[RFC][Patch] Allow not mounting a root fs

[Bodo Eggert <7eggert@gmx.de>]

This patch adds the option to not mount another root filesystem 
by specifying root=initramfs.

TODO: Documentation
---

BTW: Is it possible to mount a tmpfs on / before extracting the cpio?


While I'm at it:

In init/do_mounts.c, mount_root(void):
ROOT_NFS: Is it desirable to use the floppy as a root device if nfs-root 
failed? If I tell my system to d A, i usually dislike it to do B instead.

Is the boot-from-floppy code here still usable, even though booting from 
floppy is no longer supported?



diff -X dontdiff -pruN 2.6.21.ori/init/do_mounts.c 2.6.21/init/do_mounts.c
--- 2.6.21.ori/init/do_mounts.c	2007-07-06 03:31:57.000000000 +0200
+++ 2.6.21/init/do_mounts.c	2007-07-06 03:27:33.000000000 +0200
@@ -427,6 +427,9 @@ void __init prepare_namespace(void)
 			mount_block_root(root_device_name, root_mountflags);
 			goto out;
 		}
+		if (!strncmp(root_device_name, "initramfs", 3)) {
+			goto out_nomount;
+		}
 		ROOT_DEV = name_to_dev_t(root_device_name);
 		if (strncmp(root_device_name, "/dev/", 5) == 0)
 			root_device_name += 5;
@@ -444,6 +447,7 @@ void __init prepare_namespace(void)
 out:
 	sys_mount(".", "/", NULL, MS_MOVE, NULL);
 	sys_chroot(".");
+out_nomount:
 	security_sb_post_mountroot();
 }
 
-- 
Top 100 things you don't want the sysadmin to say:
65. What do you mean /home was on that disk?  I umounted it!
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