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

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Message-ID: <b3b62f3f-7af4-4af4-8ec3-d4f63698b103@linux.ibm.com>
Date:   Tue, 31 Oct 2023 17:02:56 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     "H. Peter Anvin" <hpa@...or.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 10/31/23 16:33, H. Peter Anvin wrote:
> 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?

Probably all machines that have root= on the boot command line use it...