FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/zvol.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 https://opensource.org/licenses/CDDL-1.0.
     * 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) 2008-2010 Lawrence Livermore National Security, LLC.
     * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
     * Rewritten for Linux by Brian Behlendorf <behlendorf1@llnl.gov>.
     * LLNL-CODE-403049.
     *
     * ZFS volume emulation driver.
     *
     * Makes a DMU object look like a volume of arbitrary size, up to 2^64 bytes.
     * Volumes are accessed through the symbolic links named:
     *
     * /dev/<pool_name>/<dataset_name>
     *
     * Volumes are persistent through reboot and module load.  No user command
     * needs to be run before opening and using a device.
     *
     * Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
     * Copyright (c) 2016 Actifio, Inc. All rights reserved.
     * Copyright (c) 2012, 2019 by Delphix. All rights reserved.
     */
    
    /*
     * Note on locking of zvol state structures.
     *
     * These structures are used to maintain internal state used to emulate block
     * devices on top of zvols. In particular, management of device minor number
     * operations - create, remove, rename, and set_snapdev - involves access to
     * these structures. The zvol_state_lock is primarily used to protect the
     * zvol_state_list. The zv->zv_state_lock is used to protect the contents
     * of the zvol_state_t structures, as well as to make sure that when the
     * time comes to remove the structure from the list, it is not in use, and
     * therefore, it can be taken off zvol_state_list and freed.
     *
     * The zv_suspend_lock was introduced to allow for suspending I/O to a zvol,
     * e.g. for the duration of receive and rollback operations. This lock can be
     * held for significant periods of time. Given that it is undesirable to hold
     * mutexes for long periods of time, the following lock ordering applies:
     * - take zvol_state_lock if necessary, to protect zvol_state_list
     * - take zv_suspend_lock if necessary, by the code path in question
     * - take zv_state_lock to protect zvol_state_t
     *
     * The minor operations are issued to spa->spa_zvol_taskq queues, that are
     * single-threaded (to preserve order of minor operations), and are executed
     * through the zvol_task_cb that dispatches the specific operations. Therefore,
     * these operations are serialized per pool. Consequently, we can be certain
     * that for a given zvol, there is only one operation at a time in progress.
     * That is why one can be sure that first, zvol_state_t for a given zvol is
     * allocated and placed on zvol_state_list, and then other minor operations
     * for this zvol are going to proceed in the order of issue.
     *
     */
    
    #include <sys/dataset_kstats.h>
    #include <sys/dbuf.h>
    #include <sys/dmu_traverse.h>
    #include <sys/dsl_dataset.h>
    #include <sys/dsl_prop.h>
    #include <sys/dsl_dir.h>
    #include <sys/zap.h>
    #include <sys/zfeature.h>
    #include <sys/zil_impl.h>
    #include <sys/dmu_tx.h>
    #include <sys/zio.h>
    #include <sys/zfs_rlock.h>
    #include <sys/spa_impl.h>
    #include <sys/zvol.h>
    #include <sys/zvol_impl.h>
    
    unsigned int zvol_inhibit_dev = 0;
    unsigned int zvol_volmode = ZFS_VOLMODE_GEOM;
    
    struct hlist_head *zvol_htable;
    static list_t zvol_state_list;
    krwlock_t zvol_state_lock;
    
    typedef enum {
            ZVOL_ASYNC_REMOVE_MINORS,
            ZVOL_ASYNC_RENAME_MINORS,
            ZVOL_ASYNC_SET_SNAPDEV,
           ZVOL_ASYNC_SET_VOLMODE,
           ZVOL_ASYNC_MAX
   } zvol_async_op_t;
   
   typedef struct {
           zvol_async_op_t op;
           char name1[MAXNAMELEN];
           char name2[MAXNAMELEN];
           uint64_t value;
   } zvol_task_t;
   
   uint64_t
   zvol_name_hash(const char *name)
   {
           int i;
           uint64_t crc = -1ULL;
           const uint8_t *p = (const uint8_t *)name;
           ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY);
           for (i = 0; i < MAXNAMELEN - 1 && *p; i++, p++) {
                   crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ (*p)) & 0xFF];
           }
           return (crc);
   }
   
   /*
    * Find a zvol_state_t given the name and hash generated by zvol_name_hash.
    * If found, return with zv_suspend_lock and zv_state_lock taken, otherwise,
    * return (NULL) without the taking locks. The zv_suspend_lock is always taken
    * before zv_state_lock. The mode argument indicates the mode (including none)
    * for zv_suspend_lock to be taken.
    */
   zvol_state_t *
   zvol_find_by_name_hash(const char *name, uint64_t hash, int mode)
   {
           zvol_state_t *zv;
           struct hlist_node *p = NULL;
   
           rw_enter(&zvol_state_lock, RW_READER);
           hlist_for_each(p, ZVOL_HT_HEAD(hash)) {
                   zv = hlist_entry(p, zvol_state_t, zv_hlink);
                   mutex_enter(&zv->zv_state_lock);
                   if (zv->zv_hash == hash &&
                       strncmp(zv->zv_name, name, MAXNAMELEN) == 0) {
                           /*
                            * this is the right zvol, take the locks in the
                            * right order
                            */
                           if (mode != RW_NONE &&
                               !rw_tryenter(&zv->zv_suspend_lock, mode)) {
                                   mutex_exit(&zv->zv_state_lock);
                                   rw_enter(&zv->zv_suspend_lock, mode);
                                   mutex_enter(&zv->zv_state_lock);
                                   /*
                                    * zvol cannot be renamed as we continue
                                    * to hold zvol_state_lock
                                    */
                                   ASSERT(zv->zv_hash == hash &&
                                       strncmp(zv->zv_name, name, MAXNAMELEN)
                                       == 0);
                           }
                           rw_exit(&zvol_state_lock);
                           return (zv);
                   }
                   mutex_exit(&zv->zv_state_lock);
           }
           rw_exit(&zvol_state_lock);
   
           return (NULL);
   }
   
   /*
    * Find a zvol_state_t given the name.
    * If found, return with zv_suspend_lock and zv_state_lock taken, otherwise,
    * return (NULL) without the taking locks. The zv_suspend_lock is always taken
    * before zv_state_lock. The mode argument indicates the mode (including none)
    * for zv_suspend_lock to be taken.
    */
   static zvol_state_t *
   zvol_find_by_name(const char *name, int mode)
   {
           return (zvol_find_by_name_hash(name, zvol_name_hash(name), mode));
   }
   
   /*
    * ZFS_IOC_CREATE callback handles dmu zvol and zap object creation.
    */
   void
   zvol_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx)
   {
           zfs_creat_t *zct = arg;
           nvlist_t *nvprops = zct->zct_props;
           int error;
           uint64_t volblocksize, volsize;
   
           VERIFY(nvlist_lookup_uint64(nvprops,
               zfs_prop_to_name(ZFS_PROP_VOLSIZE), &volsize) == 0);
           if (nvlist_lookup_uint64(nvprops,
               zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), &volblocksize) != 0)
                   volblocksize = zfs_prop_default_numeric(ZFS_PROP_VOLBLOCKSIZE);
   
           /*
            * These properties must be removed from the list so the generic
            * property setting step won't apply to them.
            */
           VERIFY(nvlist_remove_all(nvprops,
               zfs_prop_to_name(ZFS_PROP_VOLSIZE)) == 0);
           (void) nvlist_remove_all(nvprops,
               zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE));
   
           error = dmu_object_claim(os, ZVOL_OBJ, DMU_OT_ZVOL, volblocksize,
               DMU_OT_NONE, 0, tx);
           ASSERT(error == 0);
   
           error = zap_create_claim(os, ZVOL_ZAP_OBJ, DMU_OT_ZVOL_PROP,
               DMU_OT_NONE, 0, tx);
           ASSERT(error == 0);
   
           error = zap_update(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize, tx);
           ASSERT(error == 0);
   }
   
   /*
    * ZFS_IOC_OBJSET_STATS entry point.
    */
   int
   zvol_get_stats(objset_t *os, nvlist_t *nv)
   {
           int error;
           dmu_object_info_t *doi;
           uint64_t val;
   
           error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &val);
           if (error)
                   return (SET_ERROR(error));
   
           dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_VOLSIZE, val);
           doi = kmem_alloc(sizeof (dmu_object_info_t), KM_SLEEP);
           error = dmu_object_info(os, ZVOL_OBJ, doi);
   
           if (error == 0) {
                   dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_VOLBLOCKSIZE,
                       doi->doi_data_block_size);
           }
   
           kmem_free(doi, sizeof (dmu_object_info_t));
   
           return (SET_ERROR(error));
   }
   
   /*
    * Sanity check volume size.
    */
   int
   zvol_check_volsize(uint64_t volsize, uint64_t blocksize)
   {
           if (volsize == 0)
                   return (SET_ERROR(EINVAL));
   
           if (volsize % blocksize != 0)
                   return (SET_ERROR(EINVAL));
   
   #ifdef _ILP32
           if (volsize - 1 > SPEC_MAXOFFSET_T)
                   return (SET_ERROR(EOVERFLOW));
   #endif
           return (0);
   }
   
   /*
    * Ensure the zap is flushed then inform the VFS of the capacity change.
    */
   static int
   zvol_update_volsize(uint64_t volsize, objset_t *os)
   {
           dmu_tx_t *tx;
           int error;
           uint64_t txg;
   
           tx = dmu_tx_create(os);
           dmu_tx_hold_zap(tx, ZVOL_ZAP_OBJ, TRUE, NULL);
           dmu_tx_mark_netfree(tx);
           error = dmu_tx_assign(tx, TXG_WAIT);
           if (error) {
                   dmu_tx_abort(tx);
                   return (SET_ERROR(error));
           }
           txg = dmu_tx_get_txg(tx);
   
           error = zap_update(os, ZVOL_ZAP_OBJ, "size", 8, 1,
               &volsize, tx);
           dmu_tx_commit(tx);
   
           txg_wait_synced(dmu_objset_pool(os), txg);
   
           if (error == 0)
                   error = dmu_free_long_range(os,
                       ZVOL_OBJ, volsize, DMU_OBJECT_END);
   
           return (error);
   }
   
   /*
    * Set ZFS_PROP_VOLSIZE set entry point.  Note that modifying the volume
    * size will result in a udev "change" event being generated.
    */
   int
   zvol_set_volsize(const char *name, uint64_t volsize)
   {
           objset_t *os = NULL;
           uint64_t readonly;
           int error;
           boolean_t owned = B_FALSE;
   
           error = dsl_prop_get_integer(name,
               zfs_prop_to_name(ZFS_PROP_READONLY), &readonly, NULL);
           if (error != 0)
                   return (SET_ERROR(error));
           if (readonly)
                   return (SET_ERROR(EROFS));
   
           zvol_state_t *zv = zvol_find_by_name(name, RW_READER);
   
           ASSERT(zv == NULL || (MUTEX_HELD(&zv->zv_state_lock) &&
               RW_READ_HELD(&zv->zv_suspend_lock)));
   
           if (zv == NULL || zv->zv_objset == NULL) {
                   if (zv != NULL)
                           rw_exit(&zv->zv_suspend_lock);
                   if ((error = dmu_objset_own(name, DMU_OST_ZVOL, B_FALSE, B_TRUE,
                       FTAG, &os)) != 0) {
                           if (zv != NULL)
                                   mutex_exit(&zv->zv_state_lock);
                           return (SET_ERROR(error));
                   }
                   owned = B_TRUE;
                   if (zv != NULL)
                           zv->zv_objset = os;
           } else {
                   os = zv->zv_objset;
           }
   
           dmu_object_info_t *doi = kmem_alloc(sizeof (*doi), KM_SLEEP);
   
           if ((error = dmu_object_info(os, ZVOL_OBJ, doi)) ||
               (error = zvol_check_volsize(volsize, doi->doi_data_block_size)))
                   goto out;
   
           error = zvol_update_volsize(volsize, os);
           if (error == 0 && zv != NULL) {
                   zv->zv_volsize = volsize;
                   zv->zv_changed = 1;
           }
   out:
           kmem_free(doi, sizeof (dmu_object_info_t));
   
           if (owned) {
                   dmu_objset_disown(os, B_TRUE, FTAG);
                   if (zv != NULL)
                           zv->zv_objset = NULL;
           } else {
                   rw_exit(&zv->zv_suspend_lock);
           }
   
           if (zv != NULL)
                   mutex_exit(&zv->zv_state_lock);
   
           if (error == 0 && zv != NULL)
                   zvol_os_update_volsize(zv, volsize);
   
           return (SET_ERROR(error));
   }
   
   /*
    * Sanity check volume block size.
    */
   int
   zvol_check_volblocksize(const char *name, uint64_t volblocksize)
   {
           /* Record sizes above 128k need the feature to be enabled */
           if (volblocksize > SPA_OLD_MAXBLOCKSIZE) {
                   spa_t *spa;
                   int error;
   
                   if ((error = spa_open(name, &spa, FTAG)) != 0)
                           return (error);
   
                   if (!spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_BLOCKS)) {
                           spa_close(spa, FTAG);
                           return (SET_ERROR(ENOTSUP));
                   }
   
                   /*
                    * We don't allow setting the property above 1MB,
                    * unless the tunable has been changed.
                    */
                   if (volblocksize > zfs_max_recordsize)
                           return (SET_ERROR(EDOM));
   
                   spa_close(spa, FTAG);
           }
   
           if (volblocksize < SPA_MINBLOCKSIZE ||
               volblocksize > SPA_MAXBLOCKSIZE ||
               !ISP2(volblocksize))
                   return (SET_ERROR(EDOM));
   
           return (0);
   }
   
   /*
    * Replay a TX_TRUNCATE ZIL transaction if asked.  TX_TRUNCATE is how we
    * implement DKIOCFREE/free-long-range.
    */
   static int
   zvol_replay_truncate(void *arg1, void *arg2, boolean_t byteswap)
   {
           zvol_state_t *zv = arg1;
           lr_truncate_t *lr = arg2;
           uint64_t offset, length;
   
           if (byteswap)
                   byteswap_uint64_array(lr, sizeof (*lr));
   
           offset = lr->lr_offset;
           length = lr->lr_length;
   
           dmu_tx_t *tx = dmu_tx_create(zv->zv_objset);
           dmu_tx_mark_netfree(tx);
           int error = dmu_tx_assign(tx, TXG_WAIT);
           if (error != 0) {
                   dmu_tx_abort(tx);
           } else {
                   (void) zil_replaying(zv->zv_zilog, tx);
                   dmu_tx_commit(tx);
                   error = dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, offset,
                       length);
           }
   
           return (error);
   }
   
   /*
    * Replay a TX_WRITE ZIL transaction that didn't get committed
    * after a system failure
    */
   static int
   zvol_replay_write(void *arg1, void *arg2, boolean_t byteswap)
   {
           zvol_state_t *zv = arg1;
           lr_write_t *lr = arg2;
           objset_t *os = zv->zv_objset;
           char *data = (char *)(lr + 1);  /* data follows lr_write_t */
           uint64_t offset, length;
           dmu_tx_t *tx;
           int error;
   
           if (byteswap)
                   byteswap_uint64_array(lr, sizeof (*lr));
   
           offset = lr->lr_offset;
           length = lr->lr_length;
   
           /* If it's a dmu_sync() block, write the whole block */
           if (lr->lr_common.lrc_reclen == sizeof (lr_write_t)) {
                   uint64_t blocksize = BP_GET_LSIZE(&lr->lr_blkptr);
                   if (length < blocksize) {
                           offset -= offset % blocksize;
                           length = blocksize;
                   }
           }
   
           tx = dmu_tx_create(os);
           dmu_tx_hold_write(tx, ZVOL_OBJ, offset, length);
           error = dmu_tx_assign(tx, TXG_WAIT);
           if (error) {
                   dmu_tx_abort(tx);
           } else {
                   dmu_write(os, ZVOL_OBJ, offset, length, data, tx);
                   (void) zil_replaying(zv->zv_zilog, tx);
                   dmu_tx_commit(tx);
           }
   
           return (error);
   }
   
   static int
   zvol_replay_err(void *arg1, void *arg2, boolean_t byteswap)
   {
           (void) arg1, (void) arg2, (void) byteswap;
           return (SET_ERROR(ENOTSUP));
   }
   
   /*
    * Callback vectors for replaying records.
    * Only TX_WRITE and TX_TRUNCATE are needed for zvol.
    */
   zil_replay_func_t *const zvol_replay_vector[TX_MAX_TYPE] = {
           zvol_replay_err,        /* no such transaction type */
           zvol_replay_err,        /* TX_CREATE */
           zvol_replay_err,        /* TX_MKDIR */
           zvol_replay_err,        /* TX_MKXATTR */
           zvol_replay_err,        /* TX_SYMLINK */
           zvol_replay_err,        /* TX_REMOVE */
           zvol_replay_err,        /* TX_RMDIR */
           zvol_replay_err,        /* TX_LINK */
           zvol_replay_err,        /* TX_RENAME */
           zvol_replay_write,      /* TX_WRITE */
           zvol_replay_truncate,   /* TX_TRUNCATE */
           zvol_replay_err,        /* TX_SETATTR */
           zvol_replay_err,        /* TX_ACL */
           zvol_replay_err,        /* TX_CREATE_ATTR */
           zvol_replay_err,        /* TX_CREATE_ACL_ATTR */
           zvol_replay_err,        /* TX_MKDIR_ACL */
           zvol_replay_err,        /* TX_MKDIR_ATTR */
           zvol_replay_err,        /* TX_MKDIR_ACL_ATTR */
           zvol_replay_err,        /* TX_WRITE2 */
           zvol_replay_err,        /* TX_SETSAXATTR */
           zvol_replay_err,        /* TX_RENAME_EXCHANGE */
           zvol_replay_err,        /* TX_RENAME_WHITEOUT */
   };
   
   /*
    * zvol_log_write() handles synchronous writes using TX_WRITE ZIL transactions.
    *
    * We store data in the log buffers if it's small enough.
    * Otherwise we will later flush the data out via dmu_sync().
    */
   static const ssize_t zvol_immediate_write_sz = 32768;
   
   void
   zvol_log_write(zvol_state_t *zv, dmu_tx_t *tx, uint64_t offset,
       uint64_t size, int sync)
   {
           uint32_t blocksize = zv->zv_volblocksize;
           zilog_t *zilog = zv->zv_zilog;
           itx_wr_state_t write_state;
           uint64_t sz = size;
   
           if (zil_replaying(zilog, tx))
                   return;
   
           if (zilog->zl_logbias == ZFS_LOGBIAS_THROUGHPUT)
                   write_state = WR_INDIRECT;
           else if (!spa_has_slogs(zilog->zl_spa) &&
               size >= blocksize && blocksize > zvol_immediate_write_sz)
                   write_state = WR_INDIRECT;
           else if (sync)
                   write_state = WR_COPIED;
           else
                   write_state = WR_NEED_COPY;
   
           while (size) {
                   itx_t *itx;
                   lr_write_t *lr;
                   itx_wr_state_t wr_state = write_state;
                   ssize_t len = size;
   
                   if (wr_state == WR_COPIED && size > zil_max_copied_data(zilog))
                           wr_state = WR_NEED_COPY;
                   else if (wr_state == WR_INDIRECT)
                           len = MIN(blocksize - P2PHASE(offset, blocksize), size);
   
                   itx = zil_itx_create(TX_WRITE, sizeof (*lr) +
                       (wr_state == WR_COPIED ? len : 0));
                   lr = (lr_write_t *)&itx->itx_lr;
                   if (wr_state == WR_COPIED && dmu_read_by_dnode(zv->zv_dn,
                       offset, len, lr+1, DMU_READ_NO_PREFETCH) != 0) {
                           zil_itx_destroy(itx);
                           itx = zil_itx_create(TX_WRITE, sizeof (*lr));
                           lr = (lr_write_t *)&itx->itx_lr;
                           wr_state = WR_NEED_COPY;
                   }
   
                   itx->itx_wr_state = wr_state;
                   lr->lr_foid = ZVOL_OBJ;
                   lr->lr_offset = offset;
                   lr->lr_length = len;
                   lr->lr_blkoff = 0;
                   BP_ZERO(&lr->lr_blkptr);
   
                   itx->itx_private = zv;
                   itx->itx_sync = sync;
   
                   (void) zil_itx_assign(zilog, itx, tx);
   
                   offset += len;
                   size -= len;
           }
   
           if (write_state == WR_COPIED || write_state == WR_NEED_COPY) {
                   dsl_pool_wrlog_count(zilog->zl_dmu_pool, sz, tx->tx_txg);
           }
   }
   
   /*
    * Log a DKIOCFREE/free-long-range to the ZIL with TX_TRUNCATE.
    */
   void
   zvol_log_truncate(zvol_state_t *zv, dmu_tx_t *tx, uint64_t off, uint64_t len,
       boolean_t sync)
   {
           itx_t *itx;
           lr_truncate_t *lr;
           zilog_t *zilog = zv->zv_zilog;
   
           if (zil_replaying(zilog, tx))
                   return;
   
           itx = zil_itx_create(TX_TRUNCATE, sizeof (*lr));
           lr = (lr_truncate_t *)&itx->itx_lr;
           lr->lr_foid = ZVOL_OBJ;
           lr->lr_offset = off;
           lr->lr_length = len;
   
           itx->itx_sync = sync;
           zil_itx_assign(zilog, itx, tx);
   }
   
   
   static void
   zvol_get_done(zgd_t *zgd, int error)
   {
           (void) error;
           if (zgd->zgd_db)
                   dmu_buf_rele(zgd->zgd_db, zgd);
   
           zfs_rangelock_exit(zgd->zgd_lr);
   
           kmem_free(zgd, sizeof (zgd_t));
   }
   
   /*
    * Get data to generate a TX_WRITE intent log record.
    */
   int
   zvol_get_data(void *arg, uint64_t arg2, lr_write_t *lr, char *buf,
       struct lwb *lwb, zio_t *zio)
   {
           zvol_state_t *zv = arg;
           uint64_t offset = lr->lr_offset;
           uint64_t size = lr->lr_length;
           dmu_buf_t *db;
           zgd_t *zgd;
           int error;
   
           ASSERT3P(lwb, !=, NULL);
           ASSERT3P(zio, !=, NULL);
           ASSERT3U(size, !=, 0);
   
           zgd = kmem_zalloc(sizeof (zgd_t), KM_SLEEP);
           zgd->zgd_lwb = lwb;
   
           /*
            * Write records come in two flavors: immediate and indirect.
            * For small writes it's cheaper to store the data with the
            * log record (immediate); for large writes it's cheaper to
            * sync the data and get a pointer to it (indirect) so that
            * we don't have to write the data twice.
            */
           if (buf != NULL) { /* immediate write */
                   zgd->zgd_lr = zfs_rangelock_enter(&zv->zv_rangelock, offset,
                       size, RL_READER);
                   error = dmu_read_by_dnode(zv->zv_dn, offset, size, buf,
                       DMU_READ_NO_PREFETCH);
           } else { /* indirect write */
                   /*
                    * Have to lock the whole block to ensure when it's written out
                    * and its checksum is being calculated that no one can change
                    * the data. Contrarily to zfs_get_data we need not re-check
                    * blocksize after we get the lock because it cannot be changed.
                    */
                   size = zv->zv_volblocksize;
                   offset = P2ALIGN_TYPED(offset, size, uint64_t);
                   zgd->zgd_lr = zfs_rangelock_enter(&zv->zv_rangelock, offset,
                       size, RL_READER);
                   error = dmu_buf_hold_by_dnode(zv->zv_dn, offset, zgd, &db,
                       DMU_READ_NO_PREFETCH);
                   if (error == 0) {
                           blkptr_t *bp = &lr->lr_blkptr;
   
                           zgd->zgd_db = db;
                           zgd->zgd_bp = bp;
   
                           ASSERT(db != NULL);
                           ASSERT(db->db_offset == offset);
                           ASSERT(db->db_size == size);
   
                           error = dmu_sync(zio, lr->lr_common.lrc_txg,
                               zvol_get_done, zgd);
   
                           if (error == 0)
                                   return (0);
                   }
           }
   
           zvol_get_done(zgd, error);
   
           return (SET_ERROR(error));
   }
   
   /*
    * The zvol_state_t's are inserted into zvol_state_list and zvol_htable.
    */
   
   void
   zvol_insert(zvol_state_t *zv)
   {
           ASSERT(RW_WRITE_HELD(&zvol_state_lock));
           list_insert_head(&zvol_state_list, zv);
           hlist_add_head(&zv->zv_hlink, ZVOL_HT_HEAD(zv->zv_hash));
   }
   
   /*
    * Simply remove the zvol from to list of zvols.
    */
   static void
   zvol_remove(zvol_state_t *zv)
   {
           ASSERT(RW_WRITE_HELD(&zvol_state_lock));
           list_remove(&zvol_state_list, zv);
           hlist_del(&zv->zv_hlink);
   }
   
   /*
    * Setup zv after we just own the zv->objset
    */
   static int
   zvol_setup_zv(zvol_state_t *zv)
   {
           uint64_t volsize;
           int error;
           uint64_t ro;
           objset_t *os = zv->zv_objset;
   
           ASSERT(MUTEX_HELD(&zv->zv_state_lock));
           ASSERT(RW_LOCK_HELD(&zv->zv_suspend_lock));
   
           zv->zv_zilog = NULL;
           zv->zv_flags &= ~ZVOL_WRITTEN_TO;
   
           error = dsl_prop_get_integer(zv->zv_name, "readonly", &ro, NULL);
           if (error)
                   return (SET_ERROR(error));
   
           error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);
           if (error)
                   return (SET_ERROR(error));
   
           error = dnode_hold(os, ZVOL_OBJ, zv, &zv->zv_dn);
           if (error)
                   return (SET_ERROR(error));
   
           zvol_os_set_capacity(zv, volsize >> 9);
           zv->zv_volsize = volsize;
   
           if (ro || dmu_objset_is_snapshot(os) ||
               !spa_writeable(dmu_objset_spa(os))) {
                   zvol_os_set_disk_ro(zv, 1);
                   zv->zv_flags |= ZVOL_RDONLY;
           } else {
                   zvol_os_set_disk_ro(zv, 0);
                   zv->zv_flags &= ~ZVOL_RDONLY;
           }
           return (0);
   }
   
   /*
    * Shutdown every zv_objset related stuff except zv_objset itself.
    * The is the reverse of zvol_setup_zv.
    */
   static void
   zvol_shutdown_zv(zvol_state_t *zv)
   {
           ASSERT(MUTEX_HELD(&zv->zv_state_lock) &&
               RW_LOCK_HELD(&zv->zv_suspend_lock));
   
           if (zv->zv_flags & ZVOL_WRITTEN_TO) {
                   ASSERT(zv->zv_zilog != NULL);
                   zil_close(zv->zv_zilog);
           }
   
           zv->zv_zilog = NULL;
   
           dnode_rele(zv->zv_dn, zv);
           zv->zv_dn = NULL;
   
           /*
            * Evict cached data. We must write out any dirty data before
            * disowning the dataset.
            */
           if (zv->zv_flags & ZVOL_WRITTEN_TO)
                   txg_wait_synced(dmu_objset_pool(zv->zv_objset), 0);
           (void) dmu_objset_evict_dbufs(zv->zv_objset);
   }
   
   /*
    * return the proper tag for rollback and recv
    */
   void *
   zvol_tag(zvol_state_t *zv)
   {
           ASSERT(RW_WRITE_HELD(&zv->zv_suspend_lock));
           return (zv->zv_open_count > 0 ? zv : NULL);
   }
   
   /*
    * Suspend the zvol for recv and rollback.
    */
   zvol_state_t *
   zvol_suspend(const char *name)
   {
           zvol_state_t *zv;
   
           zv = zvol_find_by_name(name, RW_WRITER);
   
           if (zv == NULL)
                   return (NULL);
   
           /* block all I/O, release in zvol_resume. */
           ASSERT(MUTEX_HELD(&zv->zv_state_lock));
           ASSERT(RW_WRITE_HELD(&zv->zv_suspend_lock));
   
           atomic_inc(&zv->zv_suspend_ref);
   
           if (zv->zv_open_count > 0)
                   zvol_shutdown_zv(zv);
   
           /*
            * do not hold zv_state_lock across suspend/resume to
            * avoid locking up zvol lookups
            */
           mutex_exit(&zv->zv_state_lock);
   
           /* zv_suspend_lock is released in zvol_resume() */
           return (zv);
   }
   
   int
   zvol_resume(zvol_state_t *zv)
   {
           int error = 0;
   
           ASSERT(RW_WRITE_HELD(&zv->zv_suspend_lock));
   
           mutex_enter(&zv->zv_state_lock);
   
           if (zv->zv_open_count > 0) {
                   VERIFY0(dmu_objset_hold(zv->zv_name, zv, &zv->zv_objset));
                   VERIFY3P(zv->zv_objset->os_dsl_dataset->ds_owner, ==, zv);
                   VERIFY(dsl_dataset_long_held(zv->zv_objset->os_dsl_dataset));
                   dmu_objset_rele(zv->zv_objset, zv);
   
                   error = zvol_setup_zv(zv);
           }
   
           mutex_exit(&zv->zv_state_lock);
   
           rw_exit(&zv->zv_suspend_lock);
           /*
            * We need this because we don't hold zvol_state_lock while releasing
            * zv_suspend_lock. zvol_remove_minors_impl thus cannot check
            * zv_suspend_lock to determine it is safe to free because rwlock is
            * not inherent atomic.
            */
           atomic_dec(&zv->zv_suspend_ref);
   
           return (SET_ERROR(error));
   }
   
   int
   zvol_first_open(zvol_state_t *zv, boolean_t readonly)
   {
           objset_t *os;
           int error;
   
           ASSERT(RW_READ_HELD(&zv->zv_suspend_lock));
           ASSERT(MUTEX_HELD(&zv->zv_state_lock));
           ASSERT(mutex_owned(&spa_namespace_lock));
   
           boolean_t ro = (readonly || (strchr(zv->zv_name, '@') != NULL));
           error = dmu_objset_own(zv->zv_name, DMU_OST_ZVOL, ro, B_TRUE, zv, &os);
           if (error)
                   return (SET_ERROR(error));
   
           zv->zv_objset = os;
   
           error = zvol_setup_zv(zv);
           if (error) {
                   dmu_objset_disown(os, 1, zv);
                   zv->zv_objset = NULL;
           }
   
           return (error);
   }
   
   void
   zvol_last_close(zvol_state_t *zv)
   {
           ASSERT(RW_READ_HELD(&zv->zv_suspend_lock));
           ASSERT(MUTEX_HELD(&zv->zv_state_lock));
   
           zvol_shutdown_zv(zv);
   
           dmu_objset_disown(zv->zv_objset, 1, zv);
           zv->zv_objset = NULL;
   }
   
   typedef struct minors_job {
           list_t *list;
           list_node_t link;
           /* input */
           char *name;
           /* output */
           int error;
   } minors_job_t;
   
   /*
    * Prefetch zvol dnodes for the minors_job
    */
   static void
   zvol_prefetch_minors_impl(void *arg)
   {
           minors_job_t *job = arg;
           char *dsname = job->name;
           objset_t *os = NULL;
   
           job->error = dmu_objset_own(dsname, DMU_OST_ZVOL, B_TRUE, B_TRUE,
               FTAG, &os);
           if (job->error == 0) {
                   dmu_prefetch(os, ZVOL_OBJ, 0, 0, 0, ZIO_PRIORITY_SYNC_READ);
                   dmu_objset_disown(os, B_TRUE, FTAG);
           }
   }
   
   /*
    * Mask errors to continue dmu_objset_find() traversal
    */
   static int
   zvol_create_snap_minor_cb(const char *dsname, void *arg)
   {
           minors_job_t *j = arg;
           list_t *minors_list = j->list;
           const char *name = j->name;
   
           ASSERT0(MUTEX_HELD(&spa_namespace_lock));
   
           /* skip the designated dataset */
           if (name && strcmp(dsname, name) == 0)
                   return (0);
   
           /* at this point, the dsname should name a snapshot */
           if (strchr(dsname, '@') == 0) {
                   dprintf("zvol_create_snap_minor_cb(): "
                       "%s is not a snapshot name\n", dsname);
           } else {
                   minors_job_t *job;
                   char *n = kmem_strdup(dsname);
                   if (n == NULL)
                           return (0);
   
                   job = kmem_alloc(sizeof (minors_job_t), KM_SLEEP);
                   job->name = n;
                   job->list = minors_list;
                   job->error = 0;
                   list_insert_tail(minors_list, job);
                   /* don't care if dispatch fails, because job->error is 0 */
                   taskq_dispatch(system_taskq, zvol_prefetch_minors_impl, job,
                       TQ_SLEEP);
           }
   
           return (0);
   }
   
   /*
    * If spa_keystore_load_wkey() is called for an encrypted zvol,
    * we need to look for any clones also using the key. This function
    * is "best effort" - so we just skip over it if there are failures.
    */
   static void
   zvol_add_clones(const char *dsname, list_t *minors_list)
   {
           /* Also check if it has clones */
           dsl_dir_t *dd = NULL;
           dsl_pool_t *dp = NULL;
   
           if (dsl_pool_hold(dsname, FTAG, &dp) != 0)
                   return;
   
           if (!spa_feature_is_enabled(dp->dp_spa,
               SPA_FEATURE_ENCRYPTION))
                   goto out;
   
           if (dsl_dir_hold(dp, dsname, FTAG, &dd, NULL) != 0)
                   goto out;
   
           if (dsl_dir_phys(dd)->dd_clones == 0)
                   goto out;
   
           zap_cursor_t *zc = kmem_alloc(sizeof (zap_cursor_t), KM_SLEEP);
           zap_attribute_t *za = kmem_alloc(sizeof (zap_attribute_t), KM_SLEEP);
          objset_t *mos = dd->dd_pool->dp_meta_objset;
  
          for (zap_cursor_init(zc, mos, dsl_dir_phys(dd)->dd_clones);
              zap_cursor_retrieve(zc, za) == 0;
              zap_cursor_advance(zc)) {
                  dsl_dataset_t *clone;
                  minors_job_t *job;
  
                  if (dsl_dataset_hold_obj(dd->dd_pool,
                      za->za_first_integer, FTAG, &clone) == 0) {
  
                          char name[ZFS_MAX_DATASET_NAME_LEN];
                          dsl_dataset_name(clone, name);
  
                          char *n = kmem_strdup(name);
                          job = kmem_alloc(sizeof (minors_job_t), KM_SLEEP);
                          job->name = n;
                          job->list = minors_list;
                          job->error = 0;
                          list_insert_tail(minors_list, job);
  
                          dsl_dataset_rele(clone, FTAG);
                  }
          }
          zap_cursor_fini(zc);
          kmem_free(za, sizeof (zap_attribute_t));
          kmem_free(zc, sizeof (zap_cursor_t));
  
  out:
          if (dd != NULL)
                  dsl_dir_rele(dd, FTAG);
          dsl_pool_rele(dp, FTAG);
  }
  
  /*
   * Mask errors to continue dmu_objset_find() traversal
   */
  static int
  zvol_create_minors_cb(const char *dsname, void *arg)
  {
          uint64_t snapdev;
          int error;
          list_t *minors_list = arg;
  
          ASSERT0(MUTEX_HELD(&spa_namespace_lock));
  
          error = dsl_prop_get_integer(dsname, "snapdev", &snapdev, NULL);
          if (error)
                  return (0);
  
          /*
           * Given the name and the 'snapdev' property, create device minor nodes
           * with the linkages to zvols/snapshots as needed.
           * If the name represents a zvol, create a minor node for the zvol, then
           * check if its snapshots are 'visible', and if so, iterate over the
           * snapshots and create device minor nodes for those.
           */
          if (strchr(dsname, '@') == 0) {
                  minors_job_t *job;
                  char *n = kmem_strdup(dsname);
                  if (n == NULL)
                          return (0);
  
                  job = kmem_alloc(sizeof (minors_job_t), KM_SLEEP);
                  job->name = n;
                  job->list = minors_list;
                  job->error = 0;
                  list_insert_tail(minors_list, job);
                  /* don't care if dispatch fails, because job->error is 0 */
                  taskq_dispatch(system_taskq, zvol_prefetch_minors_impl, job,
                      TQ_SLEEP);
  
                  zvol_add_clones(dsname, minors_list);
  
                  if (snapdev == ZFS_SNAPDEV_VISIBLE) {
                          /*
                           * traverse snapshots only, do not traverse children,
                           * and skip the 'dsname'
                           */
                          (void) dmu_objset_find(dsname,
                              zvol_create_snap_minor_cb, (void *)job,
                              DS_FIND_SNAPSHOTS);
                  }
          } else {
                  dprintf("zvol_create_minors_cb(): %s is not a zvol name\n",
                      dsname);
          }
  
          return (0);
  }
  
  /*
   * Create minors for the specified dataset, including children and snapshots.
   * Pay attention to the 'snapdev' property and iterate over the snapshots
   * only if they are 'visible'. This approach allows one to assure that the
   * snapshot metadata is read from disk only if it is needed.
   *
   * The name can represent a dataset to be recursively scanned for zvols and
   * their snapshots, or a single zvol snapshot. If the name represents a
   * dataset, the scan is performed in two nested stages:
   * - scan the dataset for zvols, and
   * - for each zvol, create a minor node, then check if the zvol's snapshots
   *   are 'visible', and only then iterate over the snapshots if needed
   *
   * If the name represents a snapshot, a check is performed if the snapshot is
   * 'visible' (which also verifies that the parent is a zvol), and if so,
   * a minor node for that snapshot is created.
   */
  void
  zvol_create_minors_recursive(const char *name)
  {
          list_t minors_list;
          minors_job_t *job;
  
          if (zvol_inhibit_dev)
                  return;
  
          /*
           * This is the list for prefetch jobs. Whenever we found a match
           * during dmu_objset_find, we insert a minors_job to the list and do
           * taskq_dispatch to parallel prefetch zvol dnodes. Note we don't need
           * any lock because all list operation is done on the current thread.
           *
           * We will use this list to do zvol_os_create_minor after prefetch
           * so we don't have to traverse using dmu_objset_find again.
           */
          list_create(&minors_list, sizeof (minors_job_t),
              offsetof(minors_job_t, link));
  
  
          if (strchr(name, '@') != NULL) {
                  uint64_t snapdev;
  
                  int error = dsl_prop_get_integer(name, "snapdev",
                      &snapdev, NULL);
  
                  if (error == 0 && snapdev == ZFS_SNAPDEV_VISIBLE)
                          (void) zvol_os_create_minor(name);
          } else {
                  fstrans_cookie_t cookie = spl_fstrans_mark();
                  (void) dmu_objset_find(name, zvol_create_minors_cb,
                      &minors_list, DS_FIND_CHILDREN);
                  spl_fstrans_unmark(cookie);
          }
  
          taskq_wait_outstanding(system_taskq, 0);
  
          /*
           * Prefetch is completed, we can do zvol_os_create_minor
           * sequentially.
           */
          while ((job = list_head(&minors_list)) != NULL) {
                  list_remove(&minors_list, job);
                  if (!job->error)
                          (void) zvol_os_create_minor(job->name);
                  kmem_strfree(job->name);
                  kmem_free(job, sizeof (minors_job_t));
          }
  
          list_destroy(&minors_list);
  }
  
  void
  zvol_create_minor(const char *name)
  {
          /*
           * Note: the dsl_pool_config_lock must not be held.
           * Minor node creation needs to obtain the zvol_state_lock.
           * zvol_open() obtains the zvol_state_lock and then the dsl pool
           * config lock.  Therefore, we can't have the config lock now if
           * we are going to wait for the zvol_state_lock, because it
           * would be a lock order inversion which could lead to deadlock.
           */
  
          if (zvol_inhibit_dev)
                  return;
  
          if (strchr(name, '@') != NULL) {
                  uint64_t snapdev;
  
                  int error = dsl_prop_get_integer(name,
                      "snapdev", &snapdev, NULL);
  
                  if (error == 0 && snapdev == ZFS_SNAPDEV_VISIBLE)
                          (void) zvol_os_create_minor(name);
          } else {
                  (void) zvol_os_create_minor(name);
          }
  }
  
  /*
   * Remove minors for specified dataset including children and snapshots.
   */
  
  static void
  zvol_free_task(void *arg)
  {
          zvol_os_free(arg);
  }
  
  void
  zvol_remove_minors_impl(const char *name)
  {
          zvol_state_t *zv, *zv_next;
          int namelen = ((name) ? strlen(name) : 0);
          taskqid_t t;
          list_t free_list;
  
          if (zvol_inhibit_dev)
                  return;
  
          list_create(&free_list, sizeof (zvol_state_t),
              offsetof(zvol_state_t, zv_next));
  
          rw_enter(&zvol_state_lock, RW_WRITER);
  
          for (zv = list_head(&zvol_state_list); zv != NULL; zv = zv_next) {
                  zv_next = list_next(&zvol_state_list, zv);
  
                  mutex_enter(&zv->zv_state_lock);
                  if (name == NULL || strcmp(zv->zv_name, name) == 0 ||
                      (strncmp(zv->zv_name, name, namelen) == 0 &&
                      (zv->zv_name[namelen] == '/' ||
                      zv->zv_name[namelen] == '@'))) {
                          /*
                           * By holding zv_state_lock here, we guarantee that no
                           * one is currently using this zv
                           */
  
                          /* If in use, leave alone */
                          if (zv->zv_open_count > 0 ||
                              atomic_read(&zv->zv_suspend_ref)) {
                                  mutex_exit(&zv->zv_state_lock);
                                  continue;
                          }
  
                          zvol_remove(zv);
  
                          /*
                           * Cleared while holding zvol_state_lock as a writer
                           * which will prevent zvol_open() from opening it.
                           */
                          zvol_os_clear_private(zv);
  
                          /* Drop zv_state_lock before zvol_free() */
                          mutex_exit(&zv->zv_state_lock);
  
                          /* Try parallel zv_free, if failed do it in place */
                          t = taskq_dispatch(system_taskq, zvol_free_task, zv,
                              TQ_SLEEP);
                          if (t == TASKQID_INVALID)
                                  list_insert_head(&free_list, zv);
                  } else {
                          mutex_exit(&zv->zv_state_lock);
                  }
          }
          rw_exit(&zvol_state_lock);
  
          /* Drop zvol_state_lock before calling zvol_free() */
          while ((zv = list_head(&free_list)) != NULL) {
                  list_remove(&free_list, zv);
                  zvol_os_free(zv);
          }
  }
  
  /* Remove minor for this specific volume only */
  static void
  zvol_remove_minor_impl(const char *name)
  {
          zvol_state_t *zv = NULL, *zv_next;
  
          if (zvol_inhibit_dev)
                  return;
  
          rw_enter(&zvol_state_lock, RW_WRITER);
  
          for (zv = list_head(&zvol_state_list); zv != NULL; zv = zv_next) {
                  zv_next = list_next(&zvol_state_list, zv);
  
                  mutex_enter(&zv->zv_state_lock);
                  if (strcmp(zv->zv_name, name) == 0) {
                          /*
                           * By holding zv_state_lock here, we guarantee that no
                           * one is currently using this zv
                           */
  
                          /* If in use, leave alone */
                          if (zv->zv_open_count > 0 ||
                              atomic_read(&zv->zv_suspend_ref)) {
                                  mutex_exit(&zv->zv_state_lock);
                                  continue;
                          }
                          zvol_remove(zv);
  
                          zvol_os_clear_private(zv);
                          mutex_exit(&zv->zv_state_lock);
                          break;
                  } else {
                          mutex_exit(&zv->zv_state_lock);
                  }
          }
  
          /* Drop zvol_state_lock before calling zvol_free() */
          rw_exit(&zvol_state_lock);
  
          if (zv != NULL)
                  zvol_os_free(zv);
  }
  
  /*
   * Rename minors for specified dataset including children and snapshots.
   */
  static void
  zvol_rename_minors_impl(const char *oldname, const char *newname)
  {
          zvol_state_t *zv, *zv_next;
          int oldnamelen;
  
          if (zvol_inhibit_dev)
                  return;
  
          oldnamelen = strlen(oldname);
  
          rw_enter(&zvol_state_lock, RW_READER);
  
          for (zv = list_head(&zvol_state_list); zv != NULL; zv = zv_next) {
                  zv_next = list_next(&zvol_state_list, zv);
  
                  mutex_enter(&zv->zv_state_lock);
  
                  if (strcmp(zv->zv_name, oldname) == 0) {
                          zvol_os_rename_minor(zv, newname);
                  } else if (strncmp(zv->zv_name, oldname, oldnamelen) == 0 &&
                      (zv->zv_name[oldnamelen] == '/' ||
                      zv->zv_name[oldnamelen] == '@')) {
                          char *name = kmem_asprintf("%s%c%s", newname,
                              zv->zv_name[oldnamelen],
                              zv->zv_name + oldnamelen + 1);
                          zvol_os_rename_minor(zv, name);
                          kmem_strfree(name);
                  }
  
                  mutex_exit(&zv->zv_state_lock);
          }
  
          rw_exit(&zvol_state_lock);
  }
  
  typedef struct zvol_snapdev_cb_arg {
          uint64_t snapdev;
  } zvol_snapdev_cb_arg_t;
  
  static int
  zvol_set_snapdev_cb(const char *dsname, void *param)
  {
          zvol_snapdev_cb_arg_t *arg = param;
  
          if (strchr(dsname, '@') == NULL)
                  return (0);
  
          switch (arg->snapdev) {
                  case ZFS_SNAPDEV_VISIBLE:
                          (void) zvol_os_create_minor(dsname);
                          break;
                  case ZFS_SNAPDEV_HIDDEN:
                          (void) zvol_remove_minor_impl(dsname);
                          break;
          }
  
          return (0);
  }
  
  static void
  zvol_set_snapdev_impl(char *name, uint64_t snapdev)
  {
          zvol_snapdev_cb_arg_t arg = {snapdev};
          fstrans_cookie_t cookie = spl_fstrans_mark();
          /*
           * The zvol_set_snapdev_sync() sets snapdev appropriately
           * in the dataset hierarchy. Here, we only scan snapshots.
           */
          dmu_objset_find(name, zvol_set_snapdev_cb, &arg, DS_FIND_SNAPSHOTS);
          spl_fstrans_unmark(cookie);
  }
  
  static void
  zvol_set_volmode_impl(char *name, uint64_t volmode)
  {
          fstrans_cookie_t cookie;
          uint64_t old_volmode;
          zvol_state_t *zv;
  
          if (strchr(name, '@') != NULL)
                  return;
  
          /*
           * It's unfortunate we need to remove minors before we create new ones:
           * this is necessary because our backing gendisk (zvol_state->zv_disk)
           * could be different when we set, for instance, volmode from "geom"
           * to "dev" (or vice versa).
           */
          zv = zvol_find_by_name(name, RW_NONE);
          if (zv == NULL && volmode == ZFS_VOLMODE_NONE)
                          return;
          if (zv != NULL) {
                  old_volmode = zv->zv_volmode;
                  mutex_exit(&zv->zv_state_lock);
                  if (old_volmode == volmode)
                          return;
                  zvol_wait_close(zv);
          }
          cookie = spl_fstrans_mark();
          switch (volmode) {
                  case ZFS_VOLMODE_NONE:
                          (void) zvol_remove_minor_impl(name);
                          break;
                  case ZFS_VOLMODE_GEOM:
                  case ZFS_VOLMODE_DEV:
                          (void) zvol_remove_minor_impl(name);
                          (void) zvol_os_create_minor(name);
                          break;
                  case ZFS_VOLMODE_DEFAULT:
                          (void) zvol_remove_minor_impl(name);
                          if (zvol_volmode == ZFS_VOLMODE_NONE)
                                  break;
                          else /* if zvol_volmode is invalid defaults to "geom" */
                                  (void) zvol_os_create_minor(name);
                          break;
          }
          spl_fstrans_unmark(cookie);
  }
  
  static zvol_task_t *
  zvol_task_alloc(zvol_async_op_t op, const char *name1, const char *name2,
      uint64_t value)
  {
          zvol_task_t *task;
  
          /* Never allow tasks on hidden names. */
          if (name1[0] == '$')
                  return (NULL);
  
          task = kmem_zalloc(sizeof (zvol_task_t), KM_SLEEP);
          task->op = op;
          task->value = value;
  
          strlcpy(task->name1, name1, MAXNAMELEN);
          if (name2 != NULL)
                  strlcpy(task->name2, name2, MAXNAMELEN);
  
          return (task);
  }
  
  static void
  zvol_task_free(zvol_task_t *task)
  {
          kmem_free(task, sizeof (zvol_task_t));
  }
  
  /*
   * The worker thread function performed asynchronously.
   */
  static void
  zvol_task_cb(void *arg)
  {
          zvol_task_t *task = arg;
  
          switch (task->op) {
          case ZVOL_ASYNC_REMOVE_MINORS:
                  zvol_remove_minors_impl(task->name1);
                  break;
          case ZVOL_ASYNC_RENAME_MINORS:
                  zvol_rename_minors_impl(task->name1, task->name2);
                  break;
          case ZVOL_ASYNC_SET_SNAPDEV:
                  zvol_set_snapdev_impl(task->name1, task->value);
                  break;
          case ZVOL_ASYNC_SET_VOLMODE:
                  zvol_set_volmode_impl(task->name1, task->value);
                  break;
          default:
                  VERIFY(0);
                  break;
          }
  
          zvol_task_free(task);
  }
  
  typedef struct zvol_set_prop_int_arg {
          const char *zsda_name;
          uint64_t zsda_value;
          zprop_source_t zsda_source;
          dmu_tx_t *zsda_tx;
  } zvol_set_prop_int_arg_t;
  
  /*
   * Sanity check the dataset for safe use by the sync task.  No additional
   * conditions are imposed.
   */
  static int
  zvol_set_snapdev_check(void *arg, dmu_tx_t *tx)
  {
          zvol_set_prop_int_arg_t *zsda = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          dsl_dir_t *dd;
          int error;
  
          error = dsl_dir_hold(dp, zsda->zsda_name, FTAG, &dd, NULL);
          if (error != 0)
                  return (error);
  
          dsl_dir_rele(dd, FTAG);
  
          return (error);
  }
  
  static int
  zvol_set_snapdev_sync_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
  {
          (void) arg;
          char dsname[MAXNAMELEN];
          zvol_task_t *task;
          uint64_t snapdev;
  
          dsl_dataset_name(ds, dsname);
          if (dsl_prop_get_int_ds(ds, "snapdev", &snapdev) != 0)
                  return (0);
          task = zvol_task_alloc(ZVOL_ASYNC_SET_SNAPDEV, dsname, NULL, snapdev);
          if (task == NULL)
                  return (0);
  
          (void) taskq_dispatch(dp->dp_spa->spa_zvol_taskq, zvol_task_cb,
              task, TQ_SLEEP);
          return (0);
  }
  
  /*
   * Traverse all child datasets and apply snapdev appropriately.
   * We call dsl_prop_set_sync_impl() here to set the value only on the toplevel
   * dataset and read the effective "snapdev" on every child in the callback
   * function: this is because the value is not guaranteed to be the same in the
   * whole dataset hierarchy.
   */
  static void
  zvol_set_snapdev_sync(void *arg, dmu_tx_t *tx)
  {
          zvol_set_prop_int_arg_t *zsda = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          dsl_dir_t *dd;
          dsl_dataset_t *ds;
          int error;
  
          VERIFY0(dsl_dir_hold(dp, zsda->zsda_name, FTAG, &dd, NULL));
          zsda->zsda_tx = tx;
  
          error = dsl_dataset_hold(dp, zsda->zsda_name, FTAG, &ds);
          if (error == 0) {
                  dsl_prop_set_sync_impl(ds, zfs_prop_to_name(ZFS_PROP_SNAPDEV),
                      zsda->zsda_source, sizeof (zsda->zsda_value), 1,
                      &zsda->zsda_value, zsda->zsda_tx);
                  dsl_dataset_rele(ds, FTAG);
          }
          dmu_objset_find_dp(dp, dd->dd_object, zvol_set_snapdev_sync_cb,
              zsda, DS_FIND_CHILDREN);
  
          dsl_dir_rele(dd, FTAG);
  }
  
  int
  zvol_set_snapdev(const char *ddname, zprop_source_t source, uint64_t snapdev)
  {
          zvol_set_prop_int_arg_t zsda;
  
          zsda.zsda_name = ddname;
          zsda.zsda_source = source;
          zsda.zsda_value = snapdev;
  
          return (dsl_sync_task(ddname, zvol_set_snapdev_check,
              zvol_set_snapdev_sync, &zsda, 0, ZFS_SPACE_CHECK_NONE));
  }
  
  /*
   * Sanity check the dataset for safe use by the sync task.  No additional
   * conditions are imposed.
   */
  static int
  zvol_set_volmode_check(void *arg, dmu_tx_t *tx)
  {
          zvol_set_prop_int_arg_t *zsda = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          dsl_dir_t *dd;
          int error;
  
          error = dsl_dir_hold(dp, zsda->zsda_name, FTAG, &dd, NULL);
          if (error != 0)
                  return (error);
  
          dsl_dir_rele(dd, FTAG);
  
          return (error);
  }
  
  static int
  zvol_set_volmode_sync_cb(dsl_pool_t *dp, dsl_dataset_t *ds, void *arg)
  {
          (void) arg;
          char dsname[MAXNAMELEN];
          zvol_task_t *task;
          uint64_t volmode;
  
          dsl_dataset_name(ds, dsname);
          if (dsl_prop_get_int_ds(ds, "volmode", &volmode) != 0)
                  return (0);
          task = zvol_task_alloc(ZVOL_ASYNC_SET_VOLMODE, dsname, NULL, volmode);
          if (task == NULL)
                  return (0);
  
          (void) taskq_dispatch(dp->dp_spa->spa_zvol_taskq, zvol_task_cb,
              task, TQ_SLEEP);
          return (0);
  }
  
  /*
   * Traverse all child datasets and apply volmode appropriately.
   * We call dsl_prop_set_sync_impl() here to set the value only on the toplevel
   * dataset and read the effective "volmode" on every child in the callback
   * function: this is because the value is not guaranteed to be the same in the
   * whole dataset hierarchy.
   */
  static void
  zvol_set_volmode_sync(void *arg, dmu_tx_t *tx)
  {
          zvol_set_prop_int_arg_t *zsda = arg;
          dsl_pool_t *dp = dmu_tx_pool(tx);
          dsl_dir_t *dd;
          dsl_dataset_t *ds;
          int error;
  
          VERIFY0(dsl_dir_hold(dp, zsda->zsda_name, FTAG, &dd, NULL));
          zsda->zsda_tx = tx;
  
          error = dsl_dataset_hold(dp, zsda->zsda_name, FTAG, &ds);
          if (error == 0) {
                  dsl_prop_set_sync_impl(ds, zfs_prop_to_name(ZFS_PROP_VOLMODE),
                      zsda->zsda_source, sizeof (zsda->zsda_value), 1,
                      &zsda->zsda_value, zsda->zsda_tx);
                  dsl_dataset_rele(ds, FTAG);
          }
  
          dmu_objset_find_dp(dp, dd->dd_object, zvol_set_volmode_sync_cb,
              zsda, DS_FIND_CHILDREN);
  
          dsl_dir_rele(dd, FTAG);
  }
  
  int
  zvol_set_volmode(const char *ddname, zprop_source_t source, uint64_t volmode)
  {
          zvol_set_prop_int_arg_t zsda;
  
          zsda.zsda_name = ddname;
          zsda.zsda_source = source;
          zsda.zsda_value = volmode;
  
          return (dsl_sync_task(ddname, zvol_set_volmode_check,
              zvol_set_volmode_sync, &zsda, 0, ZFS_SPACE_CHECK_NONE));
  }
  
  void
  zvol_remove_minors(spa_t *spa, const char *name, boolean_t async)
  {
          zvol_task_t *task;
          taskqid_t id;
  
          task = zvol_task_alloc(ZVOL_ASYNC_REMOVE_MINORS, name, NULL, ~0ULL);
          if (task == NULL)
                  return;
  
          id = taskq_dispatch(spa->spa_zvol_taskq, zvol_task_cb, task, TQ_SLEEP);
          if ((async == B_FALSE) && (id != TASKQID_INVALID))
                  taskq_wait_id(spa->spa_zvol_taskq, id);
  }
  
  void
  zvol_rename_minors(spa_t *spa, const char *name1, const char *name2,
      boolean_t async)
  {
          zvol_task_t *task;
          taskqid_t id;
  
          task = zvol_task_alloc(ZVOL_ASYNC_RENAME_MINORS, name1, name2, ~0ULL);
          if (task == NULL)
                  return;
  
          id = taskq_dispatch(spa->spa_zvol_taskq, zvol_task_cb, task, TQ_SLEEP);
          if ((async == B_FALSE) && (id != TASKQID_INVALID))
                  taskq_wait_id(spa->spa_zvol_taskq, id);
  }
  
  boolean_t
  zvol_is_zvol(const char *name)
  {
  
          return (zvol_os_is_zvol(name));
  }
  
  int
  zvol_init_impl(void)
  {
          int i;
  
          list_create(&zvol_state_list, sizeof (zvol_state_t),
              offsetof(zvol_state_t, zv_next));
          rw_init(&zvol_state_lock, NULL, RW_DEFAULT, NULL);
  
          zvol_htable = kmem_alloc(ZVOL_HT_SIZE * sizeof (struct hlist_head),
              KM_SLEEP);
          for (i = 0; i < ZVOL_HT_SIZE; i++)
                  INIT_HLIST_HEAD(&zvol_htable[i]);
  
          return (0);
  }
  
  void
  zvol_fini_impl(void)
  {
          zvol_remove_minors_impl(NULL);
  
          /*
           * The call to "zvol_remove_minors_impl" may dispatch entries to
           * the system_taskq, but it doesn't wait for those entries to
           * complete before it returns. Thus, we must wait for all of the
           * removals to finish, before we can continue.
           */
          taskq_wait_outstanding(system_taskq, 0);
  
          kmem_free(zvol_htable, ZVOL_HT_SIZE * sizeof (struct hlist_head));
          list_destroy(&zvol_state_list);
          rw_destroy(&zvol_state_lock);
  }

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