fs/zfs/zvol.c

	zvol.c revision 1209a471b5681c43d839d4b890f708f500da7346
/*
 * 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 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * 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/zvol/dsk/<pool_name>/<dataset_name>
 * /dev/zvol/rdsk/<pool_name>/<dataset_name>
 *
 * These links are created by the ZFS-specific devfsadm link generator.
 * Volumes are persistent through reboot.  No user command needs to be
 * run before opening and using a device.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/errno.h>
#include <sys/uio.h>
#include <sys/buf.h>
#include <sys/modctl.h>
#include <sys/open.h>
#include <sys/kmem.h>
#include <sys/conf.h>
#include <sys/cmn_err.h>
#include <sys/stat.h>
#include <sys/zap.h>
#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/dmu_traverse.h>
#include <sys/dnode.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_prop.h>
#include <sys/dkio.h>
#include <sys/efi_partition.h>
#include <sys/byteorder.h>
#include <sys/pathname.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>
#include <sys/crc32.h>
#include <sys/dirent.h>
#include <sys/policy.h>
#include <sys/fs/zfs.h>
#include <sys/zfs_ioctl.h>
#include <sys/mkdev.h>
#include <sys/zil.h>
#include <sys/refcount.h>
#include <sys/zfs_znode.h>
#include <sys/zfs_rlock.h>
#include <sys/vdev_disk.h>
#include <sys/vdev_impl.h>
#include <sys/zvol.h>
#include <sys/dumphdr.h>
#include <sys/zil_impl.h>

#include "zfs_namecheck.h"

static void *zvol_state;

#define ZVOL_DUMPSIZE       "dumpsize"

/*
 * This lock protects the zvol_state structure from being modified
 * while it's being used, e.g. an open that comes in before a create
 * finishes.  It also protects temporary opens of the dataset so that,
 * e.g., an open doesn't get a spurious EBUSY.
 */
static kmutex_t zvol_state_lock;
static uint32_t zvol_minors;

typedef struct zvol_extent {
    list_node_t ze_node;
    dva_t       ze_dva;     /* dva associated with this extent */
    uint64_t    ze_nblks;   /* number of blocks in extent */
} zvol_extent_t;

/*
 * The in-core state of each volume.
 */
typedef struct zvol_state {
    char        zv_name[MAXPATHLEN]; /* pool/dd name */
    uint64_t    zv_volsize; /* amount of space we advertise */
    uint64_t    zv_volblocksize; /* volume block size */
    minor_t     zv_minor;   /* minor number */
    uint8_t     zv_min_bs;  /* minimum addressable block shift */
    uint8_t     zv_flags;   /* readonly; dumpified */
    objset_t    *zv_objset; /* objset handle */
    uint32_t    zv_mode;    /* DS_MODE_* flags at open time */
    uint32_t    zv_open_count[OTYPCNT]; /* open counts */
    uint32_t    zv_total_opens; /* total open count */
    zilog_t     *zv_zilog;  /* ZIL handle */
    list_t      zv_extents; /* List of extents for dump */
    znode_t     zv_znode;   /* for range locking */
} zvol_state_t;

/*
 * zvol specific flags
 */
#define ZVOL_RDONLY 0x1
#define ZVOL_DUMPIFIED  0x2
#define ZVOL_EXCL   0x4

/*
 * zvol maximum transfer in one DMU tx.
 */
int zvol_maxphys = DMU_MAX_ACCESS/2;

extern int zfs_set_prop_nvlist(const char *, nvlist_t *);
static int zvol_get_data(void *arg, lr_write_t *lr, char *buf, zio_t *zio);
static int zvol_dumpify(zvol_state_t *zv);
static int zvol_dump_fini(zvol_state_t *zv);
static int zvol_dump_init(zvol_state_t *zv, boolean_t resize);

static void
zvol_size_changed(zvol_state_t *zv, major_t maj)
{
    dev_t dev = makedevice(maj, zv->zv_minor);

    VERIFY(ddi_prop_update_int64(dev, zfs_dip,
        "Size", zv->zv_volsize) == DDI_SUCCESS);
    VERIFY(ddi_prop_update_int64(dev, zfs_dip,
        "Nblocks", lbtodb(zv->zv_volsize)) == DDI_SUCCESS);

    /* Notify specfs to invalidate the cached size */
    spec_size_invalidate(dev, VBLK);
    spec_size_invalidate(dev, VCHR);
}

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 > SPEC_MAXOFFSET_T)
        return (EOVERFLOW);
#endif
    return (0);
}

int
zvol_check_volblocksize(uint64_t volblocksize)
{
    if (volblocksize < SPA_MINBLOCKSIZE ||
        volblocksize > SPA_MAXBLOCKSIZE ||
        !ISP2(volblocksize))
        return (EDOM);

    return (0);
}

static void
zvol_readonly_changed_cb(void *arg, uint64_t newval)
{
    zvol_state_t *zv = arg;

    if (newval)
        zv->zv_flags |= ZVOL_RDONLY;
    else
        zv->zv_flags &= ~ZVOL_RDONLY;
}

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);

    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);
    }

    return (error);
}

/*
 * Find a free minor number.
 */
static minor_t
zvol_minor_alloc(void)
{
    minor_t minor;

    ASSERT(MUTEX_HELD(&zvol_state_lock));

    for (minor = 1; minor <= ZVOL_MAX_MINOR; minor++)
        if (ddi_get_soft_state(zvol_state, minor) == NULL)
            return (minor);

    return (0);
}

static zvol_state_t *
zvol_minor_lookup(const char *name)
{
    minor_t minor;
    zvol_state_t *zv;

    ASSERT(MUTEX_HELD(&zvol_state_lock));

    for (minor = 1; minor <= ZVOL_MAX_MINOR; minor++) {
        zv = ddi_get_soft_state(zvol_state, minor);
        if (zv == NULL)
            continue;
        if (strcmp(zv->zv_name, name) == 0)
            break;
    }

    return (zv);
}

/* extent mapping arg */
struct maparg {
    zvol_state_t    *ma_zv;
    uint64_t    ma_blks;
};

/*ARGSUSED*/
static int
zvol_map_block(spa_t *spa, blkptr_t *bp, const zbookmark_t *zb,
    const dnode_phys_t *dnp, void *arg)
{
    struct maparg *ma = arg;
    zvol_extent_t *ze;
    int bs = ma->ma_zv->zv_volblocksize;

    if (bp == NULL || zb->zb_object != ZVOL_OBJ || zb->zb_level != 0)
        return (0);

    VERIFY3U(ma->ma_blks, ==, zb->zb_blkid);
    ma->ma_blks++;

    /* Abort immediately if we have encountered gang blocks */
    if (BP_IS_GANG(bp))
        return (EFRAGS);

    /*
     * See if the block is at the end of the previous extent.
     */
    ze = list_tail(&ma->ma_zv->zv_extents);
    if (ze &&
        DVA_GET_VDEV(BP_IDENTITY(bp)) == DVA_GET_VDEV(&ze->ze_dva) &&
        DVA_GET_OFFSET(BP_IDENTITY(bp)) ==
        DVA_GET_OFFSET(&ze->ze_dva) + ze->ze_nblks * bs) {
        ze->ze_nblks++;
        return (0);
    }

    dprintf_bp(bp, "%s", "next blkptr:");

    /* start a new extent */
    ze = kmem_zalloc(sizeof (zvol_extent_t), KM_SLEEP);
    ze->ze_dva = bp->blk_dva[0];    /* structure assignment */
    ze->ze_nblks = 1;
    list_insert_tail(&ma->ma_zv->zv_extents, ze);
    return (0);
}

static void
zvol_free_extents(zvol_state_t *zv)
{
    zvol_extent_t *ze;

    while (ze = list_head(&zv->zv_extents)) {
        list_remove(&zv->zv_extents, ze);
        kmem_free(ze, sizeof (zvol_extent_t));
    }
}

static int
zvol_get_lbas(zvol_state_t *zv)
{
    struct maparg   ma;
    int     err;

    ma.ma_zv = zv;
    ma.ma_blks = 0;
    zvol_free_extents(zv);

    err = traverse_dataset(dmu_objset_ds(zv->zv_objset), 0,
        TRAVERSE_PRE | TRAVERSE_PREFETCH_METADATA, zvol_map_block, &ma);
    if (err || ma.ma_blks != (zv->zv_volsize / zv->zv_volblocksize)) {
        zvol_free_extents(zv);
        return (err ? err : EIO);
    }

    return (0);
}

/* ARGSUSED */
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);
}

/*
 * 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);
}

/* ARGSUSED */
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] = {
    zvol_replay_err,    /* 0 no such transaction type */
    zvol_replay_err,    /* TX_CREATE */
    zvol_replay_err,    /* TX_MKDIR */
    zvol_replay_err,    /* TX_MKXATTR */
    zvol_replay_err,    /* TX_SYMLINK */
    zvol_replay_err,    /* TX_REMOVE */
    zvol_replay_err,    /* TX_RMDIR */
    zvol_replay_err,    /* TX_LINK */
    zvol_replay_err,    /* TX_RENAME */
    zvol_replay_write,  /* TX_WRITE */
    zvol_replay_err,    /* TX_TRUNCATE */
    zvol_replay_err,    /* TX_SETATTR */
    zvol_replay_err,    /* TX_ACL */
};

/*
 * Create a minor node (plus a whole lot more) for the specified volume.
 */
int
zvol_create_minor(const char *name, major_t maj)
{
    zvol_state_t *zv;
    objset_t *os;
    dmu_object_info_t doi;
    uint64_t volsize;
    minor_t minor = 0;
    struct pathname linkpath;
    int ds_mode = DS_MODE_OWNER;
    vnode_t *vp = NULL;
    char *devpath;
    size_t devpathlen = strlen(ZVOL_FULL_DEV_DIR) + strlen(name) + 1;
    char chrbuf[30], blkbuf[30];
    int error;

    mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(name)) != NULL) {
        mutex_exit(&zvol_state_lock);
        return (EEXIST);
    }

    if (strchr(name, '@') != 0)
        ds_mode |= DS_MODE_READONLY;

    error = dmu_objset_open(name, DMU_OST_ZVOL, ds_mode, &os);

    if (error) {
        mutex_exit(&zvol_state_lock);
        return (error);
    }

    error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &volsize);

    if (error) {
        dmu_objset_close(os);
        mutex_exit(&zvol_state_lock);
        return (error);
    }

    /*
     * If there's an existing /dev/zvol symlink, try to use the
     * same minor number we used last time.
     */
    devpath = kmem_alloc(devpathlen, KM_SLEEP);

    (void) sprintf(devpath, "%s%s", ZVOL_FULL_DEV_DIR, name);

    error = lookupname(devpath, UIO_SYSSPACE, NO_FOLLOW, NULL, &vp);

    kmem_free(devpath, devpathlen);

    if (error == 0 && vp->v_type != VLNK)
        error = EINVAL;

    if (error == 0) {
        pn_alloc(&linkpath);
        error = pn_getsymlink(vp, &linkpath, kcred);
        if (error == 0) {
            char *ms = strstr(linkpath.pn_path, ZVOL_PSEUDO_DEV);
            if (ms != NULL) {
                ms += strlen(ZVOL_PSEUDO_DEV);
                minor = stoi(&ms);
            }
        }
        pn_free(&linkpath);
    }

    if (vp != NULL)
        VN_RELE(vp);

    /*
     * If we found a minor but it's already in use, we must pick a new one.
     */
    if (minor != 0 && ddi_get_soft_state(zvol_state, minor) != NULL)
        minor = 0;

    if (minor == 0)
        minor = zvol_minor_alloc();

    if (minor == 0) {
        dmu_objset_close(os);
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    if (ddi_soft_state_zalloc(zvol_state, minor) != DDI_SUCCESS) {
        dmu_objset_close(os);
        mutex_exit(&zvol_state_lock);
        return (EAGAIN);
    }

    (void) ddi_prop_update_string(minor, zfs_dip, ZVOL_PROP_NAME,
        (char *)name);

    (void) sprintf(chrbuf, "%uc,raw", minor);

    if (ddi_create_minor_node(zfs_dip, chrbuf, S_IFCHR,
        minor, DDI_PSEUDO, 0) == DDI_FAILURE) {
        ddi_soft_state_free(zvol_state, minor);
        dmu_objset_close(os);
        mutex_exit(&zvol_state_lock);
        return (EAGAIN);
    }

    (void) sprintf(blkbuf, "%uc", minor);

    if (ddi_create_minor_node(zfs_dip, blkbuf, S_IFBLK,
        minor, DDI_PSEUDO, 0) == DDI_FAILURE) {
        ddi_remove_minor_node(zfs_dip, chrbuf);
        ddi_soft_state_free(zvol_state, minor);
        dmu_objset_close(os);
        mutex_exit(&zvol_state_lock);
        return (EAGAIN);
    }

    zv = ddi_get_soft_state(zvol_state, minor);

    (void) strcpy(zv->zv_name, name);
    zv->zv_min_bs = DEV_BSHIFT;
    zv->zv_minor = minor;
    zv->zv_volsize = volsize;
    zv->zv_objset = os;
    zv->zv_mode = ds_mode;
    zv->zv_zilog = zil_open(os, zvol_get_data);
    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));
    list_create(&zv->zv_extents, sizeof (zvol_extent_t),
        offsetof(zvol_extent_t, ze_node));
    /* get and cache the blocksize */
    error = dmu_object_info(os, ZVOL_OBJ, &doi);
    ASSERT(error == 0);
    zv->zv_volblocksize = doi.doi_data_block_size;

    zil_replay(os, zv, zvol_replay_vector);
    zvol_size_changed(zv, maj);

    /* XXX this should handle the possible i/o error */
    VERIFY(dsl_prop_register(dmu_objset_ds(zv->zv_objset),
        "readonly", zvol_readonly_changed_cb, zv) == 0);

    zvol_minors++;

    mutex_exit(&zvol_state_lock);

    return (0);
}

/*
 * Remove minor node for the specified volume.
 */
int
zvol_remove_minor(const char *name)
{
    zvol_state_t *zv;
    char namebuf[30];

    mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(name)) == NULL) {
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    if (zv->zv_total_opens != 0) {
        mutex_exit(&zvol_state_lock);
        return (EBUSY);
    }

    (void) sprintf(namebuf, "%uc,raw", zv->zv_minor);
    ddi_remove_minor_node(zfs_dip, namebuf);

    (void) sprintf(namebuf, "%uc", zv->zv_minor);
    ddi_remove_minor_node(zfs_dip, namebuf);

    VERIFY(dsl_prop_unregister(dmu_objset_ds(zv->zv_objset),
        "readonly", zvol_readonly_changed_cb, zv) == 0);

    zil_close(zv->zv_zilog);
    zv->zv_zilog = NULL;
    dmu_objset_close(zv->zv_objset);
    zv->zv_objset = NULL;
    avl_destroy(&zv->zv_znode.z_range_avl);
    mutex_destroy(&zv->zv_znode.z_range_lock);

    ddi_soft_state_free(zvol_state, zv->zv_minor);

    zvol_minors--;

    mutex_exit(&zvol_state_lock);

    return (0);
}

int
zvol_prealloc(zvol_state_t *zv)
{
    objset_t *os = zv->zv_objset;
    dmu_tx_t *tx;
    uint64_t refd, avail, usedobjs, availobjs;
    uint64_t resid = zv->zv_volsize;
    uint64_t off = 0;

    /* Check the space usage before attempting to allocate the space */
    dmu_objset_space(os, &refd, &avail, &usedobjs, &availobjs);
    if (avail < zv->zv_volsize)
        return (ENOSPC);

    /* Free old extents if they exist */
    zvol_free_extents(zv);

    while (resid != 0) {
        int error;
        uint64_t bytes = MIN(resid, SPA_MAXBLOCKSIZE);

        tx = dmu_tx_create(os);
        dmu_tx_hold_write(tx, ZVOL_OBJ, off, bytes);
        error = dmu_tx_assign(tx, TXG_WAIT);
        if (error) {
            dmu_tx_abort(tx);
            (void) dmu_free_long_range(os, ZVOL_OBJ, 0, off);
            return (error);
        }
        dmu_prealloc(os, ZVOL_OBJ, off, bytes, tx);
        dmu_tx_commit(tx);
        off += bytes;
        resid -= bytes;
    }
    txg_wait_synced(dmu_objset_pool(os), 0);

    return (0);
}

int
zvol_update_volsize(zvol_state_t *zv, major_t maj, uint64_t volsize)
{
    dmu_tx_t *tx;
    int error;

    ASSERT(MUTEX_HELD(&zvol_state_lock));

    tx = dmu_tx_create(zv->zv_objset);
    dmu_tx_hold_zap(tx, ZVOL_ZAP_OBJ, TRUE, NULL);
    error = dmu_tx_assign(tx, TXG_WAIT);
    if (error) {
        dmu_tx_abort(tx);
        return (error);
    }

    error = zap_update(zv->zv_objset, ZVOL_ZAP_OBJ, "size", 8, 1,
        &volsize, tx);
    dmu_tx_commit(tx);

    if (error == 0)
        error = dmu_free_long_range(zv->zv_objset,
            ZVOL_OBJ, volsize, DMU_OBJECT_END);

    /*
     * If we are using a faked-up state (zv_minor == 0) then don't
     * try to update the in-core zvol state.
     */
    if (error == 0 && zv->zv_minor) {
        zv->zv_volsize = volsize;
        zvol_size_changed(zv, maj);
    }
    return (error);
}

int
zvol_set_volsize(const char *name, major_t maj, uint64_t volsize)
{
    zvol_state_t *zv;
    int error;
    dmu_object_info_t doi;
    uint64_t old_volsize = 0ULL;
    zvol_state_t state = { 0 };

    mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(name)) == NULL) {
        /*
         * If we are doing a "zfs clone -o volsize=", then the
         * minor node won't exist yet.
         */
        error = dmu_objset_open(name, DMU_OST_ZVOL, DS_MODE_OWNER,
            &state.zv_objset);
        if (error != 0)
            goto out;
        zv = &state;
    }
    old_volsize = zv->zv_volsize;

    if ((error = dmu_object_info(zv->zv_objset, ZVOL_OBJ, &doi)) != 0 ||
        (error = zvol_check_volsize(volsize,
        doi.doi_data_block_size)) != 0)
        goto out;

    if (zv->zv_flags & ZVOL_RDONLY || (zv->zv_mode & DS_MODE_READONLY)) {
        error = EROFS;
        goto out;
    }

    error = zvol_update_volsize(zv, maj, volsize);

    /*
     * Reinitialize the dump area to the new size. If we
     * failed to resize the dump area then restore the it back to
     * it's original size.
     */
    if (error == 0 && zv->zv_flags & ZVOL_DUMPIFIED) {
        if ((error = zvol_dumpify(zv)) != 0 ||
            (error = dumpvp_resize()) != 0) {
            (void) zvol_update_volsize(zv, maj, old_volsize);
            error = zvol_dumpify(zv);
        }
    }

out:
    if (state.zv_objset)
        dmu_objset_close(state.zv_objset);

    mutex_exit(&zvol_state_lock);

    return (error);
}

int
zvol_set_volblocksize(const char *name, uint64_t volblocksize)
{
    zvol_state_t *zv;
    dmu_tx_t *tx;
    int error;
    boolean_t needlock;

    /*
     * The lock may already be held if we are being called from
     * zvol_dump_init().
     */
    needlock = !MUTEX_HELD(&zvol_state_lock);
    if (needlock)
        mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(name)) == NULL) {
        if (needlock)
            mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }
    if (zv->zv_flags & ZVOL_RDONLY || (zv->zv_mode & DS_MODE_READONLY)) {
        if (needlock)
            mutex_exit(&zvol_state_lock);
        return (EROFS);
    }

    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;
    }

    if (needlock)
        mutex_exit(&zvol_state_lock);

    return (error);
}

/*ARGSUSED*/
int
zvol_open(dev_t *devp, int flag, int otyp, cred_t *cr)
{
    minor_t minor = getminor(*devp);
    zvol_state_t *zv;

    if (minor == 0)         /* This is the control device */
        return (0);

    mutex_enter(&zvol_state_lock);

    zv = ddi_get_soft_state(zvol_state, minor);
    if (zv == NULL) {
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    ASSERT(zv->zv_objset != NULL);

    if ((flag & FWRITE) &&
        (zv->zv_flags & ZVOL_RDONLY || (zv->zv_mode & DS_MODE_READONLY))) {
        mutex_exit(&zvol_state_lock);
        return (EROFS);
    }
    if (zv->zv_flags & ZVOL_EXCL) {
        mutex_exit(&zvol_state_lock);
        return (EBUSY);
    }
    if (flag & FEXCL) {
        if (zv->zv_total_opens != 0) {
            mutex_exit(&zvol_state_lock);
            return (EBUSY);
        }
        zv->zv_flags |= ZVOL_EXCL;
    }

    if (zv->zv_open_count[otyp] == 0 || otyp == OTYP_LYR) {
        zv->zv_open_count[otyp]++;
        zv->zv_total_opens++;
    }

    mutex_exit(&zvol_state_lock);

    return (0);
}

/*ARGSUSED*/
int
zvol_close(dev_t dev, int flag, int otyp, cred_t *cr)
{
    minor_t minor = getminor(dev);
    zvol_state_t *zv;

    if (minor == 0)     /* This is the control device */
        return (0);

    mutex_enter(&zvol_state_lock);

    zv = ddi_get_soft_state(zvol_state, minor);
    if (zv == NULL) {
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    if (zv->zv_flags & ZVOL_EXCL) {
        ASSERT(zv->zv_total_opens == 1);
        zv->zv_flags &= ~ZVOL_EXCL;
    }

    /*
     * If the open count is zero, this is a spurious close.
     * That indicates a bug in the kernel / DDI framework.
     */
    ASSERT(zv->zv_open_count[otyp] != 0);
    ASSERT(zv->zv_total_opens != 0);

    /*
     * You may get multiple opens, but only one close.
     */
    zv->zv_open_count[otyp]--;
    zv->zv_total_opens--;

    mutex_exit(&zvol_state_lock);

    return (0);
}

static void
zvol_get_done(dmu_buf_t *db, void *vzgd)
{
    zgd_t *zgd = (zgd_t *)vzgd;
    rl_t *rl = zgd->zgd_rl;

    dmu_buf_rele(db, vzgd);
    zfs_range_unlock(rl);
    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;
    dmu_buf_t *db;
    rl_t *rl;
    zgd_t *zgd;
    uint64_t boff;          /* block starting offset */
    int dlen = lr->lr_length;   /* length of user data */
    int error;

    ASSERT(zio);
    ASSERT(dlen != 0);

    /*
     * 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 */
        return (dmu_read(os, ZVOL_OBJ, lr->lr_offset, dlen, buf));

    zgd = (zgd_t *)kmem_alloc(sizeof (zgd_t), KM_SLEEP);
    zgd->zgd_zilog = zv->zv_zilog;
    zgd->zgd_bp = &lr->lr_blkptr;

    /*
     * Lock the range of the block to ensure that when the data is
     * written out and its checksum is being calculated that no other
     * thread can change the block.
     */
    boff = P2ALIGN_TYPED(lr->lr_offset, zv->zv_volblocksize, uint64_t);
    rl = zfs_range_lock(&zv->zv_znode, boff, zv->zv_volblocksize,
        RL_READER);
    zgd->zgd_rl = rl;

    VERIFY(0 == dmu_buf_hold(os, ZVOL_OBJ, lr->lr_offset, zgd, &db));
    error = dmu_sync(zio, db, &lr->lr_blkptr,
        lr->lr_common.lrc_txg, zvol_get_done, zgd);
    if (error == 0)
        zil_add_block(zv->zv_zilog, &lr->lr_blkptr);
    /*
     * If we get EINPROGRESS, then we need to wait for a
     * write IO initiated by dmu_sync() to complete before
     * we can release this dbuf.  We will finish everything
     * up in the zvol_get_done() callback.
     */
    if (error == EINPROGRESS)
        return (0);
    dmu_buf_rele(db, zgd);
    zfs_range_unlock(rl);
    kmem_free(zgd, sizeof (zgd_t));
    return (error);
}

/*
 * 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, offset_t off, ssize_t len)
{
    uint32_t blocksize = zv->zv_volblocksize;
    zilog_t *zilog = zv->zv_zilog;
    lr_write_t *lr;

    if (zilog->zl_replay) {
        dsl_dataset_dirty(dmu_objset_ds(zilog->zl_os), tx);
        zilog->zl_replayed_seq[dmu_tx_get_txg(tx) & TXG_MASK] =
            zilog->zl_replaying_seq;
        return;
    }

    while (len) {
        ssize_t nbytes = MIN(len, blocksize - P2PHASE(off, blocksize));
        itx_t *itx = zil_itx_create(TX_WRITE, sizeof (*lr));

        itx->itx_wr_state =
            len > zvol_immediate_write_sz ?  WR_INDIRECT : WR_NEED_COPY;
        itx->itx_private = zv;
        lr = (lr_write_t *)&itx->itx_lr;
        lr->lr_foid = ZVOL_OBJ;
        lr->lr_offset = off;
        lr->lr_length = nbytes;
        lr->lr_blkoff = off - P2ALIGN_TYPED(off, blocksize, uint64_t);
        BP_ZERO(&lr->lr_blkptr);

        (void) zil_itx_assign(zilog, itx, tx);
        len -= nbytes;
        off += nbytes;
    }
}

static int
zvol_dumpio_vdev(vdev_t *vd, void *addr, uint64_t offset, uint64_t size,
    boolean_t doread, boolean_t isdump)
{
    vdev_disk_t *dvd;
    int c;
    int numerrors = 0;

    for (c = 0; c < vd->vdev_children; c++) {
        ASSERT(vd->vdev_ops == &vdev_mirror_ops);
        int err = zvol_dumpio_vdev(vd->vdev_child[c],
            addr, offset, size, doread, isdump);
        if (err != 0) {
            numerrors++;
        } else if (doread) {
            break;
        }
    }

    if (!vd->vdev_ops->vdev_op_leaf)
        return (numerrors < vd->vdev_children ? 0 : EIO);

    if (doread && !vdev_readable(vd))
        return (EIO);
    else if (!doread && !vdev_writeable(vd))
        return (EIO);

    dvd = vd->vdev_tsd;
    ASSERT3P(dvd, !=, NULL);
    offset += VDEV_LABEL_START_SIZE;

    if (ddi_in_panic() || isdump) {
        ASSERT(!doread);
        if (doread)
            return (EIO);
        return (ldi_dump(dvd->vd_lh, addr, lbtodb(offset),
            lbtodb(size)));
    } else {
        return (vdev_disk_physio(dvd->vd_lh, addr, size, offset,
            doread ? B_READ : B_WRITE));
    }
}

static int
zvol_dumpio(zvol_state_t *zv, void *addr, uint64_t offset, uint64_t size,
    boolean_t doread, boolean_t isdump)
{
    vdev_t *vd;
    int error;
    zvol_extent_t *ze;
    spa_t *spa = dmu_objset_spa(zv->zv_objset);

    /* Must be sector aligned, and not stradle a block boundary. */
    if (P2PHASE(offset, DEV_BSIZE) || P2PHASE(size, DEV_BSIZE) ||
        P2BOUNDARY(offset, size, zv->zv_volblocksize)) {
        return (EINVAL);
    }
    ASSERT(size <= zv->zv_volblocksize);

    /* Locate the extent this belongs to */
    ze = list_head(&zv->zv_extents);
    while (offset >= ze->ze_nblks * zv->zv_volblocksize) {
        offset -= ze->ze_nblks * zv->zv_volblocksize;
        ze = list_next(&zv->zv_extents, ze);
    }
    spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
    vd = vdev_lookup_top(spa, DVA_GET_VDEV(&ze->ze_dva));
    offset += DVA_GET_OFFSET(&ze->ze_dva);
    error = zvol_dumpio_vdev(vd, addr, offset, size, doread, isdump);
    spa_config_exit(spa, SCL_STATE, FTAG);
    return (error);
}

int
zvol_strategy(buf_t *bp)
{
    zvol_state_t *zv = ddi_get_soft_state(zvol_state, getminor(bp->b_edev));
    uint64_t off, volsize;
    size_t resid;
    char *addr;
    objset_t *os;
    rl_t *rl;
    int error = 0;
    boolean_t doread = bp->b_flags & B_READ;
    boolean_t is_dump = zv->zv_flags & ZVOL_DUMPIFIED;

    if (zv == NULL) {
        bioerror(bp, ENXIO);
        biodone(bp);
        return (0);
    }

    if (getminor(bp->b_edev) == 0) {
        bioerror(bp, EINVAL);
        biodone(bp);
        return (0);
    }

    if (!(bp->b_flags & B_READ) &&
        (zv->zv_flags & ZVOL_RDONLY ||
        zv->zv_mode & DS_MODE_READONLY)) {
        bioerror(bp, EROFS);
        biodone(bp);
        return (0);
    }

    off = ldbtob(bp->b_blkno);
    volsize = zv->zv_volsize;

    os = zv->zv_objset;
    ASSERT(os != NULL);

    bp_mapin(bp);
    addr = bp->b_un.b_addr;
    resid = bp->b_bcount;

    if (resid > 0 && (off < 0 || off >= volsize)) {
        bioerror(bp, EIO);
        biodone(bp);
        return (0);
    }

    /*
     * There must be no buffer changes when doing a dmu_sync() because
     * we can't change the data whilst calculating the checksum.
     */
    rl = zfs_range_lock(&zv->zv_znode, off, resid,
        doread ? RL_READER : RL_WRITER);

    while (resid != 0 && off < volsize) {
        size_t size = MIN(resid, zvol_maxphys);
        if (is_dump) {
            size = MIN(size, P2END(off, zv->zv_volblocksize) - off);
            error = zvol_dumpio(zv, addr, off, size,
                doread, B_FALSE);
        } else if (doread) {
            error = dmu_read(os, ZVOL_OBJ, off, size, addr);
        } else {
            dmu_tx_t *tx = dmu_tx_create(os);
            dmu_tx_hold_write(tx, ZVOL_OBJ, off, size);
            error = dmu_tx_assign(tx, TXG_WAIT);
            if (error) {
                dmu_tx_abort(tx);
            } else {
                dmu_write(os, ZVOL_OBJ, off, size, addr, tx);
                zvol_log_write(zv, tx, off, size);
                dmu_tx_commit(tx);
            }
        }
        if (error) {
            /* convert checksum errors into IO errors */
            if (error == ECKSUM)
                error = EIO;
            break;
        }
        off += size;
        addr += size;
        resid -= size;
    }
    zfs_range_unlock(rl);

    if ((bp->b_resid = resid) == bp->b_bcount)
        bioerror(bp, off > volsize ? EINVAL : error);

    if (!(bp->b_flags & B_ASYNC) && !doread && !zil_disable && !is_dump)
        zil_commit(zv->zv_zilog, UINT64_MAX, ZVOL_OBJ);
    biodone(bp);

    return (0);
}

/*
 * Set the buffer count to the zvol maximum transfer.
 * Using our own routine instead of the default minphys()
 * means that for larger writes we write bigger buffers on X86
 * (128K instead of 56K) and flush the disk write cache less often
 * (every zvol_maxphys - currently 1MB) instead of minphys (currently
 * 56K on X86 and 128K on sparc).
 */
void
zvol_minphys(struct buf *bp)
{
    if (bp->b_bcount > zvol_maxphys)
        bp->b_bcount = zvol_maxphys;
}

int
zvol_dump(dev_t dev, caddr_t addr, daddr_t blkno, int nblocks)
{
    minor_t minor = getminor(dev);
    zvol_state_t *zv;
    int error = 0;
    uint64_t size;
    uint64_t boff;
    uint64_t resid;

    if (minor == 0)         /* This is the control device */
        return (ENXIO);

    zv = ddi_get_soft_state(zvol_state, minor);
    if (zv == NULL)
        return (ENXIO);

    boff = ldbtob(blkno);
    resid = ldbtob(nblocks);

    VERIFY3U(boff + resid, <=, zv->zv_volsize);

    while (resid) {
        size = MIN(resid, P2END(boff, zv->zv_volblocksize) - boff);
        error = zvol_dumpio(zv, addr, boff, size, B_FALSE, B_TRUE);
        if (error)
            break;
        boff += size;
        addr += size;
        resid -= size;
    }

    return (error);
}

/*ARGSUSED*/
int
zvol_read(dev_t dev, uio_t *uio, cred_t *cr)
{
    minor_t minor = getminor(dev);
    zvol_state_t *zv;
    uint64_t volsize;
    rl_t *rl;
    int error = 0;

    if (minor == 0)         /* This is the control device */
        return (ENXIO);

    zv = ddi_get_soft_state(zvol_state, minor);
    if (zv == NULL)
        return (ENXIO);

    volsize = zv->zv_volsize;
    if (uio->uio_resid > 0 &&
        (uio->uio_loffset < 0 || uio->uio_loffset >= volsize))
        return (EIO);

    if (zv->zv_flags & ZVOL_DUMPIFIED) {
        error = physio(zvol_strategy, NULL, dev, B_READ,
            zvol_minphys, uio);
        return (error);
    }

    rl = zfs_range_lock(&zv->zv_znode, uio->uio_loffset, uio->uio_resid,
        RL_READER);
    while (uio->uio_resid > 0 && uio->uio_loffset < volsize) {
        uint64_t bytes = MIN(uio->uio_resid, DMU_MAX_ACCESS >> 1);

        /* don't read past the end */
        if (bytes > volsize - uio->uio_loffset)
            bytes = volsize - uio->uio_loffset;

        error =  dmu_read_uio(zv->zv_objset, ZVOL_OBJ, uio, bytes);
        if (error) {
            /* convert checksum errors into IO errors */
            if (error == ECKSUM)
                error = EIO;
            break;
        }
    }
    zfs_range_unlock(rl);
    return (error);
}

/*ARGSUSED*/
int
zvol_write(dev_t dev, uio_t *uio, cred_t *cr)
{
    minor_t minor = getminor(dev);
    zvol_state_t *zv;
    uint64_t volsize;
    rl_t *rl;
    int error = 0;

    if (minor == 0)         /* This is the control device */
        return (ENXIO);

    zv = ddi_get_soft_state(zvol_state, minor);
    if (zv == NULL)
        return (ENXIO);

    volsize = zv->zv_volsize;
    if (uio->uio_resid > 0 &&
        (uio->uio_loffset < 0 || uio->uio_loffset >= volsize))
        return (EIO);

    if (zv->zv_flags & ZVOL_DUMPIFIED) {
        error = physio(zvol_strategy, NULL, dev, B_WRITE,
            zvol_minphys, uio);
        return (error);
    }

    rl = zfs_range_lock(&zv->zv_znode, uio->uio_loffset, uio->uio_resid,
        RL_WRITER);
    while (uio->uio_resid > 0 && uio->uio_loffset < volsize) {
        uint64_t bytes = MIN(uio->uio_resid, DMU_MAX_ACCESS >> 1);
        uint64_t off = uio->uio_loffset;
        dmu_tx_t *tx = dmu_tx_create(zv->zv_objset);

        if (bytes > volsize - off)  /* don't write past the end */
            bytes = volsize - off;

        dmu_tx_hold_write(tx, ZVOL_OBJ, off, bytes);
        error = dmu_tx_assign(tx, TXG_WAIT);
        if (error) {
            dmu_tx_abort(tx);
            break;
        }
        error = dmu_write_uio(zv->zv_objset, ZVOL_OBJ, uio, bytes, tx);
        if (error == 0)
            zvol_log_write(zv, tx, off, bytes);
        dmu_tx_commit(tx);

        if (error)
            break;
    }
    zfs_range_unlock(rl);
    return (error);
}

int
zvol_getefi(void *arg, int flag, uint64_t vs, uint8_t bs)
{
    struct uuid uuid = EFI_RESERVED;
    efi_gpe_t gpe = { 0 };
    uint32_t crc;
    dk_efi_t efi;
    int length;
    char *ptr;

    if (ddi_copyin(arg, &efi, sizeof (dk_efi_t), flag))
        return (EFAULT);
    ptr = (char *)(uintptr_t)efi.dki_data_64;
    length = efi.dki_length;
    /*
     * Some clients may attempt to request a PMBR for the
     * zvol.  Currently this interface will return EINVAL to
     * such requests.  These requests could be supported by
     * adding a check for lba == 0 and consing up an appropriate
     * PMBR.
     */
    if (efi.dki_lba < 1 || efi.dki_lba > 2 || length <= 0)
        return (EINVAL);

    gpe.efi_gpe_StartingLBA = LE_64(34ULL);
    gpe.efi_gpe_EndingLBA = LE_64((vs >> bs) - 1);
    UUID_LE_CONVERT(gpe.efi_gpe_PartitionTypeGUID, uuid);

    if (efi.dki_lba == 1) {
        efi_gpt_t gpt = { 0 };

        gpt.efi_gpt_Signature = LE_64(EFI_SIGNATURE);
        gpt.efi_gpt_Revision = LE_32(EFI_VERSION_CURRENT);
        gpt.efi_gpt_HeaderSize = LE_32(sizeof (gpt));
        gpt.efi_gpt_MyLBA = LE_64(1ULL);
        gpt.efi_gpt_FirstUsableLBA = LE_64(34ULL);
        gpt.efi_gpt_LastUsableLBA = LE_64((vs >> bs) - 1);
        gpt.efi_gpt_PartitionEntryLBA = LE_64(2ULL);
        gpt.efi_gpt_NumberOfPartitionEntries = LE_32(1);
        gpt.efi_gpt_SizeOfPartitionEntry =
            LE_32(sizeof (efi_gpe_t));
        CRC32(crc, &gpe, sizeof (gpe), -1U, crc32_table);
        gpt.efi_gpt_PartitionEntryArrayCRC32 = LE_32(~crc);
        CRC32(crc, &gpt, sizeof (gpt), -1U, crc32_table);
        gpt.efi_gpt_HeaderCRC32 = LE_32(~crc);
        if (ddi_copyout(&gpt, ptr, MIN(sizeof (gpt), length),
            flag))
            return (EFAULT);
        ptr += sizeof (gpt);
        length -= sizeof (gpt);
    }
    if (length > 0 && ddi_copyout(&gpe, ptr, MIN(sizeof (gpe),
        length), flag))
        return (EFAULT);
    return (0);
}

/*
 * Dirtbag ioctls to support mkfs(1M) for UFS filesystems.  See dkio(7I).
 */
/*ARGSUSED*/
int
zvol_ioctl(dev_t dev, int cmd, intptr_t arg, int flag, cred_t *cr, int *rvalp)
{
    zvol_state_t *zv;
    struct dk_cinfo dki;
    struct dk_minfo dkm;
    struct dk_callback *dkc;
    int error = 0;
    rl_t *rl;

    mutex_enter(&zvol_state_lock);

    zv = ddi_get_soft_state(zvol_state, getminor(dev));

    if (zv == NULL) {
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    switch (cmd) {

    case DKIOCINFO:
        bzero(&dki, sizeof (dki));
        (void) strcpy(dki.dki_cname, "zvol");
        (void) strcpy(dki.dki_dname, "zvol");
        dki.dki_ctype = DKC_UNKNOWN;
        dki.dki_maxtransfer = 1 << (SPA_MAXBLOCKSHIFT - zv->zv_min_bs);
        mutex_exit(&zvol_state_lock);
        if (ddi_copyout(&dki, (void *)arg, sizeof (dki), flag))
            error = EFAULT;
        return (error);

    case DKIOCGMEDIAINFO:
        bzero(&dkm, sizeof (dkm));
        dkm.dki_lbsize = 1U << zv->zv_min_bs;
        dkm.dki_capacity = zv->zv_volsize >> zv->zv_min_bs;
        dkm.dki_media_type = DK_UNKNOWN;
        mutex_exit(&zvol_state_lock);
        if (ddi_copyout(&dkm, (void *)arg, sizeof (dkm), flag))
            error = EFAULT;
        return (error);

    case DKIOCGETEFI:
        {
            uint64_t vs = zv->zv_volsize;
            uint8_t bs = zv->zv_min_bs;

            mutex_exit(&zvol_state_lock);
            error = zvol_getefi((void *)arg, flag, vs, bs);
            return (error);
        }

    case DKIOCFLUSHWRITECACHE:
        dkc = (struct dk_callback *)arg;
        zil_commit(zv->zv_zilog, UINT64_MAX, ZVOL_OBJ);
        if ((flag & FKIOCTL) && dkc != NULL && dkc->dkc_callback) {
            (*dkc->dkc_callback)(dkc->dkc_cookie, error);
            error = 0;
        }
        break;

    case DKIOCGGEOM:
    case DKIOCGVTOC:
        /*
         * commands using these (like prtvtoc) expect ENOTSUP
         * since we're emulating an EFI label
         */
        error = ENOTSUP;
        break;

    case DKIOCDUMPINIT:
        rl = zfs_range_lock(&zv->zv_znode, 0, zv->zv_volsize,
            RL_WRITER);
        error = zvol_dumpify(zv);
        zfs_range_unlock(rl);
        break;

    case DKIOCDUMPFINI:
        rl = zfs_range_lock(&zv->zv_znode, 0, zv->zv_volsize,
            RL_WRITER);
        error = zvol_dump_fini(zv);
        zfs_range_unlock(rl);
        break;

    default:
        error = ENOTTY;
        break;

    }
    mutex_exit(&zvol_state_lock);
    return (error);
}

int
zvol_busy(void)
{
    return (zvol_minors != 0);
}

void
zvol_init(void)
{
    VERIFY(ddi_soft_state_init(&zvol_state, sizeof (zvol_state_t), 1) == 0);
    mutex_init(&zvol_state_lock, NULL, MUTEX_DEFAULT, NULL);
}

void
zvol_fini(void)
{
    mutex_destroy(&zvol_state_lock);
    ddi_soft_state_fini(&zvol_state);
}

static boolean_t
zvol_is_swap(zvol_state_t *zv)
{
    vnode_t *vp;
    boolean_t ret = B_FALSE;
    char *devpath;
    size_t devpathlen;
    int error;

    devpathlen = strlen(ZVOL_FULL_DEV_DIR) + strlen(zv->zv_name) + 1;
    devpath = kmem_alloc(devpathlen, KM_SLEEP);
    (void) sprintf(devpath, "%s%s", ZVOL_FULL_DEV_DIR, zv->zv_name);
    error = lookupname(devpath, UIO_SYSSPACE, FOLLOW, NULLVPP, &vp);
    kmem_free(devpath, devpathlen);

    ret = !error && IS_SWAPVP(common_specvp(vp));

    if (vp != NULL)
        VN_RELE(vp);

    return (ret);
}

static int
zvol_dump_init(zvol_state_t *zv, boolean_t resize)
{
    dmu_tx_t *tx;
    int error = 0;
    objset_t *os = zv->zv_objset;
    nvlist_t *nv = NULL;

    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);
    }

    /*
     * If we are resizing the dump device then we only need to
     * update the refreservation to match the newly updated
     * zvolsize. Otherwise, we save off the original state of the
     * zvol so that we can restore them if the zvol is ever undumpified.
     */
    if (resize) {
        error = zap_update(os, ZVOL_ZAP_OBJ,
            zfs_prop_to_name(ZFS_PROP_REFRESERVATION), 8, 1,
            &zv->zv_volsize, tx);
    } else {
        uint64_t checksum, compress, refresrv, vbs;

        error = dsl_prop_get_integer(zv->zv_name,
            zfs_prop_to_name(ZFS_PROP_COMPRESSION), &compress, NULL);
        error = error ? error : dsl_prop_get_integer(zv->zv_name,
            zfs_prop_to_name(ZFS_PROP_CHECKSUM), &checksum, NULL);
        error = error ? error : dsl_prop_get_integer(zv->zv_name,
            zfs_prop_to_name(ZFS_PROP_REFRESERVATION), &refresrv, NULL);
        error = error ? error : dsl_prop_get_integer(zv->zv_name,
            zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), &vbs, NULL);

        error = error ? error : zap_update(os, ZVOL_ZAP_OBJ,
            zfs_prop_to_name(ZFS_PROP_COMPRESSION), 8, 1,
            &compress, tx);
        error = error ? error : zap_update(os, ZVOL_ZAP_OBJ,
            zfs_prop_to_name(ZFS_PROP_CHECKSUM), 8, 1, &checksum, tx);
        error = error ? error : zap_update(os, ZVOL_ZAP_OBJ,
            zfs_prop_to_name(ZFS_PROP_REFRESERVATION), 8, 1,
            &refresrv, tx);
        error = error ? error : zap_update(os, ZVOL_ZAP_OBJ,
            zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), 8, 1,
            &vbs, tx);
    }
    dmu_tx_commit(tx);

    /* Truncate the file */
    if (!error)
        error = dmu_free_long_range(zv->zv_objset,
            ZVOL_OBJ, 0, DMU_OBJECT_END);

    if (error)
        return (error);

    /*
     * We only need update the zvol's property if we are initializing
     * the dump area for the first time.
     */
    if (!resize) {
        VERIFY(nvlist_alloc(&nv, NV_UNIQUE_NAME, KM_SLEEP) == 0);
        VERIFY(nvlist_add_uint64(nv,
            zfs_prop_to_name(ZFS_PROP_REFRESERVATION), 0) == 0);
        VERIFY(nvlist_add_uint64(nv,
            zfs_prop_to_name(ZFS_PROP_COMPRESSION),
            ZIO_COMPRESS_OFF) == 0);
        VERIFY(nvlist_add_uint64(nv,
            zfs_prop_to_name(ZFS_PROP_CHECKSUM),
            ZIO_CHECKSUM_OFF) == 0);
        VERIFY(nvlist_add_uint64(nv,
            zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE),
            SPA_MAXBLOCKSIZE) == 0);

        error = zfs_set_prop_nvlist(zv->zv_name, nv);
        nvlist_free(nv);

        if (error)
            return (error);
    }

    /* Allocate the space for the dump */
    error = zvol_prealloc(zv);
    return (error);
}

static int
zvol_dumpify(zvol_state_t *zv)
{
    int error = 0;
    uint64_t dumpsize = 0;
    dmu_tx_t *tx;
    objset_t *os = zv->zv_objset;

    if (zv->zv_flags & ZVOL_RDONLY || (zv->zv_mode & DS_MODE_READONLY))
        return (EROFS);

    /*
     * We do not support swap devices acting as dump devices.
     */
    if (zvol_is_swap(zv))
        return (ENOTSUP);

    if (zap_lookup(zv->zv_objset, ZVOL_ZAP_OBJ, ZVOL_DUMPSIZE,
        8, 1, &dumpsize) != 0 || dumpsize != zv->zv_volsize) {
        boolean_t resize = (dumpsize > 0) ? B_TRUE : B_FALSE;

        if ((error = zvol_dump_init(zv, resize)) != 0) {
            (void) zvol_dump_fini(zv);
            return (error);
        }
    }

    /*
     * Build up our lba mapping.
     */
    error = zvol_get_lbas(zv);
    if (error) {
        (void) zvol_dump_fini(zv);
        return (error);
    }

    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);
        (void) zvol_dump_fini(zv);
        return (error);
    }

    zv->zv_flags |= ZVOL_DUMPIFIED;
    error = zap_update(os, ZVOL_ZAP_OBJ, ZVOL_DUMPSIZE, 8, 1,
        &zv->zv_volsize, tx);
    dmu_tx_commit(tx);

    if (error) {
        (void) zvol_dump_fini(zv);
        return (error);
    }

    txg_wait_synced(dmu_objset_pool(os), 0);
    return (0);
}

static int
zvol_dump_fini(zvol_state_t *zv)
{
    dmu_tx_t *tx;
    objset_t *os = zv->zv_objset;
    nvlist_t *nv;
    int error = 0;
    uint64_t checksum, compress, refresrv, vbs;

    /*
     * Attempt to restore the zvol back to its pre-dumpified state.
     * This is a best-effort attempt as it's possible that not all
     * of these properties were initialized during the dumpify process
     * (i.e. error during zvol_dump_init).
     */

    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);
    }
    (void) zap_remove(os, ZVOL_ZAP_OBJ, ZVOL_DUMPSIZE, tx);
    dmu_tx_commit(tx);

    (void) zap_lookup(zv->zv_objset, ZVOL_ZAP_OBJ,
        zfs_prop_to_name(ZFS_PROP_CHECKSUM), 8, 1, &checksum);
    (void) zap_lookup(zv->zv_objset, ZVOL_ZAP_OBJ,
        zfs_prop_to_name(ZFS_PROP_COMPRESSION), 8, 1, &compress);
    (void) zap_lookup(zv->zv_objset, ZVOL_ZAP_OBJ,
        zfs_prop_to_name(ZFS_PROP_REFRESERVATION), 8, 1, &refresrv);
    (void) zap_lookup(zv->zv_objset, ZVOL_ZAP_OBJ,
        zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), 8, 1, &vbs);

    VERIFY(nvlist_alloc(&nv, NV_UNIQUE_NAME, KM_SLEEP) == 0);
    (void) nvlist_add_uint64(nv,
        zfs_prop_to_name(ZFS_PROP_CHECKSUM), checksum);
    (void) nvlist_add_uint64(nv,
        zfs_prop_to_name(ZFS_PROP_COMPRESSION), compress);
    (void) nvlist_add_uint64(nv,
        zfs_prop_to_name(ZFS_PROP_REFRESERVATION), refresrv);
    (void) nvlist_add_uint64(nv,
        zfs_prop_to_name(ZFS_PROP_VOLBLOCKSIZE), vbs);
    (void) zfs_set_prop_nvlist(zv->zv_name, nv);
    nvlist_free(nv);

    zvol_free_extents(zv);
    zv->zv_flags &= ~ZVOL_DUMPIFIED;
    (void) dmu_free_long_range(os, ZVOL_OBJ, 0, DMU_OBJECT_END);

    return (0);
}