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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 2008 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/kmem.h>
#include <sys/uio.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/kcondvar.h>
#include <sys/callb.h>
#include <sys/smp.h>
#include <sys/zfs_dir.h>
#include <sys/zfs_acl.h>
#include <sys/fs/zfs.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
 *            ZHAVELOCK: Don't grab the z_name_lock for this call. The
 *                     current thread already holds it.
 *
 * 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.
       *
       * Don't grab the the lock if it is already held. However, cannot
       * have both ZSHARED and ZHAVELOCK together.
       */
      ASSERT(!(flag & ZSHARED) || !(flag & ZHAVELOCK));
      if (!(flag & ZHAVELOCK))
            rw_enter(&dzp->z_name_lock, RW_READER);

      mutex_enter(&dzp->z_lock);
      for (;;) {
            if (dzp->z_unlinked) {
                  mutex_exit(&dzp->z_lock);
                  if (!(flag & ZHAVELOCK))
                        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);
                  if (!(flag & ZHAVELOCK))
                        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_namelock = 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 the z_name_lock was NOT held for this dirlock record it.
       */
      if (flag & ZHAVELOCK)
            dl->dl_namelock = 1;

      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);

      if (!dl->dl_namelock)
            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(zp->z_phys->zp_links == 0);

      /*
       * If this is a ZIL replay then leave the object in the unlinked set.
       * Otherwise we can get a deadlock, because the delete can be
       * quite large and span multiple tx's and txgs, but each replay
       * creates a tx to atomically run the replay function and mark the
       * replay record as complete. We deadlock trying to start a tx in
       * a new txg to further the deletion but can't because the replay
       * tx hasn't finished.
       *
       * We actually delete the object if we get a failure to create an
       * object in zil_replay_log_record(), or after calling zil_replay().
       */
      if (zfsvfs->z_assign >= TXG_INITIAL) {
            zfs_znode_dmu_fini(zp);
            zfs_znode_free(zp);
            return;
      }

      /*
       * If this is an attribute directory, purge its contents.
       */
      if (ZTOV(zp) != NULL && 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 (ENOTEMPTY);
            }
            if (zp->z_phys->zp_links <= zp_is_dir) {
                  zfs_panic_recover("zfs: link count on vnode %p is %u, "
                      "should be at least %u", zp->z_vnode,
                      (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_fuid_info_t *fuidp = NULL;

      *xvpp = NULL;

      /*
       * In FreeBSD, access checking for creating an EA is being done
       * in zfs_setextattr(),
       */
#ifndef __FreeBSD__
      if (error = zfs_zaccess(zp, ACE_WRITE_NAMED_ATTRS, 0, B_FALSE, cr))
            return (error);
#endif

      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);
      if (IS_EPHEMERAL(crgetuid(cr)) || IS_EPHEMERAL(crgetgid(cr))) {
            if (zfsvfs->z_fuid_obj == 0) {
                  dmu_tx_hold_bonus(tx, DMU_NEW_OBJECT);
                  dmu_tx_hold_write(tx, DMU_NEW_OBJECT, 0,
                      FUID_SIZE_ESTIMATE(zfsvfs));
                  dmu_tx_hold_zap(tx, MASTER_NODE_OBJ, FALSE, NULL);
            } else {
                  dmu_tx_hold_bonus(tx, zfsvfs->z_fuid_obj);
                  dmu_tx_hold_write(tx, zfsvfs->z_fuid_obj, 0,
                      FUID_SIZE_ESTIMATE(zfsvfs));
            }
      }
      error = dmu_tx_assign(tx, zfsvfs->z_assign);
      if (error) {
            if (error == ERESTART && zfsvfs->z_assign == TXG_NOWAIT)
                  dmu_tx_wait(tx);
            dmu_tx_abort(tx);
            return (error);
      }
      zfs_mknode(zp, vap, tx, cr, IS_XATTR, &xzp, 0, NULL, &fuidp);
      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, fuidp, vap);
      if (fuidp)
            zfs_fuid_info_free(fuidp);
      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);
#ifdef __FreeBSD__
            return (ENOATTR);
#else
            return (ENOENT);
#endif
      }

      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 && zfsvfs->z_assign == TXG_NOWAIT) {
            /* NB: we already did dmu_tx_wait() if necessary */
            goto top;
      }
      if (error == 0)
            VOP_UNLOCK(*xvpp, 0);

      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_assign >= TXG_INITIAL)     /* ZIL 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(ZTOV(zp), cr));
}

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