Bug 1706350

Description of problem:
After a minor upgrade of collectd and collectd-dns the metrics for qtypes are no longer reported as strings (e.g. 'dns_qtype.A'), but with their numeric value (e.g. 'dns_qtype.#1').

Version-Release number of selected component (if applicable):
Old versions:
* collectd-5.8.0-3.el7.x86_64
* collectd-dns-5.8.0-3.el7.x86_64

New versions:
* collectd-5.8.0-4.el7.x86_64
* collectd-dns-5.8.0-4.el7.x86_64

How reproducible:
I'm not really sure how to reproduce this in a clean way. On our physical machines the problem is totally reproducible, but I wasn't able to reproduce it on a fully updated virtual machine (CentOS 7) with latest collectd and bind installed. I have some additional information/ideas, though (see below).

Steps to Reproduce:
$ yum downgrade collectd-5.8.0-3.el7 collectd-dns-5.8.0-3.el7  ## stringified qtype metrics are reported
$ yum install collectd-5.8.0-4.el7 collectd-dns-5.8.0-4.el7    ## numeric qtype metrics are reported

Actual results:
Metric name: host.dns.dns_qtype.#1.value 0.400000 1556968058

Expected results:
Metric name: host.dns.dns_qtype.A.value 0.400000 1556968058

Additional info:
I *guess* this problem is related to the specific configuration of the build machine that produced the packages:
* https://cbs.centos.org/koji/buildinfo?buildID=21280 build for collectd-5.8.0-3.el7.x86_64
* https://cbs.centos.org/koji/buildinfo?buildID=21737 build for collectd-5.8.0-4.el7.x86_64

I've compared the source packages for both builds and there was absolutely nothing related to the functionality of the dns plugin. Also, the build logs didn't give me a clue.

But looking at the code of src/dns.c and src/utils/dns/dns.c it totally looks like neihter the symbol __NAMESER nor __BIND is defined on the later build.

The translation from numeric qtypes to stringified metrics names happens by calling qtype_str on the numeric value here: https://github.com/collectd/collectd/blob/55cf383915/src/dns.c#L364

The function qtype_str looks for the symbols __NAMESER and __BIND (and whether their values are greater than specific dates) and if that's not the case it just prepends a '#' to the numeric value: https://github.com/collectd/collectd/blob/55cf383915/src/utils/dns/dns.c#L914 That's exactly the format I get for the qtype metrics, so I conclude that the default case is executed.

Now I've seen that the symbols __NAMESER and __BIND have been removed from newer versions of glibc in 2016: https://sourceware.org/git/?p=glibc.git;a=commit;h=006768c72a

Looking at one of our machines (with glibc-headers-2.17-260.el7_6.4.x86_64 installed) there is indeed no definition for __NAMESER or __BIND in /usr/include/arpa/nameser.h anymore.

Could you maybe verify whether my hypothesis, that said symbols were defined during the build of collectd-5.8.0-3, but not during the build of collectd-5.8.0-4, could be true? (According to build.log the version of glibc-headers was identical (glibc-headers-2.17-196.el7_4.2.x86_64) for both builds, but maybe the symbols were defined somewhere else?

In the meantime I'll open an issue for upstream, because the check for __NAMESER or __BIND in src/utils/dns/dns.c should be replaced/extended.

I might be wrong with my guess -- maybe you've got a better idea what goes wrong on our machines? If you need further details, please ask. I'll try to provide them (if possible).