Bug#19027 MySQL 5.0 starts even with Fatal InnoDB errors

It is not possible to prevent the server from starting if a mandatory
built-in plugin fails to start. This can in some cases lead to data
corruption when the old table name space suddenly is used by a different
storage engine.

A boolean command line option in the form of --foobar is automatically
created for every existing plugin "foobar". By changing this command line
option from a boolean to a tristate { OFF, ON, FORCE } it is possible to
specify the plugin loading policy for each plugin.

The behavior is specified as follows:
   OFF   = Disable the plugin and start the server
   ON    = Enable the plugin and start the server even if an error occurrs
           during plugin initialization.
   FORCE = Enable the plugin but don't start the server if an error occurrs
           during plugin initialization.

mysql-test/lib/mtr_cases.pm

@@ -887,7 +887,7 @@ sub collect_one_test_case {
   if ( $tinfo->{'innodb_test'} )
   {
     # This is a test that need innodb
-    if ( $::mysqld_variables{'innodb'} ne "TRUE" )
+    if ( $::mysqld_variables{'innodb'} eq "OFF" )
     {
       # innodb is not supported, skip it
       $tinfo->{'skip'}= 1;

mysys/my_getopt.c

@@ -410,7 +410,8 @@ invalid value '%s'",
 	  argument= optend;
 	}
 	else if (optp->arg_type == OPT_ARG &&
-		 (optp->var_type & GET_TYPE_MASK) == GET_BOOL)
+		 (((optp->var_type & GET_TYPE_MASK) == GET_BOOL) ||
+                   (optp->var_type & GET_TYPE_MASK) == GET_ENUM))
 	{
 	  if (optend == disabled_my_option)
 	    *((my_bool*) value)= (my_bool) 0;

sql/sql_plugin.h

@@ -79,6 +79,7 @@ struct st_plugin_int
   void *data;                   /* plugin type specific, e.g. handlerton */
   MEM_ROOT mem_root;            /* memory for dynamic plugin structures */
   sys_var *system_vars;         /* server variables for this plugin */
+  bool is_mandatory;            /* If true then plugin must not fail to load */
 };