Adding dependency on mountlate to mountd

[Chris Rees]

On 16/12/2012, Konstantin Belousov <kostikbel at gmail.com> wrote:
> On Sat, Dec 15, 2012 at 10:12:00PM +0000, Chris Rees wrote:
>> On 15 December 2012 20:09, Steven Hartland <killing at multiplay.co.uk>
>> wrote:
>> > ---- Original Message -----
>> >>
>> >> From: Chris Rees On 15 Dec 2012 09:14, "Konstantin Belousov"
>> >> <kostikbel at gmail.com> wrote:
>> >> > It cannot be fine. It breaks local NFS mounts.
>> >>
>> >> Given that we can't have both, but we can have nullfs and thus solve
>> >> this
>> >> problem.
>> >> Is there something that local NFS mounts can do that nullfs won't?
>> >
>> >
>> > Using local NFS mounts seems a bit of strange thing to do, whats the
>> > reason for the requirement for these?
>> >
>> > Wouldnt nullfs mounts replace this requirement and perform better?
> No, because there are different use cases. What was useful for me was
> the case of migrating services, when the client machine happens to be
> the same as the export one. Ability to do loopback nfs mounts removes
> the need for non-trivial reconfiguration.
>
>
>>
>> Here's an idea, how about in the mountlate script, we pass SIGHUP to
>> mountd at the end (or simply restart it, but that'd be slower)?  This
>> would cover your use case and Kostik's example too.
>
> The mount(8) already sends SIGHUP to mountd, it is even noted in the
> man. Sometimes it results in the quite puzzling behaviour, see e.g.
> r172577, which in fact was blamed on a bug in our TCP stack.
>
> The only case which could not be covered yet is the unability to specify
> export points in the exports(5) which only appear after some late
> mounts are performed. I think that if you really concerned with this, a
> flag to the mountd(8) might be added which allows the daemon to ignore
> non-existing export directories.
>

Having investigated, this actually happens already; missing
directories in /etc/exports are just warnings that can be ignored.

Steven, can you provide more details on exactly what the problem is?
For example, the output of showmount -e on a machine that has late
filesystems in /etc/exports?

Chris

Scratch test:

pegasus# tail -n 0 -f /var/log/messages &
[1] 93579

pegasus# cat /etc/exports
/nonexistent

pegasus# killall -HUP mountd
Dec 16 17:04:18 pegasus mountd[93469]: bad exports list line /nonexistent

pegasus# showmount -e
Exports list on localhost:

pegasus# mkdir /nonexistent

pegasus# killall -HUP mountd

pegasus# showmount -e
Exports list on localhost:
/nonexistent                       Everyone

pegasus# uname -a
FreeBSD pegasus.bayofrum.net 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Sun
Apr 29 12:29:02 BST 2012
root at pegasus.bayofrum.net:/usr/obj/usr/src/sys/PEGASUS  amd64