testing/review of atomic export update patch

[Rick Macklem]

Justin T. Gibbs wrote:
> On Sep 16, 2012, at 3:41 PM, Rick Macklem <rmacklem at uoguelph.ca>
> wrote:
> 
> > Hi,
> >
> > There is a simple patch at:
> >  http://people.freebsd.org/~rmacklem/atomic-export.patch
> > that can be applied to a kernel + mountd, so that the new
> > nfsd can be suspended by mountd while the exports are being
> > reloaded. It adds a new "-S" flag to mountd to enable this.
> > (This avoids the long standing bug where clients receive ESTALE
> > replies to RPCs while mountd is reloading exports.)
> 
> At Spectra, we are successfully using the NFSE patch set from
> nfse.sourceforge.net (FreeBSD PR 136865). It addresses
> the ESTALE problem in addition to cleaning up several aspects
> of exports processing.
> 
> Have you reviewed the NFSE work? Do you have any issues
> or concerns with it? What is the right path for getting NFSE
> integrated into FreeBSD?
> 
I, personally, have not found the time to review it. As such,
I can't state specifics, however there have been concerns w.r.t.
a switch from mountd->nfse resulting in different behaviour when
used with the same /etc/exports file used for mountd.

Some questions that need to be answered w.r.t. nfse, which I
haven't had the time to do:
- Are the differences listed here significant enough for a
  change to be considered a POLA violation?
    http://nfse.sourceforge.net/COMPATIBILITY

- If the server mount point is /sub1 and the only line
  referring to this server volume in /etc/exports looks like:

  /sub1/sub2 client.net

  Does the following mount command work on client.net
  # mount -t nfs -o nfsv3 server.net:/sub1 /mnt
  when nfse is run with -C using the /etc/exports file?
  (If this mount works, many would consider this a POLA
   violation.)

  This is typically referred to as an "administrative control",
  since it is only enforced by mountd for the Mount protocol,
  but is considered an important feature by some (rwatson@
  expressed a desire/need for it).

- Does the nfse patch handle exporting of all file systems types
  and, in particular, the `zfs share` case.

Beyond that, someone with the time to shepherd it into head as
a mountd replacement. (I`ll admit I`m mainly interested in NFSv4.1
these days and proposed the simple patch because I do not have
the time to look at nfse seriously and figured it might be
sufficient to keep people happy.)

rick

> --
> Justin