Add support for DISCARD to ZVOLs.

[mirror_zfs-debian.git] / 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 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 <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.
 */

#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>
#include <linux/blkdev_compat.h>

unsigned int zvol_major = ZVOL_MAJOR;
unsigned int zvol_threads = 32;

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[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 */
        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, MAXNAMELEN))
                        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, objset_t *os)
{
        struct block_device *bdev;
        dmu_tx_t *tx;
        int error;

        ASSERT(MUTEX_HELD(&zvol_state_lock));

        tx = dmu_tx_create(os);
        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(os, ZVOL_ZAP_OBJ, "size", 8, 1,
            &volsize, tx);
        dmu_tx_commit(tx);

        if (error)
                return (error);

        error = dmu_free_long_range(os,
            ZVOL_OBJ, volsize, DMU_OBJECT_END);
        if (error)
                return (error);

        bdev = bdget_disk(zv->zv_disk, 0);
        if (!bdev)
                return (EIO);
/*
 * 2.6.28 API change
 * Added check_disk_size_change() helper function.
 */
#ifdef HAVE_CHECK_DISK_SIZE_CHANGE
        set_capacity(zv->zv_disk, volsize >> 9);
        zv->zv_volsize = volsize;
        check_disk_size_change(zv->zv_disk, bdev);
#else
        zv->zv_volsize = volsize;
        zv->zv_changed = 1;
        (void) check_disk_change(bdev);
#endif /* HAVE_CHECK_DISK_SIZE_CHANGE */

        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, os);
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;

        if (req->cmd_flags & VDEV_REQ_FLUSH)
                zil_commit(zv->zv_zilog, ZVOL_OBJ);

        /*
         * Some requests are just for flush and nothing else.
         */
        if (size == 0) {
                blk_end_request(req, 0, size);
                return;
        }

        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,
                    req->cmd_flags & VDEV_REQ_FUA);

        dmu_tx_commit(tx);
        zfs_range_unlock(rl);

        if ((req->cmd_flags & VDEV_REQ_FUA) ||
            zv->zv_objset->os_sync == ZFS_SYNC_ALWAYS)
                zil_commit(zv->zv_zilog, ZVOL_OBJ);

        blk_end_request(req, -error, size);
}

#ifdef HAVE_BLK_QUEUE_DISCARD
static void
zvol_discard(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;

        if (offset + size > zv->zv_volsize) {
                blk_end_request(req, -EIO, size);
                return;
        }

        if (size == 0) {
                blk_end_request(req, 0, size);
                return;
        }

        rl = zfs_range_lock(&zv->zv_znode, offset, size, RL_WRITER);

        error = dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, offset, size);

        /*
         * TODO: maybe we should add the operation to the log.
         */

        zfs_range_unlock(rl);

        blk_end_request(req, -error, size);
}
#endif /* HAVE_BLK_QUEUE_DISCARD */

/*
 * 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;

        if (size == 0) {
                blk_end_request(req, 0, size);
                return;
        }

        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 (size != 0 && 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;
                        }

#ifdef HAVE_BLK_QUEUE_DISCARD
                        if (req->cmd_flags & VDEV_REQ_DISCARD) {
                                zvol_dispatch(zvol_discard, req);
                                break;
                        }
#endif /* HAVE_BLK_QUEUE_DISCARD */

                        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;
        case BLKZNAME:
                error = copy_to_user((void *)arg, zv->zv_name, MAXNAMELEN);
                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)
{
        if (file == NULL || inode == NULL)
                return -EINVAL;
        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)
{
        if (file == NULL)
                return -EINVAL;
        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;

#ifdef HAVE_BLK_QUEUE_FLUSH
        blk_queue_flush(zv->zv_queue, VDEV_REQ_FLUSH | VDEV_REQ_FUA);
#else
        blk_queue_ordered(zv->zv_queue, QUEUE_ORDERED_DRAIN, NULL);
#endif /* HAVE_BLK_QUEUE_FLUSH */

        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);

        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));
        zv->zv_znode.z_is_zvol = TRUE;

        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%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));
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);

        blk_queue_max_hw_sectors(zv->zv_queue, UINT_MAX);
        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);
#ifdef HAVE_BLK_QUEUE_DISCARD
        blk_queue_max_discard_sectors(zv->zv_queue, UINT_MAX);
        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zv->zv_queue);
#endif
#ifdef HAVE_BLK_QUEUE_NONROT
        queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zv->zv_queue);
#endif

        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;

        (void) __zvol_create_minor(dsname);
        return (0);
}

/*
 * 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(MAXNAMELEN, 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, MAXNAMELEN);
}

int
zvol_init(void)
{
        int error;

        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, 0444);
MODULE_PARM_DESC(zvol_major, "Major number for zvol device");

module_param(zvol_threads, uint, 0444);
MODULE_PARM_DESC(zvol_threads, "Number of threads for zvol device");