linux-kernel - Re: [PATCH v2] rootfs: Fix support for rootfstype= when root= is given

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Date:   Sun, 19 Nov 2023 09:12:56 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, initramfs@...r.kernel.org,
        stable@...r.kernel.org, Rob Landley <rob@...dley.net>
Subject: Re: [PATCH v2] rootfs: Fix support for rootfstype= when root= is
 given

On Tue, 2023-11-14 at 09:10 -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

^rootfstype=

>    ------------+-------------+--------------------------
>    unspecified | unspecified | tmpfs
>    unspecified | tmpfs       | tmpfs
>    unspecified | ramfs       | ramfs
>     provided   | ignored     | ramfs
> 
> initfstype= should be respected regardless whether root= is given,
> as shown below:

^rootfstype=

> 
>    root=       | initfstype= | chosen rootfs filesystem

^rootfstype=

>    ------------+-------------+--------------------------
>    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")
> Cc: <stable@...r.kernel.org>
> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>

As the patch author,  "Reviewed-by" is unnecessary.

Please add a reference to the original patch on which this is based.
Link:  https://lore.kernel.org/lkml/8244c75f-445e-b15b-9dbf-266e7ca666e2@landley.net/

> Signed-off-by: Rob Landley <rob@...dley.net>
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
> ---

Add Changelog as requested.

>  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;
> +	}
>  }

Please change all "initfstype" references to "rootfstype" in the patch
description.

Otherwise,
Reviewed-and-Tested-by: Mimi Zohar <zohar@...ux.ibm.com>

-- 
Thanks,

Mimi