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

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Date:   Tue, 31 Oct 2023 13:33:22 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     linux-kernel@...r.kernel.org,
        "Milton D. Miller II" <mdmii@...look.com>,
        Rob Landley <rob@...dley.net>,
        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>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [RFC PATCH] rootfs: Use tmpfs for rootfs even if root= is given

On October 31, 2023 10:11:01 AM PDT, Stefan Berger <stefanb@...ux.ibm.com> wrote:
>
>On 10/31/23 12:56, 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?
>
>CONFIG_TPMFS_XATTRS allows us to set xattrs, such as security.ima.
>
>   Stefan
>
>> 
>> thanks,
>> 
>> greg k-h
Why do we even keep ramfs as a standalone file system? To guarantee it cannot be swapped out? Does anyone actually use it?