[OpenAFS] backup - order of entries in volume set

Gunnar Krull gklists@cs.uni-goettingen.de
Fri, 28 Aug 2015 10:32:01 +0200

On 08/28/2015 03:02 AM, Benjamin Kaduk wrote:
> On Thu, 27 Aug 2015, Gunnar Krull wrote:
>> Hi,
>> when I have a backup Volume Set defined in this order, the volume
>> "user.backup" is not included into the backup:
>> Volume set userbackup:
>>      Entry 1: server .*, partition .*, volumes: user\..*\.backup
>>      Entry 2: server .*, partition .*, volumes: user\.backup
>> But when I change the order of the two Volume Set entries, the volume
>> "user.backup" is included:
>> Volume set userbackup:
>>      Entry   1: server .*, partition .*, volumes: user\.backup
>>      Entry   2: server .*, partition .*, volumes: user\..*\.backup
>> It's strange, but the order is irrelevant for another Volume Set. The
>> difference to the example above is, that the resulting volume list to be
>> backuped only consists of two volumes. Namely: "svn.backup" and
>> "svn.test.backup".
>> I couldn't find an explanation for this behavior.
>> Is there something wrong in my understanding of the volume set definitions?
> Most likely, there is a bug.
> Unfortunately, the backup code is some of the least-maintained and worst
> code in the tree that we still have some expectation of people actually
> using (which excludes kauth, among other things), so the reason is
> unlikely to be clear solely from code examination.  To make matters worse,
> there are a few codepaths that could be taken; in what I think is the
> common case, the regex is actually evaluated on the vlserver, not on the
> machine running the backup utility.  (Note that this means that different
> calls may get different results, if the vlservers are not homogeneous and
> have different regex libraries on them!)

All servers are running on Debian Wheezy. So it should be quite homogeneous.
I observed this behavior with OpenAFS 1.6.9 and now also with 1.6.14.

> As a first debugging step, I would suggest using wireshark or similar to
> capture traffic between the backup utility and the vlserver(s) to confirm
> whether the problem exists in the vlserver code or on the client side.

The Wireshark records show that the backup client gets the complete 
volume list from the vlserver correctly, independent of the order in the 
volume set definition.
I can see the two requests to the vlserver for both volume set entries 
and their corresponding responses including the volumes correctly.

But the output and execution of the backup client depends on the order, 
like I described above.

So, it seems to be the backup client that skips the volume and doesn't 
consider it for the actual backup.