[PATCH] rootfs: Fix support for rootfstype= when root= is given

[PATCH] rootfs: Fix support for rootfstype= when root= is given

[Stefan Berger]

Documentation/filesystems/ramfs-rootfs-initramfs.rst states:

  If CONFIG_TMPFS is enabled, rootfs will use tmpfs instead of ramfs by
  default.  To force ramfs, add "rootfstype=ramfs" to the kernel command
  line.

This currently does not work when root= is provided since then
saved_root_name contains a string and initfstype= is ignored. Therefore,
ramfs is currently always chosen when root= is provided.

The current behavior for rootfs's filesystem is:

   root=       | initfstype= | chosen rootfs filesystem
   ------------+-------------+--------------------------
   unspecified | unspecified | tmpfs
   unspecified | tmpfs       | tmpfs
   unspecified | ramfs       | ramfs
    provided   | ignored     | ramfs

initfstype= should be respected regardless whether root= is given,
as shown below:

   root=       | initfstype= | chosen rootfs filesystem
   ------------+-------------+--------------------------
   unspecified | unspecified | tmpfs  (as before)
   unspecified | tmpfs       | tmpfs  (as before)
   unspecified | ramfs       | ramfs  (as before)
    provided   | unspecified | ramfs  (compatibility with before)
    provided   | tmpfs       | tmpfs  (new)
    provided   | ramfs       | ramfs  (new)

This table represents the new behavior.

Fixes: 6e19eded3684 ("initmpfs: use initramfs if rootfstype= or root=  specified")
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Rob Landley <rob@landley.net>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 init/do_mounts.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/init/do_mounts.c b/init/do_mounts.c
index 5fdef94f0864..279ad28bf4fb 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -510,7 +510,10 @@ struct file_system_type rootfs_fs_type = {
 
 void __init init_rootfs(void)
 {
-	if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
-		(!root_fs_names || strstr(root_fs_names, "tmpfs")))
-		is_tmpfs = true;
+	if (IS_ENABLED(CONFIG_TMPFS)) {
+		if (!saved_root_name[0] && !root_fs_names)
+			is_tmpfs = true;
+		else if (root_fs_names && !!strstr(root_fs_names, "tmpfs"))
+			is_tmpfs = true;
+	}
 }
-- 
2.41.0

Re: [PATCH] rootfs: Fix support for rootfstype= when root= is given

[Greg KH]

On Mon, Nov 13, 2023 at 04:17:35PM -0500, Stefan Berger wrote:
> Documentation/filesystems/ramfs-rootfs-initramfs.rst states:
> 
>   If CONFIG_TMPFS is enabled, rootfs will use tmpfs instead of ramfs by
>   default.  To force ramfs, add "rootfstype=ramfs" to the kernel command
>   line.
> 
> This currently does not work when root= is provided since then
> saved_root_name contains a string and initfstype= is ignored. Therefore,
> ramfs is currently always chosen when root= is provided.
> 
> The current behavior for rootfs's filesystem is:
> 
>    root=       | initfstype= | chosen rootfs filesystem
>    ------------+-------------+--------------------------
>    unspecified | unspecified | tmpfs
>    unspecified | tmpfs       | tmpfs
>    unspecified | ramfs       | ramfs
>     provided   | ignored     | ramfs
> 
> initfstype= should be respected regardless whether root= is given,
> as shown below:
> 
>    root=       | initfstype= | chosen rootfs filesystem
>    ------------+-------------+--------------------------
>    unspecified | unspecified | tmpfs  (as before)
>    unspecified | tmpfs       | tmpfs  (as before)
>    unspecified | ramfs       | ramfs  (as before)
>     provided   | unspecified | ramfs  (compatibility with before)
>     provided   | tmpfs       | tmpfs  (new)
>     provided   | ramfs       | ramfs  (new)
> 
> This table represents the new behavior.
> 
> Fixes: 6e19eded3684 ("initmpfs: use initramfs if rootfstype= or root=  specified")
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> Signed-off-by: Rob Landley <rob@landley.net>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> ---
>  init/do_mounts.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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- You have marked a patch with a "Fixes:" tag for a commit that is in an
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  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
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thanks,

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