PR26125 patch: debuginfod client cache cleanup

[Mark Wielaard]

Hi Frank,

On Mon, 2021-04-26 at 11:54 -0400, Frank Ch. Eigler via Elfutils-devel wrote:
>     PR26125: debuginfod client cache - rmdir harder
>     
>     With PR25365, we accidentally lost the ability to rmdir client-cache
>     directories corresponding to buildids.  Bring this back, with some
>     attention to a possible race between a client doing cleanup and
>     another client doing lookups at the same time.

OK. So if I understand correctly the trailing / in the regexp made
directories not match (because their name doesn't actually end in a /)?

And even with the new check:

> if (now - f->fts_statp->st_mtime >= max_unused_age)

there is still a super tiny race if multiple clients might be running,
pass this check, then another client tries to create the dir and file,
but right before:

> +    fd = mkstemp (target_cache_tmppath);

one of the other clients gets to run the rmdir.

But then we just retry again and hope no other client was stuck right
before the rmdir.

Looks good. I cannot think of a better way to resolve this race.

Thanks,

Mark