Log zvol truncate/discard operations

[mirror_zfs.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.
 *
 * Copyright 2014 Nexenta Systems, Inc.  All rights reserved.
 */

#include <sys/dbuf.h>
#include <sys/dmu_traverse.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_prop.h>
#include <sys/zap.h>
#include <sys/zfeature.h>
#include <sys/zil_impl.h>
#include <sys/dmu_tx.h>
#include <sys/zio.h>
#include <sys/zfs_rlock.h>
#include <sys/zfs_znode.h>
#include <sys/zvol.h>
#include <linux/blkdev_compat.h>

unsigned int zvol_inhibit_dev = 0;
unsigned int zvol_major = ZVOL_MAJOR;
unsigned int zvol_prefetch_bytes = (128 * 1024);
unsigned long zvol_max_discard_blocks = 16384;

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 */
        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 (SET_ERROR(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) == 0)
                        return (zv);
        }

        return (NULL);
}


/*
 * 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 = 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.
 */
void
zvol_create_cb(objset_t *os, void *arg, cred_t *cr, dmu_tx_t *tx)
{
        zfs_creat_t *zct = arg;
        nvlist_t *nvprops = zct->zct_props;
        int error;
        uint64_t volblocksize, volsize;

        VERIFY(nvlist_lookup_uint64(nvprops,
            zfs_prop_to_name(ZFS_PROP_VOLSIZE), &volsize) == 0);
        if (nvlist_lookup_uint64(nvprops,
            zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), &volblocksize) != 0)
                volblocksize = zfs_prop_default_numeric(ZFS_PROP_VOLBLOCKSIZE);

        /*
         * These properties must be removed from the list so the generic
         * property setting step won't apply to them.
         */
        VERIFY(nvlist_remove_all(nvprops,
            zfs_prop_to_name(ZFS_PROP_VOLSIZE)) == 0);
        (void) nvlist_remove_all(nvprops,
            zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE));

        error = dmu_object_claim(os, ZVOL_OBJ, DMU_OT_ZVOL, volblocksize,
            DMU_OT_NONE, 0, tx);
        ASSERT(error == 0);

        error = zap_create_claim(os, ZVOL_ZAP_OBJ, DMU_OT_ZVOL_PROP,
            DMU_OT_NONE, 0, tx);
        ASSERT(error == 0);

        error = zap_update(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize, tx);
        ASSERT(error == 0);
}

/*
 * ZFS_IOC_OBJSET_STATS entry point.
 */
int
zvol_get_stats(objset_t *os, nvlist_t *nv)
{
        int error;
        dmu_object_info_t *doi;
        uint64_t val;

        error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &val);
        if (error)
                return (SET_ERROR(error));

        dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_VOLSIZE, val);
        doi = kmem_alloc(sizeof (dmu_object_info_t), KM_SLEEP);
        error = dmu_object_info(os, ZVOL_OBJ, doi);

        if (error == 0) {
                dsl_prop_nvlist_add_uint64(nv, ZFS_PROP_VOLBLOCKSIZE,
                    doi->doi_data_block_size);
        }

        kmem_free(doi, sizeof (dmu_object_info_t));

        return (SET_ERROR(error));
}

static void
zvol_size_changed(zvol_state_t *zv, uint64_t volsize)
{
        struct block_device *bdev;

        bdev = bdget_disk(zv->zv_disk, 0);
        if (bdev == NULL)
                return;
        set_capacity(zv->zv_disk, volsize >> 9);
        zv->zv_volsize = volsize;
        check_disk_size_change(zv->zv_disk, bdev);

        bdput(bdev);
}

/*
 * Sanity check volume size.
 */
int
zvol_check_volsize(uint64_t volsize, uint64_t blocksize)
{
        if (volsize == 0)
                return (SET_ERROR(EINVAL));

        if (volsize % blocksize != 0)
                return (SET_ERROR(EINVAL));

#ifdef _ILP32
        if (volsize - 1 > MAXOFFSET_T)
                return (SET_ERROR(EOVERFLOW));
#endif
        return (0);
}

/*
 * Ensure the zap is flushed then inform the VFS of the capacity change.
 */
static int
zvol_update_volsize(uint64_t volsize, objset_t *os)
{
        dmu_tx_t *tx;
        int error;

        ASSERT(MUTEX_HELD(&zvol_state_lock));

        tx = dmu_tx_create(os);
        dmu_tx_hold_zap(tx, ZVOL_ZAP_OBJ, TRUE, NULL);
        dmu_tx_mark_netfree(tx);
        error = dmu_tx_assign(tx, TXG_WAIT);
        if (error) {
                dmu_tx_abort(tx);
                return (SET_ERROR(error));
        }

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

        if (error == 0)
                error = dmu_free_long_range(os,
                    ZVOL_OBJ, volsize, DMU_OBJECT_END);

        return (error);
}

static int
zvol_update_live_volsize(zvol_state_t *zv, uint64_t volsize)
{
        zvol_size_changed(zv, volsize);

        /*
         * We should post a event here describing the expansion.  However,
         * the zfs_ereport_post() interface doesn't nicely support posting
         * events for zvols, it assumes events relate to vdevs or zios.
         */

        return (0);
}

/*
 * Set ZFS_PROP_VOLSIZE set entry point.
 */
int
zvol_set_volsize(const char *name, uint64_t volsize)
{
        zvol_state_t *zv = NULL;
        objset_t *os = NULL;
        int error;
        dmu_object_info_t *doi;
        uint64_t readonly;
        boolean_t owned = B_FALSE;

        error = dsl_prop_get_integer(name,
            zfs_prop_to_name(ZFS_PROP_READONLY), &readonly, NULL);
        if (error != 0)
                return (SET_ERROR(error));
        if (readonly)
                return (SET_ERROR(EROFS));

        mutex_enter(&zvol_state_lock);
        zv = zvol_find_by_name(name);

        if (zv == NULL || zv->zv_objset == NULL) {
                if ((error = dmu_objset_own(name, DMU_OST_ZVOL, B_FALSE,
                    FTAG, &os)) != 0) {
                        mutex_exit(&zvol_state_lock);
                        return (SET_ERROR(error));
                }
                owned = B_TRUE;
                if (zv != NULL)
                        zv->zv_objset = os;
        } else {
                os = zv->zv_objset;
        }

        doi = kmem_alloc(sizeof (dmu_object_info_t), KM_SLEEP);

        if ((error = dmu_object_info(os, ZVOL_OBJ, doi)) ||
            (error = zvol_check_volsize(volsize, doi->doi_data_block_size)))
                goto out;

        error = zvol_update_volsize(volsize, os);
        kmem_free(doi, sizeof (dmu_object_info_t));

        if (error == 0 && zv != NULL)
                error = zvol_update_live_volsize(zv, volsize);
out:
        if (owned) {
                dmu_objset_disown(os, FTAG);
                if (zv != NULL)
                        zv->zv_objset = NULL;
        }
        mutex_exit(&zvol_state_lock);
        return (error);
}

/*
 * Sanity check volume block size.
 */
int
zvol_check_volblocksize(const char *name, uint64_t volblocksize)
{
        /* Record sizes above 128k need the feature to be enabled */
        if (volblocksize > SPA_OLD_MAXBLOCKSIZE) {
                spa_t *spa;
                int error;

                if ((error = spa_open(name, &spa, FTAG)) != 0)
                        return (error);

                if (!spa_feature_is_enabled(spa, SPA_FEATURE_LARGE_BLOCKS)) {
                        spa_close(spa, FTAG);
                        return (SET_ERROR(ENOTSUP));
                }

                /*
                 * We don't allow setting the property above 1MB,
                 * unless the tunable has been changed.
                 */
                if (volblocksize > zfs_max_recordsize)
                        return (SET_ERROR(EDOM));

                spa_close(spa, FTAG);
        }

        if (volblocksize < SPA_MINBLOCKSIZE ||
            volblocksize > SPA_MAXBLOCKSIZE ||
            !ISP2(volblocksize))
                return (SET_ERROR(EDOM));

        return (0);
}

/*
 * 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 = SET_ERROR(ENXIO);
                goto out;
        }

        if (zv->zv_flags & ZVOL_RDONLY) {
                error = SET_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 = SET_ERROR(EBUSY);
                dmu_tx_commit(tx);
                if (error == 0)
                        zv->zv_volblocksize = volblocksize;
        }
out:
        mutex_exit(&zvol_state_lock);

        return (SET_ERROR(error));
}

/*
 * Replay a TX_TRUNCATE ZIL transaction if asked.  TX_TRUNCATE is how we
 * implement DKIOCFREE/free-long-range.
 */
static int
zvol_replay_truncate(zvol_state_t *zv, lr_truncate_t *lr, boolean_t byteswap)
{
        uint64_t offset, length;

        if (byteswap)
                byteswap_uint64_array(lr, sizeof (*lr));

        offset = lr->lr_offset;
        length = lr->lr_length;

        return (dmu_free_long_range(zv->zv_objset, ZVOL_OBJ, offset, length));
}

/*
 * 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 (SET_ERROR(error));
}

static int
zvol_replay_err(zvol_state_t *zv, lr_t *lr, boolean_t byteswap)
{
        return (SET_ERROR(ENOTSUP));
}

/*
 * Callback vectors for replaying records.
 * Only TX_WRITE and TX_TRUNCATE are 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_truncate, /* 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;
        ssize_t immediate_write_sz;

        if (zil_replaying(zilog, tx))
                return;

        immediate_write_sz = (zilog->zl_logbias == ZFS_LOGBIAS_THROUGHPUT)
                ? 0 : zvol_immediate_write_sz;
        slogging = spa_has_slogs(zilog->zl_spa) &&
                (zilog->zl_logbias == ZFS_LOGBIAS_LATENCY);

        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 > 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;
        }
}

static int
zvol_write(struct bio *bio)
{
        zvol_state_t *zv = bio->bi_bdev->bd_disk->private_data;
        uint64_t offset = BIO_BI_SECTOR(bio) << 9;
        uint64_t size = BIO_BI_SIZE(bio);
        int error = 0;
        dmu_tx_t *tx;
        rl_t *rl;
        uio_t uio;

        if (bio->bi_rw & VDEV_REQ_FLUSH)
                zil_commit(zv->zv_zilog, ZVOL_OBJ);

        /*
         * Some requests are just for flush and nothing else.
         */
        if (size == 0)
                goto out;

        uio.uio_bvec = &bio->bi_io_vec[BIO_BI_IDX(bio)];
        uio.uio_skip = BIO_BI_SKIP(bio);
        uio.uio_resid = size;
        uio.uio_iovcnt = bio->bi_vcnt - BIO_BI_IDX(bio);
        uio.uio_loffset = offset;
        uio.uio_limit = MAXOFFSET_T;
        uio.uio_segflg = UIO_BVEC;

        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);
                goto out;
        }

        error = dmu_write_uio(zv->zv_objset, ZVOL_OBJ, &uio, size, tx);
        if (error == 0)
                zvol_log_write(zv, tx, offset, size,
                    !!(bio->bi_rw & VDEV_REQ_FUA));

        dmu_tx_commit(tx);
        zfs_range_unlock(rl);

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

out:
        return (error);
}

/*
 * Log a DKIOCFREE/free-long-range to the ZIL with TX_TRUNCATE.
 */
static void
zvol_log_truncate(zvol_state_t *zv, dmu_tx_t *tx, uint64_t off, uint64_t len,
    boolean_t sync)
{
        itx_t *itx;
        lr_truncate_t *lr;
        zilog_t *zilog = zv->zv_zilog;

        if (zil_replaying(zilog, tx))
                return;

        itx = zil_itx_create(TX_TRUNCATE, sizeof (*lr));
        lr = (lr_truncate_t *)&itx->itx_lr;
        lr->lr_foid = ZVOL_OBJ;
        lr->lr_offset = off;
        lr->lr_length = len;

        itx->itx_sync = sync;
        zil_itx_assign(zilog, itx, tx);
}

static int
zvol_discard(struct bio *bio)
{
        zvol_state_t *zv = bio->bi_bdev->bd_disk->private_data;
        uint64_t start = BIO_BI_SECTOR(bio) << 9;
        uint64_t size = BIO_BI_SIZE(bio);
        uint64_t end = start + size;
        int error;
        rl_t *rl;
        dmu_tx_t *tx;

        if (end > zv->zv_volsize)
                return (SET_ERROR(EIO));

        /*
         * Align the request to volume block boundaries when REQ_SECURE is
         * available, but not requested. If we don't, then this will force
         * dnode_free_range() to zero out the unaligned parts, which is slow
         * (read-modify-write) and useless since we are not freeing any space
         * by doing so. Kernels that do not support REQ_SECURE (2.6.32 through
         * 2.6.35) will not receive this optimization.
         */
#ifdef REQ_SECURE
        if (!(bio->bi_rw & REQ_SECURE)) {
                start = P2ROUNDUP(start, zv->zv_volblocksize);
                end = P2ALIGN(end, zv->zv_volblocksize);
                size = end - start;
        }
#endif

        if (start >= end)
                return (0);

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

        zfs_range_unlock(rl);

        return (error);
}

static int
zvol_read(struct bio *bio)
{
        zvol_state_t *zv = bio->bi_bdev->bd_disk->private_data;
        uint64_t offset = BIO_BI_SECTOR(bio) << 9;
        uint64_t size = BIO_BI_SIZE(bio);
        int error;
        rl_t *rl;
        uio_t uio;

        if (size == 0)
                return (0);

        uio.uio_bvec = &bio->bi_io_vec[BIO_BI_IDX(bio)];
        uio.uio_skip = BIO_BI_SKIP(bio);
        uio.uio_resid = size;
        uio.uio_iovcnt = bio->bi_vcnt - BIO_BI_IDX(bio);
        uio.uio_loffset = offset;
        uio.uio_limit = MAXOFFSET_T;
        uio.uio_segflg = UIO_BVEC;

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

        error = dmu_read_uio(zv->zv_objset, ZVOL_OBJ, &uio, size);

        zfs_range_unlock(rl);

        /* convert checksum errors into IO errors */
        if (error == ECKSUM)
                error = SET_ERROR(EIO);

        return (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);
        unsigned int sectors = bio_sectors(bio);
        int rw = bio_data_dir(bio);
#ifdef HAVE_GENERIC_IO_ACCT
        unsigned long start = jiffies;
#endif
        int error = 0;

        if (bio_has_data(bio) && offset + sectors >
            get_capacity(zv->zv_disk)) {
                printk(KERN_INFO
                    "%s: bad access: block=%llu, count=%lu\n",
                    zv->zv_disk->disk_name,
                    (long long unsigned)offset,
                    (long unsigned)sectors);
                error = SET_ERROR(EIO);
                goto out1;
        }

        generic_start_io_acct(rw, sectors, &zv->zv_disk->part0);

        if (rw == WRITE) {
                if (unlikely(zv->zv_flags & ZVOL_RDONLY)) {
                        error = SET_ERROR(EROFS);
                        goto out2;
                }

                if (bio->bi_rw & VDEV_REQ_DISCARD) {
                        error = zvol_discard(bio);
                        goto out2;
                }

                error = zvol_write(bio);
        } else
                error = zvol_read(bio);

out2:
        generic_end_io_acct(rw, &zv->zv_disk->part0, start);
out1:
        BIO_END_IO(bio, -error);
        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
}

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 object = ZVOL_OBJ;
        uint64_t offset = lr->lr_offset;
        uint64_t size = lr->lr_length;
        blkptr_t *bp = &lr->lr_blkptr;
        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, object, offset, size, buf,
                    DMU_READ_NO_PREFETCH);
        } else {
                size = zv->zv_volblocksize;
                offset = P2ALIGN_TYPED(offset, size, uint64_t);
                error = dmu_buf_hold(os, object, offset, zgd, &db,
                    DMU_READ_NO_PREFETCH);
                if (error == 0) {
                        blkptr_t *obp = dmu_buf_get_blkptr(db);
                        if (obp) {
                                ASSERT(BP_IS_HOLE(bp));
                                *bp = *obp;
                        }

                        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 (SET_ERROR(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 locked = 0;
        int error;
        uint64_t ro;

        /*
         * In all other cases the spa_namespace_lock is taken before the
         * bdev->bd_mutex lock.  But in this case the Linux __blkdev_get()
         * function calls fops->open() with the bdev->bd_mutex lock held.
         *
         * To avoid a potential lock inversion deadlock we preemptively
         * try to take the spa_namespace_lock().  Normally it will not
         * be contended and this is safe because spa_open_common() handles
         * the case where the caller already holds the spa_namespace_lock.
         *
         * When it is contended we risk a lock inversion if we were to
         * block waiting for the lock.  Luckily, the __blkdev_get()
         * function allows us to return -ERESTARTSYS which will result in
         * bdev->bd_mutex being dropped, reacquired, and fops->open() being
         * called again.  This process can be repeated safely until both
         * locks are acquired.
         */
        if (!mutex_owned(&spa_namespace_lock)) {
                locked = mutex_tryenter(&spa_namespace_lock);
                if (!locked)
                        return (-SET_ERROR(ERESTARTSYS));
        }

        error = dsl_prop_get_integer(zv->zv_name, "readonly", &ro, NULL);
        if (error)
                goto out_mutex;

        /* lie and say we're read-only */
        error = dmu_objset_own(zv->zv_name, DMU_OST_ZVOL, 1, zvol_tag, &os);
        if (error)
                goto out_mutex;

        error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);
        if (error) {
                dmu_objset_disown(os, zvol_tag);
                goto out_mutex;
        }

        zv->zv_objset = os;
        error = dmu_bonus_hold(os, ZVOL_OBJ, zvol_tag, &zv->zv_dbuf);
        if (error) {
                dmu_objset_disown(os, zvol_tag);
                goto out_mutex;
        }

        set_capacity(zv->zv_disk, volsize >> 9);
        zv->zv_volsize = volsize;
        zv->zv_zilog = zil_open(os, zvol_get_data);

        if (ro || dmu_objset_is_snapshot(os) ||
            !spa_writeable(dmu_objset_spa(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;
        }

out_mutex:
        if (locked)
                mutex_exit(&spa_namespace_lock);

        return (SET_ERROR(-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;

        /*
         * Evict cached data
         */
        if (dsl_dataset_is_dirty(dmu_objset_ds(zv->zv_objset)) &&
            !(zv->zv_flags & ZVOL_RDONLY))
                txg_wait_synced(dmu_objset_pool(zv->zv_objset), 0);
        (void) dmu_objset_evict_dbufs(zv->zv_objset);

        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) && (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 (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 = disk->private_data;
        int drop_mutex = 0;

        if (!mutex_owned(&zvol_state_lock)) {
                mutex_enter(&zvol_state_lock);
                drop_mutex = 1;
        }

        if (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);

#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;

        if (zv == NULL)
                return (SET_ERROR(-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 (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

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) : NULL;
        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 (SET_ERROR(-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 (SET_ERROR(-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);

        list_link_init(&zv->zv_next);

        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);

#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;

        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));

        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_snapdev_hidden(const char *name)
{
        uint64_t snapdev;
        char *parent;
        char *atp;
        int error = 0;

        parent = kmem_alloc(MAXPATHLEN, KM_SLEEP);
        (void) strlcpy(parent, name, MAXPATHLEN);

        if ((atp = strrchr(parent, '@')) != NULL) {
                *atp = '\0';
                error = dsl_prop_get_integer(parent, "snapdev", &snapdev, NULL);
                if ((error == 0) && (snapdev == ZFS_SNAPDEV_HIDDEN))
                        error = SET_ERROR(ENODEV);
        }

        kmem_free(parent, MAXPATHLEN);

        return (SET_ERROR(error));
}

static int
__zvol_create_minor(const char *name, boolean_t ignore_snapdev)
{
        zvol_state_t *zv;
        objset_t *os;
        dmu_object_info_t *doi;
        uint64_t volsize;
        uint64_t len;
        unsigned minor = 0;
        int error = 0;

        ASSERT(MUTEX_HELD(&zvol_state_lock));

        zv = zvol_find_by_name(name);
        if (zv) {
                error = SET_ERROR(EEXIST);
                goto out;
        }

        if (ignore_snapdev == B_FALSE) {
                error = __zvol_snapdev_hidden(name);
                if (error)
                        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 = SET_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, (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);
        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zv->zv_queue);
#ifdef QUEUE_FLAG_NONROT
        queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zv->zv_queue);
#endif
#ifdef QUEUE_FLAG_ADD_RANDOM
        queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, 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);
        }

        /*
         * 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, zvol_tag);
out_doi:
        kmem_free(doi, sizeof (dmu_object_info_t));
out:

        if (error == 0) {
                zvol_insert(zv);
                add_disk(zv->zv_disk);
        }

        return (SET_ERROR(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, B_FALSE);
        mutex_exit(&zvol_state_lock);

        return (SET_ERROR(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 (SET_ERROR(ENXIO));

        if (zv->zv_open_count > 0)
                return (SET_ERROR(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 (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(MUTEX_HELD(&zvol_state_lock));

        strlcpy(zv->zv_name, newname, sizeof (zv->zv_name));

        /*
         * 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);
}

static int
zvol_create_minors_cb(const char *dsname, void *arg)
{
        (void) zvol_create_minor(dsname);

        return (0);
}

/*
 * Create minors for specified dataset including children and snapshots.
 */
int
zvol_create_minors(const char *name)
{
        int error = 0;

        if (!zvol_inhibit_dev)
                error = dmu_objset_find((char *)name, zvol_create_minors_cb,
                    NULL, DS_FIND_CHILDREN | DS_FIND_SNAPSHOTS);

        return (SET_ERROR(error));
}

/*
 * Remove minors for specified dataset including children and snapshots.
 */
void
zvol_remove_minors(const char *name)
{
        zvol_state_t *zv, *zv_next;
        int namelen = ((name) ? strlen(name) : 0);

        if (zvol_inhibit_dev)
                return;

        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 (name == NULL || strcmp(zv->zv_name, name) == 0 ||
                    (strncmp(zv->zv_name, name, namelen) == 0 &&
                    zv->zv_name[namelen] == '/')) {
                        zvol_remove(zv);
                        zvol_free(zv);
                }
        }

        mutex_exit(&zvol_state_lock);
}

/*
 * Rename minors for specified dataset including children and snapshots.
 */
void
zvol_rename_minors(const char *oldname, const char *newname)
{
        zvol_state_t *zv, *zv_next;
        int oldnamelen, newnamelen;
        char *name;

        if (zvol_inhibit_dev)
                return;

        oldnamelen = strlen(oldname);
        newnamelen = strlen(newname);
        name = kmem_alloc(MAXNAMELEN, KM_SLEEP);

        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 (strcmp(zv->zv_name, oldname) == 0) {
                        __zvol_rename_minor(zv, newname);
                } else if (strncmp(zv->zv_name, oldname, oldnamelen) == 0 &&
                    (zv->zv_name[oldnamelen] == '/' ||
                    zv->zv_name[oldnamelen] == '@')) {
                        snprintf(name, MAXNAMELEN, "%s%c%s", newname,
                            zv->zv_name[oldnamelen],
                            zv->zv_name + oldnamelen + 1);
                        __zvol_rename_minor(zv, name);
                }
        }

        mutex_exit(&zvol_state_lock);

        kmem_free(name, MAXNAMELEN);
}

static int
snapdev_snapshot_changed_cb(const char *dsname, void *arg) {
        uint64_t snapdev = *(uint64_t *) arg;

        if (strchr(dsname, '@') == NULL)
                return (0);

        switch (snapdev) {
                case ZFS_SNAPDEV_VISIBLE:
                        mutex_enter(&zvol_state_lock);
                        (void) __zvol_create_minor(dsname, B_TRUE);
                        mutex_exit(&zvol_state_lock);
                        break;
                case ZFS_SNAPDEV_HIDDEN:
                        (void) zvol_remove_minor(dsname);
                        break;
        }

        return (0);
}

int
zvol_set_snapdev(const char *dsname, uint64_t snapdev) {
        (void) dmu_objset_find((char *) dsname, snapdev_snapshot_changed_cb,
                &snapdev, DS_FIND_SNAPSHOTS | DS_FIND_CHILDREN);
        /* caller should continue to modify snapdev property */
        return (-1);
}

int
zvol_init(void)
{
        int error;

        list_create(&zvol_state_list, sizeof (zvol_state_t),
            offsetof(zvol_state_t, zv_next));

        mutex_init(&zvol_state_lock, NULL, MUTEX_DEFAULT, NULL);

        error = register_blkdev(zvol_major, ZVOL_DRIVER);
        if (error) {
                printk(KERN_INFO "ZFS: register_blkdev() failed %d\n", error);
                goto out;
        }

        blk_register_region(MKDEV(zvol_major, 0), 1UL << MINORBITS,
            THIS_MODULE, zvol_probe, NULL, NULL);

        return (0);

out:
        mutex_destroy(&zvol_state_lock);
        list_destroy(&zvol_state_list);

        return (SET_ERROR(error));
}

void
zvol_fini(void)
{
        zvol_remove_minors(NULL);
        blk_unregister_region(MKDEV(zvol_major, 0), 1UL << MINORBITS);
        unregister_blkdev(zvol_major, ZVOL_DRIVER);
        mutex_destroy(&zvol_state_lock);
        list_destroy(&zvol_state_list);
}

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_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");