[ClusterLabs/libqb] 633f26: logging: Remove linker 'magic' and just use static...

[Chrissie Caulfield]

  Branch: refs/heads/master
  Home:   https://github.com/ClusterLabs/libqb
  Commit: 633f2624a7b42eb8e227e8e0e9f584d80ee3ead2
     
https://github.com/ClusterLabs/libqb/commit/633f2624a7b42eb8e227e8e0e9f58...
  Author: Chrissie Caulfield <ccaulfie(a)redhat.com&gt;
  Date:   2018-09-27 (Thu, 27 Sep 2018)

  Changed paths:
    M configure.ac
    M include/qb/qbconfig.h.in
    M include/qb/qblog.h
    M lib/Makefile.am
    M lib/libqb.pc.in
    M lib/log.c

  Log Message:
  -----------
  logging: Remove linker 'magic' and just use statics for logging callsites
(#322)

It is my (and several others') opinion that the linker 'magic' used to
maintain callsite data in libqb is hugely over complicated and unnecessarily fragile.
It's main purpose seems to have been to improve performance but empirical testing
shows this to be tiny at best. The overhead of sprintf makes minor optimisations in this
code pointless.

With this code removed, libqb allocates callsites using a C static variable at run-time.
This sounds bad but in actuality it merely moves the allocation from program load time to
the first few milliseconds of program run-time. Applications like corosync and pacemaker
spend most of their time in small loops doing the same work over and over again so the
overhead doesn't apply and jitter does not occur.

We've tested this with corosync and pacemaker under valgrind and massif and the
differences are minimal and even then only show up under artificial stress testing.

For this change I've bumped the soname up to 20 to indicate this is an incompatible
change. I'm open to suggestions as to a release number but am currently thinking of
2.0.0



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