MDEV-12776 Do not create the InnoDB temporary tablespace in innodb_read_only mode

The InnoDB temporary tablespace is only usable if innodb_read_only=OFF.
It is useless to create the tablespace in read-only mode, because
CREATE TEMPORARY TABLE is disallowed if innodb_read_only, and nothing
can we written to the temporary tablespace if no temporary tables
can be created.

mysql-test/suite/innodb/r/temporary_table.result

@@ -130,7 +130,6 @@ ERROR HY000: The table 't1' is full
 drop procedure populate_t1;
 # test read-only mode
 # files in MYSQL_DATA_DIR
-ibtmp1
 select * from t1;
 ERROR 42S02: Table 'test.t1' doesn't exist
 show tables;

storage/innobase/srv/srv0start.cc

@@ -2475,14 +2475,6 @@ files_checked:
 	ut_ad(err == DB_SUCCESS);
 	ut_a(sum_of_new_sizes != ULINT_UNDEFINED);
 
-	/* Open temp-tablespace and keep it open until shutdown. */
-
-	err = srv_open_tmp_tablespace(create_new_db);
-
-	if (err != DB_SUCCESS) {
-		return(srv_init_abort(err));
-	}
-
 	/* Create the doublewrite buffer to a new tablespace */
 	if (!srv_read_only_mode && srv_force_recovery < SRV_FORCE_NO_TRX_UNDO
 	    && !buf_dblwr_create()) {
@@ -2557,6 +2549,18 @@ files_checked:
 		return(srv_init_abort(err));
 	}
 
+	if (!srv_read_only_mode) {
+		/* Initialize the innodb_temporary tablespace and keep
+		it open until shutdown. */
+		err = srv_open_tmp_tablespace(create_new_db);
+
+		if (err != DB_SUCCESS) {
+			return(srv_init_abort(err));
+		}
+
+		trx_temp_rseg_create();
+	}
+
 	srv_is_being_started = false;
 
 	ut_a(trx_purge_state() == PURGE_STATE_INIT);

storage/innobase/trx/trx0sys.cc

@@ -887,9 +887,6 @@ trx_sys_create_rsegs()
 		return(true);
 	}
 
-	/* Create temporary rollback segments. */
-	trx_temp_rseg_create();
-
 	/* This is executed in single-threaded mode therefore it is not
 	necessary to use the same mtr in trx_rseg_create(). n_used cannot
 	change while the function is executing. */