Fix for BUG#4544 "read_only also affects temporary tables":

the READ_ONLY global variable now allows statements which are to update only temporary tables
(note: if a statement, after parse stage, looks like it will update a non-temp table, it will be rejected,
even if at execution it would have turned out that 0 rows would be updated; for example
UPDATE my_non_tem_table SET a=1 WHERE 1 = 0; will be rejected).


sql/sql_parse.cc:
  The READ_ONLY global variable now allows statements which are to update only temporary tables
  (note: if a statement, after parse stage, looks like it will update a non-temp table, it will be rejected,
  even if at execution it would have turned out that 0 rows would be updated; for example
  UPDATE my_non_tem_table SET a=1 WHERE 1 = 0; will be rejected).
mysql-test/r/read_only.result:
  result for new test
mysql-test/t/read_only.test:
  test for READ_ONLY (there was none!) and for the new behaviour of READ_ONLY

mysql-test/r/read_only.result

+DROP TABLE IF EXISTS t1,t2,t3;
+grant CREATE, SELECT, DROP on *.* to test@localhost;
+set global read_only=0;
+create table t1 (a int);
+insert into t1 values(1);
+create table t2 select * from t1;
+set global read_only=1;
+create table t3 (a int);
+drop table t3;
+select @@global.read_only;
+@@global.read_only
+1
+create table t3 (a int);
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+insert into t1 values(1);
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+update t1,t2 set t1.a=t2.a+1 where t1.a=t2.a;
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+delete t1,t2 from t1,t2 where t1.a=t2.a;
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+create temporary table t3 (a int);
+create temporary table t4 (a int) select * from t3;
+insert into t3 values(1);
+insert into t4 select * from t3;
+update t1,t3 set t1.a=t3.a+1 where t1.a=t3.a;
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+update t1,t3 set t3.a=t1.a+1 where t1.a=t3.a;
+update t4,t3 set t4.a=t3.a+1 where t4.a=t3.a;
+delete t1 from t1,t3 where t1.a=t3.a;
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+delete t3 from t1,t3 where t1.a=t3.a;
+delete t4 from t3,t4 where t4.a=t3.a;
+create temporary table t1 (a int);
+insert into t1 values(1);
+update t1,t3 set t1.a=t3.a+1 where t1.a=t3.a;
+delete t1 from t1,t3 where t1.a=t3.a;
+drop table t1;
+insert into t1 values(1);
+ERROR HY000: The MySQL server is running with the --read-only option so it cannot execute this statement
+drop table t1,t2;
+drop user test@localhost;

mysql-test/t/read_only.test

+# Test of the READ_ONLY global variable:
+# check that it blocks updates unless they are only on temporary tables.
+
+--disable_warnings
+DROP TABLE IF EXISTS t1,t2,t3;
+--enable_warnings
+
+# READ_ONLY does nothing to SUPER users
+# so we use a non-SUPER one:
+
+grant CREATE, SELECT, DROP on *.* to test@localhost;
+
+connect (con1,localhost,test,,test);
+
+connection default;
+
+set global read_only=0;
+
+connection con1;
+
+create table t1 (a int);
+
+insert into t1 values(1);
+
+create table t2 select * from t1;
+
+connection default;
+
+set global read_only=1;
+
+# We check that SUPER can:
+
+create table t3 (a int);
+drop table t3;
+
+connection con1;
+
+select @@global.read_only;
+
+--error 1290
+create table t3 (a int);
+
+--error 1290
+insert into t1 values(1);
+
+# if a statement, after parse stage, looks like it will update a
+# non-temp table, it will be rejected, even if at execution it would
+# have turned out that 0 rows would be updated
+--error 1290
+update t1 set a=1 where 1=0;
+
+# multi-update is special (see sql_parse.cc) so we test it
+--error 1290
+update t1,t2 set t1.a=t2.a+1 where t1.a=t2.a;
+
+# check multi-delete to be sure
+--error 1290
+delete t1,t2 from t1,t2 where t1.a=t2.a;
+
+# With temp tables updates should be accepted:
+
+create temporary table t3 (a int);
+
+create temporary table t4 (a int) select * from t3;
+
+insert into t3 values(1);
+
+insert into t4 select * from t3;
+
+# a non-temp table updated:
+--error 1290
+update t1,t3 set t1.a=t3.a+1 where t1.a=t3.a;
+
+# no non-temp table updated (just swapped):
+update t1,t3 set t3.a=t1.a+1 where t1.a=t3.a;
+
+update t4,t3 set t4.a=t3.a+1 where t4.a=t3.a;
+
+--error 1290
+delete t1 from t1,t3 where t1.a=t3.a;
+
+delete t3 from t1,t3 where t1.a=t3.a;
+
+delete t4 from t3,t4 where t4.a=t3.a;
+
+# and even homonymous ones
+
+create temporary table t1 (a int);
+
+insert into t1 values(1);
+
+update t1,t3 set t1.a=t3.a+1 where t1.a=t3.a;
+
+delete t1 from t1,t3 where t1.a=t3.a;
+
+drop table t1;
+
+--error 1290
+insert into t1 values(1);
+
+connection default;
+drop table t1,t2;
+drop user test@localhost;

sql/sql_parse.cc

@@ -194,6 +194,18 @@ inline bool all_tables_not_ok(THD *thd, TABLE_LIST *tables)
 #endif
 
 
+static bool some_non_temp_table_to_be_updated(THD *thd, TABLE_LIST *tables)
+{
+  for (TABLE_LIST *table= tables; table; table= table->next_global)
+  {
+    DBUG_ASSERT(table->db && table->table_name);
+    if (table->updating &&
+        !find_temporary_table(thd, table->db, table->table_name))
+      return 1;
+  }
+  return 0;
+}
+
 static HASH hash_user_connections;
 
 static int get_or_create_user_conn(THD *thd, const char *user,
@@ -2363,7 +2375,7 @@ mysql_execute_command(THD *thd)
     mysql_reset_errors(thd, 0);
 
 #ifdef HAVE_REPLICATION
-  if (thd->slave_thread)
+  if (unlikely(thd->slave_thread))
   {
     /*
       Check if statment should be skipped because of slave filtering
@@ -2402,16 +2414,20 @@ mysql_execute_command(THD *thd)
     }
 #endif
   }
+  else
 #endif /* HAVE_REPLICATION */
 
   /*
-    When option readonly is set deny operations which change tables.
-    Except for the replication thread and the 'super' users.
+    When option readonly is set deny operations which change non-temporary
+    tables. Except for the replication thread and the 'super' users.
   */
   if (opt_readonly &&
-      !(thd->slave_thread ||
-        (thd->security_ctx->master_access & SUPER_ACL)) &&
-      uc_update_queries[lex->sql_command])
+      !(thd->security_ctx->master_access & SUPER_ACL) &&
+      uc_update_queries[lex->sql_command] &&
+      !((lex->sql_command == SQLCOM_CREATE_TABLE) &&
+        (lex->create_info.options & HA_LEX_CREATE_TMP_TABLE)) &&
+      ((lex->sql_command != SQLCOM_UPDATE_MULTI) &&
+       some_non_temp_table_to_be_updated(thd, all_tables)))
   {
     my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--read-only");
     DBUG_RETURN(-1);
@@ -3210,13 +3226,24 @@ mysql_execute_command(THD *thd)
 
 #ifdef HAVE_REPLICATION
     /* Check slave filtering rules */
-    if (thd->slave_thread && all_tables_not_ok(thd, all_tables))
+    if (unlikely(thd->slave_thread))
+    {
+      if (all_tables_not_ok(thd, all_tables))
       {
         /* we warn the slave SQL thread */
         my_error(ER_SLAVE_IGNORED_TABLE, MYF(0));
         break;
       }
+    }
+    else
 #endif /* HAVE_REPLICATION */
+    if (opt_readonly &&
+        !(thd->security_ctx->master_access & SUPER_ACL) &&
+        some_non_temp_table_to_be_updated(thd, all_tables))
+    {
+      my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--read-only");
+      break;
+    }
 
     res= mysql_multi_update(thd, all_tables,
                             &select_lex->item_list,