[rrd-developers] Improvements to rrd_strerror.

[Florian Forster]

Hi Tobi,

please consider the attached patch which changes the error handling in
`rrd_strerror' a little. A user of collectd got the following error
message:

  mmaping file '...': strerror_r failed. sorry!

It would have helped to debug his problem to know which error actually
occurred. With the attached patch, the error message will become:

  mmaping file '...': strerror_r (123) failed. sorry!

Where `123' is the error code passed to `rrd_strerror'.

I'm afraid I don't know why `strerror_r' failed in this case, the error
that was passed to it was most likely EINTR, so nothing fancy.. But I
have a suspicion..:

Please note, that error checking with
  if (strerror_r (...)) { ... }
is problematic for portability: Some systems (the GNU libc, unless given
_XOPEN_SOURCE=600, for example) export a version of `strerror_r' that
returns a pointer to the buffer it just filled, so it can be used just
like `strerror'. On such systems the block will always be executed
*except* when an error occurred.

Regards,
-octo
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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