OpenZFS restructuring - zvol

Refactor the zvol in to platform dependent and independent bits.

Reviewed-by: Allan Jude <[email protected]>
Reviewed-by: Jorgen Lundman <[email protected]>
Reviewed-by: Igor Kozhukhov <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Matt Macy <[email protected]>
Closes #9295 

1 files changed, 55 insertions, 1102 deletions

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index 840b8d008..9b26084bb 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -68,10 +68,6 @@
  * allocated and placed on zvol_state_list, and then other minor operations
  * for this zvol are going to proceed in the order of issue.
  *
- * It is also worth keeping in mind that once add_disk() is called, the zvol is
- * announced to the world, and zvol_open()/zvol_release() can be called at any
- * time. Incidentally, add_disk() itself calls zvol_open()->zvol_first_open()
- * and zvol_release()->zvol_last_close() directly as well.
  */
 
 #include <sys/dataset_kstats.h>
@@ -89,52 +85,16 @@
 #include <sys/spa_impl.h>
 #include <sys/zvol.h>
 
-#include <linux/blkdev_compat.h>
-#include <linux/task_io_accounting_ops.h>
+#include <sys/zvol_impl.h>
+
 
 unsigned int zvol_inhibit_dev = 0;
-unsigned int zvol_major = ZVOL_MAJOR;
-unsigned int zvol_threads = 32;
-unsigned int zvol_request_sync = 0;
-unsigned int zvol_prefetch_bytes = (128 * 1024);
-unsigned long zvol_max_discard_blocks = 16384;
 unsigned int zvol_volmode = ZFS_VOLMODE_GEOM;
 
-static taskq_t *zvol_taskq;
-static krwlock_t zvol_state_lock;
-static list_t zvol_state_list;
-
-#define	ZVOL_HT_SIZE	1024
-static struct hlist_head *zvol_htable;
-#define	ZVOL_HT_HEAD(hash)	(&zvol_htable[(hash) & (ZVOL_HT_SIZE-1)])
-
-static struct ida zvol_ida;
-
-/*
- * The in-core state of each volume.
- */
-struct zvol_state {
-	char			zv_name[MAXNAMELEN];	/* name */
-	uint64_t		zv_volsize;		/* advertised space */
-	uint64_t		zv_volblocksize;	/* volume block size */
-	objset_t		*zv_objset;	/* objset handle */
-	uint32_t		zv_flags;	/* ZVOL_* flags */
-	uint32_t		zv_open_count;	/* open counts */
-	uint32_t		zv_changed;	/* disk changed */
-	zilog_t			*zv_zilog;	/* ZIL handle */
-	rangelock_t		zv_rangelock;	/* for range locking */
-	dnode_t			*zv_dn;		/* dnode hold */
-	dev_t			zv_dev;		/* device id */
-	struct gendisk		*zv_disk;	/* generic disk */
-	struct request_queue	*zv_queue;	/* request queue */
-	dataset_kstats_t	zv_kstat;	/* zvol kstats */
-	list_node_t		zv_next;	/* next zvol_state_t linkage */
-	uint64_t		zv_hash;	/* name hash */
-	struct hlist_node	zv_hlink;	/* hash link */
-	kmutex_t		zv_state_lock;	/* protects zvol_state_t */
-	atomic_t		zv_suspend_ref;	/* refcount for suspend */
-	krwlock_t		zv_suspend_lock;	/* suspend lock */
-};
+struct hlist_head *zvol_htable;
+list_t zvol_state_list;
+krwlock_t zvol_state_lock;
+const zvol_platform_ops_t *ops;
 
 typedef enum {
 	ZVOL_ASYNC_CREATE_MINORS,
@@ -154,19 +114,12 @@ typedef struct {
 	uint64_t value;
 } zvol_task_t;
 
-#define	ZVOL_RDONLY	0x1
-/*
- * Whether the zvol has been written to (as opposed to ZVOL_RDONLY, which
- * specifies whether or not the zvol _can_ be written to)
- */
-#define	ZVOL_WRITTEN_TO	0x2
-
-static uint64_t
+uint64_t
 zvol_name_hash(const char *name)
 {
 	int i;
 	uint64_t crc = -1ULL;
-	uint8_t *p = (uint8_t *)name;
+	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];
@@ -175,38 +128,13 @@ zvol_name_hash(const char *name)
 }
 
 /*
- * Find a zvol_state_t given the full major+minor dev_t. If found,
- * return with zv_state_lock taken, otherwise, return (NULL) without
- * taking zv_state_lock.
- */
-static zvol_state_t *
-zvol_find_by_dev(dev_t dev)
-{
-	zvol_state_t *zv;
-
-	rw_enter(&zvol_state_lock, RW_READER);
-	for (zv = list_head(&zvol_state_list); zv != NULL;
-	    zv = list_next(&zvol_state_list, zv)) {
-		mutex_enter(&zv->zv_state_lock);
-		if (zv->zv_dev == dev) {
-			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 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.
  */
-static zvol_state_t *
+zvol_state_t *
 zvol_find_by_name_hash(const char *name, uint64_t hash, int mode)
 {
 	zvol_state_t *zv;
@@ -258,29 +186,6 @@ zvol_find_by_name(const char *name, int mode)
 	return (zvol_find_by_name_hash(name, zvol_name_hash(name), mode));
 }
 
-
-/*
- * Given a path, return TRUE if path is a ZVOL.
- */
-boolean_t
-zvol_is_zvol(const char *device)
-{
-	struct block_device *bdev;
-	unsigned int major;
-
-	bdev = vdev_lookup_bdev(device);
-	if (IS_ERR(bdev))
-		return (B_FALSE);
-
-	major = MAJOR(bdev->bd_dev);
-	bdput(bdev);
-
-	if (major == zvol_major)
-		return (B_TRUE);
-
-	return (B_FALSE);
-}
-
 /*
  * ZFS_IOC_CREATE callback handles dmu zvol and zap object creation.
  */
@@ -407,7 +312,6 @@ int
 zvol_set_volsize(const char *name, uint64_t volsize)
 {
 	objset_t *os = NULL;
-	struct gendisk *disk = NULL;
 	uint64_t readonly;
 	int error;
 	boolean_t owned = B_FALSE;
@@ -450,7 +354,6 @@ zvol_set_volsize(const char *name, uint64_t volsize)
 	if (error == 0 && zv != NULL) {
 		zv->zv_volsize = volsize;
 		zv->zv_changed = 1;
-		disk = zv->zv_disk;
 	}
 out:
 	kmem_free(doi, sizeof (dmu_object_info_t));
@@ -466,8 +369,8 @@ out:
 	if (zv != NULL)
 		mutex_exit(&zv->zv_state_lock);
 
-	if (disk != NULL)
-		revalidate_disk(disk);
+	if (error == 0 && zv != NULL)
+		ops->zv_update_volsize(zv, volsize);
 
 	return (SET_ERROR(error));
 }
@@ -657,7 +560,7 @@ zil_replay_func_t *zvol_replay_vector[TX_MAX_TYPE] = {
  */
 ssize_t zvol_immediate_write_sz = 32768;
 
-static void
+void
 zvol_log_write(zvol_state_t *zv, dmu_tx_t *tx, uint64_t offset,
     uint64_t size, int sync)
 {
@@ -717,92 +620,10 @@ zvol_log_write(zvol_state_t *zv, dmu_tx_t *tx, uint64_t offset,
 	}
 }
 
-typedef struct zv_request {
-	zvol_state_t	*zv;
-	struct bio	*bio;
-	locked_range_t	*lr;
-} zv_request_t;
-
-static void
-uio_from_bio(uio_t *uio, struct bio *bio)
-{
-	uio->uio_bvec = &bio->bi_io_vec[BIO_BI_IDX(bio)];
-	uio->uio_iovcnt = bio->bi_vcnt - BIO_BI_IDX(bio);
-	uio->uio_loffset = BIO_BI_SECTOR(bio) << 9;
-	uio->uio_segflg = UIO_BVEC;
-	uio->uio_limit = MAXOFFSET_T;
-	uio->uio_resid = BIO_BI_SIZE(bio);
-	uio->uio_skip = BIO_BI_SKIP(bio);
-}
-
-static void
-zvol_write(void *arg)
-{
-	int error = 0;
-
-	zv_request_t *zvr = arg;
-	struct bio *bio = zvr->bio;
-	uio_t uio = { { 0 }, 0 };
-	uio_from_bio(&uio, bio);
-
-	zvol_state_t *zv = zvr->zv;
-	ASSERT(zv && zv->zv_open_count > 0);
-	ASSERT(zv->zv_zilog != NULL);
-
-	ssize_t start_resid = uio.uio_resid;
-	unsigned long start_jif = jiffies;
-	blk_generic_start_io_acct(zv->zv_queue, WRITE, bio_sectors(bio),
-	    &zv->zv_disk->part0);
-
-	boolean_t sync =
-	    bio_is_fua(bio) || zv->zv_objset->os_sync == ZFS_SYNC_ALWAYS;
-
-	uint64_t volsize = zv->zv_volsize;
-	while (uio.uio_resid > 0 && uio.uio_loffset < volsize) {
-		uint64_t bytes = MIN(uio.uio_resid, DMU_MAX_ACCESS >> 1);
-		uint64_t off = uio.uio_loffset;
-		dmu_tx_t *tx = dmu_tx_create(zv->zv_objset);
-
-		if (bytes > volsize - off)	/* don't write past the end */
-			bytes = volsize - off;
-
-		dmu_tx_hold_write(tx, ZVOL_OBJ, off, bytes);
-
-		/* This will only fail for ENOSPC */
-		error = dmu_tx_assign(tx, TXG_WAIT);
-		if (error) {
-			dmu_tx_abort(tx);
-			break;
-		}
-		error = dmu_write_uio_dnode(zv->zv_dn, &uio, bytes, tx);
-		if (error == 0) {
-			zvol_log_write(zv, tx, off, bytes, sync);
-		}
-		dmu_tx_commit(tx);
-
-		if (error)
-			break;
-	}
-	rangelock_exit(zvr->lr);
-
-	int64_t nwritten = start_resid - uio.uio_resid;
-	dataset_kstats_update_write_kstats(&zv->zv_kstat, nwritten);
-	task_io_account_write(nwritten);
-
-	if (sync)
-		zil_commit(zv->zv_zilog, ZVOL_OBJ);
-
-	rw_exit(&zv->zv_suspend_lock);
-	blk_generic_end_io_acct(zv->zv_queue, WRITE, &zv->zv_disk->part0,
-	    start_jif);
-	BIO_END_IO(bio, -error);
-	kmem_free(zvr, sizeof (zv_request_t));
-}
-
 /*
  * Log a DKIOCFREE/free-long-range to the ZIL with TX_TRUNCATE.
  */
-static void
+void
 zvol_log_truncate(zvol_state_t *zv, dmu_tx_t *tx, uint64_t off, uint64_t len,
     boolean_t sync)
 {
@@ -823,119 +644,6 @@ zvol_log_truncate(zvol_state_t *zv, dmu_tx_t *tx, uint64_t off, uint64_t len,
 	zil_itx_assign(zilog, itx, tx);
 }
 
-static void
-zvol_discard(void *arg)
-{
-	zv_request_t *zvr = arg;
-	struct bio *bio = zvr->bio;
-	zvol_state_t *zv = zvr->zv;
-	uint64_t start = BIO_BI_SECTOR(bio) << 9;
-	uint64_t size = BIO_BI_SIZE(bio);
-	uint64_t end = start + size;
-	boolean_t sync;
-	int error = 0;
-	dmu_tx_t *tx;
-	unsigned long start_jif;
-
-	ASSERT(zv && zv->zv_open_count > 0);
-	ASSERT(zv->zv_zilog != NULL);
-
-	start_jif = jiffies;
-	blk_generic_start_io_acct(zv->zv_queue, WRITE, bio_sectors(bio),
-	    &zv->zv_disk->part0);
-
-	sync = bio_is_fua(bio) || zv->zv_objset->os_sync == ZFS_SYNC_ALWAYS;
-
-	if (end > zv->zv_volsize) {
-		error = SET_ERROR(EIO);
-		goto unlock;
-	}
-
-	/*
-	 * Align the request to volume block boundaries when a secure erase is
-	 * not required.  This will prevent dnode_free_range() from zeroing out
-	 * the unaligned parts which is slow (read-modify-write) and useless
-	 * since we are not freeing any space by doing so.
-	 */
-	if (!bio_is_secure_erase(bio)) {
-		start = P2ROUNDUP(start, zv->zv_volblocksize);
-		end = P2ALIGN(end, zv->zv_volblocksize);
-		size = end - start;
-	}
-
-	if (start >= end)
-		goto unlock;
-
-	tx = dmu_tx_create(zv->zv_objset);
-	dmu_tx_mark_netfree(tx);
-	error = dmu_tx_assign(tx, TXG_WAIT);
-	if (error != 0) {
-		dmu_tx_abort(tx);
-	} else {
-		zvol_log_truncate(zv, tx, start, size, B_TRUE);
-		dmu_tx_commit(tx);
-		error = dmu_free_long_range(zv->zv_objset,
-		    ZVOL_OBJ, start, size);
-	}
-unlock:
-	rangelock_exit(zvr->lr);
-
-	if (error == 0 && sync)
-		zil_commit(zv->zv_zilog, ZVOL_OBJ);
-
-	rw_exit(&zv->zv_suspend_lock);
-	blk_generic_end_io_acct(zv->zv_queue, WRITE, &zv->zv_disk->part0,
-	    start_jif);
-	BIO_END_IO(bio, -error);
-	kmem_free(zvr, sizeof (zv_request_t));
-}
-
-static void
-zvol_read(void *arg)
-{
-	int error = 0;
-
-	zv_request_t *zvr = arg;
-	struct bio *bio = zvr->bio;
-	uio_t uio = { { 0 }, 0 };
-	uio_from_bio(&uio, bio);
-
-	zvol_state_t *zv = zvr->zv;
-	ASSERT(zv && zv->zv_open_count > 0);
-
-	ssize_t start_resid = uio.uio_resid;
-	unsigned long start_jif = jiffies;
-	blk_generic_start_io_acct(zv->zv_queue, READ, bio_sectors(bio),
-	    &zv->zv_disk->part0);
-
-	uint64_t volsize = zv->zv_volsize;
-	while (uio.uio_resid > 0 && uio.uio_loffset < volsize) {
-		uint64_t bytes = MIN(uio.uio_resid, DMU_MAX_ACCESS >> 1);
-
-		/* don't read past the end */
-		if (bytes > volsize - uio.uio_loffset)
-			bytes = volsize - uio.uio_loffset;
-
-		error = dmu_read_uio_dnode(zv->zv_dn, &uio, bytes);
-		if (error) {
-			/* convert checksum errors into IO errors */
-			if (error == ECKSUM)
-				error = SET_ERROR(EIO);
-			break;
-		}
-	}
-	rangelock_exit(zvr->lr);
-
-	int64_t nread = start_resid - uio.uio_resid;
-	dataset_kstats_update_read_kstats(&zv->zv_kstat, nread);
-	task_io_account_read(nread);
-
-	rw_exit(&zv->zv_suspend_lock);
-	blk_generic_end_io_acct(zv->zv_queue, READ, &zv->zv_disk->part0,
-	    start_jif);
-	BIO_END_IO(bio, -error);
-	kmem_free(zvr, sizeof (zv_request_t));
-}
 
 /* ARGSUSED */
 static void
@@ -952,7 +660,7 @@ zvol_get_done(zgd_t *zgd, int error)
 /*
  * Get data to generate a TX_WRITE intent log record.
  */
-static int
+int
 zvol_get_data(void *arg, lr_write_t *lr, char *buf, struct lwb *lwb, zio_t *zio)
 {
 	zvol_state_t *zv = arg;
@@ -1017,141 +725,14 @@ zvol_get_data(void *arg, lr_write_t *lr, char *buf, struct lwb *lwb, zio_t *zio)
 	return (SET_ERROR(error));
 }
 
-static MAKE_REQUEST_FN_RET
-zvol_request(struct request_queue *q, struct bio *bio)
-{
-	zvol_state_t *zv = q->queuedata;
-	fstrans_cookie_t cookie = spl_fstrans_mark();
-	uint64_t offset = BIO_BI_SECTOR(bio) << 9;
-	uint64_t size = BIO_BI_SIZE(bio);
-	int rw = bio_data_dir(bio);
-	zv_request_t *zvr;
-
-	if (bio_has_data(bio) && offset + size > zv->zv_volsize) {
-		printk(KERN_INFO
-		    "%s: bad access: offset=%llu, size=%lu\n",
-		    zv->zv_disk->disk_name,
-		    (long long unsigned)offset,
-		    (long unsigned)size);
-
-		BIO_END_IO(bio, -SET_ERROR(EIO));
-		goto out;
-	}
-
-	if (rw == WRITE) {
-		boolean_t need_sync = B_FALSE;
-
-		if (unlikely(zv->zv_flags & ZVOL_RDONLY)) {
-			BIO_END_IO(bio, -SET_ERROR(EROFS));
-			goto out;
-		}
-
-		/*
-		 * To be released in the I/O function. See the comment on
-		 * rangelock_enter() below.
-		 */
-		rw_enter(&zv->zv_suspend_lock, RW_READER);
-
-		/*
-		 * Open a ZIL if this is the first time we have written to this
-		 * zvol. We protect zv->zv_zilog with zv_suspend_lock rather
-		 * than zv_state_lock so that we don't need to acquire an
-		 * additional lock in this path.
-		 */
-		if (zv->zv_zilog == NULL) {
-			rw_exit(&zv->zv_suspend_lock);
-			rw_enter(&zv->zv_suspend_lock, RW_WRITER);
-			if (zv->zv_zilog == NULL) {
-				zv->zv_zilog = zil_open(zv->zv_objset,
-				    zvol_get_data);
-				zv->zv_flags |= ZVOL_WRITTEN_TO;
-			}
-			rw_downgrade(&zv->zv_suspend_lock);
-		}
-
-		/* bio marked as FLUSH need to flush before write */
-		if (bio_is_flush(bio))
-			zil_commit(zv->zv_zilog, ZVOL_OBJ);
-
-		/* Some requests are just for flush and nothing else. */
-		if (size == 0) {
-			rw_exit(&zv->zv_suspend_lock);
-			BIO_END_IO(bio, 0);
-			goto out;
-		}
-
-		zvr = kmem_alloc(sizeof (zv_request_t), KM_SLEEP);
-		zvr->zv = zv;
-		zvr->bio = bio;
-
-		/*
-		 * To be released in the I/O function. Since the I/O functions
-		 * are asynchronous, we take it here synchronously to make
-		 * sure overlapped I/Os are properly ordered.
-		 */
-		zvr->lr = rangelock_enter(&zv->zv_rangelock, offset, size,
-		    RL_WRITER);
-		/*
-		 * Sync writes and discards execute zil_commit() which may need
-		 * to take a RL_READER lock on the whole block being modified
-		 * via its zillog->zl_get_data(): to avoid circular dependency
-		 * issues with taskq threads execute these requests
-		 * synchronously here in zvol_request().
-		 */
-		need_sync = bio_is_fua(bio) ||
-		    zv->zv_objset->os_sync == ZFS_SYNC_ALWAYS;
-		if (bio_is_discard(bio) || bio_is_secure_erase(bio)) {
-			if (zvol_request_sync || need_sync ||
-			    taskq_dispatch(zvol_taskq, zvol_discard, zvr,
-			    TQ_SLEEP) == TASKQID_INVALID)
-				zvol_discard(zvr);
-		} else {
-			if (zvol_request_sync || need_sync ||
-			    taskq_dispatch(zvol_taskq, zvol_write, zvr,
-			    TQ_SLEEP) == TASKQID_INVALID)
-				zvol_write(zvr);
-		}
-	} else {
-		/*
-		 * The SCST driver, and possibly others, may issue READ I/Os
-		 * with a length of zero bytes.  These empty I/Os contain no
-		 * data and require no additional handling.
-		 */
-		if (size == 0) {
-			BIO_END_IO(bio, 0);
-			goto out;
-		}
-
-		zvr = kmem_alloc(sizeof (zv_request_t), KM_SLEEP);
-		zvr->zv = zv;
-		zvr->bio = bio;
-
-		rw_enter(&zv->zv_suspend_lock, RW_READER);
-
-		zvr->lr = rangelock_enter(&zv->zv_rangelock, offset, size,
-		    RL_READER);
-		if (zvol_request_sync || taskq_dispatch(zvol_taskq,
-		    zvol_read, zvr, TQ_SLEEP) == TASKQID_INVALID)
-			zvol_read(zvr);
-	}
-
-out:
-	spl_fstrans_unmark(cookie);
-#ifdef HAVE_MAKE_REQUEST_FN_RET_INT
-	return (0);
-#elif defined(HAVE_MAKE_REQUEST_FN_RET_QC)
-	return (BLK_QC_T_NONE);
-#endif
-}
-
 /*
  * The zvol_state_t's are inserted into zvol_state_list and zvol_htable.
  */
-static void
+
+void
 zvol_insert(zvol_state_t *zv)
 {
 	ASSERT(RW_WRITE_HELD(&zvol_state_lock));
-	ASSERT3U(MINOR(zv->zv_dev) & ZVOL_MINOR_MASK, ==, 0);
 	list_insert_head(&zvol_state_list, zv);
 	hlist_add_head(&zv->zv_hlink, ZVOL_HT_HEAD(zv->zv_hash));
 }
@@ -1196,15 +777,15 @@ zvol_setup_zv(zvol_state_t *zv)
 	if (error)
 		return (SET_ERROR(error));
 
-	set_capacity(zv->zv_disk, volsize >> 9);
+	ops->zv_set_capacity(zv, volsize >> 9);
 	zv->zv_volsize = volsize;
 
 	if (ro || dmu_objset_is_snapshot(os) ||
 	    !spa_writeable(dmu_objset_spa(os))) {
-		set_disk_ro(zv->zv_disk, 1);
+		ops->zv_set_disk_ro(zv, 1);
 		zv->zv_flags |= ZVOL_RDONLY;
 	} else {
-		set_disk_ro(zv->zv_disk, 0);
+		ops->zv_set_disk_ro(zv, 0);
 		zv->zv_flags &= ~ZVOL_RDONLY;
 	}
 	return (0);
@@ -1313,7 +894,7 @@ zvol_resume(zvol_state_t *zv)
 	return (SET_ERROR(error));
 }
 
-static int
+int
 zvol_first_open(zvol_state_t *zv, boolean_t readonly)
 {
 	objset_t *os;
@@ -1344,7 +925,7 @@ zvol_first_open(zvol_state_t *zv, boolean_t readonly)
 	if (!mutex_owned(&spa_namespace_lock)) {
 		locked = mutex_tryenter(&spa_namespace_lock);
 		if (!locked)
-			return (-SET_ERROR(ERESTARTSYS));
+			return (SET_ERROR(EINTR));
 	}
 
 	ro = (readonly || (strchr(zv->zv_name, '@') != NULL));
@@ -1364,10 +945,10 @@ zvol_first_open(zvol_state_t *zv, boolean_t readonly)
 out_mutex:
 	if (locked)
 		mutex_exit(&spa_namespace_lock);
-	return (SET_ERROR(-error));
+	return (SET_ERROR(error));
 }
 
-static void
+void
 zvol_last_close(zvol_state_t *zv)
 {
 	ASSERT(RW_READ_HELD(&zv->zv_suspend_lock));
@@ -1379,578 +960,6 @@ zvol_last_close(zvol_state_t *zv)
 	zv->zv_objset = NULL;
 }
 
-static int
-zvol_open(struct block_device *bdev, fmode_t flag)
-{
-	zvol_state_t *zv;
-	int error = 0;
-	boolean_t drop_suspend = B_TRUE;
-
-	rw_enter(&zvol_state_lock, RW_READER);
-	/*
-	 * Obtain a copy of private_data under the zvol_state_lock to make
-	 * sure that either the result of zvol free code path setting
-	 * bdev->bd_disk->private_data to NULL is observed, or zvol_free()
-	 * is not called on this zv because of the positive zv_open_count.
-	 */
-	zv = bdev->bd_disk->private_data;
-	if (zv == NULL) {
-		rw_exit(&zvol_state_lock);
-		return (SET_ERROR(-ENXIO));
-	}
-
-	mutex_enter(&zv->zv_state_lock);
-	/*
-	 * make sure zvol is not suspended during first open
-	 * (hold zv_suspend_lock) and respect proper lock acquisition
-	 * ordering - zv_suspend_lock before zv_state_lock
-	 */
-	if (zv->zv_open_count == 0) {
-		if (!rw_tryenter(&zv->zv_suspend_lock, RW_READER)) {
-			mutex_exit(&zv->zv_state_lock);
-			rw_enter(&zv->zv_suspend_lock, RW_READER);
-			mutex_enter(&zv->zv_state_lock);
-			/* check to see if zv_suspend_lock is needed */
-			if (zv->zv_open_count != 0) {
-				rw_exit(&zv->zv_suspend_lock);
-				drop_suspend = B_FALSE;
-			}
-		}
-	} else {
-		drop_suspend = B_FALSE;
-	}
-	rw_exit(&zvol_state_lock);
-
-	ASSERT(MUTEX_HELD(&zv->zv_state_lock));
-	ASSERT(zv->zv_open_count != 0 || RW_READ_HELD(&zv->zv_suspend_lock));
-
-	if (zv->zv_open_count == 0) {
-		error = zvol_first_open(zv, !(flag & FMODE_WRITE));
-		if (error)
-			goto out_mutex;
-	}
-
-	if ((flag & FMODE_WRITE) && (zv->zv_flags & ZVOL_RDONLY)) {
-		error = -EROFS;
-		goto out_open_count;
-	}
-
-	zv->zv_open_count++;
-
-	mutex_exit(&zv->zv_state_lock);
-	if (drop_suspend)
-		rw_exit(&zv->zv_suspend_lock);
-
-	check_disk_change(bdev);
-
-	return (0);
-
-out_open_count:
-	if (zv->zv_open_count == 0)
-		zvol_last_close(zv);
-
-out_mutex:
-	mutex_exit(&zv->zv_state_lock);
-	if (drop_suspend)
-		rw_exit(&zv->zv_suspend_lock);
-	if (error == -ERESTARTSYS)
-		schedule();
-
-	return (SET_ERROR(error));
-}
-
-#ifdef HAVE_BLOCK_DEVICE_OPERATIONS_RELEASE_VOID
-static void
-#else
-static int
-#endif
-zvol_release(struct gendisk *disk, fmode_t mode)
-{
-	zvol_state_t *zv;
-	boolean_t drop_suspend = B_TRUE;
-
-	rw_enter(&zvol_state_lock, RW_READER);
-	zv = disk->private_data;
-
-	mutex_enter(&zv->zv_state_lock);
-	ASSERT(zv->zv_open_count > 0);
-	/*
-	 * make sure zvol is not suspended during last close
-	 * (hold zv_suspend_lock) and respect proper lock acquisition
-	 * ordering - zv_suspend_lock before zv_state_lock
-	 */
-	if (zv->zv_open_count == 1) {
-		if (!rw_tryenter(&zv->zv_suspend_lock, RW_READER)) {
-			mutex_exit(&zv->zv_state_lock);
-			rw_enter(&zv->zv_suspend_lock, RW_READER);
-			mutex_enter(&zv->zv_state_lock);
-			/* check to see if zv_suspend_lock is needed */
-			if (zv->zv_open_count != 1) {
-				rw_exit(&zv->zv_suspend_lock);
-				drop_suspend = B_FALSE;
-			}
-		}
-	} else {
-		drop_suspend = B_FALSE;
-	}
-	rw_exit(&zvol_state_lock);
-
-	ASSERT(MUTEX_HELD(&zv->zv_state_lock));
-	ASSERT(zv->zv_open_count != 1 || RW_READ_HELD(&zv->zv_suspend_lock));
-
-	zv->zv_open_count--;
-	if (zv->zv_open_count == 0)
-		zvol_last_close(zv);
-
-	mutex_exit(&zv->zv_state_lock);
-
-	if (drop_suspend)
-		rw_exit(&zv->zv_suspend_lock);
-
-#ifndef HAVE_BLOCK_DEVICE_OPERATIONS_RELEASE_VOID
-	return (0);
-#endif
-}
-
-static int
-zvol_ioctl(struct block_device *bdev, fmode_t mode,
-    unsigned int cmd, unsigned long arg)
-{
-	zvol_state_t *zv = bdev->bd_disk->private_data;
-	int error = 0;
-
-	ASSERT3U(zv->zv_open_count, >, 0);
-
-	switch (cmd) {
-	case BLKFLSBUF:
-		fsync_bdev(bdev);
-		invalidate_bdev(bdev);
-		rw_enter(&zv->zv_suspend_lock, RW_READER);
-
-		if (!(zv->zv_flags & ZVOL_RDONLY))
-			txg_wait_synced(dmu_objset_pool(zv->zv_objset), 0);
-
-		rw_exit(&zv->zv_suspend_lock);
-		break;
-
-	case BLKZNAME:
-		mutex_enter(&zv->zv_state_lock);
-		error = copy_to_user((void *)arg, zv->zv_name, MAXNAMELEN);
-		mutex_exit(&zv->zv_state_lock);
-		break;
-
-	default:
-		error = -ENOTTY;
-		break;
-	}
-
-	return (SET_ERROR(error));
-}
-
-#ifdef CONFIG_COMPAT
-static int
-zvol_compat_ioctl(struct block_device *bdev, fmode_t mode,
-    unsigned cmd, unsigned long arg)
-{
-	return (zvol_ioctl(bdev, mode, cmd, arg));
-}
-#else
-#define	zvol_compat_ioctl	NULL
-#endif
-
-/*
- * Linux 2.6.38 preferred interface.
- */
-#ifdef HAVE_BLOCK_DEVICE_OPERATIONS_CHECK_EVENTS
-static unsigned int
-zvol_check_events(struct gendisk *disk, unsigned int clearing)
-{
-	unsigned int mask = 0;
-
-	rw_enter(&zvol_state_lock, RW_READER);
-
-	zvol_state_t *zv = disk->private_data;
-	if (zv != NULL) {
-		mutex_enter(&zv->zv_state_lock);
-		mask = zv->zv_changed ? DISK_EVENT_MEDIA_CHANGE : 0;
-		zv->zv_changed = 0;
-		mutex_exit(&zv->zv_state_lock);
-	}
-
-	rw_exit(&zvol_state_lock);
-
-	return (mask);
-}
-#else
-static int zvol_media_changed(struct gendisk *disk)
-{
-	int changed = 0;
-
-	rw_enter(&zvol_state_lock, RW_READER);
-
-	zvol_state_t *zv = disk->private_data;
-	if (zv != NULL) {
-		mutex_enter(&zv->zv_state_lock);
-		changed = zv->zv_changed;
-		zv->zv_changed = 0;
-		mutex_exit(&zv->zv_state_lock);
-	}
-
-	rw_exit(&zvol_state_lock);
-
-	return (changed);
-}
-#endif
-
-static int zvol_revalidate_disk(struct gendisk *disk)
-{
-	rw_enter(&zvol_state_lock, RW_READER);
-
-	zvol_state_t *zv = disk->private_data;
-	if (zv != NULL) {
-		mutex_enter(&zv->zv_state_lock);
-		set_capacity(zv->zv_disk, zv->zv_volsize >> SECTOR_BITS);
-		mutex_exit(&zv->zv_state_lock);
-	}
-
-	rw_exit(&zvol_state_lock);
-
-	return (0);
-}
-
-/*
- * Provide a simple virtual geometry for legacy compatibility.  For devices
- * smaller than 1 MiB a small head and sector count is used to allow very
- * tiny devices.  For devices over 1 Mib a standard head and sector count
- * is used to keep the cylinders count reasonable.
- */
-static int
-zvol_getgeo(struct block_device *bdev, struct hd_geometry *geo)
-{
-	zvol_state_t *zv = bdev->bd_disk->private_data;
-	sector_t sectors;
-
-	ASSERT3U(zv->zv_open_count, >, 0);
-
-	sectors = get_capacity(zv->zv_disk);
-
-	if (sectors > 2048) {
-		geo->heads = 16;
-		geo->sectors = 63;
-	} else {
-		geo->heads = 2;
-		geo->sectors = 4;
-	}
-
-	geo->start = 0;
-	geo->cylinders = sectors / (geo->heads * geo->sectors);
-
-	return (0);
-}
-
-static struct kobject *
-zvol_probe(dev_t dev, int *part, void *arg)
-{
-	zvol_state_t *zv;
-	struct kobject *kobj;
-
-	zv = zvol_find_by_dev(dev);
-	kobj = zv ? get_disk_and_module(zv->zv_disk) : NULL;
-	ASSERT(zv == NULL || MUTEX_HELD(&zv->zv_state_lock));
-	if (zv)
-		mutex_exit(&zv->zv_state_lock);
-
-	return (kobj);
-}
-
-static struct block_device_operations zvol_ops = {
-	.open			= zvol_open,
-	.release		= zvol_release,
-	.ioctl			= zvol_ioctl,
-	.compat_ioctl		= zvol_compat_ioctl,
-#ifdef HAVE_BLOCK_DEVICE_OPERATIONS_CHECK_EVENTS
-	.check_events		= zvol_check_events,
-#else
-	.media_changed		= zvol_media_changed,
-#endif
-	.revalidate_disk	= zvol_revalidate_disk,
-	.getgeo			= zvol_getgeo,
-	.owner			= THIS_MODULE,
-};
-
-/*
- * Allocate memory for a new zvol_state_t and setup the required
- * request queue and generic disk structures for the block device.
- */
-static zvol_state_t *
-zvol_alloc(dev_t dev, const char *name)
-{
-	zvol_state_t *zv;
-	uint64_t volmode;
-
-	if (dsl_prop_get_integer(name, "volmode", &volmode, NULL) != 0)
-		return (NULL);
-
-	if (volmode == ZFS_VOLMODE_DEFAULT)
-		volmode = zvol_volmode;
-
-	if (volmode == ZFS_VOLMODE_NONE)
-		return (NULL);
-
-	zv = kmem_zalloc(sizeof (zvol_state_t), KM_SLEEP);
-
-	list_link_init(&zv->zv_next);
-
-	mutex_init(&zv->zv_state_lock, NULL, MUTEX_DEFAULT, NULL);
-
-	zv->zv_queue = blk_alloc_queue(GFP_ATOMIC);
-	if (zv->zv_queue == NULL)
-		goto out_kmem;
-
-	blk_queue_make_request(zv->zv_queue, zvol_request);
-	blk_queue_set_write_cache(zv->zv_queue, B_TRUE, B_TRUE);
-
-	/* Limit read-ahead to a single page to prevent over-prefetching. */
-	blk_queue_set_read_ahead(zv->zv_queue, 1);
-
-	/* Disable write merging in favor of the ZIO pipeline. */
-	blk_queue_flag_set(QUEUE_FLAG_NOMERGES, zv->zv_queue);
-
-	zv->zv_disk = alloc_disk(ZVOL_MINORS);
-	if (zv->zv_disk == NULL)
-		goto out_queue;
-
-	zv->zv_queue->queuedata = zv;
-	zv->zv_dev = dev;
-	zv->zv_open_count = 0;
-	strlcpy(zv->zv_name, name, MAXNAMELEN);
-
-	rangelock_init(&zv->zv_rangelock, NULL, NULL);
-	rw_init(&zv->zv_suspend_lock, NULL, RW_DEFAULT, NULL);
-
-	zv->zv_disk->major = zvol_major;
-#ifdef HAVE_BLOCK_DEVICE_OPERATIONS_CHECK_EVENTS
-	zv->zv_disk->events = DISK_EVENT_MEDIA_CHANGE;
-#endif
-
-	if (volmode == ZFS_VOLMODE_DEV) {
-		/*
-		 * ZFS_VOLMODE_DEV disable partitioning on ZVOL devices: set
-		 * gendisk->minors = 1 as noted in include/linux/genhd.h.
-		 * Also disable extended partition numbers (GENHD_FL_EXT_DEVT)
-		 * and suppresses partition scanning (GENHD_FL_NO_PART_SCAN)
-		 * setting gendisk->flags accordingly.
-		 */
-		zv->zv_disk->minors = 1;
-#if defined(GENHD_FL_EXT_DEVT)
-		zv->zv_disk->flags &= ~GENHD_FL_EXT_DEVT;
-#endif
-#if defined(GENHD_FL_NO_PART_SCAN)
-		zv->zv_disk->flags |= GENHD_FL_NO_PART_SCAN;
-#endif
-	}
-	zv->zv_disk->first_minor = (dev & MINORMASK);
-	zv->zv_disk->fops = &zvol_ops;
-	zv->zv_disk->private_data = zv;
-	zv->zv_disk->queue = zv->zv_queue;
-	snprintf(zv->zv_disk->disk_name, DISK_NAME_LEN, "%s%d",
-	    ZVOL_DEV_NAME, (dev & MINORMASK));
-
-	return (zv);
-
-out_queue:
-	blk_cleanup_queue(zv->zv_queue);
-out_kmem:
-	kmem_free(zv, sizeof (zvol_state_t));
-
-	return (NULL);
-}
-
-/*
- * Cleanup then free a zvol_state_t which was created by zvol_alloc().
- * At this time, the structure is not opened by anyone, is taken off
- * the zvol_state_list, and has its private data set to NULL.
- * The zvol_state_lock is dropped.
- */
-static void
-zvol_free(void *arg)
-{
-	zvol_state_t *zv = arg;
-
-	ASSERT(!RW_LOCK_HELD(&zv->zv_suspend_lock));
-	ASSERT(!MUTEX_HELD(&zv->zv_state_lock));
-	ASSERT(zv->zv_open_count == 0);
-	ASSERT(zv->zv_disk->private_data == NULL);
-
-	rw_destroy(&zv->zv_suspend_lock);
-	rangelock_fini(&zv->zv_rangelock);
-
-	del_gendisk(zv->zv_disk);
-	blk_cleanup_queue(zv->zv_queue);
-	put_disk(zv->zv_disk);
-
-	ida_simple_remove(&zvol_ida, MINOR(zv->zv_dev) >> ZVOL_MINOR_BITS);
-
-	mutex_destroy(&zv->zv_state_lock);
-	dataset_kstats_destroy(&zv->zv_kstat);
-
-	kmem_free(zv, sizeof (zvol_state_t));
-}
-
-/*
- * Create a block device minor node and setup the linkage between it
- * and the specified volume.  Once this function returns the block
- * device is live and ready for use.
- */
-static int
-zvol_create_minor_impl(const char *name)
-{
-	zvol_state_t *zv;
-	objset_t *os;
-	dmu_object_info_t *doi;
-	uint64_t volsize;
-	uint64_t len;
-	unsigned minor = 0;
-	int error = 0;
-	int idx;
-	uint64_t hash = zvol_name_hash(name);
-
-	if (zvol_inhibit_dev)
-		return (0);
-
-	idx = ida_simple_get(&zvol_ida, 0, 0, kmem_flags_convert(KM_SLEEP));
-	if (idx < 0)
-		return (SET_ERROR(-idx));
-	minor = idx << ZVOL_MINOR_BITS;
-
-	zv = zvol_find_by_name_hash(name, hash, RW_NONE);
-	if (zv) {
-		ASSERT(MUTEX_HELD(&zv->zv_state_lock));
-		mutex_exit(&zv->zv_state_lock);
-		ida_simple_remove(&zvol_ida, idx);
-		return (SET_ERROR(EEXIST));
-	}
-
-	doi = kmem_alloc(sizeof (dmu_object_info_t), KM_SLEEP);
-
-	error = dmu_objset_own(name, DMU_OST_ZVOL, B_TRUE, B_TRUE, FTAG, &os);
-	if (error)
-		goto out_doi;
-
-	error = dmu_object_info(os, ZVOL_OBJ, doi);
-	if (error)
-		goto out_dmu_objset_disown;
-
-	error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);
-	if (error)
-		goto out_dmu_objset_disown;
-
-	zv = zvol_alloc(MKDEV(zvol_major, minor), name);
-	if (zv == NULL) {
-		error = SET_ERROR(EAGAIN);
-		goto out_dmu_objset_disown;
-	}
-	zv->zv_hash = hash;
-
-	if (dmu_objset_is_snapshot(os))
-		zv->zv_flags |= ZVOL_RDONLY;
-
-	zv->zv_volblocksize = doi->doi_data_block_size;
-	zv->zv_volsize = volsize;
-	zv->zv_objset = os;
-
-	set_capacity(zv->zv_disk, zv->zv_volsize >> 9);
-
-	blk_queue_max_hw_sectors(zv->zv_queue, (DMU_MAX_ACCESS / 4) >> 9);
-	blk_queue_max_segments(zv->zv_queue, UINT16_MAX);
-	blk_queue_max_segment_size(zv->zv_queue, UINT_MAX);
-	blk_queue_physical_block_size(zv->zv_queue, zv->zv_volblocksize);
-	blk_queue_io_opt(zv->zv_queue, zv->zv_volblocksize);
-	blk_queue_max_discard_sectors(zv->zv_queue,
-	    (zvol_max_discard_blocks * zv->zv_volblocksize) >> 9);
-	blk_queue_discard_granularity(zv->zv_queue, zv->zv_volblocksize);
-	blk_queue_flag_set(QUEUE_FLAG_DISCARD, zv->zv_queue);
-#ifdef QUEUE_FLAG_NONROT
-	blk_queue_flag_set(QUEUE_FLAG_NONROT, zv->zv_queue);
-#endif
-#ifdef QUEUE_FLAG_ADD_RANDOM
-	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, zv->zv_queue);
-#endif
-	/* This flag was introduced in kernel version 4.12. */
-#ifdef QUEUE_FLAG_SCSI_PASSTHROUGH
-	blk_queue_flag_set(QUEUE_FLAG_SCSI_PASSTHROUGH, zv->zv_queue);
-#endif
-
-	if (spa_writeable(dmu_objset_spa(os))) {
-		if (zil_replay_disable)
-			zil_destroy(dmu_objset_zil(os), B_FALSE);
-		else
-			zil_replay(os, zv, zvol_replay_vector);
-	}
-	ASSERT3P(zv->zv_kstat.dk_kstats, ==, NULL);
-	dataset_kstats_create(&zv->zv_kstat, zv->zv_objset);
-
-	/*
-	 * When udev detects the addition of the device it will immediately
-	 * invoke blkid(8) to determine the type of content on the device.
-	 * Prefetching the blocks commonly scanned by blkid(8) will speed
-	 * up this process.
-	 */
-	len = MIN(MAX(zvol_prefetch_bytes, 0), SPA_MAXBLOCKSIZE);
-	if (len > 0) {
-		dmu_prefetch(os, ZVOL_OBJ, 0, 0, len, ZIO_PRIORITY_SYNC_READ);
-		dmu_prefetch(os, ZVOL_OBJ, 0, volsize - len, len,
-		    ZIO_PRIORITY_SYNC_READ);
-	}
-
-	zv->zv_objset = NULL;
-out_dmu_objset_disown:
-	dmu_objset_disown(os, B_TRUE, FTAG);
-out_doi:
-	kmem_free(doi, sizeof (dmu_object_info_t));
-
-	if (error == 0) {
-		rw_enter(&zvol_state_lock, RW_WRITER);
-		zvol_insert(zv);
-		rw_exit(&zvol_state_lock);
-		add_disk(zv->zv_disk);
-	} else {
-		ida_simple_remove(&zvol_ida, idx);
-	}
-
-	return (SET_ERROR(error));
-}
-
-/*
- * Rename a block device minor mode for the specified volume.
- */
-static void
-zvol_rename_minor(zvol_state_t *zv, const char *newname)
-{
-	int readonly = get_disk_ro(zv->zv_disk);
-
-	ASSERT(RW_LOCK_HELD(&zvol_state_lock));
-	ASSERT(MUTEX_HELD(&zv->zv_state_lock));
-
-	strlcpy(zv->zv_name, newname, sizeof (zv->zv_name));
-
-	/* move to new hashtable entry  */
-	zv->zv_hash = zvol_name_hash(zv->zv_name);
-	hlist_del(&zv->zv_hlink);
-	hlist_add_head(&zv->zv_hlink, ZVOL_HT_HEAD(zv->zv_hash));
-
-	/*
-	 * The block device's read-only state is briefly changed causing
-	 * a KOBJ_CHANGE uevent to be issued.  This ensures udev detects
-	 * the name change and fixes the symlinks.  This does not change
-	 * ZVOL_RDONLY in zv->zv_flags so the actual read-only state never
-	 * changes.  This would normally be done using kobject_uevent() but
-	 * that is a GPL-only symbol which is why we need this workaround.
-	 */
-	set_disk_ro(zv->zv_disk, !readonly);
-	set_disk_ro(zv->zv_disk, readonly);
-}
-
 typedef struct minors_job {
 	list_t *list;
 	list_node_t link;
@@ -2060,7 +1069,7 @@ zvol_create_minors_cb(const char *dsname, void *arg)
 			 * traverse snapshots only, do not traverse children,
 			 * and skip the 'dsname'
 			 */
-			error = dmu_objset_find((char *)dsname,
+			error = dmu_objset_find(dsname,
 			    zvol_create_snap_minor_cb, (void *)job,
 			    DS_FIND_SNAPSHOTS);
 		}
@@ -2124,7 +1133,7 @@ zvol_create_minors_impl(const char *name)
 		    &snapdev, NULL);
 
 		if (error == 0 && snapdev == ZFS_SNAPDEV_VISIBLE)
-			error = zvol_create_minor_impl(name);
+			error = ops->zv_create_minor(name);
 	} else {
 		cookie = spl_fstrans_mark();
 		error = dmu_objset_find(parent, zvol_create_minors_cb,
@@ -2142,7 +1151,7 @@ zvol_create_minors_impl(const char *name)
 	while ((job = list_head(&minors_list)) != NULL) {
 		list_remove(&minors_list, job);
 		if (!job->error)
-			zvol_create_minor_impl(job->name);
+			ops->zv_create_minor(job->name);
 		strfree(job->name);
 		kmem_free(job, sizeof (minors_job_t));
 	}
@@ -2155,7 +1164,8 @@ zvol_create_minors_impl(const char *name)
 /*
  * Remove minors for specified dataset including children and snapshots.
  */
-static void
+
+void
 zvol_remove_minors_impl(const char *name)
 {
 	zvol_state_t *zv, *zv_next;
@@ -2197,14 +1207,14 @@ zvol_remove_minors_impl(const char *name)
 			 * Cleared while holding zvol_state_lock as a writer
 			 * which will prevent zvol_open() from opening it.
 			 */
-			zv->zv_disk->private_data = NULL;
+			ops->zv_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, zv,
-			    TQ_SLEEP);
+			t = taskq_dispatch(system_taskq,
+			    (task_func_t *)ops->zv_free, zv, TQ_SLEEP);
 			if (t == TASKQID_INVALID)
 				list_insert_head(&free_list, zv);
 			else
@@ -2218,7 +1228,7 @@ zvol_remove_minors_impl(const char *name)
 	/* Drop zvol_state_lock before calling zvol_free() */
 	while ((zv = list_head(&free_list)) != NULL) {
 		list_remove(&free_list, zv);
-		zvol_free(zv);
+		ops->zv_free(zv);
 	}
 
 	if (tid != TASKQID_INVALID)
@@ -2254,12 +1264,7 @@ zvol_remove_minor_impl(const char *name)
 			}
 			zvol_remove(zv);
 
-			/*
-			 * Cleared while holding zvol_state_lock as a writer
-			 * which will prevent zvol_open() from opening it.
-			 */
-			zv->zv_disk->private_data = NULL;
-
+			ops->zv_clear_private(zv);
 			mutex_exit(&zv->zv_state_lock);
 			break;
 		} else {
@@ -2271,7 +1276,7 @@ zvol_remove_minor_impl(const char *name)
 	rw_exit(&zvol_state_lock);
 
 	if (zv != NULL)
-		zvol_free(zv);
+		ops->zv_free(zv);
 }
 
 /*
@@ -2297,14 +1302,14 @@ zvol_rename_minors_impl(const char *oldname, const char *newname)
 		mutex_enter(&zv->zv_state_lock);
 
 		if (strcmp(zv->zv_name, oldname) == 0) {
-			zvol_rename_minor(zv, newname);
+			ops->zv_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_rename_minor(zv, name);
+			ops->zv_rename_minor(zv, name);
 			strfree(name);
 		}
 
@@ -2328,7 +1333,7 @@ zvol_set_snapdev_cb(const char *dsname, void *param)
 
 	switch (arg->snapdev) {
 		case ZFS_SNAPDEV_VISIBLE:
-			(void) zvol_create_minor_impl(dsname);
+			(void) ops->zv_create_minor(dsname);
 			break;
 		case ZFS_SNAPDEV_HIDDEN:
 			(void) zvol_remove_minor_impl(dsname);
@@ -2378,14 +1383,14 @@ zvol_set_volmode_impl(char *name, uint64_t volmode)
 		case ZFS_VOLMODE_GEOM:
 		case ZFS_VOLMODE_DEV:
 			(void) zvol_remove_minor_impl(name);
-			(void) zvol_create_minor_impl(name);
+			(void) ops->zv_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_create_minor_impl(name);
+				(void) ops->zv_create_minor(name);
 			break;
 	}
 
@@ -2680,92 +1685,40 @@ zvol_rename_minors(spa_t *spa, const char *name1, const char *name2,
 		taskq_wait_id(spa->spa_zvol_taskq, id);
 }
 
+boolean_t
+zvol_is_zvol(const char *name)
+{
+
+	return (ops->zv_is_zvol(name));
+}
+
+void
+zvol_register_ops(const zvol_platform_ops_t *zvol_ops)
+{
+	ops = zvol_ops;
+}
+
 int
-zvol_init(void)
+zvol_init_impl(void)
 {
-	int threads = MIN(MAX(zvol_threads, 1), 1024);
-	int i, error;
+	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);
-	ida_init(&zvol_ida);
-
-	zvol_taskq = taskq_create(ZVOL_DRIVER, threads, maxclsyspri,
-	    threads * 2, INT_MAX, TASKQ_PREPOPULATE | TASKQ_DYNAMIC);
-	if (zvol_taskq == NULL) {
-		printk(KERN_INFO "ZFS: taskq_create() failed\n");
-		error = -ENOMEM;
-		goto out;
-	}
 
 	zvol_htable = kmem_alloc(ZVOL_HT_SIZE * sizeof (struct hlist_head),
 	    KM_SLEEP);
-	if (!zvol_htable) {
-		error = -ENOMEM;
-		goto out_taskq;
-	}
 	for (i = 0; i < ZVOL_HT_SIZE; i++)
 		INIT_HLIST_HEAD(&zvol_htable[i]);
 
-	error = register_blkdev(zvol_major, ZVOL_DRIVER);
-	if (error) {
-		printk(KERN_INFO "ZFS: register_blkdev() failed %d\n", error);
-		goto out_free;
-	}
-
-	blk_register_region(MKDEV(zvol_major, 0), 1UL << MINORBITS,
-	    THIS_MODULE, zvol_probe, NULL, NULL);
-
 	return (0);
-
-out_free:
-	kmem_free(zvol_htable, ZVOL_HT_SIZE * sizeof (struct hlist_head));
-out_taskq:
-	taskq_destroy(zvol_taskq);
-out:
-	ida_destroy(&zvol_ida);
-	rw_destroy(&zvol_state_lock);
-	list_destroy(&zvol_state_list);
-
-	return (SET_ERROR(error));
 }
 
 void
-zvol_fini(void)
+zvol_fini_impl(void)
 {
-	zvol_remove_minors_impl(NULL);
-
-	blk_unregister_region(MKDEV(zvol_major, 0), 1UL << MINORBITS);
-	unregister_blkdev(zvol_major, ZVOL_DRIVER);
 	kmem_free(zvol_htable, ZVOL_HT_SIZE * sizeof (struct hlist_head));
-
-	taskq_destroy(zvol_taskq);
 	list_destroy(&zvol_state_list);
 	rw_destroy(&zvol_state_lock);
-
-	ida_destroy(&zvol_ida);
 }
-
-/* BEGIN CSTYLED */
-module_param(zvol_inhibit_dev, uint, 0644);
-MODULE_PARM_DESC(zvol_inhibit_dev, "Do not create zvol device nodes");
-
-module_param(zvol_major, uint, 0444);
-MODULE_PARM_DESC(zvol_major, "Major number for zvol device");
-
-module_param(zvol_threads, uint, 0444);
-MODULE_PARM_DESC(zvol_threads, "Max number of threads to handle I/O requests");
-
-module_param(zvol_request_sync, uint, 0644);
-MODULE_PARM_DESC(zvol_request_sync, "Synchronously handle bio requests");
-
-module_param(zvol_max_discard_blocks, ulong, 0444);
-MODULE_PARM_DESC(zvol_max_discard_blocks, "Max number of blocks to discard");
-
-module_param(zvol_prefetch_bytes, uint, 0644);
-MODULE_PARM_DESC(zvol_prefetch_bytes, "Prefetch N bytes at zvol start+end");
-
-module_param(zvol_volmode, uint, 0644);
-MODULE_PARM_DESC(zvol_volmode, "Default volmode property value");
-/* END CSTYLED */