fs/zfs/dmu.c

	dmu.c revision 1934e92fc930c49429ad71a8ca97340f33227e78
/*
 * 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 2007 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

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

#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>
#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_acl_byteswap,   TRUE,   "ZFS 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"   }
};

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, void *tag, int *numbufsp, dmu_buf_t ***dbpp)
{
    dmu_buf_t **dbp;
    uint64_t blkid, nblks, i;
    uint32_t flags;
    int err;
    zio_t *zio;

    ASSERT(length <= DMU_MAX_ACCESS);

    flags = DB_RF_CANFAIL | DB_RF_NEVERWAIT;
    if (length > zfetch_array_rd_sz)
        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);

    zio = zio_root(dn->dn_objset->os_spa, NULL, NULL, TRUE);
    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, 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);
    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, 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);

    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, 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);

    return (err);
}

void
dmu_buf_rele_array(dmu_buf_t **dbp_fake, int numbufs, 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);
}

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)
{
    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);
        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);
}

#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);
}

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 = ppmapin(pp, PROT_READ, (caddr_t)-1);
            bcopy(va, (char *)db->db_data + bufoff, thiscpy);
            ppmapout(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

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

/* 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;

    if (!BP_IS_HOLE(zio->io_bp)) {
        zio->io_bp->blk_fill = 1;
        BP_SET_TYPE(zio->io_bp, db->db_dnode->dn_type);
        BP_SET_LEVEL(zio->io_bp, 0);
    }

    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;
    zio_t *zio;
    int zio_flags;
    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;
    zio_flags = ZIO_FLAG_MUSTSUCCEED;
    if (dmu_ot[db->db_dnode->dn_type].ot_metadata || zb.zb_level != 0)
        zio_flags |= ZIO_FLAG_METADATA;
    zio = arc_write(pio, os->os_spa,
        zio_checksum_select(db->db_dnode->dn_checksum, os->os_checksum),
        zio_compress_select(db->db_dnode->dn_compress, os->os_compress),
        dmu_get_replication_level(os, &zb, db->db_dnode->dn_type),
        txg, bp, dr->dt.dl.dr_data, NULL, dmu_sync_done, in,
        ZIO_PRIORITY_SYNC_WRITE, zio_flags, &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_get_replication_level(objset_impl_t *os,
    zbookmark_t *zb, dmu_object_type_t ot)
{
    int ncopies = os->os_copies;

    /* If it's the mos, it should have max copies set. */
    ASSERT(zb->zb_objset != 0 ||
        ncopies == spa_max_replication(os->os_spa));

    if (dmu_ot[ot].ot_metadata || zb->zb_level != 0)
        ncopies++;
    return (MIN(ncopies, spa_max_replication(os->os_spa)));
}

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, 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();
}

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