[Virtio-fs] Query about fuse ->sync_fs and virtiofs

[Miklos Szeredi]

On Wed, Apr 14, 2021 at 1:56 PM Greg Kurz <groug at kaod.org> wrote:
>
> On Mon, 12 Apr 2021 17:08:26 +0200
> Miklos Szeredi <miklos at szeredi.hu> wrote:
>
> > On Mon, Apr 12, 2021 at 4:59 PM Vivek Goyal <vgoyal at redhat.com> wrote:
> > >
> > > Hi Miklos,
> > >
> > > Robert Krawitz drew attention to the fact that fuse does not seem to
> > > have a ->sync_fs implementation. That probably means that in case of
> > > virtiofs, upon sync()/syncfs(), host cache will not be written back
> > > to disk. And that's not something people expect.
> > >
> > > I read somewhere that fuse did not implement ->sync_fs because file
> > > server might not be trusted and it could block sync().
> > >
> > > In case of virtiofs, file server is trusted entity (w.r.t guest kernel),
> > > so it probably should be ok to implement ->sync_fs atleast for virtiofs?
> >
> > Yes, that looks like a good idea.
> >
>
> I've started looking into this. First observation is that implementing
> ->sync_fs() is file server agnostic, so if we want this to only be used
> by a trusted file server, we need to introduce such a notion in FUSE.
> Not sure where though... in struct fuse_fs_context maybe ?

Yep, makes sense.

Thanks,
Miklos