On Tue, Feb 4, 2020 at 6:17 PM Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > > On Tue, Feb 4, 2020 at 3:59 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > > On Fri, Jan 31, 2020 at 12:50:04PM +0100, Miklos Szeredi wrote: > > > No reason to prevent upper layer being a remote filesystem. Do the > > > revalidation in that case, just as we already do for lower layers. > > > > > > This lets virtiofs be used as upper layer, which appears to be a real use > > > case. > > > > Hi Miklos, > > > > I have couple of very basic questions. > > > > - So with this change, we will allow NFS to be upper layer also? > > I haven't tested, but I think it will fail on the d_type test. But we do not fail mount on no d_type support... Besides, I though you were going to add the RENAME_WHITEOUT test to avert untested network fs as upper. > > > - What does revalidation on lower/upper mean? Does that mean that > > lower/upper can now change underneath overlayfs and overlayfs will > > cope with it. > > No, that's a more complicated thing. Especially with redirected > layers (i.e. revalidating a redirect actually means revalidating all > the path components of that redirect). > > > If we still expect underlying layers not to change, then > > what's the point of calling ->revalidate(). > > That's a good question; I guess because that's what the filesystem > expects. OTOH, it's probably unnecessary in most cases, since the > path could come from an open file descriptor, in which case the vfs > will not do any revalidation on that path. > Note that ovl_dentry_revalidate() never returns 0 and therefore, vfs will never actually redo the lookup, but instead return -ESTALE to userspace. Right? This makes some sense considering that underlying layers are not expected to change. The question is, with virtiofs, can we know that the server/host will not invalidate entries? And if it does, should it cause a permanent error in overlayfs or a transient error? If we do not want a permanent error, then ->revalidate() needs to be called to invalidate the overlay dentry. No? Thanks, Amir.
