linux-kernel - Re: [RESEND v2 PATCH] init/do_mounts.c: add virtiofs root fs support

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Message-ID: <cee2e3ea-14a6-c51f-7ce6-6a67dabff6f1@ixit.cz>
Date:   Mon, 27 Feb 2023 21:55:57 +0100
From:   David Heidelberg <david@...t.cz>
To:     Vivek Goyal <vgoyal@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, helen.koike@...labora.com,
        Al Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        wsa+renesas@...g-engineering.com, akpm@...ux-foundation.org
Subject: Re: [RESEND v2 PATCH] init/do_mounts.c: add virtiofs root fs support

Thank you all!

We'll drop this patch in next MesaCI kernel uprev without this patch!

David

On 27/02/2023 19:06, Vivek Goyal wrote:
> On Mon, Feb 27, 2023 at 10:53:45AM -0500, Stefan Hajnoczi wrote:
>> On Fri, Feb 24, 2023 at 03:37:51PM +0100, David Heidelberg wrote:
>>> From: Stefan Hajnoczi <stefanha@...hat.com>
>>>
>>> Make it possible to boot directly from a virtiofs file system with tag
>>> 'myfs' using the following kernel parameters:
>>>
>>>    rootfstype=virtiofs root=myfs rw
>>>
>>> Booting directly from virtiofs makes it possible to use a directory on
>>> the host as the root file system.  This is convenient for testing and
>>> situations where manipulating disk image files is cumbersome.
>>>
>>> Reviewed-by: Helen Koike <helen.koike@...labora.com>
>>> Signed-off-by: Stefan Hajnoczi <stefanha@...hat.com>
>>> Signed-off-by: David Heidelberg <david@...t.cz>
>>> ---
>>> v2: added Reviewed-by and CCed everyone interested.
>>>
>>> We have used this option in Mesa3D CI for testing crosvm for
>>> more than one years and it's proven to work reliably.
>>>
>>> We are working on effort to removing custom patches to be able to do
>>> automated apply and test of patches from any tree.
>>>
>>> https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/.gitlab-ci/crosvm-runner.sh#L85
>>>   init/do_mounts.c | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>> Vivek, do you remember where we ended up with boot from virtiofs? I
>> thought a different solution was merged some time ago.
> We merged a patch from Christoph Hellwig to support this.
>
> commit f9259be6a9e7c22d92e5a5000913147ae17e8321
> Author: Christoph Hellwig <hch@....de>
> Date:   Wed Jul 14 16:23:20 2021 -0400
>
>      init: allow mounting arbitrary non-blockdevice filesystems as root
>
> Now one should be able to mount virtiofs using following syntax.
>
> "root=myfs rootfstype=virtiofs rw"
>
> IIUC, this patch should not be required anymore.
>
> Thanks
> Vivek
>
>> There is documentation from the virtiofs community here:
>> https://virtio-fs.gitlab.io/howto-boot.html
>>
>> Stefan
>>
>>> diff --git a/init/do_mounts.c b/init/do_mounts.c
>>> index 811e94daf0a8..11c11abe23d7 100644
>>> --- a/init/do_mounts.c
>>> +++ b/init/do_mounts.c
>>> @@ -578,6 +578,16 @@ void __init mount_root(void)
>>>   			printk(KERN_ERR "VFS: Unable to mount root fs via SMB.\n");
>>>   		return;
>>>   	}
>>> +#endif
>>> +#ifdef CONFIG_VIRTIO_FS
>>> +	if (root_fs_names && !strcmp(root_fs_names, "virtiofs")) {
>>> +		if (!do_mount_root(root_device_name, "virtiofs",
>>> +				   root_mountflags, root_mount_data))
>>> +			return;
>>> +
>>> +		panic("VFS: Unable to mount root fs \"%s\" from virtiofs",
>>> +		      root_device_name);
>>> +	}
>>>   #endif
>>>   	if (ROOT_DEV == 0 && root_device_name && root_fs_names) {
>>>   		if (mount_nodev_root() == 0)
>>> -- 
>>> 2.39.1
>>>
>
-- 
David Heidelberg
Consultant Software Engineer