On Tue, Feb 4, 2020 at 8:42 PM Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Tue, Feb 04, 2020 at 07:02:05PM +0200, Amir Goldstein wrote: > > 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? > > I don't think virtiofs will ensure that server/host will not invalidate > entries. It will be more of a configuration thing where we will expect > users to configure things in such a way that shared directory does not > change. > > So that means, if user does not configure it properly and things change > unexpectedly, then overlayfs should be able to detect it and flag error > to user space? > > > 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? > > So as of now user space will get -ESTALE and that will get cleared when > user space retries after corresponding ovl dentry has been dropped from > cache (either dentry is evicted, cache is cleared forcibly or overlayfs > is remounted)? If yes, that kind of makes sense. Overlay does not expect > underlying layers to change and if a change it detected it is flagged > to user space (and overlayfs does not try to fix it)? > I looks like it. I don't really understand why overlayfs shouldn't drop the dentry on failure to revalidate. Maybe I am missing something. Thanks, Amir.
