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>

init/main.c

@@ -252,6 +252,27 @@ static int __init repair_env_string(char *param, char *val, const char *unused)
 	return 0;
 }
 
+/* Anything after -- gets handed straight to init. */
+static int __init set_init_arg(char *param, char *val, const char *unused)
+{
+	unsigned int i;
+
+	if (panic_later)
+		return 0;
+
+	repair_env_string(param, val, unused);
+
+	for (i = 0; argv_init[i]; i++) {
+		if (i == MAX_INIT_ARGS) {
+			panic_later = "init";
+			panic_param = param;
+			return 0;
+		}
+	}
+	argv_init[i] = param;
+	return 0;
+}
+
 /*
  * Unknown boot options get handed to init, unless they look like
  * unused parameters (modprobe will find them in /proc/cmdline).
@@ -478,7 +499,7 @@ static void __init mm_init(void)
 
 asmlinkage void __init start_kernel(void)
 {
-	char * command_line;
+	char * command_line, *after_dashes;
 	extern const struct kernel_param __start___param[], __stop___param[];
 
 	/*
@@ -519,9 +540,13 @@ asmlinkage void __init start_kernel(void)
 
 	pr_notice("Kernel command line: %s\n", boot_command_line);
 	parse_early_param();
-	parse_args("Booting kernel", static_command_line, __start___param,
-		   __stop___param - __start___param,
-		   -1, -1, &unknown_bootoption);
+	after_dashes = parse_args("Booting kernel",
+				  static_command_line, __start___param,
+				  __stop___param - __start___param,
+				  -1, -1, &unknown_bootoption);
+	if (after_dashes)
+		parse_args("Setting init args", after_dashes, NULL, 0, -1, -1,
+			   set_init_arg);
 
 	jump_label_init();