linux-kernel - Re: [PATCH 0/2] virtio-fs: Add 'file' mount option

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Message-ID: <8ebfc48f-9a93-45ed-ba88-a4e4447d997a@redhat.com>
Date: Wed, 10 Jul 2024 09:28:08 +0200
From: Hanna Czenczek <hreitz@...hat.com>
To: Josef Bacik <josef@...icpanda.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-doc@...r.kernel.org, virtualization@...ts.linux.dev,
 Miklos Szeredi <mszeredi@...hat.com>, German Maglione
 <gmaglione@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 Jonathan Corbet <corbet@....net>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 0/2] virtio-fs: Add 'file' mount option

On 09.07.24 19:56, Josef Bacik wrote:
> On Tue, Jul 09, 2024 at 01:19:16PM +0200, Hanna Czenczek wrote:
>> Hi,
>>
>> We want to be able to mount filesystems that just consist of one regular
>> file via virtio-fs, i.e. no root directory, just a file as the root
>> node.
>>
>> While that is possible via FUSE itself (through the 'rootmode' mount
>> option, which is automatically set by the fusermount help program to
>> match the mount point's inode mode), there is no virtio-fs option yet
>> that would allow changing the rootmode from S_IFDIR to S_IFREG.
>>
>> To do that, this series introduces a new 'file' mount option that does
>> precisely that.  Alternatively, we could provide the same 'rootmode'
>> option that FUSE has, but as laid out in patch 1's commit description,
>> that option is a bit cumbersome for virtio-fs (in a way that it is not
>> for FUSE), and its usefulness as a more general option is limited.
>>
> All this does is make file an alias for something a little easier for users to
> read, which can easily be done in libfuse.  Add the code to lib/mount.c to alias
> 'file' to turn it into rootmode=S_IFREG when it sends it to the kernel, it's not
> necessary to do this in the kernel.  Thanks,

This series is not about normal FUSE filesystems (file_system_type 
fuse_fs_type, “fuse”), but about virtio-fs (file_system_type 
virtio_fs_type, “virtiofs”), i.e. a case where libfuse and fusermount 
are not involved at all.  As far as I’m aware, mounting a virtio-fs 
filesystem with a non-directory root inode is currently not possible at all.

Hanna