FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/include/sys/dmu.h

     /*
      * 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 https://opensource.org/licenses/CDDL-1.0.
     * 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, 2020 by Delphix. All rights reserved.
     * Copyright 2011 Nexenta Systems, Inc. All rights reserved.
     * Copyright (c) 2012, Joyent, Inc. All rights reserved.
     * Copyright 2014 HybridCluster. All rights reserved.
     * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
     * Copyright 2013 Saso Kiselkov. All rights reserved.
     * Copyright (c) 2017, Intel Corporation.
     * Copyright (c) 2022 Hewlett Packard Enterprise Development LP.
     */
    
    /* Portions Copyright 2010 Robert Milkowski */
    
    #ifndef _SYS_DMU_H
    #define _SYS_DMU_H
    
    /*
     * This file describes the interface that the DMU provides for its
     * consumers.
     *
     * The DMU also interacts with the SPA.  That interface is described in
     * dmu_spa.h.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/inttypes.h>
    #include <sys/cred.h>
    #include <sys/fs/zfs.h>
    #include <sys/zio_compress.h>
    #include <sys/zio_priority.h>
    #include <sys/uio.h>
    #include <sys/zfs_file.h>
    
    #ifdef  __cplusplus
    extern "C" {
    #endif
    
    struct page;
    struct vnode;
    struct spa;
    struct zilog;
    struct zio;
    struct blkptr;
    struct zap_cursor;
    struct dsl_dataset;
    struct dsl_pool;
    struct dnode;
    struct drr_begin;
    struct drr_end;
    struct zbookmark_phys;
    struct spa;
    struct nvlist;
    struct arc_buf;
    struct zio_prop;
    struct sa_handle;
    struct dsl_crypto_params;
    struct locked_range;
    
    typedef struct objset objset_t;
    typedef struct dmu_tx dmu_tx_t;
    typedef struct dsl_dir dsl_dir_t;
    typedef struct dnode dnode_t;
    
    typedef enum dmu_object_byteswap {
            DMU_BSWAP_UINT8,
            DMU_BSWAP_UINT16,
            DMU_BSWAP_UINT32,
            DMU_BSWAP_UINT64,
            DMU_BSWAP_ZAP,
            DMU_BSWAP_DNODE,
            DMU_BSWAP_OBJSET,
            DMU_BSWAP_ZNODE,
            DMU_BSWAP_OLDACL,
            DMU_BSWAP_ACL,
            /*
             * Allocating a new byteswap type number makes the on-disk format
             * incompatible with any other format that uses the same number.
             *
            * Data can usually be structured to work with one of the
            * DMU_BSWAP_UINT* or DMU_BSWAP_ZAP types.
            */
           DMU_BSWAP_NUMFUNCS
   } dmu_object_byteswap_t;
   
   #define DMU_OT_NEWTYPE 0x80
   #define DMU_OT_METADATA 0x40
   #define DMU_OT_ENCRYPTED 0x20
   #define DMU_OT_BYTESWAP_MASK 0x1f
   
   /*
    * Defines a uint8_t object type. Object types specify if the data
    * in the object is metadata (boolean) and how to byteswap the data
    * (dmu_object_byteswap_t). All of the types created by this method
    * are cached in the dbuf metadata cache.
    */
   #define DMU_OT(byteswap, metadata, encrypted) \
           (DMU_OT_NEWTYPE | \
           ((metadata) ? DMU_OT_METADATA : 0) | \
           ((encrypted) ? DMU_OT_ENCRYPTED : 0) | \
           ((byteswap) & DMU_OT_BYTESWAP_MASK))
   
   #define DMU_OT_IS_VALID(ot) (((ot) & DMU_OT_NEWTYPE) ? \
           ((ot) & DMU_OT_BYTESWAP_MASK) < DMU_BSWAP_NUMFUNCS : \
           (ot) < DMU_OT_NUMTYPES)
   
   #define DMU_OT_IS_METADATA_CACHED(ot) (((ot) & DMU_OT_NEWTYPE) ? \
           B_TRUE : dmu_ot[(ot)].ot_dbuf_metadata_cache)
   
   /*
    * MDB doesn't have dmu_ot; it defines these macros itself.
    */
   #ifndef ZFS_MDB
   #define DMU_OT_IS_METADATA_IMPL(ot) (dmu_ot[ot].ot_metadata)
   #define DMU_OT_IS_ENCRYPTED_IMPL(ot) (dmu_ot[ot].ot_encrypt)
   #define DMU_OT_BYTESWAP_IMPL(ot) (dmu_ot[ot].ot_byteswap)
   #endif
   
   #define DMU_OT_IS_METADATA(ot) (((ot) & DMU_OT_NEWTYPE) ? \
           (((ot) & DMU_OT_METADATA) != 0) : \
           DMU_OT_IS_METADATA_IMPL(ot))
   
   #define DMU_OT_IS_DDT(ot) \
           ((ot) == DMU_OT_DDT_ZAP)
   
   #define DMU_OT_IS_CRITICAL(ot) \
           (DMU_OT_IS_METADATA(ot) && \
           (ot) != DMU_OT_DNODE && \
           (ot) != DMU_OT_DIRECTORY_CONTENTS && \
           (ot) != DMU_OT_SA)
   
   /* Note: ztest uses DMU_OT_UINT64_OTHER as a proxy for file blocks */
   #define DMU_OT_IS_FILE(ot) \
           ((ot) == DMU_OT_PLAIN_FILE_CONTENTS || (ot) == DMU_OT_UINT64_OTHER)
   
   #define DMU_OT_IS_ENCRYPTED(ot) (((ot) & DMU_OT_NEWTYPE) ? \
           (((ot) & DMU_OT_ENCRYPTED) != 0) : \
           DMU_OT_IS_ENCRYPTED_IMPL(ot))
   
   /*
    * These object types use bp_fill != 1 for their L0 bp's. Therefore they can't
    * have their data embedded (i.e. use a BP_IS_EMBEDDED() bp), because bp_fill
    * is repurposed for embedded BPs.
    */
   #define DMU_OT_HAS_FILL(ot) \
           ((ot) == DMU_OT_DNODE || (ot) == DMU_OT_OBJSET)
   
   #define DMU_OT_BYTESWAP(ot) (((ot) & DMU_OT_NEWTYPE) ? \
           ((ot) & DMU_OT_BYTESWAP_MASK) : \
           DMU_OT_BYTESWAP_IMPL(ot))
   
   typedef enum dmu_object_type {
           DMU_OT_NONE,
           /* general: */
           DMU_OT_OBJECT_DIRECTORY,        /* ZAP */
           DMU_OT_OBJECT_ARRAY,            /* UINT64 */
           DMU_OT_PACKED_NVLIST,           /* UINT8 (XDR by nvlist_pack/unpack) */
           DMU_OT_PACKED_NVLIST_SIZE,      /* UINT64 */
           DMU_OT_BPOBJ,                   /* UINT64 */
           DMU_OT_BPOBJ_HDR,               /* UINT64 */
           /* spa: */
           DMU_OT_SPACE_MAP_HEADER,        /* UINT64 */
           DMU_OT_SPACE_MAP,               /* UINT64 */
           /* zil: */
           DMU_OT_INTENT_LOG,              /* UINT64 */
           /* dmu: */
           DMU_OT_DNODE,                   /* DNODE */
           DMU_OT_OBJSET,                  /* OBJSET */
           /* dsl: */
           DMU_OT_DSL_DIR,                 /* UINT64 */
           DMU_OT_DSL_DIR_CHILD_MAP,       /* ZAP */
           DMU_OT_DSL_DS_SNAP_MAP,         /* ZAP */
           DMU_OT_DSL_PROPS,               /* ZAP */
           DMU_OT_DSL_DATASET,             /* UINT64 */
           /* zpl: */
           DMU_OT_ZNODE,                   /* ZNODE */
           DMU_OT_OLDACL,                  /* Old ACL */
           DMU_OT_PLAIN_FILE_CONTENTS,     /* UINT8 */
           DMU_OT_DIRECTORY_CONTENTS,      /* ZAP */
           DMU_OT_MASTER_NODE,             /* ZAP */
           DMU_OT_UNLINKED_SET,            /* ZAP */
           /* zvol: */
           DMU_OT_ZVOL,                    /* UINT8 */
           DMU_OT_ZVOL_PROP,               /* ZAP */
           /* other; for testing only! */
           DMU_OT_PLAIN_OTHER,             /* UINT8 */
           DMU_OT_UINT64_OTHER,            /* UINT64 */
           DMU_OT_ZAP_OTHER,               /* ZAP */
           /* new object types: */
           DMU_OT_ERROR_LOG,               /* ZAP */
           DMU_OT_SPA_HISTORY,             /* UINT8 */
           DMU_OT_SPA_HISTORY_OFFSETS,     /* spa_his_phys_t */
           DMU_OT_POOL_PROPS,              /* ZAP */
           DMU_OT_DSL_PERMS,               /* ZAP */
           DMU_OT_ACL,                     /* ACL */
           DMU_OT_SYSACL,                  /* SYSACL */
           DMU_OT_FUID,                    /* FUID table (Packed NVLIST UINT8) */
           DMU_OT_FUID_SIZE,               /* FUID table size UINT64 */
           DMU_OT_NEXT_CLONES,             /* ZAP */
           DMU_OT_SCAN_QUEUE,              /* ZAP */
           DMU_OT_USERGROUP_USED,          /* ZAP */
           DMU_OT_USERGROUP_QUOTA,         /* ZAP */
           DMU_OT_USERREFS,                /* ZAP */
           DMU_OT_DDT_ZAP,                 /* ZAP */
           DMU_OT_DDT_STATS,               /* ZAP */
           DMU_OT_SA,                      /* System attr */
           DMU_OT_SA_MASTER_NODE,          /* ZAP */
           DMU_OT_SA_ATTR_REGISTRATION,    /* ZAP */
           DMU_OT_SA_ATTR_LAYOUTS,         /* ZAP */
           DMU_OT_SCAN_XLATE,              /* ZAP */
           DMU_OT_DEDUP,                   /* fake dedup BP from ddt_bp_create() */
           DMU_OT_DEADLIST,                /* ZAP */
           DMU_OT_DEADLIST_HDR,            /* UINT64 */
           DMU_OT_DSL_CLONES,              /* ZAP */
           DMU_OT_BPOBJ_SUBOBJ,            /* UINT64 */
           /*
            * Do not allocate new object types here. Doing so makes the on-disk
            * format incompatible with any other format that uses the same object
            * type number.
            *
            * When creating an object which does not have one of the above types
            * use the DMU_OTN_* type with the correct byteswap and metadata
            * values.
            *
            * The DMU_OTN_* types do not have entries in the dmu_ot table,
            * use the DMU_OT_IS_METADATA() and DMU_OT_BYTESWAP() macros instead
            * of indexing into dmu_ot directly (this works for both DMU_OT_* types
            * and DMU_OTN_* types).
            */
           DMU_OT_NUMTYPES,
   
           /*
            * Names for valid types declared with DMU_OT().
            */
           DMU_OTN_UINT8_DATA = DMU_OT(DMU_BSWAP_UINT8, B_FALSE, B_FALSE),
           DMU_OTN_UINT8_METADATA = DMU_OT(DMU_BSWAP_UINT8, B_TRUE, B_FALSE),
           DMU_OTN_UINT16_DATA = DMU_OT(DMU_BSWAP_UINT16, B_FALSE, B_FALSE),
           DMU_OTN_UINT16_METADATA = DMU_OT(DMU_BSWAP_UINT16, B_TRUE, B_FALSE),
           DMU_OTN_UINT32_DATA = DMU_OT(DMU_BSWAP_UINT32, B_FALSE, B_FALSE),
           DMU_OTN_UINT32_METADATA = DMU_OT(DMU_BSWAP_UINT32, B_TRUE, B_FALSE),
           DMU_OTN_UINT64_DATA = DMU_OT(DMU_BSWAP_UINT64, B_FALSE, B_FALSE),
           DMU_OTN_UINT64_METADATA = DMU_OT(DMU_BSWAP_UINT64, B_TRUE, B_FALSE),
           DMU_OTN_ZAP_DATA = DMU_OT(DMU_BSWAP_ZAP, B_FALSE, B_FALSE),
           DMU_OTN_ZAP_METADATA = DMU_OT(DMU_BSWAP_ZAP, B_TRUE, B_FALSE),
   
           DMU_OTN_UINT8_ENC_DATA = DMU_OT(DMU_BSWAP_UINT8, B_FALSE, B_TRUE),
           DMU_OTN_UINT8_ENC_METADATA = DMU_OT(DMU_BSWAP_UINT8, B_TRUE, B_TRUE),
           DMU_OTN_UINT16_ENC_DATA = DMU_OT(DMU_BSWAP_UINT16, B_FALSE, B_TRUE),
           DMU_OTN_UINT16_ENC_METADATA = DMU_OT(DMU_BSWAP_UINT16, B_TRUE, B_TRUE),
           DMU_OTN_UINT32_ENC_DATA = DMU_OT(DMU_BSWAP_UINT32, B_FALSE, B_TRUE),
           DMU_OTN_UINT32_ENC_METADATA = DMU_OT(DMU_BSWAP_UINT32, B_TRUE, B_TRUE),
           DMU_OTN_UINT64_ENC_DATA = DMU_OT(DMU_BSWAP_UINT64, B_FALSE, B_TRUE),
           DMU_OTN_UINT64_ENC_METADATA = DMU_OT(DMU_BSWAP_UINT64, B_TRUE, B_TRUE),
           DMU_OTN_ZAP_ENC_DATA = DMU_OT(DMU_BSWAP_ZAP, B_FALSE, B_TRUE),
           DMU_OTN_ZAP_ENC_METADATA = DMU_OT(DMU_BSWAP_ZAP, B_TRUE, B_TRUE),
   } dmu_object_type_t;
   
   /*
    * These flags are intended to be used to specify the "txg_how"
    * parameter when calling the dmu_tx_assign() function. See the comment
    * above dmu_tx_assign() for more details on the meaning of these flags.
    */
   #define TXG_NOWAIT      (0ULL)
   #define TXG_WAIT        (1ULL<<0)
   #define TXG_NOTHROTTLE  (1ULL<<1)
   
   void byteswap_uint64_array(void *buf, size_t size);
   void byteswap_uint32_array(void *buf, size_t size);
   void byteswap_uint16_array(void *buf, size_t size);
   void byteswap_uint8_array(void *buf, size_t size);
   void zap_byteswap(void *buf, size_t size);
   void zfs_oldacl_byteswap(void *buf, size_t size);
   void zfs_acl_byteswap(void *buf, size_t size);
   void zfs_znode_byteswap(void *buf, size_t size);
   
   #define DS_FIND_SNAPSHOTS       (1<<0)
   #define DS_FIND_CHILDREN        (1<<1)
   #define DS_FIND_SERIALIZE       (1<<2)
   
   /*
    * The maximum number of bytes that can be accessed as part of one
    * operation, including metadata.
    */
   #define DMU_MAX_ACCESS (64 * 1024 * 1024) /* 64MB */
   #define DMU_MAX_DELETEBLKCNT (20480) /* ~5MB of indirect blocks */
   
   #define DMU_USERUSED_OBJECT     (-1ULL)
   #define DMU_GROUPUSED_OBJECT    (-2ULL)
   #define DMU_PROJECTUSED_OBJECT  (-3ULL)
   
   /*
    * Zap prefix for object accounting in DMU_{USER,GROUP,PROJECT}USED_OBJECT.
    */
   #define DMU_OBJACCT_PREFIX      "obj-"
   #define DMU_OBJACCT_PREFIX_LEN  4
   
   /*
    * artificial blkids for bonus buffer and spill blocks
    */
   #define DMU_BONUS_BLKID         (-1ULL)
   #define DMU_SPILL_BLKID         (-2ULL)
   
   /*
    * Public routines to create, destroy, open, and close objsets.
    */
   typedef void dmu_objset_create_sync_func_t(objset_t *os, void *arg,
       cred_t *cr, dmu_tx_t *tx);
   
   int dmu_objset_hold(const char *name, const void *tag, objset_t **osp);
   int dmu_objset_own(const char *name, dmu_objset_type_t type,
       boolean_t readonly, boolean_t key_required, const void *tag,
       objset_t **osp);
   void dmu_objset_rele(objset_t *os, const void *tag);
   void dmu_objset_disown(objset_t *os, boolean_t key_required, const void *tag);
   int dmu_objset_open_ds(struct dsl_dataset *ds, objset_t **osp);
   
   void dmu_objset_evict_dbufs(objset_t *os);
   int dmu_objset_create(const char *name, dmu_objset_type_t type, uint64_t flags,
       struct dsl_crypto_params *dcp, dmu_objset_create_sync_func_t func,
       void *arg);
   int dmu_objset_clone(const char *name, const char *origin);
   int dsl_destroy_snapshots_nvl(struct nvlist *snaps, boolean_t defer,
       struct nvlist *errlist);
   int dmu_objset_snapshot_one(const char *fsname, const char *snapname);
   int dmu_objset_find(const char *name, int func(const char *, void *), void *arg,
       int flags);
   void dmu_objset_byteswap(void *buf, size_t size);
   int dsl_dataset_rename_snapshot(const char *fsname,
       const char *oldsnapname, const char *newsnapname, boolean_t recursive);
   
   typedef struct dmu_buf {
           uint64_t db_object;             /* object that this buffer is part of */
           uint64_t db_offset;             /* byte offset in this object */
           uint64_t db_size;               /* size of buffer in bytes */
           void *db_data;                  /* data in buffer */
   } dmu_buf_t;
   
   /*
    * The names of zap entries in the DIRECTORY_OBJECT of the MOS.
    */
   #define DMU_POOL_DIRECTORY_OBJECT       1
   #define DMU_POOL_CONFIG                 "config"
   #define DMU_POOL_FEATURES_FOR_WRITE     "features_for_write"
   #define DMU_POOL_FEATURES_FOR_READ      "features_for_read"
   #define DMU_POOL_FEATURE_DESCRIPTIONS   "feature_descriptions"
   #define DMU_POOL_FEATURE_ENABLED_TXG    "feature_enabled_txg"
   #define DMU_POOL_ROOT_DATASET           "root_dataset"
   #define DMU_POOL_SYNC_BPOBJ             "sync_bplist"
   #define DMU_POOL_ERRLOG_SCRUB           "errlog_scrub"
   #define DMU_POOL_ERRLOG_LAST            "errlog_last"
   #define DMU_POOL_SPARES                 "spares"
   #define DMU_POOL_DEFLATE                "deflate"
   #define DMU_POOL_HISTORY                "history"
   #define DMU_POOL_PROPS                  "pool_props"
   #define DMU_POOL_L2CACHE                "l2cache"
   #define DMU_POOL_TMP_USERREFS           "tmp_userrefs"
   #define DMU_POOL_DDT                    "DDT-%s-%s-%s"
   #define DMU_POOL_DDT_STATS              "DDT-statistics"
   #define DMU_POOL_CREATION_VERSION       "creation_version"
   #define DMU_POOL_SCAN                   "scan"
   #define DMU_POOL_FREE_BPOBJ             "free_bpobj"
   #define DMU_POOL_BPTREE_OBJ             "bptree_obj"
   #define DMU_POOL_EMPTY_BPOBJ            "empty_bpobj"
   #define DMU_POOL_CHECKSUM_SALT          "org.illumos:checksum_salt"
   #define DMU_POOL_VDEV_ZAP_MAP           "com.delphix:vdev_zap_map"
   #define DMU_POOL_REMOVING               "com.delphix:removing"
   #define DMU_POOL_OBSOLETE_BPOBJ         "com.delphix:obsolete_bpobj"
   #define DMU_POOL_CONDENSING_INDIRECT    "com.delphix:condensing_indirect"
   #define DMU_POOL_ZPOOL_CHECKPOINT       "com.delphix:zpool_checkpoint"
   #define DMU_POOL_LOG_SPACEMAP_ZAP       "com.delphix:log_spacemap_zap"
   #define DMU_POOL_DELETED_CLONES         "com.delphix:deleted_clones"
   
   /*
    * Allocate an object from this objset.  The range of object numbers
    * available is (0, DN_MAX_OBJECT).  Object 0 is the meta-dnode.
    *
    * The transaction must be assigned to a txg.  The newly allocated
    * object will be "held" in the transaction (ie. you can modify the
    * newly allocated object in this transaction).
    *
    * dmu_object_alloc() chooses an object and returns it in *objectp.
    *
    * dmu_object_claim() allocates a specific object number.  If that
    * number is already allocated, it fails and returns EEXIST.
    *
    * Return 0 on success, or ENOSPC or EEXIST as specified above.
    */
   uint64_t dmu_object_alloc(objset_t *os, dmu_object_type_t ot,
       int blocksize, dmu_object_type_t bonus_type, int bonus_len, dmu_tx_t *tx);
   uint64_t dmu_object_alloc_ibs(objset_t *os, dmu_object_type_t ot, int blocksize,
       int indirect_blockshift,
       dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *tx);
   uint64_t dmu_object_alloc_dnsize(objset_t *os, dmu_object_type_t ot,
       int blocksize, dmu_object_type_t bonus_type, int bonus_len,
       int dnodesize, dmu_tx_t *tx);
   uint64_t dmu_object_alloc_hold(objset_t *os, dmu_object_type_t ot,
       int blocksize, int indirect_blockshift, dmu_object_type_t bonustype,
       int bonuslen, int dnodesize, dnode_t **allocated_dnode, const void *tag,
       dmu_tx_t *tx);
   int dmu_object_claim(objset_t *os, uint64_t object, dmu_object_type_t ot,
       int blocksize, dmu_object_type_t bonus_type, int bonus_len, dmu_tx_t *tx);
   int dmu_object_claim_dnsize(objset_t *os, uint64_t object, dmu_object_type_t ot,
       int blocksize, dmu_object_type_t bonus_type, int bonus_len,
       int dnodesize, dmu_tx_t *tx);
   int dmu_object_reclaim(objset_t *os, uint64_t object, dmu_object_type_t ot,
       int blocksize, dmu_object_type_t bonustype, int bonuslen, dmu_tx_t *txp);
   int dmu_object_reclaim_dnsize(objset_t *os, uint64_t object,
       dmu_object_type_t ot, int blocksize, dmu_object_type_t bonustype,
       int bonuslen, int dnodesize, boolean_t keep_spill, dmu_tx_t *tx);
   int dmu_object_rm_spill(objset_t *os, uint64_t object, dmu_tx_t *tx);
   
   /*
    * Free an object from this objset.
    *
    * The object's data will be freed as well (ie. you don't need to call
    * dmu_free(object, 0, -1, tx)).
    *
    * The object need not be held in the transaction.
    *
    * If there are any holds on this object's buffers (via dmu_buf_hold()),
    * or tx holds on the object (via dmu_tx_hold_object()), you can not
    * free it; it fails and returns EBUSY.
    *
    * If the object is not allocated, it fails and returns ENOENT.
    *
    * Return 0 on success, or EBUSY or ENOENT as specified above.
    */
   int dmu_object_free(objset_t *os, uint64_t object, dmu_tx_t *tx);
   
   /*
    * Find the next allocated or free object.
    *
    * The objectp parameter is in-out.  It will be updated to be the next
    * object which is allocated.  Ignore objects which have not been
    * modified since txg.
    *
    * XXX Can only be called on a objset with no dirty data.
    *
    * Returns 0 on success, or ENOENT if there are no more objects.
    */
   int dmu_object_next(objset_t *os, uint64_t *objectp,
       boolean_t hole, uint64_t txg);
   
   /*
    * Set the number of levels on a dnode. nlevels must be greater than the
    * current number of levels or an EINVAL will be returned.
    */
   int dmu_object_set_nlevels(objset_t *os, uint64_t object, int nlevels,
       dmu_tx_t *tx);
   
   /*
    * Set the data blocksize for an object.
    *
    * The object cannot have any blocks allocated beyond the first.  If
    * the first block is allocated already, the new size must be greater
    * than the current block size.  If these conditions are not met,
    * ENOTSUP will be returned.
    *
    * Returns 0 on success, or EBUSY if there are any holds on the object
    * contents, or ENOTSUP as described above.
    */
   int dmu_object_set_blocksize(objset_t *os, uint64_t object, uint64_t size,
       int ibs, dmu_tx_t *tx);
   
   /*
    * Manually set the maxblkid on a dnode. This will adjust nlevels accordingly
    * to accommodate the change. When calling this function, the caller must
    * ensure that the object's nlevels can sufficiently support the new maxblkid.
    */
   int dmu_object_set_maxblkid(objset_t *os, uint64_t object, uint64_t maxblkid,
       dmu_tx_t *tx);
   
   /*
    * Set the checksum property on a dnode.  The new checksum algorithm will
    * apply to all newly written blocks; existing blocks will not be affected.
    */
   void dmu_object_set_checksum(objset_t *os, uint64_t object, uint8_t checksum,
       dmu_tx_t *tx);
   
   /*
    * Set the compress property on a dnode.  The new compression algorithm will
    * apply to all newly written blocks; existing blocks will not be affected.
    */
   void dmu_object_set_compress(objset_t *os, uint64_t object, uint8_t compress,
       dmu_tx_t *tx);
   
   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);
   void dmu_redact(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
       dmu_tx_t *tx);
   
   /*
    * Decide how to write a block: checksum, compression, number of copies, etc.
    */
   #define WP_NOFILL       0x1
   #define WP_DMU_SYNC     0x2
   #define WP_SPILL        0x4
   
   void dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp,
       struct zio_prop *zp);
   
   /*
    * The bonus data is accessed more or less like a regular buffer.
    * You must dmu_bonus_hold() to get the buffer, which will give you a
    * dmu_buf_t with db_offset==-1ULL, and db_size = the size of the bonus
    * data.  As with any normal buffer, you must call dmu_buf_will_dirty()
    * before modifying it, and the
    * object must be held in an assigned transaction before calling
    * dmu_buf_will_dirty.  You may use dmu_buf_set_user() on the bonus
    * buffer as well.  You must release what you hold with dmu_buf_rele().
    *
    * Returns ENOENT, EIO, or 0.
    */
   int dmu_bonus_hold(objset_t *os, uint64_t object, const void *tag,
       dmu_buf_t **dbp);
   int dmu_bonus_hold_by_dnode(dnode_t *dn, const void *tag, dmu_buf_t **dbp,
       uint32_t flags);
   int dmu_bonus_max(void);
   int dmu_set_bonus(dmu_buf_t *, int, dmu_tx_t *);
   int dmu_set_bonustype(dmu_buf_t *, dmu_object_type_t, dmu_tx_t *);
   dmu_object_type_t dmu_get_bonustype(dmu_buf_t *);
   int dmu_rm_spill(objset_t *, uint64_t, dmu_tx_t *);
   
   /*
    * Special spill buffer support used by "SA" framework
    */
   
   int dmu_spill_hold_by_bonus(dmu_buf_t *bonus, uint32_t flags, const void *tag,
       dmu_buf_t **dbp);
   int dmu_spill_hold_by_dnode(dnode_t *dn, uint32_t flags,
       const void *tag, dmu_buf_t **dbp);
   int dmu_spill_hold_existing(dmu_buf_t *bonus, const void *tag, dmu_buf_t **dbp);
   
   /*
    * Obtain the DMU buffer from the specified object which contains the
    * specified offset.  dmu_buf_hold() puts a "hold" on the buffer, so
    * that it will remain in memory.  You must release the hold with
    * dmu_buf_rele().  You must not access the dmu_buf_t after releasing
    * what you hold.  You must have a hold on any dmu_buf_t* you pass to the DMU.
    *
    * You must call dmu_buf_read, dmu_buf_will_dirty, or dmu_buf_will_fill
    * on the returned buffer before reading or writing the buffer's
    * db_data.  The comments for those routines describe what particular
    * operations are valid after calling them.
    *
    * The object number must be a valid, allocated object number.
    */
   int dmu_buf_hold(objset_t *os, uint64_t object, uint64_t offset,
       const void *tag, dmu_buf_t **, int flags);
   int dmu_buf_hold_array(objset_t *os, uint64_t object, uint64_t offset,
       uint64_t length, int read, const void *tag, int *numbufsp,
       dmu_buf_t ***dbpp);
   int dmu_buf_hold_by_dnode(dnode_t *dn, uint64_t offset,
       const void *tag, dmu_buf_t **dbp, int flags);
   int dmu_buf_hold_array_by_dnode(dnode_t *dn, uint64_t offset,
       uint64_t length, boolean_t read, const void *tag, int *numbufsp,
       dmu_buf_t ***dbpp, uint32_t flags);
   /*
    * Add a reference to a dmu buffer that has already been held via
    * dmu_buf_hold() in the current context.
    */
   void dmu_buf_add_ref(dmu_buf_t *db, const void *tag);
   
   /*
    * Attempt to add a reference to a dmu buffer that is in an unknown state,
    * using a pointer that may have been invalidated by eviction processing.
    * The request will succeed if the passed in dbuf still represents the
    * same os/object/blkid, is ineligible for eviction, and has at least
    * one hold by a user other than the syncer.
    */
   boolean_t dmu_buf_try_add_ref(dmu_buf_t *, objset_t *os, uint64_t object,
       uint64_t blkid, const void *tag);
   
   void dmu_buf_rele(dmu_buf_t *db, const void *tag);
   uint64_t dmu_buf_refcount(dmu_buf_t *db);
   uint64_t dmu_buf_user_refcount(dmu_buf_t *db);
   
   /*
    * dmu_buf_hold_array holds the DMU buffers which contain all bytes in a
    * range of an object.  A pointer to an array of dmu_buf_t*'s is
    * returned (in *dbpp).
    *
    * dmu_buf_rele_array releases the hold on an array of dmu_buf_t*'s, and
    * frees the array.  The hold on the array of buffers MUST be released
    * with dmu_buf_rele_array.  You can NOT release the hold on each buffer
    * individually with dmu_buf_rele.
    */
   int dmu_buf_hold_array_by_bonus(dmu_buf_t *db, uint64_t offset,
       uint64_t length, boolean_t read, const void *tag,
       int *numbufsp, dmu_buf_t ***dbpp);
   void dmu_buf_rele_array(dmu_buf_t **, int numbufs, const void *tag);
   
   typedef void dmu_buf_evict_func_t(void *user_ptr);
   
   /*
    * A DMU buffer user object may be associated with a dbuf for the
    * duration of its lifetime.  This allows the user of a dbuf (client)
    * to attach private data to a dbuf (e.g. in-core only data such as a
    * dnode_children_t, zap_t, or zap_leaf_t) and be optionally notified
    * when that dbuf has been evicted.  Clients typically respond to the
    * eviction notification by freeing their private data, thus ensuring
    * the same lifetime for both dbuf and private data.
    *
    * The mapping from a dmu_buf_user_t to any client private data is the
    * client's responsibility.  All current consumers of the API with private
    * data embed a dmu_buf_user_t as the first member of the structure for
    * their private data.  This allows conversions between the two types
    * with a simple cast.  Since the DMU buf user API never needs access
    * to the private data, other strategies can be employed if necessary
    * or convenient for the client (e.g. using container_of() to do the
    * conversion for private data that cannot have the dmu_buf_user_t as
    * its first member).
    *
    * Eviction callbacks are executed without the dbuf mutex held or any
    * other type of mechanism to guarantee that the dbuf is still available.
    * For this reason, users must assume the dbuf has already been freed
    * and not reference the dbuf from the callback context.
    *
    * Users requesting "immediate eviction" are notified as soon as the dbuf
    * is only referenced by dirty records (dirties == holds).  Otherwise the
    * notification occurs after eviction processing for the dbuf begins.
    */
   typedef struct dmu_buf_user {
           /*
            * Asynchronous user eviction callback state.
            */
           taskq_ent_t     dbu_tqent;
   
           /*
            * This instance's eviction function pointers.
            *
            * dbu_evict_func_sync is called synchronously and then
            * dbu_evict_func_async is executed asynchronously on a taskq.
            */
           dmu_buf_evict_func_t *dbu_evict_func_sync;
           dmu_buf_evict_func_t *dbu_evict_func_async;
   #ifdef ZFS_DEBUG
           /*
            * Pointer to user's dbuf pointer.  NULL for clients that do
            * not associate a dbuf with their user data.
            *
            * The dbuf pointer is cleared upon eviction so as to catch
            * use-after-evict bugs in clients.
            */
           dmu_buf_t **dbu_clear_on_evict_dbufp;
   #endif
   } dmu_buf_user_t;
   
   /*
    * Initialize the given dmu_buf_user_t instance with the eviction function
    * evict_func, to be called when the user is evicted.
    *
    * NOTE: This function should only be called once on a given dmu_buf_user_t.
    *       To allow enforcement of this, dbu must already be zeroed on entry.
    */
   static inline void
   dmu_buf_init_user(dmu_buf_user_t *dbu, dmu_buf_evict_func_t *evict_func_sync,
       dmu_buf_evict_func_t *evict_func_async,
       dmu_buf_t **clear_on_evict_dbufp __maybe_unused)
   {
           ASSERT(dbu->dbu_evict_func_sync == NULL);
           ASSERT(dbu->dbu_evict_func_async == NULL);
   
           /* must have at least one evict func */
           IMPLY(evict_func_sync == NULL, evict_func_async != NULL);
           dbu->dbu_evict_func_sync = evict_func_sync;
           dbu->dbu_evict_func_async = evict_func_async;
           taskq_init_ent(&dbu->dbu_tqent);
   #ifdef ZFS_DEBUG
           dbu->dbu_clear_on_evict_dbufp = clear_on_evict_dbufp;
   #endif
   }
   
   /*
    * Attach user data to a dbuf and mark it for normal (when the dbuf's
    * data is cleared or its reference count goes to zero) eviction processing.
    *
    * Returns NULL on success, or the existing user if another user currently
    * owns the buffer.
    */
   void *dmu_buf_set_user(dmu_buf_t *db, dmu_buf_user_t *user);
   
   /*
    * Attach user data to a dbuf and mark it for immediate (its dirty and
    * reference counts are equal) eviction processing.
    *
    * Returns NULL on success, or the existing user if another user currently
    * owns the buffer.
    */
   void *dmu_buf_set_user_ie(dmu_buf_t *db, dmu_buf_user_t *user);
   
   /*
    * Replace the current user of a dbuf.
    *
    * If given the current user of a dbuf, replaces the dbuf's user with
    * "new_user" and returns the user data pointer that was replaced.
    * Otherwise returns the current, and unmodified, dbuf user pointer.
    */
   void *dmu_buf_replace_user(dmu_buf_t *db,
       dmu_buf_user_t *old_user, dmu_buf_user_t *new_user);
   
   /*
    * Remove the specified user data for a DMU buffer.
    *
    * Returns the user that was removed on success, or the current user if
    * another user currently owns the buffer.
    */
   void *dmu_buf_remove_user(dmu_buf_t *db, dmu_buf_user_t *user);
   
   /*
    * Returns the user data (dmu_buf_user_t *) associated with this dbuf.
    */
   void *dmu_buf_get_user(dmu_buf_t *db);
   
   objset_t *dmu_buf_get_objset(dmu_buf_t *db);
   dnode_t *dmu_buf_dnode_enter(dmu_buf_t *db);
   void dmu_buf_dnode_exit(dmu_buf_t *db);
   
   /* Block until any in-progress dmu buf user evictions complete. */
   void dmu_buf_user_evict_wait(void);
   
   /*
    * Returns the blkptr associated with this dbuf, or NULL if not set.
    */
   struct blkptr *dmu_buf_get_blkptr(dmu_buf_t *db);
   
   /*
    * Indicate that you are going to modify the buffer's data (db_data).
    *
    * The transaction (tx) must be assigned to a txg (ie. you've called
    * dmu_tx_assign()).  The buffer's object must be held in the tx
    * (ie. you've called dmu_tx_hold_object(tx, db->db_object)).
    */
   void dmu_buf_will_dirty(dmu_buf_t *db, dmu_tx_t *tx);
   boolean_t dmu_buf_is_dirty(dmu_buf_t *db, dmu_tx_t *tx);
   void dmu_buf_set_crypt_params(dmu_buf_t *db_fake, boolean_t byteorder,
       const uint8_t *salt, const uint8_t *iv, const uint8_t *mac, dmu_tx_t *tx);
   
   /*
    * You must create a transaction, then hold the objects which you will
    * (or might) modify as part of this transaction.  Then you must assign
    * the transaction to a transaction group.  Once the transaction has
    * been assigned, you can modify buffers which belong to held objects as
    * part of this transaction.  You can't modify buffers before the
    * transaction has been assigned; you can't modify buffers which don't
    * belong to objects which this transaction holds; you can't hold
    * objects once the transaction has been assigned.  You may hold an
    * object which you are going to free (with dmu_object_free()), but you
    * don't have to.
    *
    * You can abort the transaction before it has been assigned.
    *
    * Note that you may hold buffers (with dmu_buf_hold) at any time,
    * regardless of transaction state.
    */
   
   #define DMU_NEW_OBJECT  (-1ULL)
   #define DMU_OBJECT_END  (-1ULL)
   
   dmu_tx_t *dmu_tx_create(objset_t *os);
   void dmu_tx_hold_write(dmu_tx_t *tx, uint64_t object, uint64_t off, int len);
   void dmu_tx_hold_write_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off,
       int len);
   void dmu_tx_hold_free(dmu_tx_t *tx, uint64_t object, uint64_t off,
       uint64_t len);
   void dmu_tx_hold_free_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off,
       uint64_t len);
   void dmu_tx_hold_zap(dmu_tx_t *tx, uint64_t object, int add, const char *name);
   void dmu_tx_hold_zap_by_dnode(dmu_tx_t *tx, dnode_t *dn, int add,
       const char *name);
   void dmu_tx_hold_bonus(dmu_tx_t *tx, uint64_t object);
   void dmu_tx_hold_bonus_by_dnode(dmu_tx_t *tx, dnode_t *dn);
   void dmu_tx_hold_spill(dmu_tx_t *tx, uint64_t object);
   void dmu_tx_hold_sa(dmu_tx_t *tx, struct sa_handle *hdl, boolean_t may_grow);
   void dmu_tx_hold_sa_create(dmu_tx_t *tx, int total_size);
   void dmu_tx_abort(dmu_tx_t *tx);
   int dmu_tx_assign(dmu_tx_t *tx, uint64_t txg_how);
   void dmu_tx_wait(dmu_tx_t *tx);
   void dmu_tx_commit(dmu_tx_t *tx);
   void dmu_tx_mark_netfree(dmu_tx_t *tx);
   
   /*
    * To register a commit callback, dmu_tx_callback_register() must be called.
    *
    * dcb_data is a pointer to caller private data that is passed on as a
    * callback parameter. The caller is responsible for properly allocating and
    * freeing it.
    *
    * When registering a callback, the transaction must be already created, but
    * it cannot be committed or aborted. It can be assigned to a txg or not.
    *
    * The callback will be called after the transaction has been safely written
    * to stable storage and will also be called if the dmu_tx is aborted.
    * If there is any error which prevents the transaction from being committed to
    * disk, the callback will be called with a value of error != 0.
    *
    * When multiple callbacks are registered to the transaction, the callbacks
    * will be called in reverse order to let Lustre, the only user of commit
    * callback currently, take the fast path of its commit callback handling.
    */
   typedef void dmu_tx_callback_func_t(void *dcb_data, int error);
   
   void dmu_tx_callback_register(dmu_tx_t *tx, dmu_tx_callback_func_t *dcb_func,
       void *dcb_data);
   void dmu_tx_do_callbacks(list_t *cb_list, int error);
   
   /*
    * Free up the data blocks for a defined range of a file.  If size is
    * -1, the range from offset to end-of-file is freed.
    */
   int dmu_free_range(objset_t *os, uint64_t object, uint64_t offset,
       uint64_t size, dmu_tx_t *tx);
   int dmu_free_long_range(objset_t *os, uint64_t object, uint64_t offset,
       uint64_t size);
   int dmu_free_long_object(objset_t *os, uint64_t object);
   
   /*
    * Convenience functions.
    *
    * Canfail routines will return 0 on success, or an errno if there is a
    * nonrecoverable I/O error.
    */
   #define DMU_READ_PREFETCH       0 /* prefetch */
   #define DMU_READ_NO_PREFETCH    1 /* don't prefetch */
   #define DMU_READ_NO_DECRYPT     2 /* don't decrypt */
   int dmu_read(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
           void *buf, uint32_t flags);
   int dmu_read_by_dnode(dnode_t *dn, uint64_t offset, uint64_t size, void *buf,
       uint32_t flags);
   void dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
           const void *buf, dmu_tx_t *tx);
   void dmu_write_by_dnode(dnode_t *dn, uint64_t offset, uint64_t size,
       const void *buf, dmu_tx_t *tx);
   void dmu_prealloc(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
           dmu_tx_t *tx);
   #ifdef _KERNEL
   int dmu_read_uio(objset_t *os, uint64_t object, zfs_uio_t *uio, uint64_t size);
   int dmu_read_uio_dbuf(dmu_buf_t *zdb, zfs_uio_t *uio, uint64_t size);
   int dmu_read_uio_dnode(dnode_t *dn, zfs_uio_t *uio, uint64_t size);
   int dmu_write_uio(objset_t *os, uint64_t object, zfs_uio_t *uio, uint64_t size,
           dmu_tx_t *tx);
   int dmu_write_uio_dbuf(dmu_buf_t *zdb, zfs_uio_t *uio, uint64_t size,
           dmu_tx_t *tx);
   int dmu_write_uio_dnode(dnode_t *dn, zfs_uio_t *uio, uint64_t size,
           dmu_tx_t *tx);
   #endif
   struct arc_buf *dmu_request_arcbuf(dmu_buf_t *handle, int size);
   void dmu_return_arcbuf(struct arc_buf *buf);
   int dmu_assign_arcbuf_by_dnode(dnode_t *dn, uint64_t offset,
       struct arc_buf *buf, dmu_tx_t *tx);
   int dmu_assign_arcbuf_by_dbuf(dmu_buf_t *handle, uint64_t offset,
       struct arc_buf *buf, dmu_tx_t *tx);
   #define dmu_assign_arcbuf       dmu_assign_arcbuf_by_dbuf
   extern uint_t zfs_max_recordsize;
   
   /*
    * Asynchronously try to read in the data.
    */
   void dmu_prefetch(objset_t *os, uint64_t object, int64_t level, uint64_t offset,
           uint64_t len, enum zio_priority pri);
   
   typedef struct dmu_object_info {
           /* All sizes are in bytes unless otherwise indicated. */
           uint32_t doi_data_block_size;
           uint32_t doi_metadata_block_size;
           dmu_object_type_t doi_type;
           dmu_object_type_t doi_bonus_type;
           uint64_t doi_bonus_size;
           uint8_t doi_indirection;                /* 2 = dnode->indirect->data */
           uint8_t doi_checksum;
           uint8_t doi_compress;
           uint8_t doi_nblkptr;
           uint8_t doi_pad[4];
           uint64_t doi_dnodesize;
           uint64_t doi_physical_blocks_512;       /* data + metadata, 512b blks */
           uint64_t doi_max_offset;
           uint64_t doi_fill_count;                /* number of non-empty blocks */
   } dmu_object_info_t;
   
   typedef void (*const arc_byteswap_func_t)(void *buf, size_t size);
   
   typedef struct dmu_object_type_info {
           dmu_object_byteswap_t   ot_byteswap;
           boolean_t               ot_metadata;
           boolean_t               ot_dbuf_metadata_cache;
           boolean_t               ot_encrypt;
           const char              *ot_name;
   } dmu_object_type_info_t;
   
   typedef const struct dmu_object_byteswap_info {
           arc_byteswap_func_t      ob_func;
           const char              *ob_name;
   } dmu_object_byteswap_info_t;
   
   extern const dmu_object_type_info_t dmu_ot[DMU_OT_NUMTYPES];
   extern dmu_object_byteswap_info_t dmu_ot_byteswap[DMU_BSWAP_NUMFUNCS];
   
   /*
    * Get information on a DMU object.
    *
    * Return 0 on success or ENOENT if object is not allocated.
    *
    * 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);
   void __dmu_object_info_from_dnode(struct dnode *dn, dmu_object_info_t *doi);
   /* Like dmu_object_info, but faster if you have a held dnode in hand. */
   void dmu_object_info_from_dnode(dnode_t *dn, dmu_object_info_t *doi);
   /* Like dmu_object_info, but faster if you have a held dbuf in hand. */
   void dmu_object_info_from_db(dmu_buf_t *db, dmu_object_info_t *doi);
   /*
    * Like dmu_object_info_from_db, but faster still when you only care about
    * the size.
    */
   void dmu_object_size_from_db(dmu_buf_t *db, uint32_t *blksize,
       u_longlong_t *nblk512);
   
   void dmu_object_dnsize_from_db(dmu_buf_t *db, int *dnsize);
   
   typedef struct dmu_objset_stats {
           uint64_t dds_num_clones; /* number of clones of this */
           uint64_t dds_creation_txg;
           uint64_t dds_guid;
           dmu_objset_type_t dds_type;
           uint8_t dds_is_snapshot;
           uint8_t dds_inconsistent;
           uint8_t dds_redacted;
           char dds_origin[ZFS_MAX_DATASET_NAME_LEN];
   } dmu_objset_stats_t;
   
   /*
    * Get stats on a dataset.
    */
   void dmu_objset_fast_stat(objset_t *os, dmu_objset_stats_t *stat);
   
   /*
    * Add entries to the nvlist for all the objset's properties.  See
    * zfs_prop_table[] and zfs(1m) for details on the properties.
    */
   void dmu_objset_stats(objset_t *os, struct nvlist *nv);
   
   /*
    * Get the space usage statistics for statvfs().
    *
    * refdbytes is the amount of space "referenced" by this objset.
    * availbytes is the amount of space available to this objset, taking
    * into account quotas & reservations, assuming that no other objsets
    * use the space first.  These values correspond to the 'referenced' and
    * 'available' properties, described in the zfs(1m) manpage.
    *
    * usedobjs and availobjs are the number of objects currently allocated,
    * and available.
    */
   void dmu_objset_space(objset_t *os, uint64_t *refdbytesp, uint64_t *availbytesp,
       uint64_t *usedobjsp, uint64_t *availobjsp);
   
   /*
    * The fsid_guid is a 56-bit ID that can change to avoid collisions.
    * (Contrast with the ds_guid which is a 64-bit ID that will never
    * change, so there is a small probability that it will collide.)
    */
   uint64_t dmu_objset_fsid_guid(objset_t *os);
   
   /*
    * Get the [cm]time for an objset's snapshot dir
    */
   inode_timespec_t dmu_objset_snap_cmtime(objset_t *os);
   
   int dmu_objset_is_snapshot(objset_t *os);
   
   extern struct spa *dmu_objset_spa(objset_t *os);
   extern struct zilog *dmu_objset_zil(objset_t *os);
   extern struct dsl_pool *dmu_objset_pool(objset_t *os);
   extern struct dsl_dataset *dmu_objset_ds(objset_t *os);
   extern void dmu_objset_name(objset_t *os, char *buf);
   extern dmu_objset_type_t dmu_objset_type(objset_t *os);
   extern uint64_t dmu_objset_id(objset_t *os);
   extern uint64_t dmu_objset_dnodesize(objset_t *os);
  extern zfs_sync_type_t dmu_objset_syncprop(objset_t *os);
  extern zfs_logbias_op_t dmu_objset_logbias(objset_t *os);
  extern int dmu_objset_blksize(objset_t *os);
  extern int dmu_snapshot_list_next(objset_t *os, int namelen, char *name,
      uint64_t *id, uint64_t *offp, boolean_t *case_conflict);
  extern int dmu_snapshot_lookup(objset_t *os, const char *name, uint64_t *val);
  extern int dmu_snapshot_realname(objset_t *os, const char *name, char *real,
      int maxlen, boolean_t *conflict);
  extern int dmu_dir_list_next(objset_t *os, int namelen, char *name,
      uint64_t *idp, uint64_t *offp);
  
  typedef struct zfs_file_info {
          uint64_t zfi_user;
          uint64_t zfi_group;
          uint64_t zfi_project;
          uint64_t zfi_generation;
  } zfs_file_info_t;
  
  typedef int file_info_cb_t(dmu_object_type_t bonustype, const void *data,
      struct zfs_file_info *zoi);
  extern void dmu_objset_register_type(dmu_objset_type_t ost,
      file_info_cb_t *cb);
  extern void dmu_objset_set_user(objset_t *os, void *user_ptr);
  extern void *dmu_objset_get_user(objset_t *os);
  
  /*
   * Return the txg number for the given assigned transaction.
   */
  uint64_t dmu_tx_get_txg(dmu_tx_t *tx);
  
  /*
   * Synchronous write.
   * If a parent zio is provided this function initiates a write on the
   * provided buffer as a child of the parent zio.
   * In the absence of a parent zio, the write is completed synchronously.
   * At write completion, blk is filled with the bp of the written block.
   * Note that while the data covered by this function will be on stable
   * storage when the write completes this new data does not become a
   * permanent part of the file until the associated transaction commits.
   */
  
  /*
   * {zfs,zvol,ztest}_get_done() args
   */
  typedef struct zgd {
          struct lwb      *zgd_lwb;
          struct blkptr   *zgd_bp;
          dmu_buf_t       *zgd_db;
          struct zfs_locked_range *zgd_lr;
          void            *zgd_private;
  } zgd_t;
  
  typedef void dmu_sync_cb_t(zgd_t *arg, int error);
  int dmu_sync(struct zio *zio, uint64_t txg, dmu_sync_cb_t *done, zgd_t *zgd);
  
  /*
   * Find the next hole or data block in file starting at *off
   * Return found offset in *off. Return ESRCH for end of file.
   */
  int dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole,
      uint64_t *off);
  
  /*
   * Initial setup and final teardown.
   */
  extern void dmu_init(void);
  extern void dmu_fini(void);
  
  typedef void (*dmu_traverse_cb_t)(objset_t *os, void *arg, struct blkptr *bp,
      uint64_t object, uint64_t offset, int len);
  void dmu_traverse_objset(objset_t *os, uint64_t txg_start,
      dmu_traverse_cb_t cb, void *arg);
  
  int dmu_diff(const char *tosnap_name, const char *fromsnap_name,
      zfs_file_t *fp, offset_t *offp);
  
  /* CRC64 table */
  #define ZFS_CRC64_POLY  0xC96C5795D7870F42ULL   /* ECMA-182, reflected form */
  extern uint64_t zfs_crc64_table[256];
  
  extern uint_t dmu_prefetch_max;
  
  #ifdef  __cplusplus
  }
  #endif
  
  #endif  /* _SYS_DMU_H */

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