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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 2009 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"

#if 0
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, etc. */
      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
#define     ZVOL_WCE    0x8

/*
 * 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;
}
#endif

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);
}

#if 0
/*
 * 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,
                DMU_READ_NO_PREFETCH));

      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 resid,
    boolean_t sync)
{
      uint32_t blocksize = zv->zv_volblocksize;
      zilog_t *zilog = zv->zv_zilog;
      boolean_t slogging;

      if (zil_disable)
            return;

      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;
      }

      slogging = spa_has_slogs(zilog->zl_spa);

      while (resid) {
            itx_t *itx;
            lr_write_t *lr;
            ssize_t len;
            itx_wr_state_t write_state;

            /*
             * Unlike zfs_log_write() we can be called with
             * upto DMU_MAX_ACCESS/2 (5MB) writes.
             */
            if (blocksize > zvol_immediate_write_sz && !slogging &&
                resid >= blocksize && off % blocksize == 0) {
                  write_state = WR_INDIRECT; /* uses dmu_sync */
                  len = blocksize;
            } else if (sync) {
                  write_state = WR_COPIED;
                  len = MIN(ZIL_MAX_LOG_DATA, resid);
            } else {
                  write_state = WR_NEED_COPY;
                  len = MIN(ZIL_MAX_LOG_DATA, resid);
            }

            itx = zil_itx_create(TX_WRITE, sizeof (*lr) +
                (write_state == WR_COPIED ? len : 0));
            lr = (lr_write_t *)&itx->itx_lr;
            if (write_state == WR_COPIED && dmu_read(zv->zv_objset,
                ZVOL_OBJ, off, len, lr + 1, DMU_READ_NO_PREFETCH) != 0) {
                  kmem_free(itx, offsetof(itx_t, itx_lr) +
                      itx->itx_lr.lrc_reclen);
                  itx = zil_itx_create(TX_WRITE, sizeof (*lr));
                  lr = (lr_write_t *)&itx->itx_lr;
                  write_state = WR_NEED_COPY;
            }

            itx->itx_wr_state = write_state;
            if (write_state == WR_NEED_COPY)
                  itx->itx_sod += len;
            lr->lr_foid = ZVOL_OBJ;
            lr->lr_offset = off;
            lr->lr_length = len;
            lr->lr_blkoff = off - P2ALIGN_TYPED(off, blocksize, uint64_t);
            BP_ZERO(&lr->lr_blkptr);

            itx->itx_private = zv;
            itx->itx_sync = sync;

            (void) zil_itx_assign(zilog, itx, tx);

            off += len;
            resid -= len;
      }
}

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;
      boolean_t sync;

      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);
      }

      sync = !(bp->b_flags & B_ASYNC) && !doread && !is_dump &&
          !(zv->zv_flags & ZVOL_WCE) && !zil_disable;

      /*
       * 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,
                      DMU_READ_PREFETCH);
            } 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, sync);
                        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 (sync)
            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;
      boolean_t sync;

      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);
      }

      sync = !(zv->zv_flags & ZVOL_WCE) && !zil_disable;

      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, sync);
            dmu_tx_commit(tx);

            if (error)
                  break;
      }
      zfs_range_unlock(rl);
      if (sync)
            zil_commit(zv->zv_zilog, UINT64_MAX, ZVOL_OBJ);
      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);
      }
      ASSERT(zv->zv_total_opens > 0);

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

      case DKIOCGETWCE:
            {
                  int wce = (zv->zv_flags & ZVOL_WCE) ? 1 : 0;
                  if (ddi_copyout(&wce, (void *)arg, sizeof (int),
                      flag))
                        error = EFAULT;
                  break;
            }
      case DKIOCSETWCE:
            {
                  int wce;
                  if (ddi_copyin((void *)arg, &wce, sizeof (int),
                      flag)) {
                        error = EFAULT;
                        break;
                  }
                  if (wce) {
                        zv->zv_flags |= ZVOL_WCE;
                        mutex_exit(&zvol_state_lock);
                  } else {
                        zv->zv_flags &= ~ZVOL_WCE;
                        mutex_exit(&zvol_state_lock);
                        zil_commit(zv->zv_zilog, UINT64_MAX, ZVOL_OBJ);
                  }
                  return (0);
            }

      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:
            if (!(zv->zv_flags & ZVOL_DUMPIFIED))
                  break;
            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);
}
#endif

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