Function dbuf_read

freebsd/contrib/openzfs/module/zfs/dbuf.c:1587–1717

}

int
dbuf_read(dmu_buf_impl_t *db, zio_t *zio, uint32_t flags)
{
	int err = 0;
	boolean_t prefetch;
	dnode_t *dn;

	/*
	 * We don't have to hold the mutex to check db_state because it
	 * can't be freed while we have a hold on the buffer.
	 */
	ASSERT(!zfs_refcount_is_zero(&db->db_holds));

	if (db->db_state == DB_NOFILL)
		return (SET_ERROR(EIO));

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

	prefetch = db->db_level == 0 && db->db_blkid != DMU_BONUS_BLKID &&
	    (flags & DB_RF_NOPREFETCH) == 0 && dn != NULL &&
	    DBUF_IS_CACHEABLE(db);

	mutex_enter(&db->db_mtx);
	if (db->db_state == DB_CACHED) {
		spa_t *spa = dn->dn_objset->os_spa;

		/*
		 * Ensure that this block's dnode has been decrypted if
		 * the caller has requested decrypted data.
		 */
		err = dbuf_read_verify_dnode_crypt(db, flags);

		/*
		 * If the arc buf is compressed or encrypted and the caller
		 * requested uncompressed data, we need to untransform it
		 * before returning. We also call arc_untransform() on any
		 * unauthenticated blocks, which will verify their MAC if
		 * the key is now available.
		 */
		if (err == 0 && db->db_buf != NULL &&
		    (flags & DB_RF_NO_DECRYPT) == 0 &&
		    (arc_is_encrypted(db->db_buf) ||
		    arc_is_unauthenticated(db->db_buf) ||
		    arc_get_compression(db->db_buf) != ZIO_COMPRESS_OFF)) {
			zbookmark_phys_t zb;

			SET_BOOKMARK(&zb, dmu_objset_id(db->db_objset),
			    db->db.db_object, db->db_level, db->db_blkid);
			dbuf_fix_old_data(db, spa_syncing_txg(spa));
			err = arc_untransform(db->db_buf, spa, &zb, B_FALSE);
			dbuf_set_data(db, db->db_buf);
		}
		mutex_exit(&db->db_mtx);
		if (err == 0 && prefetch) {
			dmu_zfetch(&dn->dn_zfetch, db->db_blkid, 1, B_TRUE,
			    flags & DB_RF_HAVESTRUCT);
		}