param: hand arguments after -- straight to init

The kernel passes any args it doesn't need through to init, except it
assumes anything containing '.' belongs to the kernel (for a module).
This change means all users can clearly distinguish which arguments
are for init.

For example, the kernel uses debug ("dee-bug") to mean log everything to
the console, where systemd uses the debug from the Scandinavian "day-boog"
meaning "fail to boot".  If a future versions uses argv[] instead of
reading /proc/cmdline, this confusion will be avoided.

eg: test 'FOO="this is --foo"' -- 'systemd.debug="true true true"'

Gives:
argv[0] = '/debug-init'
argv[1] = 'test'
argv[2] = 'systemd.debug=true true true'
envp[0] = 'HOME=/'
envp[1] = 'TERM=linux'
envp[2] = 'FOO=this is --foo'

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/kernel/module.c b/kernel/module.c
index 1186940..66e4e0d 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3193,6 +3193,7 @@
 {
 	struct module *mod;
 	long err;
+	char *after_dashes;
 
 	err = module_sig_check(info);
 	if (err)
@@ -3277,10 +3278,15 @@
 		goto ddebug_cleanup;
 
 	/* Module is ready to execute: parsing args may do that. */
-	err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
-			 -32768, 32767, unknown_module_param_cb);
-	if (err < 0)
+	after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
+				  -32768, 32767, unknown_module_param_cb);
+	if (IS_ERR(after_dashes)) {
+		err = PTR_ERR(after_dashes);
 		goto bug_cleanup;
+	} else if (after_dashes) {
+		pr_warn("%s: parameters '%s' after `--' ignored\n",
+		       mod->name, after_dashes);
+	}
 
 	/* Link in to syfs. */
 	err = mod_sysfs_setup(mod, info, mod->kp, mod->num_kp);