[GPGME PATCH] core: Restore get_max_fds optimization on Linux

[Daniel Kahn Gillmor]

On Wed 2017-09-20 08:52:22 +0200, Werner Koch wrote:
> No question, it is on my shortlist and will be part of the next release.

great!  Should we open a ticket to keep track of it?

> Colin: Thanks for coming up with the method.  We might need a test or at
> least a configure option to disable it for older linux kernels.  I also
> need to see whether it needas to be ported to other components of GnuPG.

If we make it optional, a configure option should be sufficient, and it
should default to using this optimization.  Please *don't* make the
build choose a default based on the features of the currently-running
kernel interface, most people who run GnuPG run it on a different
machine than they build it on.

>> pretty severe performance degradation in GPGME on Linux platforms that
>> was introduced between version 1.8.0 and 1.9.0.
>
> Actually the Linux specific optimization was only introduced with 1.7.0
> on 2016-09-21 and disabled in 1.9.0 on 2017-03-28.  I didn't liked to
> disable it but had to do it because of a real world race condition.

is there an explicit example of this race condition?  debian stable is
currently shipping gpgme 1.8.0, and if there's a real risk here i might
want to backport this for a future point release.

     --dkg
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