[PATCH] init: Introduce rootdir bootparm to select which dir to sys_chroot

[Al Boldi <a1426z@gawab.com>]

This patch introduces a rootdir kernel boot parameter, which specifies the 
path to the kernel sys_chroot boot dir.

This is useful for systems that have more than one distribution installed on 
the same fs/partition.


Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Boldi <a1426z@gawab.com>

---

--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -252,6 +252,15 @@ __setup("rootflags=", root_data_setup);
 __setup("rootfstype=", fs_names_setup);
 __setup("rootdelay=", root_delay_setup);
 
+static char * __initdata root_dir;
+static int __init root_dir_setup(char *str)
+{
+	root_dir = strcat("./",str);
+	return 1;
+}
+
+__setup("rootdir=", root_dir_setup);
+
 static void __init get_fs_names(char *page)
 {
 	char *s = page;
@@ -469,6 +478,10 @@ void __init prepare_namespace(void)
 	mount_root();
 out:
 	sys_mount(".", "/", NULL, MS_MOVE, NULL);
+
+	if(root_dir)
+		sys_chdir(root_dir);
+
 	sys_chroot(".");
 	security_sb_post_mountroot();
 }