Re: Occassional "permission denied" in the middle of a large transfer over NFS

Vincent Hoffman wrote:
> Just a note to say I have tested this on -CURRENT with the new nfs
> server and it is still the case.
> 
> On the client (FreeBSD seaurchin 8.3-RELEASE-p3 FreeBSD 8.3-RELEASE-p3
> #0: Tue Jun 12 00:39:29 UTC 2012
> root_at_amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC amd64)
> 
> [root_at_seaurchin /mnt/nfs/vm]# date ; tar -cf foo.tar
> /var/nfsen/profiles-data/ ; date
> Thu Jun 28 20:12:36 BST 2012
> tar: Removing leading '/' from member names
> tar: Write error
> Thu Jun 28 20:12:38 BST 2012
> [root_at_seaurchin /mnt/nfs/vm]#
> 
> 
> 
> on the Server
> [root_at_fbsd /var/tmp]# uname -a ; date ; while true ; do mount /dev/md0
> /mnt/tmp/ ; umount /mnt/tmp ; done
> FreeBSD fbsd 10.0-CURRENT FreeBSD 10.0-CURRENT #22 r237646: Wed Jun 27
> 19:13:26 BST 2012
> toor_at_fbsd.bmk.namesco.net:/usr/obj/usr/src/sys/unsane-vm amd64
> Thu Jun 28 20:12:38 BST 2012
> ^C
> [root_at_fbsd /var/tmp]#
> 
> any suggestions welcome.
> 
> Vince
> 
> 
> On 27/06/2012 16:27, Vincent Hoffman wrote:
> > Hi,
> > After only one off-list reply from the author of kern/136865 (see
> > below)
> > after asking -questions, I thought it worth asking -CURRENT.
> > Basically:
> >
> > I seem to have run into the problems described in this old thread.
> > http://lists.freebsd.org/pipermail/freebsd-questions/2004-April/044927.html
> >
> > tl:dr mountd may give incorrect permission denied errors when it is
> > refreshing the exports list due to non-atomic operations,
> > /sbin/mount has code that sends SIGHUP to
> > mountd on any mount operation, which implies that any manual mount
> > request would cause the problem.
> >
> > Currently I have still only tested on 8.3-RELEASE but the svn log
> > doesnt
> > seem to mention a fix since then. I'm currently taking a VM up to
> > -CURRENT to test.
> >
> > Looking though old PRs I see the following related.
> > kern/131342
> > kern/136865 (with patch for 7.2 and links to
> > http://nfse.sourceforge.net/ for -CURRENT )
> >
> > Does anyone who is qualified (sadly not me) feel like looking at the
> > code to see if its suitable for inclusion in part/whole as not
> > having
> > NFS transfers interrupted by local mount operations on the nfs
> > server
> > would be very handy :)
> >
I haven't looked at Andrey's patch, but conceptually it sounds like
the best approach. As I understand it, the problem with replacing
mountd with nfse (at least in the FreeBSD source tree) is that nfse
is not 100% backwards compatible with /etc/exports and, as such, is
a POLA violation.

To modify mountd to use the kernel changes is more work than I have
time for, in part because mountd.c is a very ugly old piece of C code, imho.

I do have a patch that suspends/resumes execution of the nfsd threads
(new, experimental for FreeBSD8.n only) when mountd reloads /etc/exports.
This approach has certain disadvantages vs Andrey's transactional load/commit
model, but it is simple and might be sufficient for your problem.
If you want to try this patch, it is at:
   http://people.freebsd.org/~rmacklem/atomic-export.patch
(The patch affects both the kernel and mountd.c.)

Also, you could easily hack mount.c so that it doesn't send a SIGHUP
to mountd (which causes the exports to be reloaded) every time a local
fs is mounted.

rick

> >
> > thanks, Vince
> >
> >
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> 
> 
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