Revert Consolidate arc_buf allocation checks

This reverts commit 13fac09868.

Per the discussion in #11531, the reverted commit---which intended only
to be a cleanup commit---introduced a subtle, unintended change in
behavior.

Care was taken to partially revert and then reapply 10b3c7f5e4
which would otherwise have caused a conflict.  These changes were
squashed in to this commit.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Suggested-by: @chrisrd
Suggested-by: robn@despairlabs.com
Signed-off-by: Antonio Russo <aerusso@aerusso.net>
Closes #11531 
Closes #12227

module/zfs/dbuf.c

@@ -1152,42 +1152,6 @@ dbuf_set_data(dmu_buf_impl_t *db, arc_buf_t *buf)
 	db->db.db_data = buf->b_data;
 }
 
-static arc_buf_t *
-dbuf_alloc_arcbuf_from_arcbuf(dmu_buf_impl_t *db, arc_buf_t *data)
-{
-	objset_t *os = db->db_objset;
-	spa_t *spa = os->os_spa;
-	arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
-	enum zio_compress compress_type;
-	uint8_t complevel;
-	int psize, lsize;
-
-	psize = arc_buf_size(data);
-	lsize = arc_buf_lsize(data);
-	compress_type = arc_get_compression(data);
-	complevel = arc_get_complevel(data);
-
-	if (arc_is_encrypted(data)) {
-		boolean_t byteorder;
-		uint8_t salt[ZIO_DATA_SALT_LEN];
-		uint8_t iv[ZIO_DATA_IV_LEN];
-		uint8_t mac[ZIO_DATA_MAC_LEN];
-		dnode_t *dn = DB_DNODE(db);
-
-		arc_get_raw_params(data, &byteorder, salt, iv, mac);
-		data = arc_alloc_raw_buf(spa, db, dmu_objset_id(os),
-		    byteorder, salt, iv, mac, dn->dn_type, psize, lsize,
-		    compress_type, complevel);
-	} else if (compress_type != ZIO_COMPRESS_OFF) {
-		ASSERT3U(type, ==, ARC_BUFC_DATA);
-		data = arc_alloc_compressed_buf(spa, db,
-		    psize, lsize, compress_type, complevel);
-	} else {
-		data = arc_alloc_buf(spa, db, type, psize);
-	}
-	return (data);
-}
-
 static arc_buf_t *
 dbuf_alloc_arcbuf(dmu_buf_impl_t *db)
 {
@@ -1637,9 +1601,35 @@ dbuf_fix_old_data(dmu_buf_impl_t *db, uint64_t txg)
 		arc_space_consume(bonuslen, ARC_SPACE_BONUS);
 		bcopy(db->db.db_data, dr->dt.dl.dr_data, bonuslen);
 	} else if (zfs_refcount_count(&db->db_holds) > db->db_dirtycnt) {
-		arc_buf_t *buf = dbuf_alloc_arcbuf_from_arcbuf(db, db->db_buf);
+		dnode_t *dn = DB_DNODE(db);
-		dr->dt.dl.dr_data = buf;
+		int size = arc_buf_size(db->db_buf);
-		bcopy(db->db.db_data, buf->b_data, arc_buf_size(buf));
+		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
+		spa_t *spa = db->db_objset->os_spa;
+		enum zio_compress compress_type =
+		    arc_get_compression(db->db_buf);
+		uint8_t complevel = arc_get_complevel(db->db_buf);
+
+		if (arc_is_encrypted(db->db_buf)) {
+			boolean_t byteorder;
+			uint8_t salt[ZIO_DATA_SALT_LEN];
+			uint8_t iv[ZIO_DATA_IV_LEN];
+			uint8_t mac[ZIO_DATA_MAC_LEN];
+
+			arc_get_raw_params(db->db_buf, &byteorder, salt,
+			    iv, mac);
+			dr->dt.dl.dr_data = arc_alloc_raw_buf(spa, db,
+			    dmu_objset_id(dn->dn_objset), byteorder, salt, iv,
+			    mac, dn->dn_type, size, arc_buf_lsize(db->db_buf),
+			    compress_type, complevel);
+		} else if (compress_type != ZIO_COMPRESS_OFF) {
+			ASSERT3U(type, ==, ARC_BUFC_DATA);
+			dr->dt.dl.dr_data = arc_alloc_compressed_buf(spa, db,
+			    size, arc_buf_lsize(db->db_buf), compress_type,
+			    complevel);
+		} else {
+			dr->dt.dl.dr_data = arc_alloc_buf(spa, db, type, size);
+		}
+		bcopy(db->db.db_data, dr->dt.dl.dr_data->b_data, size);
 	} else {
 		db->db_buf = NULL;
 		dbuf_clear_data(db);
@@ -3440,10 +3430,30 @@ noinline static void
 dbuf_hold_copy(dnode_t *dn, dmu_buf_impl_t *db)
 {
 	dbuf_dirty_record_t *dr = db->db_data_pending;
-	arc_buf_t *newdata, *data = dr->dt.dl.dr_data;
+	arc_buf_t *data = dr->dt.dl.dr_data;
+	enum zio_compress compress_type = arc_get_compression(data);
+	uint8_t complevel = arc_get_complevel(data);
+
+	if (arc_is_encrypted(data)) {
+		boolean_t byteorder;
+		uint8_t salt[ZIO_DATA_SALT_LEN];
+		uint8_t iv[ZIO_DATA_IV_LEN];
+		uint8_t mac[ZIO_DATA_MAC_LEN];
+
+		arc_get_raw_params(data, &byteorder, salt, iv, mac);
+		dbuf_set_data(db, arc_alloc_raw_buf(dn->dn_objset->os_spa, db,
+		    dmu_objset_id(dn->dn_objset), byteorder, salt, iv, mac,
+		    dn->dn_type, arc_buf_size(data), arc_buf_lsize(data),
+		    compress_type, complevel));
+	} else if (compress_type != ZIO_COMPRESS_OFF) {
+		dbuf_set_data(db, arc_alloc_compressed_buf(
+		    dn->dn_objset->os_spa, db, arc_buf_size(data),
+		    arc_buf_lsize(data), compress_type, complevel));
+	} else {
+		dbuf_set_data(db, arc_alloc_buf(dn->dn_objset->os_spa, db,
+		    DBUF_GET_BUFC_TYPE(db), db->db.db_size));
+	}
 
-	newdata = dbuf_alloc_arcbuf_from_arcbuf(db, data);
-	dbuf_set_data(db, newdata);
 	rw_enter(&db->db_rwlock, RW_WRITER);
 	bcopy(data->b_data, db->db.db_data, arc_buf_size(data));
 	rw_exit(&db->db_rwlock);
@@ -4365,8 +4375,31 @@ dbuf_sync_leaf(dbuf_dirty_record_t *dr, dmu_tx_t *tx)
 		 * objects only modified in the syncing context (e.g.
 		 * DNONE_DNODE blocks).
 		 */
-		*datap = dbuf_alloc_arcbuf_from_arcbuf(db, db->db_buf);
+		int psize = arc_buf_size(*datap);
-		bcopy(db->db.db_data, (*datap)->b_data, arc_buf_size(*datap));
+		int lsize = arc_buf_lsize(*datap);
+		arc_buf_contents_t type = DBUF_GET_BUFC_TYPE(db);
+		enum zio_compress compress_type = arc_get_compression(*datap);
+		uint8_t complevel = arc_get_complevel(*datap);
+
+		if (arc_is_encrypted(*datap)) {
+			boolean_t byteorder;
+			uint8_t salt[ZIO_DATA_SALT_LEN];
+			uint8_t iv[ZIO_DATA_IV_LEN];
+			uint8_t mac[ZIO_DATA_MAC_LEN];
+
+			arc_get_raw_params(*datap, &byteorder, salt, iv, mac);
+			*datap = arc_alloc_raw_buf(os->os_spa, db,
+			    dmu_objset_id(os), byteorder, salt, iv, mac,
+			    dn->dn_type, psize, lsize, compress_type,
+			    complevel);
+		} else if (compress_type != ZIO_COMPRESS_OFF) {
+			ASSERT3U(type, ==, ARC_BUFC_DATA);
+			*datap = arc_alloc_compressed_buf(os->os_spa, db,
+			    psize, lsize, compress_type, complevel);
+		} else {
+			*datap = arc_alloc_buf(os->os_spa, db, type, psize);
+		}
+		bcopy(db->db.db_data, (*datap)->b_data, psize);
 	}
 	db->db_data_pending = dr;