN: 0 on success
 *              error number on failure
 */
int
zfs_get_xattrdir(znode_t *zp, vnode_t **xvpp, cred_t *cr, int flags)
{
        zfsvfs_t        *zfsvfs = zp->z_zfsvfs;
        znode_t         *xzp;
        zfs_dirlock_t   *dl;
        vattr_t         va;
        int             error;
top:
        error = zfs_dirent_lock(&dl, zp, "", &xzp, ZXATTR, NULL, NULL);
        if (error)
                return (error);

        if (xzp != NULL) {
                *xvpp = ZTOV(xzp);
                zfs_dirent_unlock(dl);
                return (0);
        }

        ASSERT(zp->z_phys->zp_xattr == 0);

        if (!(flags & CREATE_XATTR_DIR)) {
                zfs_dirent_unlock(dl);
                return (ENOENT);
        }

        if (zfsvfs->z_vfs->vfs_flag & VFS_RDONLY) {
                zfs_dirent_unlock(dl);
                return (EROFS);
        }

        /*
         * The ability to 'create' files in an attribute
         * directory comes from the write_xattr permission on the base file.
         *
         * The ability to 'search' an attribute directory requires
         * read_xattr permission on the base file.
         *
         * Once in a directory the ability to read/write attributes
         * is controlled by the permissions on the attribute file.
         */
        va.va_mask = AT_TYPE | AT_MODE | AT_UID | AT_GID;
        va.va_type = VDIR;
        va.va_mode = S_IFDIR | S_ISVTX | 0777;
        zfs_fuid_map_ids(zp, cr, &va.va_uid, &va.va_gid);

        error = zfs_make_xattrdir(zp, &va, xvpp, cr);
        zfs_dirent_unlock(dl);

        if (error == ERESTART) {
                /* NB: we already did dmu_tx_wait() if necessary */
                goto top;
        }

        return (error);
}

/*
 * Decide whether it is okay to remove within a sticky directory.
 *
 * In sticky directories, write access is not sufficient;
 * you can remove entries from a directory only if:
 *
 *      you own the directory,
 *      you own the entry,
 *      the entry is a plain file and you have write access,
 *      or you are privileged (checked in secpolicy...).
 *
 * The function returns 0 if remove access is granted.
 */
int
zfs_sticky_remove_access(znode_t *zdp, znode_t *zp, cred_t *cr)
{
        uid_t           uid;
        uid_t           downer;
        uid_t           fowner;
        zfsvfs_t        *zfsvfs = zdp->z_zfsvfs;

        if (zdp->z_zfsvfs->z_replay)
                return (0);

        if ((zdp->z_phys->zp_mode & S_ISVTX) == 0)
                return (0);

        downer = zfs_fuid_map_id(zfsvfs, zdp->z_phys->zp_uid, cr, ZFS_OWNER);
        fowner = zfs_fuid_map_id(zfsvfs, zp->z_phys->zp_uid, cr, ZFS_OWNER);

        if ((uid = crgetuid(cr)) == downer || uid == fowner ||
            (ZTOV(zp)->v_type == VREG &&
            zfs_zaccess(zp, ACE_WRITE_DATA, 0, B_FALSE, cr) == 0))
                return (0);
        else
                return (secpolicy_vnode_remove(cr));
}