Move the world out of /zfs/ and seperate out module build tree

[mirror_zfs-debian.git] / module / zfs / zvol.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 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 "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 */
        uint64_t        zv_txg_assign;  /* txg to assign during ZIL replay */
        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, zv->zv_txg_assign);
        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, &zv->zv_txg_assign, zvol_replay_vector, NULL);
        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;
        lr_write_t *lr;

        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(zv->zv_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);
}