Bug#31177: Server variables can't be set to their current values

Bounds-checks and blocksize corrections were applied to user-input,
but constants in the server were trusted implicitly. If these values
did not actually meet the requirements, the user could not set change
a variable, then set it back to the (wonky) factory default or maximum
by explicitly specifying it (SET <var>=<value> vs SET <var>=DEFAULT).

Now checks also apply to the server's presets. Wonky values and maxima
get corrected at startup. Consequently all non-offsetted values the user
sees are valid, and users can set the variable to that exact value if
they so desire.

mysql-test/r/read_buffer_size_basic.result

@@ -86,6 +86,8 @@ SELECT @@global.read_buffer_size= 8200 OR @@global.read_buffer_size= 8228 ;
 @@global.read_buffer_size= 8200 OR @@global.read_buffer_size= 8228
 1
 SET @@global.read_buffer_size = 2147479553;
+Warnings:
+Warning	1292	Truncated incorrect read_buffer_size value: '2147479553'
 SELECT @@global.read_buffer_size;
 @@global.read_buffer_size
 2147479552
@@ -114,6 +116,8 @@ SELECT @@session.read_buffer_size= 8200 OR @@session.read_buffer_size= 8228 ;
 SET @@session.read_buffer_size = 65530.34.;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.' at line 1
 SET @@session.read_buffer_size = 2147479553;
+Warnings:
+Warning	1292	Truncated incorrect read_buffer_size value: '2147479553'
 SELECT @@session.read_buffer_size;
 @@session.read_buffer_size
 2147479552

mysql-test/r/read_rnd_buffer_size_basic.result

@@ -88,6 +88,8 @@ SELECT @@global.read_rnd_buffer_size= 8200 OR @@global.read_rnd_buffer_size= 822
 @@global.read_rnd_buffer_size= 8200 OR @@global.read_rnd_buffer_size= 8228
 1
 SET @@global.read_rnd_buffer_size = 2147479553;
+Warnings:
+Warning	1292	Truncated incorrect read_rnd_buffer_size value: '2147479553'
 SELECT @@global.read_rnd_buffer_size;
 @@global.read_rnd_buffer_size
 2147479552
@@ -116,6 +118,8 @@ SELECT @@session.read_rnd_buffer_size= 8200 OR @@session.read_rnd_buffer_size= 8
 SET @@session.read_rnd_buffer_size = 65530.34.;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.' at line 1
 SET @@session.read_rnd_buffer_size = 2147479553;
+Warnings:
+Warning	1292	Truncated incorrect read_rnd_buffer_size value: '2147479553'
 SELECT @@session.read_rnd_buffer_size;
 @@session.read_rnd_buffer_size
 2147479552

mysys/my_getopt.c

@@ -976,24 +976,26 @@ static void init_one_value(const struct my_option *option, uchar* *variable,
     *((my_bool*) variable)= (my_bool) value;
     break;
   case GET_INT:
-    *((int*) variable)= (int) value;
+    *((int*) variable)= (int) getopt_ll_limit_value((int) value, option, NULL);
     break;
-  case GET_UINT:
   case GET_ENUM:
     *((uint*) variable)= (uint) value;
     break;
+  case GET_UINT:
+    *((uint*) variable)= (uint) getopt_ull_limit_value((uint) value, option, NULL);
+    break;
   case GET_LONG:
-    *((long*) variable)= (long) value;
+    *((long*) variable)= (long) getopt_ll_limit_value((long) value, option, NULL);
     break;
   case GET_ULONG:
-    *((ulong*) variable)= (ulong) value;
+    *((ulong*) variable)= (ulong) getopt_ull_limit_value((ulong) value, option, NULL);
     break;
   case GET_LL:
-    *((longlong*) variable)= (longlong) value;
+    *((longlong*) variable)= (longlong) getopt_ll_limit_value((longlong) value, option, NULL);
     break;
   case GET_ULL:
   case GET_SET:
-    *((ulonglong*) variable)=  (ulonglong) value;
+    *((ulonglong*) variable)= (ulonglong) getopt_ull_limit_value((ulonglong) value, option, NULL);
     break;
   case GET_DOUBLE:
     *((double*) variable)=  (double) value;

sql/mysqld.cc

@@ -6611,7 +6611,7 @@ The minimum value for this variable is 4096.",
   {"max_user_connections", OPT_MAX_USER_CONNECTIONS,
    "The maximum number of active connections for a single user (0 = no limit).",
    (uchar**) &max_user_connections, (uchar**) &max_user_connections, 0, GET_UINT,
-   REQUIRED_ARG, 0, 1, UINT_MAX, 0, 1, 0},
+   REQUIRED_ARG, 0, 0, UINT_MAX, 0, 1, 0},
   {"max_write_lock_count", OPT_MAX_WRITE_LOCK_COUNT,
    "After this many write locks, allow some read locks to run in between.",
    (uchar**) &max_write_lock_count, (uchar**) &max_write_lock_count, 0, GET_ULONG,

storage/innobase/handler/ha_innodb.cc

@@ -8249,7 +8249,7 @@ static MYSQL_SYSVAR_BOOL(adaptive_hash_index, innobase_adaptive_hash_index,
 static MYSQL_SYSVAR_LONG(additional_mem_pool_size, innobase_additional_mem_pool_size,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
   "Size of a memory pool InnoDB uses to store data dictionary information and other internal data structures.",
-  NULL, NULL, 1*1024*1024L, 512*1024L, ~0L, 1024);
+  NULL, NULL, 1*1024*1024L, 512*1024L, LONG_MAX, 1024);
 
 static MYSQL_SYSVAR_ULONG(autoextend_increment, srv_auto_extend_increment,
   PLUGIN_VAR_RQCMDARG,
@@ -8289,7 +8289,7 @@ static MYSQL_SYSVAR_LONG(lock_wait_timeout, innobase_lock_wait_timeout,
 static MYSQL_SYSVAR_LONG(log_buffer_size, innobase_log_buffer_size,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
   "The size of the buffer which InnoDB uses to write log to the log files on disk.",
-  NULL, NULL, 1024*1024L, 256*1024L, ~0L, 1024);
+  NULL, NULL, 1024*1024L, 256*1024L, LONG_MAX, 1024);
 
 static MYSQL_SYSVAR_LONGLONG(log_file_size, innobase_log_file_size,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
@@ -8309,7 +8309,7 @@ static MYSQL_SYSVAR_LONG(mirrored_log_groups, innobase_mirrored_log_groups,
 static MYSQL_SYSVAR_LONG(open_files, innobase_open_files,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
   "How many files at the maximum InnoDB keeps open at the same time.",
-  NULL, NULL, 300L, 10L, ~0L, 0);
+  NULL, NULL, 300L, 10L, LONG_MAX, 0);
 
 static MYSQL_SYSVAR_ULONG(sync_spin_loops, srv_n_spin_wait_rounds,
   PLUGIN_VAR_RQCMDARG,