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

[Hanna Czenczek]

On 10.07.24 19:28, Stefan Hajnoczi 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.
> >
> >
> > Hanna Czenczek (2):
> >    virtio-fs: Add 'file' mount option
> >    virtio-fs: Document 'file' mount option
> >
> >   fs/fuse/virtio_fs.c                    | 9 ++++++++-
> >   Documentation/filesystems/virtiofs.rst | 5 ++++-
> >   2 files changed, 12 insertions(+), 2 deletions(-)
> >
> > --
> > 2.45.1
> Looks good to me. Maybe add the 'file' option to FUSE as well to keep
> them in sync (eventually rootmode could be exposed to virtiofs too, if
> necessary)?

I don’t think this option makes much sense for FUSE, like Josef has 
said; it would just duplicate a subset of 'rootmode', and because FUSE 
filesystems are rarely mounted by hand, I don’t think anyone would ever 
use it.

If it were important to keep them in sync, I’d rather have virtio-fs 
provide 'rootmode' instead.  Personally, I don’t think it’s that 
important, and I’d rather have a simple '-o file' instead of '-o 
rootmode=0100000' (hope I counted the 0s right) for a filesystem that is 
actually not rarely mounted by hand.

If we ever do find out that we want to support other root modes than 
S_IFREG and S_IFDIR, we will probably want 'rootmode' for virtio-fs, 
too, yes.  But I can’t see that right now.

> Reviewed-by: Stefan Hajnoczi <stefanha@xxxxxxxxxx>

Thanks!

Hanna