__ASSUME_PRIVATE_FUTEX and __ASSUME_FUTEX_CLOCK_REALTIME

[Torvald Riegel]

On Fri, 2014-06-20 at 16:15 -0700, Roland McGrath wrote: 
> > __ASSUME_PRIVATE_FUTEX and __ASSUME_FUTEX_CLOCK_REALTIME are defined for 
> > all supported Linux kernel versions.  Should we say they are a required 
> > part of the futex interface for any system, whether or not using the Linux 
> > kernel, that may wish to use NPTL, and so remove these macros and all 
> > conditionals testing them everywhere in glibc, not just in 
> > sysdeps/unix/sysv/linux/ files?
> 
> Please, no.  Other systems that provide a futex layer may well provide a
> much less fully featureful one than Linux has.

Roland, do you see any reason why having __ASSUME_FUTEX_CLOCK_REALTIME
or not couldn't be contained in the internal futex abstraction layer?
That is, we could have a futex_timed_wait that just does the right thing
on Linux, and does something different but conforming on non-Linux?
This might be similar for __ASSUME_PRIVATE_FUTEX, but I haven't looked
at this closely.

Thoughts?