linux-kernel - Re: [RFC PATCH] rootfs: Use tmpfs for rootfs even if root= is given

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Message-ID: <e30c9f81-959f-418d-a4b1-d34d47391e09@linux.ibm.com>
Date:   Wed, 1 Nov 2023 08:11:12 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Rob Landley <rob@...dley.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        "Milton D. Miller II" <mdmii@...look.com>,
        Jeff Layton <jlayton@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        Jim Cromie <jim.cromie@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "H. Peter Anvin" <hpa@...or.com>, Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [RFC PATCH] rootfs: Use tmpfs for rootfs even if root= is given



On 11/1/23 07:35, Rob Landley wrote:
> On 10/31/23 11:56, Greg Kroah-Hartman wrote:
>> On Tue, Oct 31, 2023 at 11:44:17AM -0400, Stefan Berger wrote:
>>> rootfs currently does not use tmpfs if the root= boot option is passed
>>> even though the documentation about rootfs (added in 6e19eded3684) in
>>> 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.
>>
>> At this point in time, is there even any difference between ramfs and
>> tmpfs anymore?  Why would you want to choose one over the other here?
> 
> I submitted a patch to fix this to the list multiple times, which got ignored as
> always. Most recently here:
> 
> https://lore.kernel.org/lkml/8244c75f-445e-b15b-9dbf-266e7ca666e2@landley.net/

I just tried it with your patch and the machine I am using this with 
(OpenBMC) uses the boot command line 'console=ttyS4,115200n8 
root=/dev/ram rw'. When I append rootfstype=tmpfs to this boot command 
line then it starts actually using tmpfs. So I think this would work for me.
I can add my Tested-by tag to the patch if this helps to get it merged. 
Ideally it would also propagate back with a Fixes tag...

    Stefan

> 
> Rob