WL#1339 "Add per account max_user_connections limit (maximum number

of concurrent connections for the same account)"

Added support of account specific max_user_connections limit. Made all
user limits to be counted per account instead of the old behavior,
which was per user/host accounting. Added option which enables the old
behavior. Added testing of these to the test suite.

(After review version).


client/mysqltest.c:
  Extended mysqltest to be able to handle connect() statements for which
  error is expected.
  
  - Added replace_dynstr_append() utility function.
  - added connect_n_handle_errors() function which connects with server
    without retries and handles errors as if "connect" was usual
    statement.
  - do_connect(): added ability to handle connects which are expected
    to return an error.
  - run_query_normal(): Moved all expected-error-handling code to separate
    normal_handle_error()/normal_handle_no_error() functions to be able
    to reuse them in connect_n_handle_errors().
mysql-test/r/grant.result:
  Fixed test results since one more column to mysql.user was added.
mysql-test/r/system_mysql_db.result:
  Fixed test results since one more column to mysql.user was added.
scripts/mysql_create_system_tables.sh:
  Added max_user_connections column to mysql.user table for storing
  new maximal concurrent connections per account limit.
scripts/mysql_fix_privilege_tables.sql:
  Added max_user_connections column to mysql.user table for storing
  new maximal concurrent connections per account limit.
sql/lex.h:
  Added MAX_USER_CONNECTIONS symbol used for specifying
  maximum number of concurrent connections per account.
sql/mysql_priv.h:
  Added declaration of opt_old_style_user_limits variable which is defined
  in sql/mysqld.cc used in sql/sql_parse.cc.
sql/mysqld.cc:
  Added "old-style-user-limits" option which forces user limits to behave
  in old way i.e. to be counted per user/host pair instead of per account.
  Added comment describing mqh_used variable.
sql/set_var.cc:
  Added sys_var_max_user_conn class which implements support for the new 
  behavior of max_user_connections variable. Now the global instance of
  this variable holds default maximum number of concurrent connections per
  account (as it was before) and the session instance gives read-only
  access to account-specific version of this limit.
sql/set_var.h:
  Added sys_var_max_user_conn class which implements support for the new 
  behavior of max_user_connections variable. Now the global instance of
  this variable holds default maximum number of concurrent connections per
  account (as it was before) and the session instance gives read-only
  access to account-specific version of this limit.
sql/sql_acl.cc:
  Added support for account-specific MAX_USER_CONNECTIONS limit.
  Tweaked USER_RESOURCES and their handling for better clarity.
sql/sql_parse.cc:
  Added support for account-specific MAX_USER_CONNECTIONS (maximum number
  of concurrent connections per account) limit. Changed default behavior
  of all user limits to be per account instead of per user+host.
  '--old-style-user-limits' option was added to enable the old behavior.
  Made maximum number of connections per hour to be independant on the
  value of global max_user_connections variable.
sql/sql_yacc.yy:
  Added support of new MAX_USER_CONNECTIONS limit to grammar.
  Renamed USER_RESOURCES::connections member to conn_per_hour and bits
  member to specified_limits. Also enum is used instead of naked numbers
  when we are working with specified_limits.
sql/structs.h:
  USER_RESOURCES struct:
   - Added user_conn member to store the maximum number of concurrent 
     connections for an account. Renamed connections member to 
     conn_per_hour for less ambiguity.
   - Renamed member 'bits' to 'specified_limits' for the sake of clarity.
     The member was used as a flag indicating which limits were mentioned
     in GRANT clause.
   - Added comments.
  USER_CONN struct:
   - Removed unused user_len member.
   - Added comments.

sql/sql_parse.cc

@@ -172,14 +172,10 @@ static int get_or_create_user_conn(THD *thd, const char *user,
     }
     uc->user=(char*) (uc+1);
     memcpy(uc->user,temp_user,temp_len+1);
-    uc->user_len= user_len;
-    uc->host=uc->user + uc->user_len +  1;
+    uc->host= uc->user + user_len +  1;
     uc->len = temp_len;
-    uc->connections = 1;
-    uc->questions=uc->updates=uc->conn_per_hour=0;
+    uc->connections= uc->questions= uc->updates= uc->conn_per_hour= 0;
     uc->user_resources=*mqh;
-    if (max_user_connections && mqh->connections > max_user_connections)
-      uc->user_resources.connections = max_user_connections;
     uc->intime=thd->thr_create_time;
     if (my_hash_insert(&hash_user_connections, (byte*) uc))
     {
@@ -352,12 +348,16 @@ int check_user(THD *thd, enum enum_server_command command,
       thd->db_access=0;
 
       /* Don't allow user to connect if he has done too many queries */
-      if ((ur.questions || ur.updates || ur.connections ||
+      if ((ur.questions || ur.updates || ur.conn_per_hour || ur.user_conn ||
 	   max_user_connections) &&
-	  get_or_create_user_conn(thd,thd->user,thd->host_or_ip,&ur))
+	  get_or_create_user_conn(thd,
+            opt_old_style_user_limits ? thd->user : thd->priv_user,
+            opt_old_style_user_limits ? thd->host_or_ip : thd->priv_host,
+            &ur))
 	DBUG_RETURN(-1);
       if (thd->user_connect &&
-	  (thd->user_connect->user_resources.connections ||
+	  (thd->user_connect->user_resources.conn_per_hour ||
+	   thd->user_connect->user_resources.user_conn ||
 	   max_user_connections) &&
 	  check_for_max_user_connections(thd, thd->user_connect))
 	DBUG_RETURN(-1);
@@ -448,19 +448,28 @@ static int check_for_max_user_connections(THD *thd, USER_CONN *uc)
   DBUG_ENTER("check_for_max_user_connections");
 
   (void) pthread_mutex_lock(&LOCK_user_conn);
-  if (max_user_connections &&
+  if (max_user_connections && !uc->user_resources.user_conn &&
       max_user_connections < (uint) uc->connections)
   {
     net_printf_error(thd, ER_TOO_MANY_USER_CONNECTIONS, uc->user);
     error=1;
     goto end;
   }
-  if (uc->user_resources.connections &&
-      uc->user_resources.connections <= uc->conn_per_hour)
+  if (uc->user_resources.user_conn &&
+      uc->user_resources.user_conn < uc->connections)
+  {
+    net_printf_error(thd, ER_USER_LIMIT_REACHED, uc->user,
+                     "max_user_connections",
+                     (long) uc->user_resources.user_conn);
+    error= 1;
+    goto end;
+  }
+  if (uc->user_resources.conn_per_hour &&
+      uc->user_resources.conn_per_hour <= uc->conn_per_hour)
   {
     net_printf_error(thd, ER_USER_LIMIT_REACHED, uc->user,
                      "max_connections",
-                     (long) uc->user_resources.connections);
+                     (long) uc->user_resources.conn_per_hour);
     error=1;
     goto end;
   }
@@ -3507,7 +3516,7 @@ create_error:
 	  Query_log_event qinfo(thd, thd->query, thd->query_length, 0);
 	  mysql_bin_log.write(&qinfo);
 	}
-	if (mqh_used && lex->sql_command == SQLCOM_GRANT)
+	if (lex->sql_command == SQLCOM_GRANT)
 	{
 	  List_iterator <LEX_USER> str_list(lex->users_list);
 	  LEX_USER *user;
@@ -5682,8 +5691,7 @@ bool reload_acl_and_cache(THD *thd, ulong options, TABLE_LIST *tables,
   {
     acl_reload(thd);
     grant_reload(thd);
-    if (mqh_used)
-      reset_mqh(thd,(LEX_USER *) NULL,TRUE);
+    reset_mqh(thd, (LEX_USER *) NULL, TRUE);
   }
 #endif
   if (options & REFRESH_LOG)