MDEV-35889 set information_schema.system_variables NUMERIC_MIN_VALUE ...

for the innodb_buffer_pool_size system variable based on innodb_page_size.

The innodb_buffer_pool_size is dependent on the innodb_page_size. While
the minimum is enforced for resizing the minimum isn't exposed by the
information_schema.system_variables table.

Add a bunch of assertions to ensure that the plugin relations between
default, minimum, maximum and block size hold.

Expose the plugin_var point from sys_var and while retreiving fill_sysvars
update the limits in case the plugin happens to have changed them.

mysql-test/suite/innodb/t/restart.test

@@ -95,10 +95,11 @@ let $wait_condition =
 
 --disable_cursor_protocol
 SELECT @@innodb_buffer_pool_size INTO @innodb_buffer_pool_size_orig;
-SELECT CEILING((256 + 64) * @@innodb_page_size / 1048576) * 1048576 INTO @min_pool_size;
+SELECT CAST(NUMERIC_MIN_VALUE AS UNSIGNED) INTO @min_pool_size FROM information_schema.system_variables WHERE variable_name='INNODB_BUFFER_POOL_SIZE';
+SET @out_of_bounds_pool_size=@min_pool_size - @@innodb_buffer_pool_chunk_size;
 --enable_cursor_protocol
 --error ER_WRONG_VALUE_FOR_VAR
-EXECUTE IMMEDIATE 'SET GLOBAL innodb_buffer_pool_size = ?' USING (@min_pool_size -1);
+EXECUTE IMMEDIATE 'SET GLOBAL innodb_buffer_pool_size = ?' USING (@out_of_bounds_pool_size);
 
 SHOW WARNINGS;
 

sql/set_var.cc

@@ -1117,6 +1117,9 @@ int fill_sysvars(THD *thd, TABLE_LIST *tables, COND *cond)
 
     mysql_mutex_lock(&LOCK_global_system_variables);
 
+    if (var->cast_pluginvar())
+      plugin_opt_set_limits(&var->option, var->cast_mysql_sys_var());
+
     // SESSION_VALUE
     store_var(fields[1], var, OPT_SESSION, &strbuf);
 

sql/set_var.h

@@ -111,6 +111,7 @@ class sys_var: protected Value_source // for double_from_string_with_check
     of sys_var_pluginvar, and 0 otherwise.
   */
   virtual sys_var_pluginvar *cast_pluginvar() { return 0; }
+  virtual const struct st_mysql_sys_var *cast_mysql_sys_var() const { return nullptr; }
 
   bool check(THD *thd, set_var *var);
   const uchar *value_ptr(THD *thd, enum_var_type type, const LEX_CSTRING *base) const;

sql/sql_plugin.cc

@@ -315,6 +315,7 @@ class sys_var_pluginvar: public sys_var, public Sql_alloc
                     st_plugin_int *p, st_mysql_sys_var *plugin_var_arg,
                     const char *substitute);
   sys_var_pluginvar *cast_pluginvar() override { return this; }
+  virtual const struct st_mysql_sys_var *cast_mysql_sys_var() const override { return plugin_var; }
   uchar* real_value_ptr(THD *thd, enum_var_type type) const;
   TYPELIB* plugin_var_typelib(void) const;
   const uchar* do_value_ptr(THD *thd, enum_var_type type, const LEX_CSTRING *base) const;
@@ -3683,17 +3684,24 @@ bool sys_var_pluginvar::global_update(THD *thd, set_var *var)
 
 #define OPTION_SET_LIMITS(type, options, opt) \
   options->var_type= type; \
+  assert((opt)->def_val >= (opt)->min_val); \
+  assert((opt)->def_val <= (opt)->max_val); \
   options->def_value= (opt)->def_val; \
+  assert((opt)->min_val <= (opt)->max_val); \
   options->min_value= (opt)->min_val; \
   options->max_value= (opt)->max_val; \
+  assert((opt)->blk_sz == 0 || ((opt)->min_val % (opt)->blk_sz) == 0); \
+  assert((opt)->blk_sz == 0 || ((opt)->max_val % (opt)->blk_sz) == 0); \
   options->block_size= (long) (opt)->blk_sz
 
 #define OPTION_SET_LIMITS_DOUBLE(options, opt) \
   options->var_type= GET_DOUBLE; \
   options->def_value= (longlong) getopt_double2ulonglong((opt)->def_val); \
   options->min_value= (longlong) getopt_double2ulonglong((opt)->min_val); \
   options->max_value= getopt_double2ulonglong((opt)->max_val); \
-  options->block_size= (long) (opt)->blk_sz;
+  options->block_size= (long) (opt)->blk_sz; \
+  assert(options->def_value >= options->min_value); \
+  assert(options->def_value <= options->max_value);
 
 void plugin_opt_set_limits(struct my_option *options,
                            const struct st_mysql_sys_var *opt)