Fix dnode_hold_impl() soft lockup

[mirror_zfs.git] / module / zfs / 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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
 * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
 * Copyright (c) 2013, Joyent, Inc. All rights reserved.
 * Copyright (c) 2016, Nexenta Systems, Inc. All rights reserved.
 * Copyright (c) 2015 by Chunwei Chen. All rights reserved.
 * Copyright (c) 2019 Datto Inc.
 */

#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>
#include <sys/zio_compress.h>
#include <sys/sa.h>
#include <sys/zfeature.h>
#include <sys/abd.h>
#include <sys/trace_dmu.h>
#include <sys/zfs_rlock.h>
#ifdef _KERNEL
#include <sys/vmsystm.h>
#include <sys/zfs_znode.h>
#endif

/*
 * Enable/disable nopwrite feature.
 */
int zfs_nopwrite_enabled = 1;

/*
 * Tunable to control percentage of dirtied L1 blocks from frees allowed into
 * one TXG. After this threshold is crossed, additional dirty blocks from frees
 * will wait until the next TXG.
 * A value of zero will disable this throttle.
 */
unsigned long zfs_per_txg_dirty_frees_percent = 5;

/*
 * Enable/disable forcing txg sync when dirty in dmu_offset_next.
 */
int zfs_dmu_offset_next_sync = 0;

/*
 * This can be used for testing, to ensure that certain actions happen
 * while in the middle of a remap (which might otherwise complete too
 * quickly).  Used by ztest(8).
 */
int zfs_object_remap_one_indirect_delay_ms = 0;

const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES] = {
        {DMU_BSWAP_UINT8,  TRUE,  FALSE, FALSE, "unallocated"           },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "object directory"      },
        {DMU_BSWAP_UINT64, TRUE,  TRUE,  FALSE, "object array"          },
        {DMU_BSWAP_UINT8,  TRUE,  FALSE, FALSE, "packed nvlist"         },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "packed nvlist size"    },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "bpobj"                 },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "bpobj header"          },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "SPA space map header"  },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "SPA space map"         },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, TRUE,  "ZIL intent log"        },
        {DMU_BSWAP_DNODE,  TRUE,  FALSE, TRUE,  "DMU dnode"             },
        {DMU_BSWAP_OBJSET, TRUE,  TRUE,  FALSE, "DMU objset"            },
        {DMU_BSWAP_UINT64, TRUE,  TRUE,  FALSE, "DSL directory"         },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL directory child map"},
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL dataset snap map"  },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL props"             },
        {DMU_BSWAP_UINT64, TRUE,  TRUE,  FALSE, "DSL dataset"           },
        {DMU_BSWAP_ZNODE,  TRUE,  FALSE, FALSE, "ZFS znode"             },
        {DMU_BSWAP_OLDACL, TRUE,  FALSE, TRUE,  "ZFS V0 ACL"            },
        {DMU_BSWAP_UINT8,  FALSE, FALSE, TRUE,  "ZFS plain file"        },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "ZFS directory"         },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "ZFS master node"       },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "ZFS delete queue"      },
        {DMU_BSWAP_UINT8,  FALSE, FALSE, TRUE,  "zvol object"           },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "zvol prop"             },
        {DMU_BSWAP_UINT8,  FALSE, FALSE, TRUE,  "other uint8[]"         },
        {DMU_BSWAP_UINT64, FALSE, FALSE, TRUE,  "other uint64[]"        },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "other ZAP"             },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "persistent error log"  },
        {DMU_BSWAP_UINT8,  TRUE,  FALSE, FALSE, "SPA history"           },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "SPA history offsets"   },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "Pool properties"       },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL permissions"       },
        {DMU_BSWAP_ACL,    TRUE,  FALSE, TRUE,  "ZFS ACL"               },
        {DMU_BSWAP_UINT8,  TRUE,  FALSE, TRUE,  "ZFS SYSACL"            },
        {DMU_BSWAP_UINT8,  TRUE,  FALSE, TRUE,  "FUID table"            },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "FUID table size"       },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL dataset next clones"},
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "scan work queue"       },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "ZFS user/group/project used" },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "ZFS user/group/project quota"},
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "snapshot refcount tags"},
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "DDT ZAP algorithm"     },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "DDT statistics"        },
        {DMU_BSWAP_UINT8,  TRUE,  FALSE, TRUE,  "System attributes"     },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "SA master node"        },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "SA attr registration"  },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, TRUE,  "SA attr layouts"       },
        {DMU_BSWAP_ZAP,    TRUE,  FALSE, FALSE, "scan translations"     },
        {DMU_BSWAP_UINT8,  FALSE, FALSE, TRUE,  "deduplicated block"    },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL deadlist map"      },
        {DMU_BSWAP_UINT64, TRUE,  TRUE,  FALSE, "DSL deadlist map hdr"  },
        {DMU_BSWAP_ZAP,    TRUE,  TRUE,  FALSE, "DSL dir clones"        },
        {DMU_BSWAP_UINT64, TRUE,  FALSE, FALSE, "bpobj subobj"          }
};

const dmu_object_byteswap_info_t dmu_ot_byteswap[DMU_BSWAP_NUMFUNCS] = {
        {       byteswap_uint8_array,   "uint8"         },
        {       byteswap_uint16_array,  "uint16"        },
        {       byteswap_uint32_array,  "uint32"        },
        {       byteswap_uint64_array,  "uint64"        },
        {       zap_byteswap,           "zap"           },
        {       dnode_buf_byteswap,     "dnode"         },
        {       dmu_objset_byteswap,    "objset"        },
        {       zfs_znode_byteswap,     "znode"         },
        {       zfs_oldacl_byteswap,    "oldacl"        },
        {       zfs_acl_byteswap,       "acl"           }
};

int
dmu_buf_hold_noread_by_dnode(dnode_t *dn, uint64_t offset,
    void *tag, dmu_buf_t **dbp)
{
        uint64_t blkid;
        dmu_buf_impl_t *db;

        blkid = dbuf_whichblock(dn, 0, offset);
        rw_enter(&dn->dn_struct_rwlock, RW_READER);
        db = dbuf_hold(dn, blkid, tag);
        rw_exit(&dn->dn_struct_rwlock);

        if (db == NULL) {
                *dbp = NULL;
                return (SET_ERROR(EIO));
        }

        *dbp = &db->db;
        return (0);
}
int
dmu_buf_hold_noread(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, object, FTAG, &dn);
        if (err)
                return (err);
        blkid = dbuf_whichblock(dn, 0, offset);
        rw_enter(&dn->dn_struct_rwlock, RW_READER);
        db = dbuf_hold(dn, blkid, tag);
        rw_exit(&dn->dn_struct_rwlock);
        dnode_rele(dn, FTAG);

        if (db == NULL) {
                *dbp = NULL;
                return (SET_ERROR(EIO));
        }

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

int
dmu_buf_hold_by_dnode(dnode_t *dn, uint64_t offset,
    void *tag, dmu_buf_t **dbp, int flags)
{
        int err;
        int db_flags = DB_RF_CANFAIL;

        if (flags & DMU_READ_NO_PREFETCH)
                db_flags |= DB_RF_NOPREFETCH;
        if (flags & DMU_READ_NO_DECRYPT)
                db_flags |= DB_RF_NO_DECRYPT;

        err = dmu_buf_hold_noread_by_dnode(dn, offset, tag, dbp);
        if (err == 0) {
                dmu_buf_impl_t *db = (dmu_buf_impl_t *)(*dbp);
                err = dbuf_read(db, NULL, db_flags);
                if (err != 0) {
                        dbuf_rele(db, tag);
                        *dbp = NULL;
                }
        }

        return (err);
}

int
dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
    void *tag, dmu_buf_t **dbp, int flags)
{
        int err;
        int db_flags = DB_RF_CANFAIL;

        if (flags & DMU_READ_NO_PREFETCH)
                db_flags |= DB_RF_NOPREFETCH;
        if (flags & DMU_READ_NO_DECRYPT)
                db_flags |= DB_RF_NO_DECRYPT;

        err = dmu_buf_hold_noread(os, object, offset, tag, dbp);
        if (err == 0) {
                dmu_buf_impl_t *db = (dmu_buf_impl_t *)(*dbp);
                err = dbuf_read(db, NULL, db_flags);
                if (err != 0) {
                        dbuf_rele(db, tag);
                        *dbp = NULL;
                }
        }

        return (err);
}

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

int
dmu_set_bonus(dmu_buf_t *db_fake, int newsize, dmu_tx_t *tx)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
        dnode_t *dn;
        int error;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);

        if (dn->dn_bonus != db) {
                error = SET_ERROR(EINVAL);
        } else if (newsize < 0 || newsize > db_fake->db_size) {
                error = SET_ERROR(EINVAL);
        } else {
                dnode_setbonuslen(dn, newsize, tx);
                error = 0;
        }

        DB_DNODE_EXIT(db);
        return (error);
}

int
dmu_set_bonustype(dmu_buf_t *db_fake, dmu_object_type_t type, dmu_tx_t *tx)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
        dnode_t *dn;
        int error;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);

        if (!DMU_OT_IS_VALID(type)) {
                error = SET_ERROR(EINVAL);
        } else if (dn->dn_bonus != db) {
                error = SET_ERROR(EINVAL);
        } else {
                dnode_setbonus_type(dn, type, tx);
                error = 0;
        }

        DB_DNODE_EXIT(db);
        return (error);
}

dmu_object_type_t
dmu_get_bonustype(dmu_buf_t *db_fake)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
        dnode_t *dn;
        dmu_object_type_t type;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        type = dn->dn_bonustype;
        DB_DNODE_EXIT(db);

        return (type);
}

int
dmu_rm_spill(objset_t *os, uint64_t object, dmu_tx_t *tx)
{
        dnode_t *dn;
        int error;

        error = dnode_hold(os, object, FTAG, &dn);
        dbuf_rm_spill(dn, tx);
        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
        dnode_rm_spill(dn, tx);
        rw_exit(&dn->dn_struct_rwlock);
        dnode_rele(dn, FTAG);
        return (error);
}

/*
 * Lookup and hold the bonus buffer for the provided dnode.  If the dnode
 * has not yet been allocated a new bonus dbuf a will be allocated.
 * Returns ENOENT, EIO, or 0.
 */
int dmu_bonus_hold_by_dnode(dnode_t *dn, void *tag, dmu_buf_t **dbp,
    uint32_t flags)
{
        dmu_buf_impl_t *db;
        int error;
        uint32_t db_flags = DB_RF_MUST_SUCCEED;

        if (flags & DMU_READ_NO_PREFETCH)
                db_flags |= DB_RF_NOPREFETCH;
        if (flags & DMU_READ_NO_DECRYPT)
                db_flags |= DB_RF_NO_DECRYPT;

        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;

        /* as long as the bonus buf is held, the dnode will be held */
        if (zfs_refcount_add(&db->db_holds, tag) == 1) {
                VERIFY(dnode_add_ref(dn, db));
                atomic_inc_32(&dn->dn_dbufs_count);
        }

        /*
         * Wait to drop dn_struct_rwlock until after adding the bonus dbuf's
         * hold and incrementing the dbuf count to ensure that dnode_move() sees
         * a dnode hold for every dbuf.
         */
        rw_exit(&dn->dn_struct_rwlock);

        error = dbuf_read(db, NULL, db_flags);
        if (error) {
                dnode_evict_bonus(dn);
                dbuf_rele(db, tag);
                *dbp = NULL;
                return (error);
        }

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

int
dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp)
{
        dnode_t *dn;
        int error;

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

        error = dmu_bonus_hold_by_dnode(dn, tag, dbp, DMU_READ_NO_PREFETCH);
        dnode_rele(dn, FTAG);

        return (error);
}

/*
 * returns ENOENT, EIO, or 0.
 *
 * This interface will allocate a blank spill dbuf when a spill blk
 * doesn't already exist on the dnode.
 *
 * if you only want to find an already existing spill db, then
 * dmu_spill_hold_existing() should be used.
 */
int
dmu_spill_hold_by_dnode(dnode_t *dn, uint32_t flags, void *tag, dmu_buf_t **dbp)
{
        dmu_buf_impl_t *db = NULL;
        int err;

        if ((flags & DB_RF_HAVESTRUCT) == 0)
                rw_enter(&dn->dn_struct_rwlock, RW_READER);

        db = dbuf_hold(dn, DMU_SPILL_BLKID, tag);

        if ((flags & DB_RF_HAVESTRUCT) == 0)
                rw_exit(&dn->dn_struct_rwlock);

        if (db == NULL) {
                *dbp = NULL;
                return (SET_ERROR(EIO));
        }
        err = dbuf_read(db, NULL, flags);
        if (err == 0)
                *dbp = &db->db;
        else {
                dbuf_rele(db, tag);
                *dbp = NULL;
        }
        return (err);
}

int
dmu_spill_hold_existing(dmu_buf_t *bonus, void *tag, dmu_buf_t **dbp)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)bonus;
        dnode_t *dn;
        int err;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);

        if (spa_version(dn->dn_objset->os_spa) < SPA_VERSION_SA) {
                err = SET_ERROR(EINVAL);
        } else {
                rw_enter(&dn->dn_struct_rwlock, RW_READER);

                if (!dn->dn_have_spill) {
                        err = SET_ERROR(ENOENT);
                } else {
                        err = dmu_spill_hold_by_dnode(dn,
                            DB_RF_HAVESTRUCT | DB_RF_CANFAIL, tag, dbp);
                }

                rw_exit(&dn->dn_struct_rwlock);
        }

        DB_DNODE_EXIT(db);
        return (err);
}

int
dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, void *tag,
    dmu_buf_t **dbp)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)bonus;
        dnode_t *dn;
        int err;
        uint32_t db_flags = DB_RF_CANFAIL;

        if (flags & DMU_READ_NO_DECRYPT)
                db_flags |= DB_RF_NO_DECRYPT;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        err = dmu_spill_hold_by_dnode(dn, db_flags, tag, dbp);
        DB_DNODE_EXIT(db);

        return (err);
}

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

        ASSERT(length <= DMU_MAX_ACCESS);

        /*
         * Note: We directly notify the prefetch code of this read, so that
         * we can tell it about the multi-block read.  dbuf_read() only knows
         * about the one block it is accessing.
         */
        dbuf_flags = DB_RF_CANFAIL | DB_RF_NEVERWAIT | DB_RF_HAVESTRUCT |
            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);
                        rw_exit(&dn->dn_struct_rwlock);
                        return (SET_ERROR(EIO));
                }
                nblks = 1;
        }
        dbp = kmem_zalloc(sizeof (dmu_buf_t *) * nblks, KM_SLEEP);

        zio = zio_root(dn->dn_objset->os_spa, NULL, NULL, ZIO_FLAG_CANFAIL);
        blkid = dbuf_whichblock(dn, 0, 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 (SET_ERROR(EIO));
                }

                /* initiate async i/o */
                if (read)
                        (void) dbuf_read(db, zio, dbuf_flags);
                dbp[i] = &db->db;
        }

        if ((flags & DMU_READ_NO_PREFETCH) == 0 &&
            DNODE_META_IS_CACHEABLE(dn) && length <= zfetch_array_rd_sz) {
                dmu_zfetch(&dn->dn_zfetch, blkid, nblks,
                    read && DNODE_IS_CACHEABLE(dn));
        }
        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 = SET_ERROR(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, 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_fake, uint64_t offset,
    uint64_t length, boolean_t read, void *tag, int *numbufsp,
    dmu_buf_t ***dbpp)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
        dnode_t *dn;
        int err;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        err = dmu_buf_hold_array_by_dnode(dn, offset, length, read, tag,
            numbufsp, dbpp, DMU_READ_PREFETCH);
        DB_DNODE_EXIT(db);

        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);
}

/*
 * Issue prefetch i/os for the given blocks.  If level is greater than 0, the
 * indirect blocks prefeteched will be those that point to the blocks containing
 * the data starting at offset, and continuing to offset + len.
 *
 * Note that if the indirect blocks above the blocks being prefetched are not
 * in cache, they will be asychronously read in.
 */
void
dmu_prefetch(objset_t *os, uint64_t object, int64_t level, uint64_t offset,
    uint64_t len, zio_priority_t pri)
{
        dnode_t *dn;
        uint64_t blkid;
        int nblks, err;

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

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

                rw_enter(&dn->dn_struct_rwlock, RW_READER);
                blkid = dbuf_whichblock(dn, level,
                    object * sizeof (dnode_phys_t));
                dbuf_prefetch(dn, level, blkid, pri, 0);
                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, object, FTAG, &dn);
        if (err != 0)
                return;

        rw_enter(&dn->dn_struct_rwlock, RW_READER);
        /*
         * offset + len - 1 is the last byte we want to prefetch for, and offset
         * is the first.  Then dbuf_whichblk(dn, level, off + len - 1) is the
         * last block we want to prefetch, and dbuf_whichblock(dn, level,
         * offset)  is the first.  Then the number we need to prefetch is the
         * last - first + 1.
         */
        if (level > 0 || dn->dn_datablkshift != 0) {
                nblks = dbuf_whichblock(dn, level, offset + len - 1) -
                    dbuf_whichblock(dn, level, offset) + 1;
        } else {
                nblks = (offset < dn->dn_datablksz);
        }

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

        rw_exit(&dn->dn_struct_rwlock);

        dnode_rele(dn, FTAG);
}

/*
 * Get the next "chunk" of file data to free.  We traverse the file from
 * the end so that the file gets shorter over time (if we crashes in the
 * middle, this will leave us in a better state).  We find allocated file
 * data by simply searching the allocated level 1 indirects.
 *
 * On input, *start should be the first offset that does not need to be
 * freed (e.g. "offset + length").  On return, *start will be the first
 * offset that should be freed and l1blks is set to the number of level 1
 * indirect blocks found within the chunk.
 */
static int
get_next_chunk(dnode_t *dn, uint64_t *start, uint64_t minimum, uint64_t *l1blks)
{
        uint64_t blks;
        uint64_t maxblks = DMU_MAX_ACCESS >> (dn->dn_indblkshift + 1);
        /* bytes of data covered by a level-1 indirect block */
        uint64_t iblkrange =
            dn->dn_datablksz * EPB(dn->dn_indblkshift, SPA_BLKPTRSHIFT);

        ASSERT3U(minimum, <=, *start);

        if (*start - minimum <= iblkrange * maxblks) {
                *start = minimum;
                /*
                 * Assume full L1 blocks and 128k recordsize to approximate the
                 * expected number of L1 blocks in this chunk
                 */
                *l1blks = minimum / (1024 * 128 * 1024);
                return (0);
        }
        ASSERT(ISP2(iblkrange));

        for (blks = 0; *start > minimum && blks < maxblks; blks++) {
                int err;

                /*
                 * dnode_next_offset(BACKWARDS) will find an allocated L1
                 * indirect block at or before the input offset.  We must
                 * decrement *start so that it is at the end of the region
                 * to search.
                 */
                (*start)--;
                err = dnode_next_offset(dn,
                    DNODE_FIND_BACKWARDS, start, 2, 1, 0);

                /* if there are no indirect blocks before start, we are done */
                if (err == ESRCH) {
                        *start = minimum;
                        break;
                } else if (err != 0) {
                        *l1blks = blks;
                        return (err);
                }

                /* set start to the beginning of this L1 indirect */
                *start = P2ALIGN(*start, iblkrange);
        }
        if (*start < minimum)
                *start = minimum;
        *l1blks = blks;
        return (0);
}

/*
 * If this objset is of type OST_ZFS return true if vfs's unmounted flag is set,
 * otherwise return false.
 * Used below in dmu_free_long_range_impl() to enable abort when unmounting
 */
/*ARGSUSED*/
static boolean_t
dmu_objset_zfs_unmounting(objset_t *os)
{
#ifdef _KERNEL
        if (dmu_objset_type(os) == DMU_OST_ZFS)
                return (zfs_get_vfs_flag_unmounted(os));
#endif
        return (B_FALSE);
}

static int
dmu_free_long_range_impl(objset_t *os, dnode_t *dn, uint64_t offset,
    uint64_t length)
{
        uint64_t object_size;
        int err;
        uint64_t dirty_frees_threshold;
        dsl_pool_t *dp = dmu_objset_pool(os);

        if (dn == NULL)
                return (SET_ERROR(EINVAL));

        object_size = (dn->dn_maxblkid + 1) * dn->dn_datablksz;
        if (offset >= object_size)
                return (0);

        if (zfs_per_txg_dirty_frees_percent <= 100)
                dirty_frees_threshold =
                    zfs_per_txg_dirty_frees_percent * zfs_dirty_data_max / 100;
        else
                dirty_frees_threshold = zfs_dirty_data_max / 20;

        if (length == DMU_OBJECT_END || offset + length > object_size)
                length = object_size - offset;

        while (length != 0) {
                uint64_t chunk_end, chunk_begin, chunk_len;
                uint64_t long_free_dirty_all_txgs = 0;
                uint64_t l1blks;
                dmu_tx_t *tx;

                if (dmu_objset_zfs_unmounting(dn->dn_objset))
                        return (SET_ERROR(EINTR));

                chunk_end = chunk_begin = offset + length;

                /* move chunk_begin backwards to the beginning of this chunk */
                err = get_next_chunk(dn, &chunk_begin, offset, &l1blks);
                if (err)
                        return (err);
                ASSERT3U(chunk_begin, >=, offset);
                ASSERT3U(chunk_begin, <=, chunk_end);

                chunk_len = chunk_end - chunk_begin;

                mutex_enter(&dp->dp_lock);
                for (int t = 0; t < TXG_SIZE; t++) {
                        long_free_dirty_all_txgs +=
                            dp->dp_long_free_dirty_pertxg[t];
                }
                mutex_exit(&dp->dp_lock);

                /*
                 * To avoid filling up a TXG with just frees wait for
                 * the next TXG to open before freeing more chunks if
                 * we have reached the threshold of frees
                 */
                if (dirty_frees_threshold != 0 &&
                    long_free_dirty_all_txgs >= dirty_frees_threshold) {
                        DMU_TX_STAT_BUMP(dmu_tx_dirty_frees_delay);
                        txg_wait_open(dp, 0);
                        continue;
                }

                tx = dmu_tx_create(os);
                dmu_tx_hold_free(tx, dn->dn_object, chunk_begin, chunk_len);

                /*
                 * Mark this transaction as typically resulting in a net
                 * reduction in space used.
                 */
                dmu_tx_mark_netfree(tx);
                err = dmu_tx_assign(tx, TXG_WAIT);
                if (err) {
                        dmu_tx_abort(tx);
                        return (err);
                }

                /*
                 * In order to prevent unnecessary write throttling, for each
                 * TXG, we track the cumulative size of L1 blocks being dirtied
                 * in dnode_free_range() below. We compare this number to a
                 * tunable threshold, past which we prevent new L1 dirty freeing
                 * blocks from being added into the open TXG. See
                 * dmu_free_long_range_impl() for details. The threshold
                 * prevents write throttle activation due to dirty freeing L1
                 * blocks taking up a large percentage of zfs_dirty_data_max.
                 */
                mutex_enter(&dp->dp_lock);
                dp->dp_long_free_dirty_pertxg[dmu_tx_get_txg(tx) & TXG_MASK] +=
                    l1blks << dn->dn_indblkshift;
                mutex_exit(&dp->dp_lock);
                DTRACE_PROBE3(free__long__range,
                    uint64_t, long_free_dirty_all_txgs, uint64_t, chunk_len,
                    uint64_t, dmu_tx_get_txg(tx));
                dnode_free_range(dn, chunk_begin, chunk_len, tx);

                dmu_tx_commit(tx);

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

        /*
         * It is important to zero out the maxblkid when freeing the entire
         * file, so that (a) subsequent calls to dmu_free_long_range_impl()
         * will take the fast path, and (b) dnode_reallocate() can verify
         * that the entire file has been freed.
         */
        if (err == 0 && offset == 0 && length == DMU_OBJECT_END)
                dn->dn_maxblkid = 0;

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

int
dmu_free_long_object(objset_t *os, uint64_t object)
{
        dmu_tx_t *tx;
        int err;

        err = dmu_free_long_range(os, object, 0, DMU_OBJECT_END);
        if (err != 0)
                return (err);

        tx = dmu_tx_create(os);
        dmu_tx_hold_bonus(tx, object);
        dmu_tx_hold_free(tx, object, 0, DMU_OBJECT_END);
        dmu_tx_mark_netfree(tx);
        err = dmu_tx_assign(tx, TXG_WAIT);
        if (err == 0) {
                if (err == 0)
                        err = dmu_object_free(os, object, tx);

                dmu_tx_commit(tx);
        } else {
                dmu_tx_abort(tx);
        }

        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, object, FTAG, &dn);
        if (err)
                return (err);
        ASSERT(offset < UINT64_MAX);
        ASSERT(size == DMU_OBJECT_END || size <= UINT64_MAX - offset);
        dnode_free_range(dn, offset, size, tx);
        dnode_rele(dn, FTAG);
        return (0);
}

static int
dmu_read_impl(dnode_t *dn, uint64_t offset, uint64_t size,
    void *buf, uint32_t flags)
{
        dmu_buf_t **dbp;
        int numbufs, err = 0;

        /*
         * 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_maxblkid == 0) {
                uint64_t 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);
                int i;

                /*
                 * 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++) {
                        uint64_t tocpy;
                        int64_t bufoff;
                        dmu_buf_t *db = dbp[i];

                        ASSERT(size > 0);

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

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

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

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

        err = dnode_hold(os, object, FTAG, &dn);
        if (err != 0)
                return (err);

        err = dmu_read_impl(dn, offset, size, buf, flags);
        dnode_rele(dn, FTAG);
        return (err);
}

int
dmu_read_by_dnode(dnode_t *dn, uint64_t offset, uint64_t size, void *buf,
    uint32_t flags)
{
        return (dmu_read_impl(dn, offset, size, buf, flags));
}

static void
dmu_write_impl(dmu_buf_t **dbp, int numbufs, uint64_t offset, uint64_t size,
    const void *buf, dmu_tx_t *tx)
{
        int i;

        for (i = 0; i < numbufs; i++) {
                uint64_t tocpy;
                int64_t bufoff;
                dmu_buf_t *db = dbp[i];

                ASSERT(size > 0);

                bufoff = offset - db->db_offset;
                tocpy = 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);

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

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

                offset += tocpy;
                size -= tocpy;
                buf = (char *)buf + tocpy;
        }
}

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;

        if (size == 0)
                return;

        VERIFY0(dmu_buf_hold_array(os, object, offset, size,
            FALSE, FTAG, &numbufs, &dbp));
        dmu_write_impl(dbp, numbufs, offset, size, buf, tx);
        dmu_buf_rele_array(dbp, numbufs, FTAG);
}

void
dmu_write_by_dnode(dnode_t *dn, uint64_t offset, uint64_t size,
    const void *buf, dmu_tx_t *tx)
{
        dmu_buf_t **dbp;
        int numbufs;

        if (size == 0)
                return;

        VERIFY0(dmu_buf_hold_array_by_dnode(dn, offset, size,
            FALSE, FTAG, &numbufs, &dbp, DMU_READ_PREFETCH));
        dmu_write_impl(dbp, numbufs, offset, size, buf, tx);
        dmu_buf_rele_array(dbp, numbufs, FTAG);
}

static int
dmu_object_remap_one_indirect(objset_t *os, dnode_t *dn,
    uint64_t last_removal_txg, uint64_t offset)
{
        uint64_t l1blkid = dbuf_whichblock(dn, 1, offset);
        dnode_t *dn_tx;
        int err = 0;

        rw_enter(&dn->dn_struct_rwlock, RW_READER);
        dmu_buf_impl_t *dbuf = dbuf_hold_level(dn, 1, l1blkid, FTAG);
        ASSERT3P(dbuf, !=, NULL);

        /*
         * If the block hasn't been written yet, this default will ensure
         * we don't try to remap it.
         */
        uint64_t birth = UINT64_MAX;
        ASSERT3U(last_removal_txg, !=, UINT64_MAX);
        if (dbuf->db_blkptr != NULL)
                birth = dbuf->db_blkptr->blk_birth;
        rw_exit(&dn->dn_struct_rwlock);

        /*
         * If this L1 was already written after the last removal, then we've
         * already tried to remap it.  An additional hold is taken after the
         * dmu_tx_assign() to handle the case where the dnode is freed while
         * waiting for the next open txg.
         */
        if (birth <= last_removal_txg &&
            dbuf_read(dbuf, NULL, DB_RF_MUST_SUCCEED) == 0 &&
            dbuf_can_remap(dbuf)) {
                dmu_tx_t *tx = dmu_tx_create(os);
                dmu_tx_hold_remap_l1indirect(tx, dn->dn_object);
                err = dmu_tx_assign(tx, TXG_WAIT);
                if (err == 0) {
                        err = dnode_hold(os, dn->dn_object, FTAG, &dn_tx);
                        if (err == 0) {
                                (void) dbuf_dirty(dbuf, tx);
                                dnode_rele(dn_tx, FTAG);
                        }
                        dmu_tx_commit(tx);
                } else {
                        dmu_tx_abort(tx);
                }
        }

        dbuf_rele(dbuf, FTAG);

        delay(MSEC_TO_TICK(zfs_object_remap_one_indirect_delay_ms));

        return (err);
}

/*
 * Remap all blockpointers in the object, if possible, so that they reference
 * only concrete vdevs.
 *
 * To do this, iterate over the L0 blockpointers and remap any that reference
 * an indirect vdev. Note that we only examine L0 blockpointers; since we
 * cannot guarantee that we can remap all blockpointer anyways (due to split
 * blocks), we do not want to make the code unnecessarily complicated to
 * catch the unlikely case that there is an L1 block on an indirect vdev that
 * contains no indirect blockpointers.
 */
int
dmu_object_remap_indirects(objset_t *os, uint64_t object,
    uint64_t last_removal_txg)
{
        uint64_t offset, l1span;
        int err;
        dnode_t *dn, *dn_tx;

        err = dnode_hold(os, object, FTAG, &dn);
        if (err != 0) {
                return (err);
        }

        if (dn->dn_nlevels <= 1) {
                if (issig(JUSTLOOKING) && issig(FORREAL)) {
                        err = SET_ERROR(EINTR);
                }

                /*
                 * If the dnode has no indirect blocks, we cannot dirty them.
                 * We still want to remap the blkptr(s) in the dnode if
                 * appropriate, so mark it as dirty.  An additional hold is
                 * taken after the dmu_tx_assign() to handle the case where
                 * the dnode is freed while waiting for the next open txg.
                 */
                if (err == 0 && dnode_needs_remap(dn)) {
                        dmu_tx_t *tx = dmu_tx_create(os);
                        dmu_tx_hold_bonus(tx, object);
                        err = dmu_tx_assign(tx, TXG_WAIT);
                        if (err == 0) {
                                err = dnode_hold(os, object, FTAG, &dn_tx);
                                if (err == 0) {
                                        dnode_setdirty(dn_tx, tx);
                                        dnode_rele(dn_tx, FTAG);
                                }
                                dmu_tx_commit(tx);
                        } else {
                                dmu_tx_abort(tx);
                        }
                }

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

        offset = 0;
        l1span = 1ULL << (dn->dn_indblkshift - SPA_BLKPTRSHIFT +
            dn->dn_datablkshift);
        /*
         * Find the next L1 indirect that is not a hole.
         */
        while (dnode_next_offset(dn, 0, &offset, 2, 1, 0) == 0) {
                if (issig(JUSTLOOKING) && issig(FORREAL)) {
                        err = SET_ERROR(EINTR);
                        break;
                }
                if ((err = dmu_object_remap_one_indirect(os, dn,
                    last_removal_txg, offset)) != 0) {
                        break;
                }
                offset += l1span;
        }

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

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);
}

void
dmu_write_embedded(objset_t *os, uint64_t object, uint64_t offset,
    void *data, uint8_t etype, uint8_t comp, int uncompressed_size,
    int compressed_size, int byteorder, dmu_tx_t *tx)
{
        dmu_buf_t *db;

        ASSERT3U(etype, <, NUM_BP_EMBEDDED_TYPES);
        ASSERT3U(comp, <, ZIO_COMPRESS_FUNCTIONS);
        VERIFY0(dmu_buf_hold_noread(os, object, offset,
            FTAG, &db));

        dmu_buf_write_embedded(db,
            data, (bp_embedded_type_t)etype, (enum zio_compress)comp,
            uncompressed_size, compressed_size, byteorder, tx);

        dmu_buf_rele(db, FTAG);
}

/*
 * DMU support for xuio
 */
kstat_t *xuio_ksp = NULL;

typedef struct xuio_stats {
        /* loaned yet not returned arc_buf */
        kstat_named_t xuiostat_onloan_rbuf;
        kstat_named_t xuiostat_onloan_wbuf;
        /* whether a copy is made when loaning out a read buffer */
        kstat_named_t xuiostat_rbuf_copied;
        kstat_named_t xuiostat_rbuf_nocopy;
        /* whether a copy is made when assigning a write buffer */
        kstat_named_t xuiostat_wbuf_copied;
        kstat_named_t xuiostat_wbuf_nocopy;
} xuio_stats_t;

static xuio_stats_t xuio_stats = {
        { "onloan_read_buf",    KSTAT_DATA_UINT64 },
        { "onloan_write_buf",   KSTAT_DATA_UINT64 },
        { "read_buf_copied",    KSTAT_DATA_UINT64 },
        { "read_buf_nocopy",    KSTAT_DATA_UINT64 },
        { "write_buf_copied",   KSTAT_DATA_UINT64 },
        { "write_buf_nocopy",   KSTAT_DATA_UINT64 }
};

#define XUIOSTAT_INCR(stat, val)        \
        atomic_add_64(&xuio_stats.stat.value.ui64, (val))
#define XUIOSTAT_BUMP(stat)     XUIOSTAT_INCR(stat, 1)

#ifdef HAVE_UIO_ZEROCOPY
int
dmu_xuio_init(xuio_t *xuio, int nblk)
{
        dmu_xuio_t *priv;
        uio_t *uio = &xuio->xu_uio;

        uio->uio_iovcnt = nblk;
        uio->uio_iov = kmem_zalloc(nblk * sizeof (iovec_t), KM_SLEEP);

        priv = kmem_zalloc(sizeof (dmu_xuio_t), KM_SLEEP);
        priv->cnt = nblk;
        priv->bufs = kmem_zalloc(nblk * sizeof (arc_buf_t *), KM_SLEEP);
        priv->iovp = (iovec_t *)uio->uio_iov;
        XUIO_XUZC_PRIV(xuio) = priv;

        if (XUIO_XUZC_RW(xuio) == UIO_READ)
                XUIOSTAT_INCR(xuiostat_onloan_rbuf, nblk);
        else
                XUIOSTAT_INCR(xuiostat_onloan_wbuf, nblk);

        return (0);
}

void
dmu_xuio_fini(xuio_t *xuio)
{
        dmu_xuio_t *priv = XUIO_XUZC_PRIV(xuio);
        int nblk = priv->cnt;

        kmem_free(priv->iovp, nblk * sizeof (iovec_t));
        kmem_free(priv->bufs, nblk * sizeof (arc_buf_t *));
        kmem_free(priv, sizeof (dmu_xuio_t));

        if (XUIO_XUZC_RW(xuio) == UIO_READ)
                XUIOSTAT_INCR(xuiostat_onloan_rbuf, -nblk);
        else
                XUIOSTAT_INCR(xuiostat_onloan_wbuf, -nblk);
}

/*
 * Initialize iov[priv->next] and priv->bufs[priv->next] with { off, n, abuf }
 * and increase priv->next by 1.
 */
int
dmu_xuio_add(xuio_t *xuio, arc_buf_t *abuf, offset_t off, size_t n)
{
        struct iovec *iov;
        uio_t *uio = &xuio->xu_uio;
        dmu_xuio_t *priv = XUIO_XUZC_PRIV(xuio);
        int i = priv->next++;

        ASSERT(i < priv->cnt);
        ASSERT(off + n <= arc_buf_lsize(abuf));
        iov = (iovec_t *)uio->uio_iov + i;
        iov->iov_base = (char *)abuf->b_data + off;
        iov->iov_len = n;
        priv->bufs[i] = abuf;
        return (0);
}

int
dmu_xuio_cnt(xuio_t *xuio)
{
        dmu_xuio_t *priv = XUIO_XUZC_PRIV(xuio);
        return (priv->cnt);
}

arc_buf_t *
dmu_xuio_arcbuf(xuio_t *xuio, int i)
{
        dmu_xuio_t *priv = XUIO_XUZC_PRIV(xuio);

        ASSERT(i < priv->cnt);
        return (priv->bufs[i]);
}

void
dmu_xuio_clear(xuio_t *xuio, int i)
{
        dmu_xuio_t *priv = XUIO_XUZC_PRIV(xuio);

        ASSERT(i < priv->cnt);
        priv->bufs[i] = NULL;
}
#endif /* HAVE_UIO_ZEROCOPY */

static void
xuio_stat_init(void)
{
        xuio_ksp = kstat_create("zfs", 0, "xuio_stats", "misc",
            KSTAT_TYPE_NAMED, sizeof (xuio_stats) / sizeof (kstat_named_t),
            KSTAT_FLAG_VIRTUAL);
        if (xuio_ksp != NULL) {
                xuio_ksp->ks_data = &xuio_stats;
                kstat_install(xuio_ksp);
        }
}

static void
xuio_stat_fini(void)
{
        if (xuio_ksp != NULL) {
                kstat_delete(xuio_ksp);
                xuio_ksp = NULL;
        }
}

void
xuio_stat_wbuf_copied(void)
{
        XUIOSTAT_BUMP(xuiostat_wbuf_copied);
}

void
xuio_stat_wbuf_nocopy(void)
{
        XUIOSTAT_BUMP(xuiostat_wbuf_nocopy);
}

#ifdef _KERNEL
int
dmu_read_uio_dnode(dnode_t *dn, uio_t *uio, uint64_t size)
{
        dmu_buf_t **dbp;
        int numbufs, i, err;
#ifdef HAVE_UIO_ZEROCOPY
        xuio_t *xuio = NULL;
#endif

        /*
         * 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, uio->uio_loffset, size,
            TRUE, FTAG, &numbufs, &dbp, 0);
        if (err)
                return (err);

        for (i = 0; i < numbufs; i++) {
                uint64_t tocpy;
                int64_t bufoff;
                dmu_buf_t *db = dbp[i];

                ASSERT(size > 0);

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

#ifdef HAVE_UIO_ZEROCOPY
                if (xuio) {
                        dmu_buf_impl_t *dbi = (dmu_buf_impl_t *)db;
                        arc_buf_t *dbuf_abuf = dbi->db_buf;
                        arc_buf_t *abuf = dbuf_loan_arcbuf(dbi);
                        err = dmu_xuio_add(xuio, abuf, bufoff, tocpy);
                        if (!err) {
                                uio->uio_resid -= tocpy;
                                uio->uio_loffset += tocpy;
                        }

                        if (abuf == dbuf_abuf)
                                XUIOSTAT_BUMP(xuiostat_rbuf_nocopy);
                        else
                                XUIOSTAT_BUMP(xuiostat_rbuf_copied);
                } else
#endif
                        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);
}

/*
 * Read 'size' bytes into the uio buffer.
 * From object zdb->db_object.
 * Starting at offset uio->uio_loffset.
 *
 * If the caller already has a dbuf in the target object
 * (e.g. its bonus buffer), this routine is faster than dmu_read_uio(),
 * because we don't have to find the dnode_t for the object.
 */
int
dmu_read_uio_dbuf(dmu_buf_t *zdb, uio_t *uio, uint64_t size)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)zdb;
        dnode_t *dn;
        int err;

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

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        err = dmu_read_uio_dnode(dn, uio, size);
        DB_DNODE_EXIT(db);

        return (err);
}

/*
 * Read 'size' bytes into the uio buffer.
 * From the specified object
 * Starting at offset uio->uio_loffset.
 */
int
dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
{
        dnode_t *dn;
        int err;

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

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

        err = dmu_read_uio_dnode(dn, uio, size);

        dnode_rele(dn, FTAG);

        return (err);
}

int
dmu_write_uio_dnode(dnode_t *dn, uio_t *uio, uint64_t size, dmu_tx_t *tx)
{
        dmu_buf_t **dbp;
        int numbufs;
        int err = 0;
        int i;

        err = dmu_buf_hold_array_by_dnode(dn, uio->uio_loffset, size,
            FALSE, FTAG, &numbufs, &dbp, DMU_READ_PREFETCH);
        if (err)
                return (err);

        for (i = 0; i < numbufs; i++) {
                uint64_t tocpy;
                int64_t bufoff;
                dmu_buf_t *db = dbp[i];

                ASSERT(size > 0);

                bufoff = uio->uio_loffset - db->db_offset;
                tocpy = 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);
}

/*
 * Write 'size' bytes from the uio buffer.
 * To object zdb->db_object.
 * Starting at offset uio->uio_loffset.
 *
 * If the caller already has a dbuf in the target object
 * (e.g. its bonus buffer), this routine is faster than dmu_write_uio(),
 * because we don't have to find the dnode_t for the object.
 */
int
dmu_write_uio_dbuf(dmu_buf_t *zdb, uio_t *uio, uint64_t size,
    dmu_tx_t *tx)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)zdb;
        dnode_t *dn;
        int err;

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

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        err = dmu_write_uio_dnode(dn, uio, size, tx);
        DB_DNODE_EXIT(db);

        return (err);
}

/*
 * Write 'size' bytes from the uio buffer.
 * To the specified object.
 * Starting at offset uio->uio_loffset.
 */
int
dmu_write_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size,
    dmu_tx_t *tx)
{
        dnode_t *dn;
        int err;

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

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

        err = dmu_write_uio_dnode(dn, uio, size, tx);

        dnode_rele(dn, FTAG);

        return (err);
}
#endif /* _KERNEL */

/*
 * Allocate a loaned anonymous arc buffer.
 */
arc_buf_t *
dmu_request_arcbuf(dmu_buf_t *handle, int size)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)handle;

        return (arc_loan_buf(db->db_objset->os_spa, B_FALSE, size));
}

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

void
dmu_copy_from_buf(objset_t *os, uint64_t object, uint64_t offset,
    dmu_buf_t *handle, dmu_tx_t *tx)
{
        dmu_buf_t *dst_handle;
        dmu_buf_impl_t *dstdb;
        dmu_buf_impl_t *srcdb = (dmu_buf_impl_t *)handle;
        dmu_object_type_t type;
        arc_buf_t *abuf;
        uint64_t datalen;
        boolean_t byteorder;
        uint8_t salt[ZIO_DATA_SALT_LEN];
        uint8_t iv[ZIO_DATA_IV_LEN];
        uint8_t mac[ZIO_DATA_MAC_LEN];

        ASSERT3P(srcdb->db_buf, !=, NULL);

        /* hold the db that we want to write to */
        VERIFY0(dmu_buf_hold(os, object, offset, FTAG, &dst_handle,
            DMU_READ_NO_DECRYPT));
        dstdb = (dmu_buf_impl_t *)dst_handle;
        datalen = arc_buf_size(srcdb->db_buf);

        DB_DNODE_ENTER(dstdb);
        type = DB_DNODE(dstdb)->dn_type;
        DB_DNODE_EXIT(dstdb);

        /* allocated an arc buffer that matches the type of srcdb->db_buf */
        if (arc_is_encrypted(srcdb->db_buf)) {
                arc_get_raw_params(srcdb->db_buf, &byteorder, salt, iv, mac);
                abuf = arc_loan_raw_buf(os->os_spa, dmu_objset_id(os),
                    byteorder, salt, iv, mac, type,
                    datalen, arc_buf_lsize(srcdb->db_buf),
                    arc_get_compression(srcdb->db_buf));
        } else {
                /* we won't get a compressed db back from dmu_buf_hold() */
                ASSERT3U(arc_get_compression(srcdb->db_buf),
                    ==, ZIO_COMPRESS_OFF);
                abuf = arc_loan_buf(os->os_spa,
                    DMU_OT_IS_METADATA(type), datalen);
        }

        ASSERT3U(datalen, ==, arc_buf_size(abuf));

        /* copy the data to the new buffer and assign it to the dstdb */
        bcopy(srcdb->db_buf->b_data, abuf->b_data, datalen);
        dbuf_assign_arcbuf(dstdb, abuf, tx);
        dmu_buf_rele(dst_handle, FTAG);
}

/*
 * 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().
 */
int
dmu_assign_arcbuf_by_dnode(dnode_t *dn, uint64_t offset, arc_buf_t *buf,
    dmu_tx_t *tx)
{
        dmu_buf_impl_t *db;
        objset_t *os = dn->dn_objset;
        uint64_t object = dn->dn_object;
        uint32_t blksz = (uint32_t)arc_buf_lsize(buf);
        uint64_t blkid;

        rw_enter(&dn->dn_struct_rwlock, RW_READER);
        blkid = dbuf_whichblock(dn, 0, offset);
        db = dbuf_hold(dn, blkid, FTAG);
        if (db == NULL)
                return (SET_ERROR(EIO));
        rw_exit(&dn->dn_struct_rwlock);

        /*
         * We can only assign if the offset is aligned, the arc buf is the
         * same size as the dbuf, and the dbuf is not metadata.
         */
        if (offset == db->db.db_offset && blksz == db->db.db_size) {
                dbuf_assign_arcbuf(db, buf, tx);
                dbuf_rele(db, FTAG);
        } else {
                /* compressed bufs must always be assignable to their dbuf */
                ASSERT3U(arc_get_compression(buf), ==, ZIO_COMPRESS_OFF);
                ASSERT(!(buf->b_flags & ARC_BUF_FLAG_COMPRESSED));

                dbuf_rele(db, FTAG);
                dmu_write(os, object, offset, blksz, buf->b_data, tx);
                dmu_return_arcbuf(buf);
                XUIOSTAT_BUMP(xuiostat_wbuf_copied);
        }

        return (0);
}

int
dmu_assign_arcbuf_by_dbuf(dmu_buf_t *handle, uint64_t offset, arc_buf_t *buf,
    dmu_tx_t *tx)
{
        int err;
        dmu_buf_impl_t *dbuf = (dmu_buf_impl_t *)handle;

        DB_DNODE_ENTER(dbuf);
        err = dmu_assign_arcbuf_by_dnode(DB_DNODE(dbuf), offset, buf, tx);
        DB_DNODE_EXIT(dbuf);

        return (err);
}

typedef struct {
        dbuf_dirty_record_t     *dsa_dr;
        dmu_sync_cb_t           *dsa_done;
        zgd_t                   *dsa_zgd;
        dmu_tx_t                *dsa_tx;
} dmu_sync_arg_t;

/* ARGSUSED */
static void
dmu_sync_ready(zio_t *zio, arc_buf_t *buf, void *varg)
{
        dmu_sync_arg_t *dsa = varg;
        dmu_buf_t *db = dsa->dsa_zgd->zgd_db;
        blkptr_t *bp = zio->io_bp;

        if (zio->io_error == 0) {
                if (BP_IS_HOLE(bp)) {
                        /*
                         * A block of zeros may compress to a hole, but the
                         * block size still needs to be known for replay.
                         */
                        BP_SET_LSIZE(bp, db->db_size);
                } else if (!BP_IS_EMBEDDED(bp)) {
                        ASSERT(BP_GET_LEVEL(bp) == 0);
                        BP_SET_FILL(bp, 1);
                }
        }
}

static void
dmu_sync_late_arrival_ready(zio_t *zio)
{
        dmu_sync_ready(zio, NULL, zio->io_private);
}

/* ARGSUSED */
static void
dmu_sync_done(zio_t *zio, arc_buf_t *buf, void *varg)
{
        dmu_sync_arg_t *dsa = varg;
        dbuf_dirty_record_t *dr = dsa->dsa_dr;
        dmu_buf_impl_t *db = dr->dr_dbuf;
        zgd_t *zgd = dsa->dsa_zgd;

        /*
         * Record the vdev(s) backing this blkptr so they can be flushed after
         * the writes for the lwb have completed.
         */
        if (zio->io_error == 0) {
                zil_lwb_add_block(zgd->zgd_lwb, zgd->zgd_bp);
        }

        mutex_enter(&db->db_mtx);
        ASSERT(dr->dt.dl.dr_override_state == DR_IN_DMU_SYNC);
        if (zio->io_error == 0) {
                dr->dt.dl.dr_nopwrite = !!(zio->io_flags & ZIO_FLAG_NOPWRITE);
                if (dr->dt.dl.dr_nopwrite) {
                        blkptr_t *bp = zio->io_bp;
                        blkptr_t *bp_orig = &zio->io_bp_orig;
                        uint8_t chksum = BP_GET_CHECKSUM(bp_orig);

                        ASSERT(BP_EQUAL(bp, bp_orig));
                        VERIFY(BP_EQUAL(bp, db->db_blkptr));
                        ASSERT(zio->io_prop.zp_compress != ZIO_COMPRESS_OFF);
                        VERIFY(zio_checksum_table[chksum].ci_flags &
                            ZCHECKSUM_FLAG_NOPWRITE);
                }
                dr->dt.dl.dr_overridden_by = *zio->io_bp;
                dr->dt.dl.dr_override_state = DR_OVERRIDDEN;
                dr->dt.dl.dr_copies = zio->io_prop.zp_copies;

                /*
                 * Old style holes are filled with all zeros, whereas
                 * new-style holes maintain their lsize, type, level,
                 * and birth time (see zio_write_compress). While we
                 * need to reset the BP_SET_LSIZE() call that happened
                 * in dmu_sync_ready for old style holes, we do *not*
                 * want to wipe out the information contained in new
                 * style holes. Thus, only zero out the block pointer if
                 * it's an old style hole.
                 */
                if (BP_IS_HOLE(&dr->dt.dl.dr_overridden_by) &&
                    dr->dt.dl.dr_overridden_by.blk_birth == 0)
                        BP_ZERO(&dr->dt.dl.dr_overridden_by);
        } else {
                dr->dt.dl.dr_override_state = DR_NOT_OVERRIDDEN;
        }
        cv_broadcast(&db->db_changed);
        mutex_exit(&db->db_mtx);

        dsa->dsa_done(dsa->dsa_zgd, zio->io_error);

        kmem_free(dsa, sizeof (*dsa));
}

static void
dmu_sync_late_arrival_done(zio_t *zio)
{
        blkptr_t *bp = zio->io_bp;
        dmu_sync_arg_t *dsa = zio->io_private;
        zgd_t *zgd = dsa->dsa_zgd;

        if (zio->io_error == 0) {
                /*
                 * Record the vdev(s) backing this blkptr so they can be
                 * flushed after the writes for the lwb have completed.
                 */
                zil_lwb_add_block(zgd->zgd_lwb, zgd->zgd_bp);

                if (!BP_IS_HOLE(bp)) {
                        ASSERTV(blkptr_t *bp_orig = &zio->io_bp_orig);
                        ASSERT(!(zio->io_flags & ZIO_FLAG_NOPWRITE));
                        ASSERT(BP_IS_HOLE(bp_orig) || !BP_EQUAL(bp, bp_orig));
                        ASSERT(zio->io_bp->blk_birth == zio->io_txg);
                        ASSERT(zio->io_txg > spa_syncing_txg(zio->io_spa));
                        zio_free(zio->io_spa, zio->io_txg, zio->io_bp);
                }
        }

        dmu_tx_commit(dsa->dsa_tx);

        dsa->dsa_done(dsa->dsa_zgd, zio->io_error);

        abd_put(zio->io_abd);
        kmem_free(dsa, sizeof (*dsa));
}

static int
dmu_sync_late_arrival(zio_t *pio, objset_t *os, dmu_sync_cb_t *done, zgd_t *zgd,
    zio_prop_t *zp, zbookmark_phys_t *zb)
{
        dmu_sync_arg_t *dsa;
        dmu_tx_t *tx;

        tx = dmu_tx_create(os);
        dmu_tx_hold_space(tx, zgd->zgd_db->db_size);
        if (dmu_tx_assign(tx, TXG_WAIT) != 0) {
                dmu_tx_abort(tx);
                /* Make zl_get_data do txg_waited_synced() */
                return (SET_ERROR(EIO));
        }

        /*
         * In order to prevent the zgd's lwb from being free'd prior to
         * dmu_sync_late_arrival_done() being called, we have to ensure
         * the lwb's "max txg" takes this tx's txg into account.
         */
        zil_lwb_add_txg(zgd->zgd_lwb, dmu_tx_get_txg(tx));

        dsa = kmem_alloc(sizeof (dmu_sync_arg_t), KM_SLEEP);
        dsa->dsa_dr = NULL;
        dsa->dsa_done = done;
        dsa->dsa_zgd = zgd;
        dsa->dsa_tx = tx;

        /*
         * Since we are currently syncing this txg, it's nontrivial to
         * determine what BP to nopwrite against, so we disable nopwrite.
         *
         * When syncing, the db_blkptr is initially the BP of the previous
         * txg.  We can not nopwrite against it because it will be changed
         * (this is similar to the non-late-arrival case where the dbuf is
         * dirty in a future txg).
         *
         * Then dbuf_write_ready() sets bp_blkptr to the location we will write.
         * We can not nopwrite against it because although the BP will not
         * (typically) be changed, the data has not yet been persisted to this
         * location.
         *
         * Finally, when dbuf_write_done() is called, it is theoretically
         * possible to always nopwrite, because the data that was written in
         * this txg is the same data that we are trying to write.  However we
         * would need to check that this dbuf is not dirty in any future
         * txg's (as we do in the normal dmu_sync() path). For simplicity, we
         * don't nopwrite in this case.
         */
        zp->zp_nopwrite = B_FALSE;

        zio_nowait(zio_write(pio, os->os_spa, dmu_tx_get_txg(tx), zgd->zgd_bp,
            abd_get_from_buf(zgd->zgd_db->db_data, zgd->zgd_db->db_size),
            zgd->zgd_db->db_size, zgd->zgd_db->db_size, zp,
            dmu_sync_late_arrival_ready, NULL, NULL, dmu_sync_late_arrival_done,
            dsa, ZIO_PRIORITY_SYNC_WRITE, ZIO_FLAG_CANFAIL, zb));

        return (0);
}

/*
 * 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 do.
 *              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).
 *
 *      EIO: could not do the I/O.
 *              The caller should do a txg_wait_synced().
 *
 *      0: the I/O has been initiated.
 *              The caller should log this blkptr in the done callback.
 *              It is possible that the I/O will fail, in which case
 *              the error will be reported to the done callback and
 *              propagated to pio from zio_done().
 */
int
dmu_sync(zio_t *pio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)zgd->zgd_db;
        objset_t *os = db->db_objset;
        dsl_dataset_t *ds = os->os_dsl_dataset;
        dbuf_dirty_record_t *dr;
        dmu_sync_arg_t *dsa;
        zbookmark_phys_t zb;
        zio_prop_t zp;
        dnode_t *dn;

        ASSERT(pio != NULL);
        ASSERT(txg != 0);

        SET_BOOKMARK(&zb, ds->ds_object,
            db->db.db_object, db->db_level, db->db_blkid);

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        dmu_write_policy(os, dn, db->db_level, WP_DMU_SYNC, &zp);
        DB_DNODE_EXIT(db);

        /*
         * If we're frozen (running ziltest), we always need to generate a bp.
         */
        if (txg > spa_freeze_txg(os->os_spa))
                return (dmu_sync_late_arrival(pio, os, done, zgd, &zp, &zb));

        /*
         * Grabbing db_mtx now provides a barrier between dbuf_sync_leaf()
         * and us.  If we determine that this txg is not yet syncing,
         * but it begins to sync a moment later, that's OK because the
         * sync thread will block in dbuf_sync_leaf() until we drop db_mtx.
         */
        mutex_enter(&db->db_mtx);

        if (txg <= spa_last_synced_txg(os->os_spa)) {
                /*
                 * This txg has already synced.  There's nothing to do.
                 */
                mutex_exit(&db->db_mtx);
                return (SET_ERROR(EEXIST));
        }

        if (txg <= spa_syncing_txg(os->os_spa)) {
                /*
                 * This txg is currently syncing, so we can't mess with
                 * the dirty record anymore; just write a new log block.
                 */
                mutex_exit(&db->db_mtx);
                return (dmu_sync_late_arrival(pio, os, done, zgd, &zp, &zb));
        }

        dr = db->db_last_dirty;
        while (dr && dr->dr_txg != txg)
                dr = dr->dr_next;

        if (dr == NULL) {
                /*
                 * There's no dr for this dbuf, so it must have been freed.
                 * There's no need to log writes to freed blocks, so we're done.
                 */
                mutex_exit(&db->db_mtx);
                return (SET_ERROR(ENOENT));
        }

        ASSERT(dr->dr_next == NULL || dr->dr_next->dr_txg < txg);

        if (db->db_blkptr != NULL) {
                /*
                 * We need to fill in zgd_bp with the current blkptr so that
                 * the nopwrite code can check if we're writing the same
                 * data that's already on disk.  We can only nopwrite if we
                 * are sure that after making the copy, db_blkptr will not
                 * change until our i/o completes.  We ensure this by
                 * holding the db_mtx, and only allowing nopwrite if the
                 * block is not already dirty (see below).  This is verified
                 * by dmu_sync_done(), which VERIFYs that the db_blkptr has
                 * not changed.
                 */
                *zgd->zgd_bp = *db->db_blkptr;
        }

        /*
         * Assume the on-disk data is X, the current syncing data (in
         * txg - 1) is Y, and the current in-memory data is Z (currently
         * in dmu_sync).
         *
         * We usually want to perform a nopwrite if X and Z are the
         * same.  However, if Y is different (i.e. the BP is going to
         * change before this write takes effect), then a nopwrite will
         * be incorrect - we would override with X, which could have
         * been freed when Y was written.
         *
         * (Note that this is not a concern when we are nop-writing from
         * syncing context, because X and Y must be identical, because
         * all previous txgs have been synced.)
         *
         * Therefore, we disable nopwrite if the current BP could change
         * before this TXG.  There are two ways it could change: by
         * being dirty (dr_next is non-NULL), or by being freed
         * (dnode_block_freed()).  This behavior is verified by
         * zio_done(), which VERIFYs that the override BP is identical
         * to the on-disk BP.
         */
        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        if (dr->dr_next != NULL || dnode_block_freed(dn, db->db_blkid))
                zp.zp_nopwrite = B_FALSE;
        DB_DNODE_EXIT(db);

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

        ASSERT(dr->dt.dl.dr_override_state == DR_NOT_OVERRIDDEN);
        dr->dt.dl.dr_override_state = DR_IN_DMU_SYNC;
        mutex_exit(&db->db_mtx);

        dsa = kmem_alloc(sizeof (dmu_sync_arg_t), KM_SLEEP);
        dsa->dsa_dr = dr;
        dsa->dsa_done = done;
        dsa->dsa_zgd = zgd;
        dsa->dsa_tx = NULL;

        zio_nowait(arc_write(pio, os->os_spa, txg,
            zgd->zgd_bp, dr->dt.dl.dr_data, DBUF_IS_L2CACHEABLE(db),
            &zp, dmu_sync_ready, NULL, NULL, dmu_sync_done, dsa,
            ZIO_PRIORITY_SYNC_WRITE, ZIO_FLAG_CANFAIL, &zb));

        return (0);
}

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

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

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

        err = dnode_hold(os, object, FTAG, &dn);
        if (err)
                return (err);
        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
        dnode_new_blkid(dn, maxblkid, tx, B_FALSE);
        rw_exit(&dn->dn_struct_rwlock);
        dnode_rele(dn, FTAG);
        return (0);
}

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

        /*
         * Send streams include each object's checksum function.  This
         * check ensures that the receiving system can understand the
         * checksum function transmitted.
         */
        ASSERT3U(checksum, <, ZIO_CHECKSUM_LEGACY_FUNCTIONS);

        VERIFY0(dnode_hold(os, object, FTAG, &dn));
        ASSERT3U(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;

        /*
         * Send streams include each object's compression function.  This
         * check ensures that the receiving system can understand the
         * compression function transmitted.
         */
        ASSERT3U(compress, <, ZIO_COMPRESS_LEGACY_FUNCTIONS);

        VERIFY0(dnode_hold(os, object, FTAG, &dn));
        dn->dn_compress = compress;
        dnode_setdirty(dn, tx);
        dnode_rele(dn, FTAG);
}

/*
 * When the "redundant_metadata" property is set to "most", only indirect
 * blocks of this level and higher will have an additional ditto block.
 */
int zfs_redundant_metadata_most_ditto_level = 2;

void
dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp, zio_prop_t *zp)
{
        dmu_object_type_t type = dn ? dn->dn_type : DMU_OT_OBJSET;
        boolean_t ismd = (level > 0 || DMU_OT_IS_METADATA(type) ||
            (wp & WP_SPILL));
        enum zio_checksum checksum = os->os_checksum;
        enum zio_compress compress = os->os_compress;
        enum zio_checksum dedup_checksum = os->os_dedup_checksum;
        boolean_t dedup = B_FALSE;
        boolean_t nopwrite = B_FALSE;
        boolean_t dedup_verify = os->os_dedup_verify;
        boolean_t encrypt = B_FALSE;
        int copies = os->os_copies;

        /*
         * We maintain different write policies for each of the following
         * types of data:
         *       1. metadata
         *       2. preallocated blocks (i.e. level-0 blocks of a dump device)
         *       3. all other level 0 blocks
         */
        if (ismd) {
                /*
                 * XXX -- we should design a compression algorithm
                 * that specializes in arrays of bps.
                 */
                compress = zio_compress_select(os->os_spa,
                    ZIO_COMPRESS_ON, ZIO_COMPRESS_ON);

                /*
                 * Metadata always gets checksummed.  If the data
                 * checksum is multi-bit correctable, and it's not a
                 * ZBT-style checksum, then it's suitable for metadata
                 * as well.  Otherwise, the metadata checksum defaults
                 * to fletcher4.
                 */
                if (!(zio_checksum_table[checksum].ci_flags &
                    ZCHECKSUM_FLAG_METADATA) ||
                    (zio_checksum_table[checksum].ci_flags &
                    ZCHECKSUM_FLAG_EMBEDDED))
                        checksum = ZIO_CHECKSUM_FLETCHER_4;

                if (os->os_redundant_metadata == ZFS_REDUNDANT_METADATA_ALL ||
                    (os->os_redundant_metadata ==
                    ZFS_REDUNDANT_METADATA_MOST &&
                    (level >= zfs_redundant_metadata_most_ditto_level ||
                    DMU_OT_IS_METADATA(type) || (wp & WP_SPILL))))
                        copies++;
        } else if (wp & WP_NOFILL) {
                ASSERT(level == 0);

                /*
                 * If we're writing preallocated blocks, we aren't actually
                 * writing them so don't set any policy properties.  These
                 * blocks are currently only used by an external subsystem
                 * outside of zfs (i.e. dump) and not written by the zio
                 * pipeline.
                 */
                compress = ZIO_COMPRESS_OFF;
                checksum = ZIO_CHECKSUM_OFF;
        } else {
                compress = zio_compress_select(os->os_spa, dn->dn_compress,
                    compress);

                checksum = (dedup_checksum == ZIO_CHECKSUM_OFF) ?
                    zio_checksum_select(dn->dn_checksum, checksum) :
                    dedup_checksum;

                /*
                 * Determine dedup setting.  If we are in dmu_sync(),
                 * we won't actually dedup now because that's all
                 * done in syncing context; but we do want to use the
                 * dedup checkum.  If the checksum is not strong
                 * enough to ensure unique signatures, force
                 * dedup_verify.
                 */
                if (dedup_checksum != ZIO_CHECKSUM_OFF) {
                        dedup = (wp & WP_DMU_SYNC) ? B_FALSE : B_TRUE;
                        if (!(zio_checksum_table[checksum].ci_flags &
                            ZCHECKSUM_FLAG_DEDUP))
                                dedup_verify = B_TRUE;
                }

                /*
                 * Enable nopwrite if we have secure enough checksum
                 * algorithm (see comment in zio_nop_write) and
                 * compression is enabled.  We don't enable nopwrite if
                 * dedup is enabled as the two features are mutually
                 * exclusive.
                 */
                nopwrite = (!dedup && (zio_checksum_table[checksum].ci_flags &
                    ZCHECKSUM_FLAG_NOPWRITE) &&
                    compress != ZIO_COMPRESS_OFF && zfs_nopwrite_enabled);
        }

        /*
         * All objects in an encrypted objset are protected from modification
         * via a MAC. Encrypted objects store their IV and salt in the last DVA
         * in the bp, so we cannot use all copies. Encrypted objects are also
         * not subject to nopwrite since writing the same data will still
         * result in a new ciphertext. Only encrypted blocks can be dedup'd
         * to avoid ambiguity in the dedup code since the DDT does not store
         * object types.
         */
        if (os->os_encrypted && (wp & WP_NOFILL) == 0) {
                encrypt = B_TRUE;

                if (DMU_OT_IS_ENCRYPTED(type)) {
                        copies = MIN(copies, SPA_DVAS_PER_BP - 1);
                        nopwrite = B_FALSE;
                } else {
                        dedup = B_FALSE;
                }

                if (level <= 0 &&
                    (type == DMU_OT_DNODE || type == DMU_OT_OBJSET)) {
                        compress = ZIO_COMPRESS_EMPTY;
                }
        }

        zp->zp_compress = compress;
        zp->zp_checksum = checksum;
        zp->zp_type = (wp & WP_SPILL) ? dn->dn_bonustype : type;
        zp->zp_level = level;
        zp->zp_copies = MIN(copies, spa_max_replication(os->os_spa));
        zp->zp_dedup = dedup;
        zp->zp_dedup_verify = dedup && dedup_verify;
        zp->zp_nopwrite = nopwrite;
        zp->zp_encrypt = encrypt;
        zp->zp_byteorder = ZFS_HOST_BYTEORDER;
        bzero(zp->zp_salt, ZIO_DATA_SALT_LEN);
        bzero(zp->zp_iv, ZIO_DATA_IV_LEN);
        bzero(zp->zp_mac, ZIO_DATA_MAC_LEN);
        zp->zp_zpl_smallblk = DMU_OT_IS_FILE(zp->zp_type) ?
            os->os_zpl_special_smallblock : 0;

        ASSERT3U(zp->zp_compress, !=, ZIO_COMPRESS_INHERIT);
}

/*
 * This function is only called from zfs_holey_common() for zpl_llseek()
 * in order to determine the location of holes.  In order to accurately
 * report holes all dirty data must be synced to disk.  This causes extremely
 * poor performance when seeking for holes in a dirty file.  As a compromise,
 * only provide hole data when the dnode is clean.  When a dnode is dirty
 * report the dnode as having no holes which is always a safe thing to do.
 */
int
dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
{
        dnode_t *dn;
        int i, err;
        boolean_t clean = B_TRUE;

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

        /*
         * Check if dnode is dirty
         */
        for (i = 0; i < TXG_SIZE; i++) {
                if (multilist_link_active(&dn->dn_dirty_link[i])) {
                        clean = B_FALSE;
                        break;
                }
        }

        /*
         * If compatibility option is on, sync any current changes before
         * we go trundling through the block pointers.
         */
        if (!clean && zfs_dmu_offset_next_sync) {
                clean = B_TRUE;
                dnode_rele(dn, FTAG);
                txg_wait_synced(dmu_objset_pool(os), 0);
                err = dnode_hold(os, object, FTAG, &dn);
                if (err)
                        return (err);
        }

        if (clean)
                err = dnode_next_offset(dn,
                    (hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
        else
                err = SET_ERROR(EBUSY);

        dnode_rele(dn, FTAG);

        return (err);
}

void
__dmu_object_info_from_dnode(dnode_t *dn, dmu_object_info_t *doi)
{
        dnode_phys_t *dnp = dn->dn_phys;

        doi->doi_data_block_size = dn->dn_datablksz;
        doi->doi_metadata_block_size = dn->dn_indblkshift ?
            1ULL << dn->dn_indblkshift : 0;
        doi->doi_type = dn->dn_type;
        doi->doi_bonus_type = dn->dn_bonustype;
        doi->doi_bonus_size = dn->dn_bonuslen;
        doi->doi_dnodesize = dn->dn_num_slots << DNODE_SHIFT;
        doi->doi_indirection = dn->dn_nlevels;
        doi->doi_checksum = dn->dn_checksum;
        doi->doi_compress = dn->dn_compress;
        doi->doi_nblkptr = dn->dn_nblkptr;
        doi->doi_physical_blocks_512 = (DN_USED_BYTES(dnp) + 256) >> 9;
        doi->doi_max_offset = (dn->dn_maxblkid + 1) * dn->dn_datablksz;
        doi->doi_fill_count = 0;
        for (int i = 0; i < dnp->dn_nblkptr; i++)
                doi->doi_fill_count += BP_GET_FILL(&dnp->dn_blkptr[i]);
}

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);

        __dmu_object_info_from_dnode(dn, doi);

        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, 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_fake, dmu_object_info_t *doi)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;

        DB_DNODE_ENTER(db);
        dmu_object_info_from_dnode(DB_DNODE(db), doi);
        DB_DNODE_EXIT(db);
}

/*
 * 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_fake, uint32_t *blksize,
    u_longlong_t *nblk512)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
        dnode_t *dn;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);

        *blksize = dn->dn_datablksz;
        /* add in number of slots used for the dnode itself */
        *nblk512 = ((DN_USED_BYTES(dn->dn_phys) + SPA_MINBLOCKSIZE/2) >>
            SPA_MINBLOCKSHIFT) + dn->dn_num_slots;
        DB_DNODE_EXIT(db);
}

void
dmu_object_dnsize_from_db(dmu_buf_t *db_fake, int *dnsize)
{
        dmu_buf_impl_t *db = (dmu_buf_impl_t *)db_fake;
        dnode_t *dn;

        DB_DNODE_ENTER(db);
        dn = DB_DNODE(db);
        *dnsize = dn->dn_num_slots << DNODE_SHIFT;
        DB_DNODE_EXIT(db);
}

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)
{
        abd_init();
        zfs_dbgmsg_init();
        sa_cache_init();
        xuio_stat_init();
        dmu_objset_init();
        dnode_init();
        zfetch_init();
        dmu_tx_init();
        l2arc_init();
        arc_init();
        dbuf_init();
}

void
dmu_fini(void)
{
        arc_fini(); /* arc depends on l2arc, so arc must go first */
        l2arc_fini();
        dmu_tx_fini();
        zfetch_fini();
        dbuf_fini();
        dnode_fini();
        dmu_objset_fini();
        xuio_stat_fini();
        sa_cache_fini();
        zfs_dbgmsg_fini();
        abd_fini();
}

#if defined(_KERNEL)
EXPORT_SYMBOL(dmu_bonus_hold);
EXPORT_SYMBOL(dmu_bonus_hold_by_dnode);
EXPORT_SYMBOL(dmu_buf_hold_array_by_bonus);
EXPORT_SYMBOL(dmu_buf_rele_array);
EXPORT_SYMBOL(dmu_prefetch);
EXPORT_SYMBOL(dmu_free_range);
EXPORT_SYMBOL(dmu_free_long_range);
EXPORT_SYMBOL(dmu_free_long_object);
EXPORT_SYMBOL(dmu_read);
EXPORT_SYMBOL(dmu_read_by_dnode);
EXPORT_SYMBOL(dmu_write);
EXPORT_SYMBOL(dmu_write_by_dnode);
EXPORT_SYMBOL(dmu_prealloc);
EXPORT_SYMBOL(dmu_object_info);
EXPORT_SYMBOL(dmu_object_info_from_dnode);
EXPORT_SYMBOL(dmu_object_info_from_db);
EXPORT_SYMBOL(dmu_object_size_from_db);
EXPORT_SYMBOL(dmu_object_dnsize_from_db);
EXPORT_SYMBOL(dmu_object_set_nlevels);
EXPORT_SYMBOL(dmu_object_set_blocksize);
EXPORT_SYMBOL(dmu_object_set_maxblkid);
EXPORT_SYMBOL(dmu_object_set_checksum);
EXPORT_SYMBOL(dmu_object_set_compress);
EXPORT_SYMBOL(dmu_write_policy);
EXPORT_SYMBOL(dmu_sync);
EXPORT_SYMBOL(dmu_request_arcbuf);
EXPORT_SYMBOL(dmu_return_arcbuf);
EXPORT_SYMBOL(dmu_assign_arcbuf_by_dnode);
EXPORT_SYMBOL(dmu_assign_arcbuf_by_dbuf);
EXPORT_SYMBOL(dmu_buf_hold);
EXPORT_SYMBOL(dmu_ot);

/* BEGIN CSTYLED */
module_param(zfs_nopwrite_enabled, int, 0644);
MODULE_PARM_DESC(zfs_nopwrite_enabled, "Enable NOP writes");

module_param(zfs_per_txg_dirty_frees_percent, ulong, 0644);
MODULE_PARM_DESC(zfs_per_txg_dirty_frees_percent,
        "percentage of dirtied blocks from frees in one TXG");

module_param(zfs_dmu_offset_next_sync, int, 0644);
MODULE_PARM_DESC(zfs_dmu_offset_next_sync,
        "Enable forcing txg sync to find holes");

/* END CSTYLED */

#endif