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

[Greg Kurz]

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 ?

> Thanks,
> Miklos