module: add kernel param to force disable module load

Sometimes we need to test a kernel of same version with code or config
option changes.

We already have sysctl to disable module load, but add a kernel
parameter will be more convenient.

Since modules_disabled is int, so here use bint type in core_param.
TODO: make sysctl accept bool and change modules_disabled to bool

Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Documentation/kernel-parameters.txt

@@ -1869,6 +1869,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			shutdown the other cpus.  Instead use the REBOOT_VECTOR
 			irq.
 
+	nomodule	Disable module load
+
 	nopat		[X86] Disable PAT (page attribute table extension of
 			pagetables) support.
 

kernel/module.c

@@ -105,6 +105,7 @@ struct list_head *kdb_modules = &modules; /* kdb needs the list of modules */
 
 /* Block module loading/unloading? */
 int modules_disabled = 0;
+core_param(nomodule, modules_disabled, bint, 0);
 
 /* Waiting for a module to finish initializing? */
 static DECLARE_WAIT_QUEUE_HEAD(module_wq);