On Thu, 2020-09-10 at 13:02 -0400, J. Bruce Fields wrote:
> On Tue, Sep 08, 2020 at 05:19:58PM -0400, trondmy@xxxxxxxxxx wrote:
> > From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> >
> > If the mount point check in nfsd_export fails due to a transient
> > error,
> > then ignore it to avoid spurious NFSERR_STALE errors being returned
> > by
> > knfsd.
>
> What sort of transient errors?
>
> I guess this makes the upcall (and the original rpc) eventually time
> out?
The point here is that is_mountpoint() is making the assumption that
_any_ error from stat() can be used to infer that there is nothing
mounted. In reality, only a subset of errors allow it to make that
assumption (specifically the errors ELOOP, ENAMETOOLONG, ENOENT, and
ENOTDIR).
In our case, we're seeing a problem when the underlying filesystem is a
soft mounted NFSv4.2 client (i.e. we're running our Hammerspace use
case of proxying NFSv4.2 to legacy NFSv3 clients) and that NFS4.2 mount
times out due to a reboot of the underlying server, for instance.
So, yes, in that case we want the upcall to time out instead of poking
knfsd into declaring that the directory is stale.
>
> --b.
>
> > Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> > ---
> > utils/mountd/cache.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> > index 6cba2883026f..93e868341d15 100644
> > --- a/utils/mountd/cache.c
> > +++ b/utils/mountd/cache.c
> > @@ -1411,7 +1411,10 @@ static void nfsd_export(int f)
> >
> > if (mp && !*mp)
> > mp = found->m_export.e_path;
> > - if (mp && !is_mountpoint(mp))
> > + errno = 0;
> > + if (mp && !is_mountpoint(mp)) {
> > + if (errno != 0 && !path_lookup_error(errno))
> > + goto out;
> > /* Exportpoint is not mounted, so tell kernel
> > it is
> > * not available.
> > * This will cause it not to appear in the V4
> > Pseudo-root
> > @@ -1420,9 +1423,12 @@ static void nfsd_export(int f)
> > * And filehandle for this mountpoint from an
> > earlier
> > * mount will block in nfsd.fh lookup.
> > */
> > + xlog(L_WARNING,
> > + "Cannot export path '%s': not a
> > mountpoint",
> > + path);
> > dump_to_cache(f, buf, sizeof(buf), dom, path,
> > NULL, 60);
> > - else if (dump_to_cache(f, buf, sizeof(buf), dom, path,
> > + } else if (dump_to_cache(f, buf, sizeof(buf), dom,
> > path,
> > &found->m_export, 0) < 0) {
> > xlog(L_WARNING,
> > "Cannot export %s, possibly unsupported
> > filesystem"
> > --
> > 2.26.2
--
Trond Myklebust
CTO, Hammerspace Inc
4984 El Camino Real, Suite 208
Los Altos, CA 94022
www.hammer.space
