On 08/28/2015 10:32 AM, Gunnar Krull wrote:
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.
I think the reason for this is a strncmp in "src/bucoord/commands.c"
line 311:
for (tavols = ps->dupvdlist; add && tavols;
tavols = tavols->next) {
if (strncmp(tavols->name, entries[e].name, l) == 0) {
if ((strcmp(&entries[e].name[l], ".backup") == 0)
|| (strcmp(&entries[e].name[l], ".readonly")
== 0)
|| (strcmp(&entries[e].name[l], "") == 0))
add = 0;
}
}
To find and discard duplicate volumes, the list of volumes as a result
of the current volume set entry is compared to the list of volumes of
the previous volume set entry. A duplicate volume will not be added to
the list.
Unfortunately, the strncmp only compares the first l characters of the
string (l = length of the current volume name).
Also, it compares volume names with and without extensions (e.g .backup):
tavols->name : with extension (e.g. user.test1.backup)
entries[e].name : without extension (e.g. user.test1)
This leads to the problem I described above, for example:
Names of volumes: user.backup, user.test1.backup, user.test2.backup, ...
Volume set userbackup:
Entry 1: server .*, partition .*, volumes: user\..*\.backup
Entry 2: server .*, partition .*, volumes: user\.backup
Resulting list for Entry 1: user.test1.backup, user.test2.backup, ...
Resulting list for Entry 2: user
The string compare for Entry 2 would be:
strncmp("user.test1.backup", "user", 4)
This is true and the volume "user.backup" will not be added to the list.
(I don't understand the following if statement with three strcmp ...)
I hope this is correct and the explanation understandable.
Regards,
Gunnar
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