semaphore problem with Bakbone's Netvault on FreeBSD 4.10

[Georg Altmann]

In the meantime Bakbone support managed to send me a working (binary) patch 
fixing the problem and I was asked by Bakbone to post this information. So, 
if you experience the problem described below, please contact Bakbone 
support.

Best regards,
Georg Altmann

--On Montag, November 22, 2004 19:33:51 +0100 Georg Altmann 
<galtmann at las-cad.com> wrote:

> I have a problem running the backup software Netvault from Bakbone
> (http://www.bakbone.com) under FreeBSD 4.10.
> We are using Netvault to make backups of two servers and several
> workstations in our network. Backups are first staged to disk and later
> transferred to an ADIC FastStor 2 (LTO 1) library.
>
> The problem occurs when the backup is transferred from disk to tape and
> if the backup job spans multiple tapes (not virtual media!): Netvault
> recognizes the end-of-media, loads a new media for the job and then hangs
> endlessly trying to write to the new media.
>
> Bakbone claims, that this is a problem with SysV shared memory and
> semaphores in FreeBSD (and therefore not their software). Their support
> also sent me a patch for Netvault (unfortunately not a binary one, so I
> cannot test it) which is allegedly known to work around the problem. I
> attached it below. Note the added "#if defined(PLATFORM_FREEBSD)" bits in
> the code. To my understanding, the patched code polls the semaphore
> instead of waiting for it.
> Please also note, that I configured Netvault to use network sockets
> instead of shared mem for the transfer and the problem persists (I did
> this by only selecting "TCP Data Transfer" in the configure device tab
> for both the tape and the virtual library and by adding [Data
> Channels]\nForce Sockets=TRUE to configure.cfg as proposed by Bakbone
> support, for anyone familiar with netvault). So I assume, the problem is
> really only related to semaphores and not at all to shared memory(?).
>
> I hope that someone can guess from the code if this really leads to a
> deadlock because of a FreeBSD bug in SysV sempaphore handling.
> I have already skimmed FreeBSD PRs for semaphore bugs, but no post really
> seemed related to this specific problem (see
> http://www.freebsd.org/cgi/query-pr-summary.cgi?category=&severity=&prior
> ity=&class=&state=&sort=none&text=semaphore&responsible=&multitext=&origi
> nator=&closedtoo=on&release=). So, maybe somebody is able to make clear
> whether I should urge Bakbone to fix their buggy software or look for a
> patch for the FreeBSD kernel and/or libraries.

[ removed ]


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