Function dbuf_hold_impl

freebsd/contrib/openzfs/module/zfs/dbuf.c:3393–3498

* Returns with db_holds incremented, and db_mtx not held. * Note: dn_struct_rwlock must be held. */

 * Note: dn_struct_rwlock must be held.
 */
int
dbuf_hold_impl(dnode_t *dn, uint8_t level, uint64_t blkid,
    boolean_t fail_sparse, boolean_t fail_uncached,
    void *tag, dmu_buf_impl_t **dbp)
{
	dmu_buf_impl_t *db, *parent = NULL;

	/* If the pool has been created, verify the tx_sync_lock is not held */
	spa_t *spa = dn->dn_objset->os_spa;
	dsl_pool_t *dp = spa->spa_dsl_pool;
	if (dp != NULL) {
		ASSERT(!MUTEX_HELD(&dp->dp_tx.tx_sync_lock));
	}

	ASSERT(blkid != DMU_BONUS_BLKID);
	ASSERT(RW_LOCK_HELD(&dn->dn_struct_rwlock));
	ASSERT3U(dn->dn_nlevels, >, level);

	*dbp = NULL;

	/* dbuf_find() returns with db_mtx held */
	db = dbuf_find(dn->dn_objset, dn->dn_object, level, blkid);

	if (db == NULL) {
		blkptr_t *bp = NULL;
		int err;

		if (fail_uncached)
			return (SET_ERROR(ENOENT));

		ASSERT3P(parent, ==, NULL);
		err = dbuf_findbp(dn, level, blkid, fail_sparse, &parent, &bp);
		if (fail_sparse) {
			if (err == 0 && bp && BP_IS_HOLE(bp))
				err = SET_ERROR(ENOENT);
			if (err) {
				if (parent)
					dbuf_rele(parent, NULL);
				return (err);
			}
		}
		if (err && err != ENOENT)
			return (err);
		db = dbuf_create(dn, level, blkid, parent, bp);
	}

	if (fail_uncached && db->db_state != DB_CACHED) {
		mutex_exit(&db->db_mtx);
		return (SET_ERROR(ENOENT));
	}

	if (db->db_buf != NULL) {
		arc_buf_access(db->db_buf);
		ASSERT3P(db->db.db_data, ==, db->db_buf->b_data);
	}

	ASSERT(db->db_buf == NULL || arc_referenced(db->db_buf));