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>

kernel/params.c

@@ -177,13 +177,13 @@ static char *next_arg(char *args, char **param, char **val)
 }
 
 /* Args looks like "foo=bar,bar2 baz=fuz wiz". */
-int parse_args(const char *doing,
-	       char *args,
-	       const struct kernel_param *params,
-	       unsigned num,
-	       s16 min_level,
-	       s16 max_level,
-	       int (*unknown)(char *param, char *val, const char *doing))
+char *parse_args(const char *doing,
+		 char *args,
+		 const struct kernel_param *params,
+		 unsigned num,
+		 s16 min_level,
+		 s16 max_level,
+		 int (*unknown)(char *param, char *val, const char *doing))
 {
 	char *param, *val;
 
@@ -198,6 +198,9 @@ int parse_args(const char *doing,
 		int irq_was_disabled;
 
 		args = next_arg(args, &param, &val);
+		/* Stop at -- */
+		if (!val && strcmp(param, "--") == 0)
+			return args;
 		irq_was_disabled = irqs_disabled();
 		ret = parse_one(param, val, doing, params, num,
 				min_level, max_level, unknown);
@@ -208,22 +211,22 @@ int parse_args(const char *doing,
 		switch (ret) {
 		case -ENOENT:
 			pr_err("%s: Unknown parameter `%s'\n", doing, param);
-			return ret;
+			return ERR_PTR(ret);
 		case -ENOSPC:
 			pr_err("%s: `%s' too large for parameter `%s'\n",
 			       doing, val ?: "", param);
-			return ret;
+			return ERR_PTR(ret);
 		case 0:
 			break;
 		default:
 			pr_err("%s: `%s' invalid for parameter `%s'\n",
 			       doing, val ?: "", param);
-			return ret;
+			return ERR_PTR(ret);
 		}
 	}
 
 	/* All parsed OK. */
-	return 0;
+	return NULL;
 }
 
 /* Lazy bastard, eh? */