Add linux kernel disk support

Native Linux vdev disk interfaces

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 1337 insertions, 0 deletions

diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
new file mode 100644
index 000000000..6e9294292
--- /dev/null
+++ b/module/zfs/zvol.c
@@ -0,0 +1,1337 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (C) 2008-2010 Lawrence Livermore National Security, LLC.
+ * Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
+ * Rewritten for Linux by Brian Behlendorf <[email protected]>.
+ * 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.
+ */
+
+#include <sys/dmu_traverse.h>
+#include <sys/dsl_dataset.h>
+#include <sys/dsl_prop.h>
+#include <sys/zap.h>
+#include <sys/zil_impl.h>
+#include <sys/zio.h>
+#include <sys/zfs_rlock.h>
+#include <sys/zfs_znode.h>
+#include <sys/zvol.h>
+
+unsigned int zvol_major = ZVOL_MAJOR;
+unsigned int zvol_threads = 0;
+
+static taskq_t *zvol_taskq;
+static kmutex_t zvol_state_lock;
+static list_t zvol_state_list;
+static char *zvol_tag = "zvol_tag";
+
+/*
+ * The in-core state of each volume.
+ */
+typedef struct zvol_state {
+	char			zv_name[DISK_NAME_LEN];	/* 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 */
+	znode_t			zv_znode;	/* for range locking */
+	dmu_buf_t		*zv_dbuf;	/* bonus handle */
+	dev_t			zv_dev;		/* device id */
+	struct gendisk		*zv_disk;	/* generic disk */
+	struct request_queue	*zv_queue;	/* request queue */
+	spinlock_t		zv_lock;	/* request queue lock */
+	list_node_t		zv_next;	/* next zvol_state_t linkage */
+} zvol_state_t;
+
+#define	ZVOL_RDONLY	0x1
+
+/*
+ * Find the next available range of ZVOL_MINORS minor numbers.  The
+ * zvol_state_list is kept in ascending minor order so we simply need
+ * to scan the list for the first gap in the sequence.  This allows us
+ * to recycle minor number as devices are created and removed.
+ */
+static int
+zvol_find_minor(unsigned *minor)
+{
+	zvol_state_t *zv;
+
+	*minor = 0;
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+	for (zv = list_head(&zvol_state_list); zv != NULL;
+	     zv = list_next(&zvol_state_list, zv), *minor += ZVOL_MINORS) {
+		if (MINOR(zv->zv_dev) != MINOR(*minor))
+			break;
+	}
+
+	/* All minors are in use */
+	if (*minor >= (1 << MINORBITS))
+		return ENXIO;
+
+	return 0;
+}
+
+/*
+ * Find a zvol_state_t given the full major+minor dev_t.
+ */
+static zvol_state_t *
+zvol_find_by_dev(dev_t dev)
+{
+	zvol_state_t *zv;
+
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+	for (zv = list_head(&zvol_state_list); zv != NULL;
+	     zv = list_next(&zvol_state_list, zv)) {
+		if (zv->zv_dev == dev)
+			return zv;
+	}
+
+	return NULL;
+}
+
+/*
+ * Find a zvol_state_t given the name provided at zvol_alloc() time.
+ */
+static zvol_state_t *
+zvol_find_by_name(const char *name)
+{
+	zvol_state_t *zv;
+
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+	for (zv = list_head(&zvol_state_list); zv != NULL;
+	     zv = list_next(&zvol_state_list, zv)) {
+		if (!strncmp(zv->zv_name, name, DISK_NAME_LEN))
+			return zv;
+	}
+
+	return NULL;
+}
+
+/*
+ * 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 (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 (error);
+}
+
+/*
+ * Sanity check volume size.
+ */
+int
+zvol_check_volsize(uint64_t volsize, uint64_t blocksize)
+{
+	if (volsize == 0)
+		return (EINVAL);
+
+	if (volsize % blocksize != 0)
+		return (EINVAL);
+
+#ifdef _ILP32
+	if (volsize - 1 > MAXOFFSET_T)
+		return (EOVERFLOW);
+#endif
+	return (0);
+}
+
+/*
+ * Ensure the zap is flushed then inform the VFS of the capacity change.
+ */
+static int
+zvol_update_volsize(zvol_state_t *zv, uint64_t volsize)
+{
+	struct block_device *bdev;
+	dmu_tx_t *tx;
+	int error;
+
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+
+	tx = dmu_tx_create(zv->zv_objset);
+	dmu_tx_hold_zap(tx, ZVOL_ZAP_OBJ, TRUE, NULL);
+	error = dmu_tx_assign(tx, TXG_WAIT);
+	if (error) {
+		dmu_tx_abort(tx);
+		return (error);
+	}
+
+	error = zap_update(zv->zv_objset, ZVOL_ZAP_OBJ, "size", 8, 1,
+	    &volsize, tx);
+	dmu_tx_commit(tx);
+
+	if (error)
+		return (error);
+
+	error = dmu_free_long_range(zv->zv_objset,
+	    ZVOL_OBJ, volsize, DMU_OBJECT_END);
+	if (error)
+		return (error);
+
+	zv->zv_volsize = volsize;
+	zv->zv_changed = 1;
+
+	bdev = bdget_disk(zv->zv_disk, 0);
+	if (!bdev)
+		return EIO;
+
+	error = check_disk_change(bdev);
+	ASSERT3U(error, !=, 0);
+	bdput(bdev);
+
+	return (0);
+}
+
+/*
+ * Set ZFS_PROP_VOLSIZE set entry point.
+ */
+int
+zvol_set_volsize(const char *name, uint64_t volsize)
+{
+	zvol_state_t *zv;
+	dmu_object_info_t *doi;
+	objset_t *os = NULL;
+	uint64_t readonly;
+	int error;
+
+	mutex_enter(&zvol_state_lock);
+
+	zv = zvol_find_by_name(name);
+	if (zv == NULL) {
+		error = ENXIO;
+		goto out;
+	}
+
+	doi = kmem_alloc(sizeof(dmu_object_info_t), KM_SLEEP);
+
+	error = dmu_objset_hold(name, FTAG, &os);
+	if (error)
+		goto out_doi;
+
+	if ((error = dmu_object_info(os, ZVOL_OBJ, doi)) != 0 ||
+	    (error = zvol_check_volsize(volsize,doi->doi_data_block_size)) != 0)
+		goto out_doi;
+
+	VERIFY(dsl_prop_get_integer(name, "readonly", &readonly, NULL) == 0);
+	if (readonly) {
+		error = EROFS;
+		goto out_doi;
+	}
+
+	if (get_disk_ro(zv->zv_disk) || (zv->zv_flags & ZVOL_RDONLY)) {
+		error = EROFS;
+		goto out_doi;
+	}
+
+	error = zvol_update_volsize(zv, volsize);
+out_doi:
+	kmem_free(doi, sizeof(dmu_object_info_t));
+out:
+	if (os)
+		dmu_objset_rele(os, FTAG);
+
+	mutex_exit(&zvol_state_lock);
+
+	return (error);
+}
+
+/*
+ * Sanity check volume block size.
+ */
+int
+zvol_check_volblocksize(uint64_t volblocksize)
+{
+	if (volblocksize < SPA_MINBLOCKSIZE ||
+	    volblocksize > SPA_MAXBLOCKSIZE ||
+	    !ISP2(volblocksize))
+		return (EDOM);
+
+	return (0);
+}
+
+/*
+ * Set ZFS_PROP_VOLBLOCKSIZE set entry point.
+ */
+int
+zvol_set_volblocksize(const char *name, uint64_t volblocksize)
+{
+	zvol_state_t *zv;
+	dmu_tx_t *tx;
+	int error;
+
+	mutex_enter(&zvol_state_lock);
+
+	zv = zvol_find_by_name(name);
+	if (zv == NULL) {
+		error = ENXIO;
+		goto out;
+	}
+
+	if (get_disk_ro(zv->zv_disk) || (zv->zv_flags & ZVOL_RDONLY)) {
+		error = EROFS;
+		goto out;
+	}
+
+	tx = dmu_tx_create(zv->zv_objset);
+	dmu_tx_hold_bonus(tx, ZVOL_OBJ);
+	error = dmu_tx_assign(tx, TXG_WAIT);
+	if (error) {
+		dmu_tx_abort(tx);
+	} else {
+		error = dmu_object_set_blocksize(zv->zv_objset, ZVOL_OBJ,
+		    volblocksize, 0, tx);
+		if (error == ENOTSUP)
+			error = EBUSY;
+		dmu_tx_commit(tx);
+		if (error == 0)
+			zv->zv_volblocksize = volblocksize;
+	}
+out:
+	mutex_exit(&zvol_state_lock);
+
+	return (error);
+}
+
+/*
+ * Replay a TX_WRITE ZIL transaction that didn't get committed
+ * after a system failure
+ */
+static int
+zvol_replay_write(zvol_state_t *zv, lr_write_t *lr, boolean_t byteswap)
+{
+	objset_t *os = zv->zv_objset;
+	char *data = (char *)(lr + 1);	/* data follows lr_write_t */
+	uint64_t off = lr->lr_offset;
+	uint64_t len = lr->lr_length;
+	dmu_tx_t *tx;
+	int error;
+
+	if (byteswap)
+		byteswap_uint64_array(lr, sizeof (*lr));
+
+	tx = dmu_tx_create(os);
+	dmu_tx_hold_write(tx, ZVOL_OBJ, off, len);
+	error = dmu_tx_assign(tx, TXG_WAIT);
+	if (error) {
+		dmu_tx_abort(tx);
+	} else {
+		dmu_write(os, ZVOL_OBJ, off, len, data, tx);
+		dmu_tx_commit(tx);
+	}
+
+	return (error);
+}
+
+static int
+zvol_replay_err(zvol_state_t *zv, lr_t *lr, boolean_t byteswap)
+{
+	return (ENOTSUP);
+}
+
+/*
+ * Callback vectors for replaying records.
+ * Only TX_WRITE is needed for zvol.
+ */
+zil_replay_func_t *zvol_replay_vector[TX_MAX_TYPE] = {
+	(zil_replay_func_t *)zvol_replay_err,	/* no such transaction type */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_CREATE */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_MKDIR */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_MKXATTR */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_SYMLINK */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_REMOVE */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_RMDIR */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_LINK */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_RENAME */
+	(zil_replay_func_t *)zvol_replay_write,	/* TX_WRITE */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_TRUNCATE */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_SETATTR */
+	(zil_replay_func_t *)zvol_replay_err,	/* TX_ACL */
+};
+
+/*
+ * 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().
+ */
+ssize_t zvol_immediate_write_sz = 32768;
+
+static 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;
+	boolean_t slogging;
+
+	if (zil_replaying(zilog, tx))
+		return;
+
+	slogging = spa_has_slogs(zilog->zl_spa);
+
+	while (size) {
+		itx_t *itx;
+		lr_write_t *lr;
+		ssize_t len;
+		itx_wr_state_t write_state;
+
+		/*
+		 * Unlike zfs_log_write() we can be called with
+		 * up to DMU_MAX_ACCESS/2 (5MB) writes.
+		 */
+		if (blocksize > zvol_immediate_write_sz && !slogging &&
+		    size >= blocksize && offset % blocksize == 0) {
+			write_state = WR_INDIRECT; /* uses dmu_sync */
+			len = blocksize;
+		} else if (sync) {
+			write_state = WR_COPIED;
+			len = MIN(ZIL_MAX_LOG_DATA, size);
+		} else {
+			write_state = WR_NEED_COPY;
+			len = MIN(ZIL_MAX_LOG_DATA, size);
+		}
+
+		itx = zil_itx_create(TX_WRITE, sizeof (*lr) +
+		    (write_state == WR_COPIED ? len : 0));
+		lr = (lr_write_t *)&itx->itx_lr;
+		if (write_state == WR_COPIED && dmu_read(zv->zv_objset,
+		    ZVOL_OBJ, 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;
+			write_state = WR_NEED_COPY;
+		}
+
+		itx->itx_wr_state = write_state;
+		if (write_state == WR_NEED_COPY)
+			itx->itx_sod += len;
+		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;
+	}
+}
+
+/*
+ * Common write path running under the zvol taskq context.  This function
+ * is responsible for copying the request structure data in to the DMU and
+ * signaling the request queue with the result of the copy.
+ */
+static void
+zvol_write(void *arg)
+{
+	struct request *req = (struct request *)arg;
+	struct request_queue *q = req->q;
+	zvol_state_t *zv = q->queuedata;
+	uint64_t offset = blk_rq_pos(req) << 9;
+	uint64_t size = blk_rq_bytes(req);
+	int error = 0;
+	dmu_tx_t *tx;
+	rl_t *rl;
+
+	rl = zfs_range_lock(&zv->zv_znode, offset, size, RL_WRITER);
+
+	tx = dmu_tx_create(zv->zv_objset);
+	dmu_tx_hold_write(tx, ZVOL_OBJ, offset, size);
+
+	/* This will only fail for ENOSPC */
+	error = dmu_tx_assign(tx, TXG_WAIT);
+	if (error) {
+		dmu_tx_abort(tx);
+		zfs_range_unlock(rl);
+		blk_end_request(req, -error, size);
+		return;
+	}
+
+	error = dmu_write_req(zv->zv_objset, ZVOL_OBJ, req, tx);
+	if (error == 0)
+		zvol_log_write(zv, tx, offset, size, rq_is_sync(req));
+
+	dmu_tx_commit(tx);
+	zfs_range_unlock(rl);
+
+	if (rq_is_sync(req))
+		zil_commit(zv->zv_zilog, ZVOL_OBJ);
+
+	blk_end_request(req, -error, size);
+}
+
+/*
+ * Common read path running under the zvol taskq context.  This function
+ * is responsible for copying the requested data out of the DMU and in to
+ * a linux request structure.  It then must signal the request queue with
+ * an error code describing the result of the copy.
+ */
+static void
+zvol_read(void *arg)
+{
+	struct request *req = (struct request *)arg;
+	struct request_queue *q = req->q;
+	zvol_state_t *zv = q->queuedata;
+	uint64_t offset = blk_rq_pos(req) << 9;
+	uint64_t size = blk_rq_bytes(req);
+	int error;
+	rl_t *rl;
+
+	rl = zfs_range_lock(&zv->zv_znode, offset, size, RL_READER);
+
+	error = dmu_read_req(zv->zv_objset, ZVOL_OBJ, req);
+
+	zfs_range_unlock(rl);
+
+	/* convert checksum errors into IO errors */
+	if (error == ECKSUM)
+		error = EIO;
+
+	blk_end_request(req, -error, size);
+}
+
+/*
+ * Request will be added back to the request queue and retried if
+ * it cannot be immediately dispatched to the taskq for handling
+ */
+static inline void
+zvol_dispatch(task_func_t func, struct request *req)
+{
+	if (!taskq_dispatch(zvol_taskq, func, (void *)req, TQ_NOSLEEP))
+		blk_requeue_request(req->q, req);
+}
+
+/*
+ * Common request path.  Rather than registering a custom make_request()
+ * function we use the generic Linux version.  This is done because it allows
+ * us to easily merge read requests which would otherwise we performed
+ * synchronously by the DMU.  This is less critical in write case where the
+ * DMU will perform the correct merging within a transaction group.  Using
+ * the generic make_request() also let's use leverage the fact that the
+ * elevator with ensure correct ordering in regards to barrior IOs.  On
+ * the downside it means that in the write case we end up doing request
+ * merging twice once in the elevator and once in the DMU.
+ *
+ * The request handler is called under a spin lock so all the real work
+ * is handed off to be done in the context of the zvol taskq.  This function
+ * simply performs basic request sanity checking and hands off the request.
+ */
+static void
+zvol_request(struct request_queue *q)
+{
+	zvol_state_t *zv = q->queuedata;
+	struct request *req;
+	unsigned int size;
+
+	while ((req = blk_fetch_request(q)) != NULL) {
+		size = blk_rq_bytes(req);
+
+		if (blk_rq_pos(req) + blk_rq_sectors(req) >
+		    get_capacity(zv->zv_disk)) {
+			printk(KERN_INFO
+			       "%s: bad access: block=%llu, count=%lu\n",
+			       req->rq_disk->disk_name,
+			       (long long unsigned)blk_rq_pos(req),
+			       (long unsigned)blk_rq_sectors(req));
+			__blk_end_request(req, -EIO, size);
+			continue;
+		}
+
+		if (!blk_fs_request(req)) {
+			printk(KERN_INFO "%s: non-fs cmd\n",
+			       req->rq_disk->disk_name);
+			__blk_end_request(req, -EIO, size);
+			continue;
+		}
+
+		switch (rq_data_dir(req)) {
+		case READ:
+			zvol_dispatch(zvol_read, req);
+			break;
+		case WRITE:
+			if (unlikely(get_disk_ro(zv->zv_disk)) ||
+			    unlikely(zv->zv_flags & ZVOL_RDONLY)) {
+				__blk_end_request(req, -EROFS, size);
+				break;
+			}
+
+			zvol_dispatch(zvol_write, req);
+			break;
+		default:
+			printk(KERN_INFO "%s: unknown cmd: %d\n",
+			       req->rq_disk->disk_name, (int)rq_data_dir(req));
+			__blk_end_request(req, -EIO, size);
+			break;
+		}
+	}
+}
+
+static void
+zvol_get_done(zgd_t *zgd, int error)
+{
+	if (zgd->zgd_db)
+		dmu_buf_rele(zgd->zgd_db, zgd);
+
+	zfs_range_unlock(zgd->zgd_rl);
+
+	if (error == 0 && zgd->zgd_bp)
+		zil_add_block(zgd->zgd_zilog, zgd->zgd_bp);
+
+	kmem_free(zgd, sizeof (zgd_t));
+}
+
+/*
+ * Get data to generate a TX_WRITE intent log record.
+ */
+static int
+zvol_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio)
+{
+	zvol_state_t *zv = arg;
+	objset_t *os = zv->zv_objset;
+	uint64_t offset = lr->lr_offset;
+	uint64_t size = lr->lr_length;
+	dmu_buf_t *db;
+	zgd_t *zgd;
+	int error;
+
+	ASSERT(zio != NULL);
+	ASSERT(size != 0);
+
+	zgd = (zgd_t *)kmem_zalloc(sizeof (zgd_t), KM_SLEEP);
+	zgd->zgd_zilog = zv->zv_zilog;
+	zgd->zgd_rl = zfs_range_lock(&zv->zv_znode, offset, size, RL_READER);
+
+	/*
+	 * 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 */
+		error = dmu_read(os, ZVOL_OBJ, offset, size, buf,
+		    DMU_READ_NO_PREFETCH);
+	} else {
+		size = zv->zv_volblocksize;
+		offset = P2ALIGN_TYPED(offset, size, uint64_t);
+		error = dmu_buf_hold(os, ZVOL_OBJ, offset, zgd, &db,
+		    DMU_READ_NO_PREFETCH);
+		if (error == 0) {
+			zgd->zgd_db = db;
+			zgd->zgd_bp = &lr->lr_blkptr;
+
+			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 (error);
+}
+
+/*
+ * The zvol_state_t's are inserted in increasing MINOR(dev_t) order.
+ */
+static void
+zvol_insert(zvol_state_t *zv_insert)
+{
+	zvol_state_t *zv = NULL;
+
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+	ASSERT3U(MINOR(zv_insert->zv_dev) & ZVOL_MINOR_MASK, ==, 0);
+	for (zv = list_head(&zvol_state_list); zv != NULL;
+	     zv = list_next(&zvol_state_list, zv)) {
+		if (MINOR(zv->zv_dev) > MINOR(zv_insert->zv_dev))
+			break;
+	}
+
+	list_insert_before(&zvol_state_list, zv, zv_insert);
+}
+
+/*
+ * Simply remove the zvol from to list of zvols.
+ */
+static void
+zvol_remove(zvol_state_t *zv_remove)
+{
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+	list_remove(&zvol_state_list, zv_remove);
+}
+
+static int
+zvol_first_open(zvol_state_t *zv)
+{
+	objset_t *os;
+	uint64_t volsize;
+	int error;
+	uint64_t ro;
+
+	/* lie and say we're read-only */
+	error = dmu_objset_own(zv->zv_name, DMU_OST_ZVOL, 1, zvol_tag, &os);
+	if (error)
+		return (-error);
+
+	error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);
+	if (error) {
+	        dmu_objset_disown(os, zvol_tag);
+	        return (-error);
+	}
+
+	zv->zv_objset = os;
+	error = dmu_bonus_hold(os, ZVOL_OBJ, zvol_tag, &zv->zv_dbuf);
+	if (error) {
+	        dmu_objset_disown(os, zvol_tag);
+	        return (-error);
+	}
+
+	set_capacity(zv->zv_disk, volsize >> 9);
+	zv->zv_volsize = volsize;
+	zv->zv_zilog = zil_open(os, zvol_get_data);
+
+	VERIFY(dsl_prop_get_integer(zv->zv_name, "readonly", &ro, NULL) == 0);
+	if (ro || dmu_objset_is_snapshot(os)) {
+                set_disk_ro(zv->zv_disk, 1);
+	        zv->zv_flags |= ZVOL_RDONLY;
+	} else {
+                set_disk_ro(zv->zv_disk, 0);
+	        zv->zv_flags &= ~ZVOL_RDONLY;
+	}
+
+	return (-error);
+}
+
+static void
+zvol_last_close(zvol_state_t *zv)
+{
+	zil_close(zv->zv_zilog);
+	zv->zv_zilog = NULL;
+	dmu_buf_rele(zv->zv_dbuf, zvol_tag);
+	zv->zv_dbuf = NULL;
+	dmu_objset_disown(zv->zv_objset, zvol_tag);
+	zv->zv_objset = NULL;
+}
+
+static int
+zvol_open(struct block_device *bdev, fmode_t flag)
+{
+	zvol_state_t *zv = bdev->bd_disk->private_data;
+	int error = 0, drop_mutex = 0;
+
+	/*
+	 * If the caller is already holding the mutex do not take it
+	 * again, this will happen as part of zvol_create_minor().
+	 * Once add_disk() is called the device is live and the kernel
+	 * will attempt to open it to read the partition information.
+	 */
+	if (!mutex_owned(&zvol_state_lock)) {
+		mutex_enter(&zvol_state_lock);
+		drop_mutex = 1;
+	}
+
+	ASSERT3P(zv, !=, NULL);
+
+	if (zv->zv_open_count == 0) {
+		error = zvol_first_open(zv);
+		if (error)
+			goto out_mutex;
+	}
+
+	if ((flag & FMODE_WRITE) &&
+	    (get_disk_ro(zv->zv_disk) || (zv->zv_flags & ZVOL_RDONLY))) {
+		error = -EROFS;
+		goto out_open_count;
+	}
+
+	zv->zv_open_count++;
+
+out_open_count:
+	if (zv->zv_open_count == 0)
+		zvol_last_close(zv);
+
+out_mutex:
+	if (drop_mutex)
+		mutex_exit(&zvol_state_lock);
+
+	check_disk_change(bdev);
+
+	return (error);
+}
+
+static int
+zvol_release(struct gendisk *disk, fmode_t mode)
+{
+	zvol_state_t *zv = disk->private_data;
+	int drop_mutex = 0;
+
+	if (!mutex_owned(&zvol_state_lock)) {
+		mutex_enter(&zvol_state_lock);
+		drop_mutex = 1;
+	}
+
+	ASSERT3P(zv, !=, NULL);
+	ASSERT3U(zv->zv_open_count, >, 0);
+	zv->zv_open_count--;
+	if (zv->zv_open_count == 0)
+		zvol_last_close(zv);
+
+	if (drop_mutex)
+		mutex_exit(&zvol_state_lock);
+
+	return (0);
+}
+
+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;
+
+	if (zv == NULL)
+		return (-ENXIO);
+
+	switch (cmd) {
+	case BLKFLSBUF:
+		zil_commit(zv->zv_zilog, ZVOL_OBJ);
+		break;
+
+	default:
+		error = -ENOTTY;
+		break;
+
+	}
+
+	return (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
+
+static int zvol_media_changed(struct gendisk *disk)
+{
+	zvol_state_t *zv = disk->private_data;
+
+	return zv->zv_changed;
+}
+
+static int zvol_revalidate_disk(struct gendisk *disk)
+{
+	zvol_state_t *zv = disk->private_data;
+
+	zv->zv_changed = 0;
+	set_capacity(zv->zv_disk, zv->zv_volsize >> 9);
+
+	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 = 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;
+
+	mutex_enter(&zvol_state_lock);
+	zv = zvol_find_by_dev(dev);
+	kobj = zv ? get_disk(zv->zv_disk) : ERR_PTR(-ENOENT);
+	mutex_exit(&zvol_state_lock);
+
+	return kobj;
+}
+
+#ifdef HAVE_BDEV_BLOCK_DEVICE_OPERATIONS
+static struct block_device_operations zvol_ops = {
+	.open            = zvol_open,
+	.release         = zvol_release,
+	.ioctl           = zvol_ioctl,
+	.compat_ioctl    = zvol_compat_ioctl,
+	.media_changed   = zvol_media_changed,
+	.revalidate_disk = zvol_revalidate_disk,
+	.getgeo          = zvol_getgeo,
+        .owner           = THIS_MODULE,
+};
+
+#else /* HAVE_BDEV_BLOCK_DEVICE_OPERATIONS */
+
+static int
+zvol_open_by_inode(struct inode *inode, struct file *file)
+{
+	return zvol_open(inode->i_bdev, file->f_mode);
+}
+
+static int
+zvol_release_by_inode(struct inode *inode, struct file *file)
+{
+	return zvol_release(inode->i_bdev->bd_disk, file->f_mode);
+}
+
+static int
+zvol_ioctl_by_inode(struct inode *inode, struct file *file,
+                    unsigned int cmd, unsigned long arg)
+{
+	return zvol_ioctl(inode->i_bdev, file->f_mode, cmd, arg);
+}
+
+# ifdef CONFIG_COMPAT
+static long
+zvol_compat_ioctl_by_inode(struct file *file,
+                           unsigned int cmd, unsigned long arg)
+{
+	return zvol_compat_ioctl(file->f_dentry->d_inode->i_bdev,
+	                         file->f_mode, cmd, arg);
+}
+# else
+# define zvol_compat_ioctl_by_inode   NULL
+# endif
+
+static struct block_device_operations zvol_ops = {
+	.open            = zvol_open_by_inode,
+	.release         = zvol_release_by_inode,
+	.ioctl           = zvol_ioctl_by_inode,
+	.compat_ioctl    = zvol_compat_ioctl_by_inode,
+	.media_changed   = zvol_media_changed,
+	.revalidate_disk = zvol_revalidate_disk,
+	.getgeo          = zvol_getgeo,
+        .owner           = THIS_MODULE,
+};
+#endif /* HAVE_BDEV_BLOCK_DEVICE_OPERATIONS */
+
+/*
+ * 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;
+
+	zv = kmem_zalloc(sizeof (zvol_state_t), KM_SLEEP);
+	if (zv == NULL)
+		goto out;
+
+	zv->zv_queue = blk_init_queue(zvol_request, &zv->zv_lock);
+	if (zv->zv_queue == NULL)
+		goto out_kmem;
+
+	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, DISK_NAME_LEN);
+
+	mutex_init(&zv->zv_znode.z_range_lock, NULL, MUTEX_DEFAULT, NULL);
+	avl_create(&zv->zv_znode.z_range_avl, zfs_range_compare,
+	    sizeof (rl_t), offsetof(rl_t, r_node));
+	spin_lock_init(&zv->zv_lock);
+	list_link_init(&zv->zv_next);
+
+	zv->zv_disk->major = zvol_major;
+	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", name);
+
+	return zv;
+
+out_queue:
+	blk_cleanup_queue(zv->zv_queue);
+out_kmem:
+	kmem_free(zv, sizeof (zvol_state_t));
+out:
+	return NULL;
+}
+
+/*
+ * Cleanup then free a zvol_state_t which was created by zvol_alloc().
+ */
+static void
+zvol_free(zvol_state_t *zv)
+{
+	avl_destroy(&zv->zv_znode.z_range_avl);
+	mutex_destroy(&zv->zv_znode.z_range_lock);
+
+	del_gendisk(zv->zv_disk);
+	blk_cleanup_queue(zv->zv_queue);
+	put_disk(zv->zv_disk);
+
+	kmem_free(zv, sizeof (zvol_state_t));
+}
+
+static int
+__zvol_create_minor(const char *name)
+{
+	zvol_state_t *zv;
+	objset_t *os;
+	dmu_object_info_t *doi;
+	uint64_t volsize;
+	unsigned minor = 0;
+	int error = 0;
+
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+
+	zv = zvol_find_by_name(name);
+	if (zv) {
+		error = EEXIST;
+		goto out;
+	}
+
+	doi = kmem_alloc(sizeof(dmu_object_info_t), KM_SLEEP);
+
+	error = dmu_objset_own(name, DMU_OST_ZVOL, B_TRUE, zvol_tag, &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;
+
+	error = zvol_find_minor(&minor);
+	if (error)
+		goto out_dmu_objset_disown;
+
+	zv = zvol_alloc(MKDEV(zvol_major, minor), name);
+	if (zv == NULL) {
+		error = EAGAIN;
+		goto out_dmu_objset_disown;
+	}
+
+	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);
+
+	if (zil_replay_disable)
+		zil_destroy(dmu_objset_zil(os), B_FALSE);
+	else
+		zil_replay(os, zv, zvol_replay_vector);
+
+out_dmu_objset_disown:
+	dmu_objset_disown(os, zvol_tag);
+	zv->zv_objset = NULL;
+out_doi:
+	kmem_free(doi, sizeof(dmu_object_info_t));
+out:
+
+	if (error == 0) {
+		zvol_insert(zv);
+		add_disk(zv->zv_disk);
+	}
+
+	return (error);
+}
+
+/*
+ * 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.
+ */
+int
+zvol_create_minor(const char *name)
+{
+	int error;
+
+	mutex_enter(&zvol_state_lock);
+	error = __zvol_create_minor(name);
+	mutex_exit(&zvol_state_lock);
+
+	return (error);
+}
+
+static int
+__zvol_remove_minor(const char *name)
+{
+	zvol_state_t *zv;
+
+	ASSERT(MUTEX_HELD(&zvol_state_lock));
+
+	zv = zvol_find_by_name(name);
+	if (zv == NULL)
+		return (ENXIO);
+
+	if (zv->zv_open_count > 0)
+		return (EBUSY);
+
+	zvol_remove(zv);
+	zvol_free(zv);
+
+	return (0);
+}
+
+/*
+ * Remove a block device minor node for the specified volume.
+ */
+int
+zvol_remove_minor(const char *name)
+{
+	int error;
+
+	mutex_enter(&zvol_state_lock);
+	error = __zvol_remove_minor(name);
+	mutex_exit(&zvol_state_lock);
+
+	return (error);
+}
+
+static int
+zvol_create_minors_cb(spa_t *spa, uint64_t dsobj,
+		      const char *dsname, void *arg)
+{
+	if (strchr(dsname, '/') == NULL)
+		return 0;
+
+	return __zvol_create_minor(dsname);
+}
+
+/*
+ * Create minors for specified pool, if pool is NULL create minors
+ * for all available pools.
+ */
+int
+zvol_create_minors(const char *pool)
+{
+	spa_t *spa = NULL;
+	int error = 0;
+
+	mutex_enter(&zvol_state_lock);
+	if (pool) {
+		error = dmu_objset_find_spa(NULL, pool, zvol_create_minors_cb,
+		    NULL, DS_FIND_CHILDREN | DS_FIND_SNAPSHOTS);
+	} else {
+		mutex_enter(&spa_namespace_lock);
+		while ((spa = spa_next(spa)) != NULL) {
+			error = dmu_objset_find_spa(NULL,
+			    spa_name(spa), zvol_create_minors_cb, NULL,
+			    DS_FIND_CHILDREN | DS_FIND_SNAPSHOTS);
+			if (error)
+				break;
+		}
+		mutex_exit(&spa_namespace_lock);
+	}
+	mutex_exit(&zvol_state_lock);
+
+	return error;
+}
+
+/*
+ * Remove minors for specified pool, if pool is NULL remove all minors.
+ */
+void
+zvol_remove_minors(const char *pool)
+{
+	zvol_state_t *zv, *zv_next;
+	char *str;
+
+	str = kmem_zalloc(DISK_NAME_LEN, KM_SLEEP);
+	if (pool) {
+		(void) strncpy(str, pool, strlen(pool));
+		(void) strcat(str, "/");
+	}
+
+	mutex_enter(&zvol_state_lock);
+	for (zv = list_head(&zvol_state_list); zv != NULL; zv = zv_next) {
+		zv_next = list_next(&zvol_state_list, zv);
+
+		if (pool == NULL || !strncmp(str, zv->zv_name, strlen(str))) {
+			zvol_remove(zv);
+			zvol_free(zv);
+		}
+	}
+	mutex_exit(&zvol_state_lock);
+	kmem_free(str, DISK_NAME_LEN);
+}
+
+int
+zvol_init(void)
+{
+	int error;
+
+	if (!zvol_threads)
+		zvol_threads = num_online_cpus();
+
+	zvol_taskq = taskq_create(ZVOL_DRIVER, zvol_threads, maxclsyspri,
+		                  zvol_threads, INT_MAX, TASKQ_PREPOPULATE);
+	if (zvol_taskq == NULL) {
+		printk(KERN_INFO "ZFS: taskq_create() failed\n");
+		return (-ENOMEM);
+	}
+
+	error = register_blkdev(zvol_major, ZVOL_DRIVER);
+	if (error) {
+		printk(KERN_INFO "ZFS: register_blkdev() failed %d\n", error);
+		taskq_destroy(zvol_taskq);
+		return (error);
+	}
+
+	blk_register_region(MKDEV(zvol_major, 0), 1UL << MINORBITS,
+	                    THIS_MODULE, zvol_probe, NULL, NULL);
+
+	mutex_init(&zvol_state_lock, NULL, MUTEX_DEFAULT, NULL);
+	list_create(&zvol_state_list, sizeof (zvol_state_t),
+	            offsetof(zvol_state_t, zv_next));
+
+	(void) zvol_create_minors(NULL);
+
+	return (0);
+}
+
+void
+zvol_fini(void)
+{
+	zvol_remove_minors(NULL);
+	blk_unregister_region(MKDEV(zvol_major, 0), 1UL << MINORBITS);
+	unregister_blkdev(zvol_major, ZVOL_DRIVER);
+	taskq_destroy(zvol_taskq);
+	mutex_destroy(&zvol_state_lock);
+	list_destroy(&zvol_state_list);
+}
+
+module_param(zvol_major, uint, 0);
+MODULE_PARM_DESC(zvol_major, "Major number for zvol device");
+
+module_param(zvol_threads, uint, 0);
+MODULE_PARM_DESC(zvol_threads, "Number of threads for zvol device");