From: Manfred Spraul <manfred@colorfullife.com>

My discussion with Ulrich had one result:

- mq_setattr can accept implementation defined flags.  Right now we have
  none, but we might add some later (e.g.  switch to CLOCK_MONOTONIC for
  mq_timed{send,receive} or something similar).  When we add flags, we
  might need the fields for additional information.  And they don't hurt.
  Therefore add four __reserved fields to mq_attr.

- fail mq_setattr if we get unknown flags - otherwise glibc can't detect
  if it's running on a future kernel that supports new features.

- use memset to initialize the mq_attr structure - theoretically we could
  leak kernel memory.

- Only set O_NONBLOCK in mq_attr, explicitely clear O_RDWR & friends.
  openposix uses getattr, attr |=O_NONBLOCK, setattr - a sane approach. 
  Without clearing O_RDWR, this fails.

I've retested all openposix conformance tests with the new patch - the two
new FAILED tests check undefined behavior.  Note that I won't have net
access until Sunday - if the message queue patch breaks something important
either ask Krzysztof or drop it.

Ulrich had another good idea for SIGEV_THREAD, but I must think about it.
It would mean less complexitiy in glibc, but more code in the kernel.  I'm
not yet convinced that it's overall better.