Simplify sendmmsg code

[Joseph Myers]

On Fri, 12 May 2017, Florian Weimer wrote:

> On 05/10/2017 02:14 PM, Adhemerval Zanella wrote:
> > Indeed the emulation brings a lot of issue, but it allows us to use the
> > system
> > specific syscalls on generic code without relying on additional checks for
> > functionality existence.  However I think we can to Linux optimizations in
> > generic code less intrusive way if necessary with a different approach,
> > maybe
> > by implementing the functionally in a more constrained way and reimplement
> > in the target system.
> 
> Yes, optimizations are fine.  But I think it is wrong to expose the fallback
> implementation to applications as an implementation of the system call, when
> in fact the semantics are different.  Every time we do this, it comes back to
> haunt as eventually (see posix_fallocate or euidaccess for examples).

Or the pselect emulation (for Linux, now only used on MicroBlaze); see bug 
9813.

-- 
Joseph S. Myers
joseph@codesourcery.com