fs/zfs/zvol.c

	zvol.c revision 8a2f1b9190d1dc288470a1fd2776d79ce82cb129
/*
 * 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 2006 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#pragma ident   "%Z%%M% %I% %E% SMI"

/*
 * 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/aio_req.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/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 "zfs_namecheck.h"

#define ZVOL_OBJ        1ULL
#define ZVOL_ZAP_OBJ        2ULL

static void *zvol_state;

/*
 * 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;

/*
 * 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 */
    minor_t     zv_minor;   /* minor number */
    uint8_t     zv_min_bs;  /* minimum addressable block shift */
    uint8_t     zv_readonly;    /* hard readonly; like write-protect */
    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 */
    uint64_t    zv_txg_assign;  /* txg to assign during ZIL replay */
    krwlock_t   zv_dslock;  /* dmu_sync() rwlock */
} zvol_state_t;

static void
zvol_size_changed(zvol_state_t *zv, dev_t dev)
{
    dev = makedevice(getmajor(dev), 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);
}

int
zvol_check_volsize(zfs_cmd_t *zc, uint64_t blocksize)
{
    if (zc->zc_volsize == 0)
        return (EINVAL);

    if (zc->zc_volsize % blocksize != 0)
        return (EINVAL);

#ifdef _ILP32
    if (zc->zc_volsize - 1 > SPEC_MAXOFFSET_T)
        return (EOVERFLOW);
#endif
    return (0);
}

int
zvol_check_volblocksize(zfs_cmd_t *zc)
{
    if (zc->zc_volblocksize < SPA_MINBLOCKSIZE ||
        zc->zc_volblocksize > SPA_MAXBLOCKSIZE ||
        !ISP2(zc->zc_volblocksize))
        return (EDOM);

    return (0);
}

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

    zv->zv_readonly = (uint8_t)newval;
}

int
zvol_get_stats(zfs_cmd_t *zc, objset_t *os)
{
    int error;
    dmu_object_info_t doi;

    error = zap_lookup(os, ZVOL_ZAP_OBJ, "size", 8, 1, &zc->zc_volsize);

    if (error)
        return (error);

    error = dmu_object_info(os, ZVOL_OBJ, &doi);

    if (error == 0)
        zc->zc_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(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);
}

void
zvol_create_cb(objset_t *os, void *arg, dmu_tx_t *tx)
{
    zfs_cmd_t *zc = arg;
    int error;

    error = dmu_object_claim(os, ZVOL_OBJ, DMU_OT_ZVOL, zc->zc_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, &zc->zc_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 for the specified volume.
 */
int
zvol_create_minor(zfs_cmd_t *zc)
{
    char *name = zc->zc_name;
    dev_t dev = zc->zc_dev;
    zvol_state_t *zv;
    objset_t *os;
    uint64_t volsize;
    minor_t minor = 0;
    struct pathname linkpath;
    int ds_mode = DS_MODE_PRIMARY;
    vnode_t *vp = NULL;
    char *devpath;
    size_t devpathlen = strlen(ZVOL_FULL_DEV_DIR) + 1 + 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, 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, NULL);

    rw_init(&zv->zv_dslock, NULL, RW_DEFAULT, NULL);

    zil_replay(os, zv, &zv->zv_txg_assign, zvol_replay_vector, NULL);

    zvol_size_changed(zv, dev);

    /* 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(zfs_cmd_t *zc)
{
    zvol_state_t *zv;
    char namebuf[30];

    mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(zc->zc_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;

    ddi_soft_state_free(zvol_state, zv->zv_minor);

    zvol_minors--;

    mutex_exit(&zvol_state_lock);

    return (0);
}

int
zvol_set_volsize(zfs_cmd_t *zc)
{
    zvol_state_t *zv;
    dev_t dev = zc->zc_dev;
    dmu_tx_t *tx;
    int error;
    dmu_object_info_t doi;

    mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(zc->zc_name)) == NULL) {
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    if ((error = dmu_object_info(zv->zv_objset, ZVOL_OBJ, &doi)) != 0 ||
        (error = zvol_check_volsize(zc, doi.doi_data_block_size)) != 0) {
        mutex_exit(&zvol_state_lock);
        return (error);
    }

    if (zv->zv_readonly || (zv->zv_mode & DS_MODE_READONLY)) {
        mutex_exit(&zvol_state_lock);
        return (EROFS);
    }

    tx = dmu_tx_create(zv->zv_objset);
    dmu_tx_hold_zap(tx, ZVOL_ZAP_OBJ, TRUE, NULL);
    dmu_tx_hold_free(tx, ZVOL_OBJ, zc->zc_volsize, DMU_OBJECT_END);
    error = dmu_tx_assign(tx, TXG_WAIT);
    if (error) {
        dmu_tx_abort(tx);
        mutex_exit(&zvol_state_lock);
        return (error);
    }

    error = zap_update(zv->zv_objset, ZVOL_ZAP_OBJ, "size", 8, 1,
        &zc->zc_volsize, tx);
    if (error == 0) {
        error = dmu_free_range(zv->zv_objset, ZVOL_OBJ, zc->zc_volsize,
            DMU_OBJECT_END, tx);
    }

    dmu_tx_commit(tx);

    if (error == 0) {
        zv->zv_volsize = zc->zc_volsize;
        zvol_size_changed(zv, dev);
    }

    mutex_exit(&zvol_state_lock);

    return (error);
}

int
zvol_set_volblocksize(zfs_cmd_t *zc)
{
    zvol_state_t *zv;
    dmu_tx_t *tx;
    int error;

    mutex_enter(&zvol_state_lock);

    if ((zv = zvol_minor_lookup(zc->zc_name)) == NULL) {
        mutex_exit(&zvol_state_lock);
        return (ENXIO);
    }

    if (zv->zv_readonly || (zv->zv_mode & DS_MODE_READONLY)) {
        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,
            zc->zc_volblocksize, 0, tx);
        if (error == ENOTSUP)
            error = EBUSY;
        dmu_tx_commit(tx);
    }

    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_readonly || (zv->zv_mode & DS_MODE_READONLY))) {
        mutex_exit(&zvol_state_lock);
        return (EROFS);
    }

    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);
    }

    /*
     * The next statement is a workaround for the following DDI bug:
     * 6343604 specfs race: multiple "last-close" of the same device
     */
    if (zv->zv_total_opens == 0) {
        mutex_exit(&zvol_state_lock);
        return (0);
    }

    /*
     * 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);
}

/*
 * Create and return an immediate write ZIL transaction.
 */
itx_t *
zvol_immediate_itx(offset_t off, ssize_t len, char *addr)
{
    itx_t *itx;
    lr_write_t *lr;

    itx = zil_itx_create(TX_WRITE, sizeof (*lr) + len);
    lr = (lr_write_t *)&itx->itx_lr;
    lr->lr_foid = ZVOL_OBJ;
    lr->lr_offset = off;
    lr->lr_length = len;
    lr->lr_blkoff = 0;
    BP_ZERO(&lr->lr_blkptr);
    bcopy(addr, (char *)itx + offsetof(itx_t, itx_lr) +
        sizeof (*lr), len);
    itx->itx_wr_state = WR_COPIED;
    return (itx);
}

/*
 * 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 flush the data out via dmu_sync().
 */
ssize_t zvol_immediate_write_sz = 65536;

int
zvol_log_write(zvol_state_t *zv, dmu_tx_t *tx, offset_t off, ssize_t len,
    char *addr)
{
    dmu_object_info_t doi;
    ssize_t nbytes;
    itx_t *itx;
    lr_write_t *lr;
    objset_t *os;
    uint64_t txg;
    int error;
    uint32_t blocksize;

    /* handle common case */
    if (len <= zvol_immediate_write_sz) {
        itx = zvol_immediate_itx(off, len, addr);
        (void) zil_itx_assign(zv->zv_zilog, itx, tx);
        return (0);
    }

    txg = dmu_tx_get_txg(tx);
    os = zv->zv_objset;

    /*
     * We need to dmu_sync() each block in the range.
     * For this we need the blocksize.
     */
    error = dmu_object_info(os, ZVOL_OBJ, &doi);
    if (error)
        return (error);
    blocksize = doi.doi_data_block_size;

    /*
     * We need to immediate write or dmu_sync() each block in the range.
     */
    while (len) {
        nbytes = MIN(len, blocksize - P2PHASE(off, blocksize));
        if (nbytes <= zvol_immediate_write_sz) {
            itx = zvol_immediate_itx(off, nbytes, addr);
        } else {
            itx = zil_itx_create(TX_WRITE, sizeof (*lr));
            lr = (lr_write_t *)&itx->itx_lr;
            lr->lr_foid = ZVOL_OBJ;
            lr->lr_offset = off;
            lr->lr_length = nbytes;
            lr->lr_blkoff = 0;
            BP_ZERO(&lr->lr_blkptr);

            txg_suspend(dmu_objset_pool(os));
            error = dmu_sync(os, ZVOL_OBJ, off, &lr->lr_blkoff,
                &lr->lr_blkptr, txg);
            txg_resume(dmu_objset_pool(os));
            if (error) {
                kmem_free(itx, offsetof(itx_t, itx_lr));
                return (error);
            }
            itx->itx_wr_state = WR_COPIED;
        }
        (void) zil_itx_assign(zv->zv_zilog, itx, tx);
        len -= nbytes;
        off += nbytes;
    }
    return (0);
}

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 size, resid;
    char *addr;
    objset_t *os;
    int error = 0;
    int sync;
    int reading;
    int txg_sync_needed = B_FALSE;

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

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

    if (zv->zv_readonly && !(bp->b_flags & B_READ)) {
        bioerror(bp, EROFS);
        biodone(bp);
        return (0);
    }

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

    os = zv->zv_objset;
    ASSERT(os != NULL);
    sync = !(bp->b_flags & B_ASYNC) && !(zil_disable);

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

    /*
     * There must be no buffer changes when doing a dmu_sync() because
     * we can't change the data whilst calculating the checksum.
     * A better approach than a per zvol rwlock would be to lock ranges.
     */
    reading = bp->b_flags & B_READ;
    if (reading || resid <= zvol_immediate_write_sz)
        rw_enter(&zv->zv_dslock, RW_READER);
    else
        rw_enter(&zv->zv_dslock, RW_WRITER);

    while (resid != 0 && off < volsize) {

        size = MIN(resid, 1UL << 20);   /* cap at 1MB per tx */

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

        if (reading) {
            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);
                if (sync) {
                    /* use the ZIL to commit this write */
                    if (zvol_log_write(zv, tx, off, size,
                        addr) != 0) {
                        txg_sync_needed = B_TRUE;
                    }
                }
                dmu_tx_commit(tx);
            }
        }
        if (error)
            break;
        off += size;
        addr += size;
        resid -= size;
    }
    rw_exit(&zv->zv_dslock);

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

    biodone(bp);

    if (sync) {
        if (txg_sync_needed)
            txg_wait_synced(dmu_objset_pool(os), 0);
        else
            zil_commit(zv->zv_zilog, UINT64_MAX, FDSYNC);
    }

    return (0);
}

/*ARGSUSED*/
int
zvol_read(dev_t dev, uio_t *uiop, cred_t *cr)
{
    return (physio(zvol_strategy, NULL, dev, B_READ, minphys, uiop));
}

/*ARGSUSED*/
int
zvol_write(dev_t dev, uio_t *uiop, cred_t *cr)
{
    return (physio(zvol_strategy, NULL, dev, B_WRITE, minphys, uiop));
}

/*ARGSUSED*/
int
zvol_aread(dev_t dev, struct aio_req *aio, cred_t *cr)
{
    return (aphysio(zvol_strategy, anocancel, dev, B_READ, minphys, aio));
}

/*ARGSUSED*/
int
zvol_awrite(dev_t dev, struct aio_req *aio, cred_t *cr)
{
    return (aphysio(zvol_strategy, anocancel, dev, B_WRITE, minphys, aio));
}

/*
 * 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 dkc;
    struct dk_minfo dkm;
    dk_efi_t efi;
    efi_gpt_t gpt;
    efi_gpe_t gpe;
    struct uuid uuid = EFI_RESERVED;
    uint32_t crc;
    int error = 0;

    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(&dkc, sizeof (dkc));
        (void) strcpy(dkc.dki_cname, "zvol");
        (void) strcpy(dkc.dki_dname, "zvol");
        dkc.dki_ctype = DKC_UNKNOWN;
        dkc.dki_maxtransfer = 1 << (SPA_MAXBLOCKSHIFT - zv->zv_min_bs);
        mutex_exit(&zvol_state_lock);
        if (ddi_copyout(&dkc, (void *)arg, sizeof (dkc), 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:
        if (ddi_copyin((void *)arg, &efi, sizeof (dk_efi_t), flag)) {
            mutex_exit(&zvol_state_lock);
            return (EFAULT);
        }

        bzero(&gpt, sizeof (gpt));
        bzero(&gpe, sizeof (gpe));

        efi.dki_data = (void *)(uintptr_t)efi.dki_data_64;

        if (efi.dki_length < sizeof (gpt) + sizeof (gpe)) {
            mutex_exit(&zvol_state_lock);
            return (EINVAL);
        }

        efi.dki_length = sizeof (gpt) + sizeof (gpe);

        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_FirstUsableLBA = LE_64(0ULL);
        gpt.efi_gpt_LastUsableLBA =
            LE_64((zv->zv_volsize >> zv->zv_min_bs) - 1);
        gpt.efi_gpt_NumberOfPartitionEntries = LE_32(1);
        gpt.efi_gpt_SizeOfPartitionEntry = LE_32(sizeof (gpe));

        UUID_LE_CONVERT(gpe.efi_gpe_PartitionTypeGUID, uuid);
        gpe.efi_gpe_StartingLBA = gpt.efi_gpt_FirstUsableLBA;
        gpe.efi_gpe_EndingLBA = gpt.efi_gpt_LastUsableLBA;

        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);

        mutex_exit(&zvol_state_lock);
        if (ddi_copyout(&gpt, efi.dki_data, sizeof (gpt), flag) ||
            ddi_copyout(&gpe, efi.dki_data + 1, sizeof (gpe), flag))
            error = EFAULT;
        return (error);

    default:
        error = ENOTSUP;
        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);
}