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dmu.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.
 */

#include <sys/dmu.h>
#include <sys/dmu_impl.h>
#include <sys/dmu_tx.h>
#include <sys/dbuf.h>
#include <sys/dnode.h>
#include <sys/zfs_context.h>
#include <sys/dmu_objset.h>
#include <sys/dmu_traverse.h>
#include <sys/dsl_dataset.h>
#include <sys/dsl_dir.h>
#include <sys/dsl_pool.h>
#include <sys/dsl_synctask.h>
#include <sys/dsl_prop.h>
#include <sys/dmu_zfetch.h>
#include <sys/zfs_ioctl.h>
#include <sys/zap.h>
#include <sys/zio_checksum.h>
#ifdef _KERNEL
#include <sys/vmsystm.h>
#include <sys/zfs_znode.h>
#endif

const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES] = {
      {     byteswap_uint8_array,   TRUE, "unallocated"           },
      {     zap_byteswap,           TRUE, "object directory"      },
      {     byteswap_uint64_array,  TRUE, "object array"          },
      {     byteswap_uint8_array,   TRUE, "packed nvlist"         },
      {     byteswap_uint64_array,  TRUE, "packed nvlist size"    },
      {     byteswap_uint64_array,  TRUE, "bplist"          },
      {     byteswap_uint64_array,  TRUE, "bplist header"         },
      {     byteswap_uint64_array,  TRUE, "SPA space map header"  },
      {     byteswap_uint64_array,  TRUE, "SPA space map"         },
      {     byteswap_uint64_array,  TRUE, "ZIL intent log"  },
      {     dnode_buf_byteswap,     TRUE, "DMU dnode"       },
      {     dmu_objset_byteswap,    TRUE, "DMU objset"            },
      {     byteswap_uint64_array,  TRUE, "DSL directory"         },
      {     zap_byteswap,           TRUE, "DSL directory child map"},
      {     zap_byteswap,           TRUE, "DSL dataset snap map"  },
      {     zap_byteswap,           TRUE, "DSL props"       },
      {     byteswap_uint64_array,  TRUE, "DSL dataset"           },
      {     zfs_znode_byteswap,     TRUE, "ZFS znode"       },
      {     zfs_oldacl_byteswap,    TRUE, "ZFS V0 ACL"            },
      {     byteswap_uint8_array,   FALSE,      "ZFS plain file"  },
      {     zap_byteswap,           TRUE, "ZFS directory"         },
      {     zap_byteswap,           TRUE, "ZFS master node" },
      {     zap_byteswap,           TRUE, "ZFS delete queue"      },
      {     byteswap_uint8_array,   FALSE,      "zvol object"           },
      {     zap_byteswap,           TRUE, "zvol prop"       },
      {     byteswap_uint8_array,   FALSE,      "other uint8[]"         },
      {     byteswap_uint64_array,  FALSE,      "other uint64[]"  },
      {     zap_byteswap,           TRUE, "other ZAP"       },
      {     zap_byteswap,           TRUE, "persistent error log"  },
      {     byteswap_uint8_array,   TRUE, "SPA history"           },
      {     byteswap_uint64_array,  TRUE, "SPA history offsets"   },
      {     zap_byteswap,           TRUE, "Pool properties" },
      {     zap_byteswap,           TRUE, "DSL permissions" },
      {     zfs_acl_byteswap, TRUE, "ZFS ACL"         },
      {     byteswap_uint8_array,   TRUE, "ZFS SYSACL"            },
      {     byteswap_uint8_array,   TRUE, "FUID table"            },
      {     byteswap_uint64_array,  TRUE, "FUID table size" },
      {     zap_byteswap,           TRUE, "DSL dataset next clones"},
      {     zap_byteswap,           TRUE, "scrub work queue"      },
      {     zap_byteswap,           TRUE, "ZFS user/group used"   },
      {     zap_byteswap,           TRUE, "ZFS user/group quota"  },
};

int
dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
    void *tag, dmu_buf_t **dbp)
{
      dnode_t *dn;
      uint64_t blkid;
      dmu_buf_impl_t *db;
      int err;

      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err)
            return (err);
      blkid = dbuf_whichblock(dn, offset);
      rw_enter(&dn->dn_struct_rwlock, RW_READER);
      db = dbuf_hold(dn, blkid, tag);
      rw_exit(&dn->dn_struct_rwlock);
      if (db == NULL) {
            err = EIO;
      } else {
            err = dbuf_read(db, NULL, DB_RF_CANFAIL);
            if (err) {
                  dbuf_rele(db, tag);
                  db = NULL;
            }
      }

      dnode_rele(dn, FTAG);
      *dbp = &db->db;
      return (err);
}

int
dmu_bonus_max(void)
{
      return (DN_MAX_BONUSLEN);
}

int
dmu_set_bonus(dmu_buf_t *db, int newsize, dmu_tx_t *tx)
{
      dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode;

      if (dn->dn_bonus != (dmu_buf_impl_t *)db)
            return (EINVAL);
      if (newsize < 0 || newsize > db->db_size)
            return (EINVAL);
      dnode_setbonuslen(dn, newsize, tx);
      return (0);
}

/*
 * returns ENOENT, EIO, or 0.
 */
int
dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp)
{
      dnode_t *dn;
      dmu_buf_impl_t *db;
      int error;

      error = dnode_hold(os->os, object, FTAG, &dn);
      if (error)
            return (error);

      rw_enter(&dn->dn_struct_rwlock, RW_READER);
      if (dn->dn_bonus == NULL) {
            rw_exit(&dn->dn_struct_rwlock);
            rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
            if (dn->dn_bonus == NULL)
                  dbuf_create_bonus(dn);
      }
      db = dn->dn_bonus;
      rw_exit(&dn->dn_struct_rwlock);

      /* as long as the bonus buf is held, the dnode will be held */
      if (refcount_add(&db->db_holds, tag) == 1)
            VERIFY(dnode_add_ref(dn, db));

      dnode_rele(dn, FTAG);

      VERIFY(0 == dbuf_read(db, NULL, DB_RF_MUST_SUCCEED));

      *dbp = &db->db;
      return (0);
}

/*
 * Note: longer-term, we should modify all of the dmu_buf_*() interfaces
 * to take a held dnode rather than <os, object> -- the lookup is wasteful,
 * and can induce severe lock contention when writing to several files
 * whose dnodes are in the same block.
 */
static int
dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset, uint64_t length,
    int read, const void *tag, int *numbufsp, dmu_buf_t ***dbpp, uint32_t flags)
{
      dsl_pool_t *dp = NULL;
      dmu_buf_t **dbp;
      uint64_t blkid, nblks, i;
      uint32_t dbuf_flags;
      int err;
      zio_t *zio;
      hrtime_t start;

      ASSERT(length <= DMU_MAX_ACCESS);

      dbuf_flags = DB_RF_CANFAIL | DB_RF_NEVERWAIT;
      if (flags & DMU_READ_NO_PREFETCH || length > zfetch_array_rd_sz)
            dbuf_flags |= DB_RF_NOPREFETCH;

      rw_enter(&dn->dn_struct_rwlock, RW_READER);
      if (dn->dn_datablkshift) {
            int blkshift = dn->dn_datablkshift;
            nblks = (P2ROUNDUP(offset+length, 1ULL<<blkshift) -
                P2ALIGN(offset, 1ULL<<blkshift)) >> blkshift;
      } else {
            if (offset + length > dn->dn_datablksz) {
                  zfs_panic_recover("zfs: accessing past end of object "
                      "%llx/%llx (size=%u access=%llu+%llu)",
                      (longlong_t)dn->dn_objset->
                      os_dsl_dataset->ds_object,
                      (longlong_t)dn->dn_object, dn->dn_datablksz,
                      (longlong_t)offset, (longlong_t)length);
                  return (EIO);
            }
            nblks = 1;
      }
      dbp = kmem_zalloc(sizeof (dmu_buf_t *) * nblks, KM_SLEEP);

      if (dn->dn_objset->os_dsl_dataset)
            dp = dn->dn_objset->os_dsl_dataset->ds_dir->dd_pool;
      if (dp && dsl_pool_sync_context(dp))
            start = gethrtime();
      zio = zio_root(dn->dn_objset->os_spa, NULL, NULL, ZIO_FLAG_CANFAIL);
      blkid = dbuf_whichblock(dn, offset);
      for (i = 0; i < nblks; i++) {
            dmu_buf_impl_t *db = dbuf_hold(dn, blkid+i, tag);
            if (db == NULL) {
                  rw_exit(&dn->dn_struct_rwlock);
                  dmu_buf_rele_array(dbp, nblks, tag);
                  zio_nowait(zio);
                  return (EIO);
            }
            /* initiate async i/o */
            if (read) {
                  rw_exit(&dn->dn_struct_rwlock);
                  (void) dbuf_read(db, zio, dbuf_flags);
                  rw_enter(&dn->dn_struct_rwlock, RW_READER);
            }
            dbp[i] = &db->db;
      }
      rw_exit(&dn->dn_struct_rwlock);

      /* wait for async i/o */
      err = zio_wait(zio);
      /* track read overhead when we are in sync context */
      if (dp && dsl_pool_sync_context(dp))
            dp->dp_read_overhead += gethrtime() - start;
      if (err) {
            dmu_buf_rele_array(dbp, nblks, tag);
            return (err);
      }

      /* wait for other io to complete */
      if (read) {
            for (i = 0; i < nblks; i++) {
                  dmu_buf_impl_t *db = (dmu_buf_impl_t *)dbp[i];
                  mutex_enter(&db->db_mtx);
                  while (db->db_state == DB_READ ||
                      db->db_state == DB_FILL)
                        cv_wait(&db->db_changed, &db->db_mtx);
                  if (db->db_state == DB_UNCACHED)
                        err = EIO;
                  mutex_exit(&db->db_mtx);
                  if (err) {
                        dmu_buf_rele_array(dbp, nblks, tag);
                        return (err);
                  }
            }
      }

      *numbufsp = nblks;
      *dbpp = dbp;
      return (0);
}

static int
dmu_buf_hold_array(objset_t *os, uint64_t object, uint64_t offset,
    uint64_t length, int read, const void *tag, int *numbufsp, dmu_buf_t ***dbpp)
{
      dnode_t *dn;
      int err;

      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err)
            return (err);

      err = dmu_buf_hold_array_by_dnode(dn, offset, length, read, tag,
          numbufsp, dbpp, DMU_READ_PREFETCH);

      dnode_rele(dn, FTAG);

      return (err);
}

int
dmu_buf_hold_array_by_bonus(dmu_buf_t *db, uint64_t offset,
    uint64_t length, int read, const void *tag, int *numbufsp, dmu_buf_t ***dbpp)
{
      dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode;
      int err;

      err = dmu_buf_hold_array_by_dnode(dn, offset, length, read, tag,
          numbufsp, dbpp, DMU_READ_PREFETCH);

      return (err);
}

void
dmu_buf_rele_array(dmu_buf_t **dbp_fake, int numbufs, const void *tag)
{
      int i;
      dmu_buf_impl_t **dbp = (dmu_buf_impl_t **)dbp_fake;

      if (numbufs == 0)
            return;

      for (i = 0; i < numbufs; i++) {
            if (dbp[i])
                  dbuf_rele(dbp[i], tag);
      }

      kmem_free(dbp, sizeof (dmu_buf_t *) * numbufs);
}

void
dmu_prefetch(objset_t *os, uint64_t object, uint64_t offset, uint64_t len)
{
      dnode_t *dn;
      uint64_t blkid;
      int nblks, i, err;

      if (zfs_prefetch_disable)
            return;

      if (len == 0) {  /* they're interested in the bonus buffer */
            dn = os->os->os_meta_dnode;

            if (object == 0 || object >= DN_MAX_OBJECT)
                  return;

            rw_enter(&dn->dn_struct_rwlock, RW_READER);
            blkid = dbuf_whichblock(dn, object * sizeof (dnode_phys_t));
            dbuf_prefetch(dn, blkid);
            rw_exit(&dn->dn_struct_rwlock);
            return;
      }

      /*
       * XXX - Note, if the dnode for the requested object is not
       * already cached, we will do a *synchronous* read in the
       * dnode_hold() call.  The same is true for any indirects.
       */
      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err != 0)
            return;

      rw_enter(&dn->dn_struct_rwlock, RW_READER);
      if (dn->dn_datablkshift) {
            int blkshift = dn->dn_datablkshift;
            nblks = (P2ROUNDUP(offset+len, 1<<blkshift) -
                P2ALIGN(offset, 1<<blkshift)) >> blkshift;
      } else {
            nblks = (offset < dn->dn_datablksz);
      }

      if (nblks != 0) {
            blkid = dbuf_whichblock(dn, offset);
            for (i = 0; i < nblks; i++)
                  dbuf_prefetch(dn, blkid+i);
      }

      rw_exit(&dn->dn_struct_rwlock);

      dnode_rele(dn, FTAG);
}

static int
get_next_chunk(dnode_t *dn, uint64_t *offset, uint64_t limit)
{
      uint64_t len = *offset - limit;
      uint64_t chunk_len = dn->dn_datablksz * DMU_MAX_DELETEBLKCNT;
      uint64_t subchunk =
          dn->dn_datablksz * EPB(dn->dn_indblkshift, SPA_BLKPTRSHIFT);

      ASSERT(limit <= *offset);

      if (len <= chunk_len) {
            *offset = limit;
            return (0);
      }

      ASSERT(ISP2(subchunk));

      while (*offset > limit) {
            uint64_t initial_offset = P2ROUNDUP(*offset, subchunk);
            uint64_t delta;
            int err;

            /* skip over allocated data */
            err = dnode_next_offset(dn,
                DNODE_FIND_HOLE|DNODE_FIND_BACKWARDS, offset, 1, 1, 0);
            if (err == ESRCH)
                  *offset = limit;
            else if (err)
                  return (err);

            ASSERT3U(*offset, <=, initial_offset);
            *offset = P2ALIGN(*offset, subchunk);
            delta = initial_offset - *offset;
            if (delta >= chunk_len) {
                  *offset += delta - chunk_len;
                  return (0);
            }
            chunk_len -= delta;

            /* skip over unallocated data */
            err = dnode_next_offset(dn,
                DNODE_FIND_BACKWARDS, offset, 1, 1, 0);
            if (err == ESRCH)
                  *offset = limit;
            else if (err)
                  return (err);

            if (*offset < limit)
                  *offset = limit;
            ASSERT3U(*offset, <, initial_offset);
      }
      return (0);
}

static int
dmu_free_long_range_impl(objset_t *os, dnode_t *dn, uint64_t offset,
    uint64_t length, boolean_t free_dnode)
{
      dmu_tx_t *tx;
      uint64_t object_size, start, end, len;
      boolean_t trunc = (length == DMU_OBJECT_END);
      int align, err;

      align = 1 << dn->dn_datablkshift;
      ASSERT(align > 0);
      object_size = align == 1 ? dn->dn_datablksz :
          (dn->dn_maxblkid + 1) << dn->dn_datablkshift;

      end = offset + length;
      if (trunc || end > object_size)
            end = object_size;
      if (end <= offset)
            return (0);
      length = end - offset;

      while (length) {
            start = end;
            /* assert(offset <= start) */
            err = get_next_chunk(dn, &start, offset);
            if (err)
                  return (err);
            len = trunc ? DMU_OBJECT_END : end - start;

            tx = dmu_tx_create(os);
            dmu_tx_hold_free(tx, dn->dn_object, start, len);
            err = dmu_tx_assign(tx, TXG_WAIT);
            if (err) {
                  dmu_tx_abort(tx);
                  return (err);
            }

            dnode_free_range(dn, start, trunc ? -1 : len, tx);

            if (start == 0 && free_dnode) {
                  ASSERT(trunc);
                  dnode_free(dn, tx);
            }

            length -= end - start;

            dmu_tx_commit(tx);
            end = start;
      }
      return (0);
}

int
dmu_free_long_range(objset_t *os, uint64_t object,
    uint64_t offset, uint64_t length)
{
      dnode_t *dn;
      int err;

      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err != 0)
            return (err);
      err = dmu_free_long_range_impl(os, dn, offset, length, FALSE);
      dnode_rele(dn, FTAG);
      return (err);
}

int
dmu_free_object(objset_t *os, uint64_t object)
{
      dnode_t *dn;
      dmu_tx_t *tx;
      int err;

      err = dnode_hold_impl(os->os, object, DNODE_MUST_BE_ALLOCATED,
          FTAG, &dn);
      if (err != 0)
            return (err);
      if (dn->dn_nlevels == 1) {
            tx = dmu_tx_create(os);
            dmu_tx_hold_bonus(tx, object);
            dmu_tx_hold_free(tx, dn->dn_object, 0, DMU_OBJECT_END);
            err = dmu_tx_assign(tx, TXG_WAIT);
            if (err == 0) {
                  dnode_free_range(dn, 0, DMU_OBJECT_END, tx);
                  dnode_free(dn, tx);
                  dmu_tx_commit(tx);
            } else {
                  dmu_tx_abort(tx);
            }
      } else {
            err = dmu_free_long_range_impl(os, dn, 0, DMU_OBJECT_END, TRUE);
      }
      dnode_rele(dn, FTAG);
      return (err);
}

int
dmu_free_range(objset_t *os, uint64_t object, uint64_t offset,
    uint64_t size, dmu_tx_t *tx)
{
      dnode_t *dn;
      int err = dnode_hold(os->os, object, FTAG, &dn);
      if (err)
            return (err);
      ASSERT(offset < UINT64_MAX);
      ASSERT(size == -1ULL || size <= UINT64_MAX - offset);
      dnode_free_range(dn, offset, size, tx);
      dnode_rele(dn, FTAG);
      return (0);
}

int
dmu_read(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    void *buf, uint32_t flags)
{
      dnode_t *dn;
      dmu_buf_t **dbp;
      int numbufs, i, err;

      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err)
            return (err);

      /*
       * Deal with odd block sizes, where there can't be data past the first
       * block.  If we ever do the tail block optimization, we will need to
       * handle that here as well.
       */
      if (dn->dn_datablkshift == 0) {
            int newsz = offset > dn->dn_datablksz ? 0 :
                MIN(size, dn->dn_datablksz - offset);
            bzero((char *)buf + newsz, size - newsz);
            size = newsz;
      }

      while (size > 0) {
            uint64_t mylen = MIN(size, DMU_MAX_ACCESS / 2);

            /*
             * NB: we could do this block-at-a-time, but it's nice
             * to be reading in parallel.
             */
            err = dmu_buf_hold_array_by_dnode(dn, offset, mylen,
                TRUE, FTAG, &numbufs, &dbp, flags);
            if (err)
                  break;

            for (i = 0; i < numbufs; i++) {
                  int tocpy;
                  int bufoff;
                  dmu_buf_t *db = dbp[i];

                  ASSERT(size > 0);

                  bufoff = offset - db->db_offset;
                  tocpy = (int)MIN(db->db_size - bufoff, size);

                  bcopy((char *)db->db_data + bufoff, buf, tocpy);

                  offset += tocpy;
                  size -= tocpy;
                  buf = (char *)buf + tocpy;
            }
            dmu_buf_rele_array(dbp, numbufs, FTAG);
      }
      dnode_rele(dn, FTAG);
      return (err);
}

void
dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    const void *buf, dmu_tx_t *tx)
{
      dmu_buf_t **dbp;
      int numbufs, i;

      if (size == 0)
            return;

      VERIFY(0 == dmu_buf_hold_array(os, object, offset, size,
          FALSE, FTAG, &numbufs, &dbp));

      for (i = 0; i < numbufs; i++) {
            int tocpy;
            int bufoff;
            dmu_buf_t *db = dbp[i];

            ASSERT(size > 0);

            bufoff = offset - db->db_offset;
            tocpy = (int)MIN(db->db_size - bufoff, size);

            ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);

            if (tocpy == db->db_size)
                  dmu_buf_will_fill(db, tx);
            else
                  dmu_buf_will_dirty(db, tx);

            bcopy(buf, (char *)db->db_data + bufoff, tocpy);

            if (tocpy == db->db_size)
                  dmu_buf_fill_done(db, tx);

            offset += tocpy;
            size -= tocpy;
            buf = (char *)buf + tocpy;
      }
      dmu_buf_rele_array(dbp, numbufs, FTAG);
}

void
dmu_prealloc(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    dmu_tx_t *tx)
{
      dmu_buf_t **dbp;
      int numbufs, i;

      if (size == 0)
            return;

      VERIFY(0 == dmu_buf_hold_array(os, object, offset, size,
          FALSE, FTAG, &numbufs, &dbp));

      for (i = 0; i < numbufs; i++) {
            dmu_buf_t *db = dbp[i];

            dmu_buf_will_not_fill(db, tx);
      }
      dmu_buf_rele_array(dbp, numbufs, FTAG);
}

#ifdef _KERNEL
int
dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
{
      dmu_buf_t **dbp;
      int numbufs, i, err;

      /*
       * NB: we could do this block-at-a-time, but it's nice
       * to be reading in parallel.
       */
      err = dmu_buf_hold_array(os, object, uio->uio_loffset, size, TRUE, FTAG,
          &numbufs, &dbp);
      if (err)
            return (err);

      for (i = 0; i < numbufs; i++) {
            int tocpy;
            int bufoff;
            dmu_buf_t *db = dbp[i];

            ASSERT(size > 0);

            bufoff = uio->uio_loffset - db->db_offset;
            tocpy = (int)MIN(db->db_size - bufoff, size);

            err = uiomove((char *)db->db_data + bufoff, tocpy,
                UIO_READ, uio);
            if (err)
                  break;

            size -= tocpy;
      }
      dmu_buf_rele_array(dbp, numbufs, FTAG);

      return (err);
}

int
dmu_write_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size,
    dmu_tx_t *tx)
{
      dmu_buf_t **dbp;
      int numbufs, i;
      int err = 0;

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

      err = dmu_buf_hold_array(os, object, uio->uio_loffset, size,
          FALSE, FTAG, &numbufs, &dbp);
      if (err)
            return (err);

      for (i = 0; i < numbufs; i++) {
            int tocpy;
            int bufoff;
            dmu_buf_t *db = dbp[i];

            ASSERT(size > 0);

            bufoff = uio->uio_loffset - db->db_offset;
            tocpy = (int)MIN(db->db_size - bufoff, size);

            ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);

            if (tocpy == db->db_size)
                  dmu_buf_will_fill(db, tx);
            else
                  dmu_buf_will_dirty(db, tx);

            /*
             * XXX uiomove could block forever (eg. nfs-backed
             * pages).  There needs to be a uiolockdown() function
             * to lock the pages in memory, so that uiomove won't
             * block.
             */
            err = uiomove((char *)db->db_data + bufoff, tocpy,
                UIO_WRITE, uio);

            if (tocpy == db->db_size)
                  dmu_buf_fill_done(db, tx);

            if (err)
                  break;

            size -= tocpy;
      }
      dmu_buf_rele_array(dbp, numbufs, FTAG);
      return (err);
}

#if 0
int
dmu_write_pages(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
    page_t *pp, dmu_tx_t *tx)
{
      dmu_buf_t **dbp;
      int numbufs, i;
      int err;

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

      err = dmu_buf_hold_array(os, object, offset, size,
          FALSE, FTAG, &numbufs, &dbp);
      if (err)
            return (err);

      for (i = 0; i < numbufs; i++) {
            int tocpy, copied, thiscpy;
            int bufoff;
            dmu_buf_t *db = dbp[i];
            caddr_t va;

            ASSERT(size > 0);
            ASSERT3U(db->db_size, >=, PAGESIZE);

            bufoff = offset - db->db_offset;
            tocpy = (int)MIN(db->db_size - bufoff, size);

            ASSERT(i == 0 || i == numbufs-1 || tocpy == db->db_size);

            if (tocpy == db->db_size)
                  dmu_buf_will_fill(db, tx);
            else
                  dmu_buf_will_dirty(db, tx);

            for (copied = 0; copied < tocpy; copied += PAGESIZE) {
                  ASSERT3U(pp->p_offset, ==, db->db_offset + bufoff);
                  thiscpy = MIN(PAGESIZE, tocpy - copied);
                  va = zfs_map_page(pp, S_READ);
                  bcopy(va, (char *)db->db_data + bufoff, thiscpy);
                  zfs_unmap_page(pp, va);
                  pp = pp->p_next;
                  bufoff += PAGESIZE;
            }

            if (tocpy == db->db_size)
                  dmu_buf_fill_done(db, tx);

            if (err)
                  break;

            offset += tocpy;
            size -= tocpy;
      }
      dmu_buf_rele_array(dbp, numbufs, FTAG);
      return (err);
}
#endif
#endif

/*
 * Allocate a loaned anonymous arc buffer.
 */
arc_buf_t *
dmu_request_arcbuf(dmu_buf_t *handle, int size)
{
      dnode_t *dn = ((dmu_buf_impl_t *)handle)->db_dnode;

      return (arc_loan_buf(dn->dn_objset->os_spa, size));
}

/*
 * Free a loaned arc buffer.
 */
void
dmu_return_arcbuf(arc_buf_t *buf)
{
      arc_return_buf(buf, FTAG);
      VERIFY(arc_buf_remove_ref(buf, FTAG) == 1);
}

/*
 * When possible directly assign passed loaned arc buffer to a dbuf.
 * If this is not possible copy the contents of passed arc buf via
 * dmu_write().
 */
void
dmu_assign_arcbuf(dmu_buf_t *handle, uint64_t offset, arc_buf_t *buf,
    dmu_tx_t *tx)
{
      dnode_t *dn = ((dmu_buf_impl_t *)handle)->db_dnode;
      dmu_buf_impl_t *db;
      uint32_t blksz = (uint32_t)arc_buf_size(buf);
      uint64_t blkid;

      rw_enter(&dn->dn_struct_rwlock, RW_READER);
      blkid = dbuf_whichblock(dn, offset);
      VERIFY((db = dbuf_hold(dn, blkid, FTAG)) != NULL);
      rw_exit(&dn->dn_struct_rwlock);

      if (offset == db->db.db_offset && blksz == db->db.db_size) {
            dbuf_assign_arcbuf(db, buf, tx);
            dbuf_rele(db, FTAG);
      } else {
            dbuf_rele(db, FTAG);
            ASSERT(dn->dn_objset->os.os == dn->dn_objset);
            dmu_write(&dn->dn_objset->os, dn->dn_object, offset, blksz,
                buf->b_data, tx);
            dmu_return_arcbuf(buf);
      }
}

typedef struct {
      dbuf_dirty_record_t     *dr;
      dmu_sync_cb_t           *done;
      void              *arg;
} dmu_sync_arg_t;

/* ARGSUSED */
static void
dmu_sync_ready(zio_t *zio, arc_buf_t *buf, void *varg)
{
      blkptr_t *bp = zio->io_bp;

      if (!BP_IS_HOLE(bp)) {
            dmu_sync_arg_t *in = varg;
            dbuf_dirty_record_t *dr = in->dr;
            dmu_buf_impl_t *db = dr->dr_dbuf;
            ASSERT(BP_GET_TYPE(bp) == db->db_dnode->dn_type);
            ASSERT(BP_GET_LEVEL(bp) == 0);
            bp->blk_fill = 1;
      }
}

/* ARGSUSED */
static void
dmu_sync_done(zio_t *zio, arc_buf_t *buf, void *varg)
{
      dmu_sync_arg_t *in = varg;
      dbuf_dirty_record_t *dr = in->dr;
      dmu_buf_impl_t *db = dr->dr_dbuf;
      dmu_sync_cb_t *done = in->done;

      mutex_enter(&db->db_mtx);
      ASSERT(dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC);
      dr->dt.dl.dr_overridden_by = *zio->io_bp; /* structure assignment */
      dr->dt.dl.dr_override_state = DR_OVERRIDDEN;
      cv_broadcast(&db->db_changed);
      mutex_exit(&db->db_mtx);

      if (done)
            done(&(db->db), in->arg);

      kmem_free(in, sizeof (dmu_sync_arg_t));
}

/*
 * Intent log support: sync the block associated with db to disk.
 * N.B. and XXX: the caller is responsible for making sure that the
 * data isn't changing while dmu_sync() is writing it.
 *
 * Return values:
 *
 *    EEXIST: this txg has already been synced, so there's nothing to to.
 *          The caller should not log the write.
 *
 *    ENOENT: the block was dbuf_free_range()'d, so there's nothing to do.
 *          The caller should not log the write.
 *
 *    EALREADY: this block is already in the process of being synced.
 *          The caller should track its progress (somehow).
 *
 *    EINPROGRESS: the IO has been initiated.
 *          The caller should log this blkptr in the callback.
 *
 *    0: completed.  Sets *bp to the blkptr just written.
 *          The caller should log this blkptr immediately.
 */
int
dmu_sync(zio_t *pio, dmu_buf_t *db_fake,
    blkptr_t *bp, uint64_t txg, dmu_sync_cb_t *done, void *arg)
{
      dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
      objset_impl_t *os = db->db_objset;
      dsl_pool_t *dp = os->os_dsl_dataset->ds_dir->dd_pool;
      tx_state_t *tx = &dp->dp_tx;
      dbuf_dirty_record_t *dr;
      dmu_sync_arg_t *in;
      zbookmark_t zb;
      writeprops_t wp = { 0 };
      zio_t *zio;
      int err;

      ASSERT(BP_IS_HOLE(bp));
      ASSERT(txg != 0);

      dprintf("dmu_sync txg=%llu, s,o,q %llu %llu %llu\n",
          txg, tx->tx_synced_txg, tx->tx_open_txg, tx->tx_quiesced_txg);

      /*
       * XXX - would be nice if we could do this without suspending...
       */
      txg_suspend(dp);

      /*
       * If this txg already synced, there's nothing to do.
       */
      if (txg <= tx->tx_synced_txg) {
            txg_resume(dp);
            /*
             * If we're running ziltest, we need the blkptr regardless.
             */
            if (txg > spa_freeze_txg(dp->dp_spa)) {
                  /* if db_blkptr == NULL, this was an empty write */
                  if (db->db_blkptr)
                        *bp = *db->db_blkptr; /* structure assignment */
                  return (0);
            }
            return (EEXIST);
      }

      mutex_enter(&db->db_mtx);

      if (txg == tx->tx_syncing_txg) {
            while (db->db_data_pending) {
                  /*
                   * IO is in-progress.  Wait for it to finish.
                   * XXX - would be nice to be able to somehow "attach"
                   * this zio to the parent zio passed in.
                   */
                  cv_wait(&db->db_changed, &db->db_mtx);
                  if (!db->db_data_pending &&
                      db->db_blkptr && BP_IS_HOLE(db->db_blkptr)) {
                        /*
                         * IO was compressed away
                         */
                        *bp = *db->db_blkptr; /* structure assignment */
                        mutex_exit(&db->db_mtx);
                        txg_resume(dp);
                        return (0);
                  }
                  ASSERT(db->db_data_pending ||
                      (db->db_blkptr && db->db_blkptr->blk_birth == txg));
            }

            if (db->db_blkptr && db->db_blkptr->blk_birth == txg) {
                  /*
                   * IO is already completed.
                   */
                  *bp = *db->db_blkptr; /* structure assignment */
                  mutex_exit(&db->db_mtx);
                  txg_resume(dp);
                  return (0);
            }
      }

      dr = db->db_last_dirty;
      while (dr && dr->dr_txg > txg)
            dr = dr->dr_next;
      if (dr == NULL || dr->dr_txg < txg) {
            /*
             * This dbuf isn't dirty, must have been free_range'd.
             * There's no need to log writes to freed blocks, so we're done.
             */
            mutex_exit(&db->db_mtx);
            txg_resume(dp);
            return (ENOENT);
      }

      ASSERT(dr->dr_txg == txg);
      if (dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC) {
            /*
             * We have already issued a sync write for this buffer.
             */
            mutex_exit(&db->db_mtx);
            txg_resume(dp);
            return (EALREADY);
      } else if (dr->dt.dl.dr_override_state == DR_OVERRIDDEN) {
            /*
             * This buffer has already been synced.  It could not
             * have been dirtied since, or we would have cleared the state.
             */
            *bp = dr->dt.dl.dr_overridden_by; /* structure assignment */
            mutex_exit(&db->db_mtx);
            txg_resume(dp);
            return (0);
      }

      dr->dt.dl.dr_override_state = DR_IN_DMU_SYNC;
      in = kmem_alloc(sizeof (dmu_sync_arg_t), KM_SLEEP);
      in->dr = dr;
      in->done = done;
      in->arg = arg;
      mutex_exit(&db->db_mtx);
      txg_resume(dp);

      zb.zb_objset = os->os_dsl_dataset->ds_object;
      zb.zb_object = db->db.db_object;
      zb.zb_level = db->db_level;
      zb.zb_blkid = db->db_blkid;

      wp.wp_type = db->db_dnode->dn_type;
      wp.wp_level = db->db_level;
      wp.wp_copies = os->os_copies;
      wp.wp_dnchecksum = db->db_dnode->dn_checksum;
      wp.wp_oschecksum = os->os_checksum;
      wp.wp_dncompress = db->db_dnode->dn_compress;
      wp.wp_oscompress = os->os_compress;

      ASSERT(BP_IS_HOLE(bp));

      zio = arc_write(pio, os->os_spa, &wp, DBUF_IS_L2CACHEABLE(db),
          txg, bp, dr->dt.dl.dr_data, dmu_sync_ready, dmu_sync_done, in,
          ZIO_PRIORITY_SYNC_WRITE, ZIO_FLAG_MUSTSUCCEED, &zb);
      if (pio) {
            zio_nowait(zio);
            err = EINPROGRESS;
      } else {
            err = zio_wait(zio);
            ASSERT(err == 0);
      }
      return (err);
}

int
dmu_object_set_blocksize(objset_t *os, uint64_t object, uint64_t size, int ibs,
      dmu_tx_t *tx)
{
      dnode_t *dn;
      int err;

      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err)
            return (err);
      err = dnode_set_blksz(dn, size, ibs, tx);
      dnode_rele(dn, FTAG);
      return (err);
}

void
dmu_object_set_checksum(objset_t *os, uint64_t object, uint8_t checksum,
      dmu_tx_t *tx)
{
      dnode_t *dn;

      /* XXX assumes dnode_hold will not get an i/o error */
      (void) dnode_hold(os->os, object, FTAG, &dn);
      ASSERT(checksum < ZIO_CHECKSUM_FUNCTIONS);
      dn->dn_checksum = checksum;
      dnode_setdirty(dn, tx);
      dnode_rele(dn, FTAG);
}

void
dmu_object_set_compress(objset_t *os, uint64_t object, uint8_t compress,
      dmu_tx_t *tx)
{
      dnode_t *dn;

      /* XXX assumes dnode_hold will not get an i/o error */
      (void) dnode_hold(os->os, object, FTAG, &dn);
      ASSERT(compress < ZIO_COMPRESS_FUNCTIONS);
      dn->dn_compress = compress;
      dnode_setdirty(dn, tx);
      dnode_rele(dn, FTAG);
}

int
dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
{
      dnode_t *dn;
      int i, err;

      err = dnode_hold(os->os, object, FTAG, &dn);
      if (err)
            return (err);
      /*
       * Sync any current changes before
       * we go trundling through the block pointers.
       */
      for (i = 0; i < TXG_SIZE; i++) {
            if (list_link_active(&dn->dn_dirty_link[i]))
                  break;
      }
      if (i != TXG_SIZE) {
            dnode_rele(dn, FTAG);
            txg_wait_synced(dmu_objset_pool(os), 0);
            err = dnode_hold(os->os, object, FTAG, &dn);
            if (err)
                  return (err);
      }

      err = dnode_next_offset(dn, (hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
      dnode_rele(dn, FTAG);

      return (err);
}

void
dmu_object_info_from_dnode(dnode_t *dn, dmu_object_info_t *doi)
{
      rw_enter(&dn->dn_struct_rwlock, RW_READER);
      mutex_enter(&dn->dn_mtx);

      doi->doi_data_block_size = dn->dn_datablksz;
      doi->doi_metadata_block_size = dn->dn_indblkshift ?
          1ULL << dn->dn_indblkshift : 0;
      doi->doi_indirection = dn->dn_nlevels;
      doi->doi_checksum = dn->dn_checksum;
      doi->doi_compress = dn->dn_compress;
      doi->doi_physical_blks = (DN_USED_BYTES(dn->dn_phys) +
          SPA_MINBLOCKSIZE/2) >> SPA_MINBLOCKSHIFT;
      doi->doi_max_block_offset = dn->dn_phys->dn_maxblkid;
      doi->doi_type = dn->dn_type;
      doi->doi_bonus_size = dn->dn_bonuslen;
      doi->doi_bonus_type = dn->dn_bonustype;

      mutex_exit(&dn->dn_mtx);
      rw_exit(&dn->dn_struct_rwlock);
}

/*
 * Get information on a DMU object.
 * If doi is NULL, just indicates whether the object exists.
 */
int
dmu_object_info(objset_t *os, uint64_t object, dmu_object_info_t *doi)
{
      dnode_t *dn;
      int err = dnode_hold(os->os, object, FTAG, &dn);

      if (err)
            return (err);

      if (doi != NULL)
            dmu_object_info_from_dnode(dn, doi);

      dnode_rele(dn, FTAG);
      return (0);
}

/*
 * As above, but faster; can be used when you have a held dbuf in hand.
 */
void
dmu_object_info_from_db(dmu_buf_t *db, dmu_object_info_t *doi)
{
      dmu_object_info_from_dnode(((dmu_buf_impl_t *)db)->db_dnode, doi);
}

/*
 * Faster still when you only care about the size.
 * This is specifically optimized for zfs_getattr().
 */
void
dmu_object_size_from_db(dmu_buf_t *db, uint32_t *blksize, u_longlong_t *nblk512)
{
      dnode_t *dn = ((dmu_buf_impl_t *)db)->db_dnode;

      *blksize = dn->dn_datablksz;
      /* add 1 for dnode space */
      *nblk512 = ((DN_USED_BYTES(dn->dn_phys) + SPA_MINBLOCKSIZE/2) >>
          SPA_MINBLOCKSHIFT) + 1;
}

void
byteswap_uint64_array(void *vbuf, size_t size)
{
      uint64_t *buf = vbuf;
      size_t count = size >> 3;
      int i;

      ASSERT((size & 7) == 0);

      for (i = 0; i < count; i++)
            buf[i] = BSWAP_64(buf[i]);
}

void
byteswap_uint32_array(void *vbuf, size_t size)
{
      uint32_t *buf = vbuf;
      size_t count = size >> 2;
      int i;

      ASSERT((size & 3) == 0);

      for (i = 0; i < count; i++)
            buf[i] = BSWAP_32(buf[i]);
}

void
byteswap_uint16_array(void *vbuf, size_t size)
{
      uint16_t *buf = vbuf;
      size_t count = size >> 1;
      int i;

      ASSERT((size & 1) == 0);

      for (i = 0; i < count; i++)
            buf[i] = BSWAP_16(buf[i]);
}

/* ARGSUSED */
void
byteswap_uint8_array(void *vbuf, size_t size)
{
}

void
dmu_init(void)
{
      dbuf_init();
      dnode_init();
      arc_init();
      l2arc_init();
}

void
dmu_fini(void)
{
      arc_fini();
      dnode_fini();
      dbuf_fini();
      l2arc_fini();
}

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