Re: [PATCH] Fix multiple minor tzset glitches [BZ #24004]

[Florian Weimer <fw at deneb dot enyo dot de>]

* Yann Droneaud:

>> With the mapped file, there is no file polling as such, just a few
>> memory loads.  The cost is that the system administrator needs to run a
>> command after updating any of the covered configuration files, which is
>> why this has to be optional (and opt-in per configuration file).  There
>> probably aren't that many configuration files where this is needed.
>
> I think there's a caveat with memory mapped file: if a new version of 
> the configuration file is created and renamed to the configuration
> location, replacing the previous one, applications won't notice the
> update, as the memory mapping will still reference the previous file.

Sure, but the configuration compiler can write a flag to the old
mapping that indicates it is out of date.  Checking that flag has to
be part of the sequence that verifies if polling is required.

I believe nscd does something similar when it invalidates a mapping.