Re: implementing Futex

[Darren Hart]

Arnd Bergmann wrote:
> On Friday 14 August 2009, Michael Schnell wrote:
> > Arnd Bergmann wrote:
> > > The man page says that the last parameter is ignored for op=FUTEX_WAKE,
> > > which is correct. The code that you were looking at however is for
> > > of=FUTEX_WAKE_OP, which is not documented as of manpages-3.22.
> > >
> > > It was added by Jakub back in 2005, but if he wrote a documentation
> > > for it, it never went into the man pages package. On a similar
> > > note, Ingo also added other futex operations that are not documented
> > > yet.
> > Thus in any documented software, the quite complex stuff in
> > "futex_atomic_op_inuser", which is provided in several different
> > "futex.h" files for all those architectures never is used ?
>
> No, my point was that futex_atomic_op_inuser is indeed used
> correctly, it's just not documented.
> See http://lwn.net/Articles/148830/ for the initial posting
>
> > Is there any viable use for this ?
>
> glibc heavily uses it for the pthreads implementation.
>
> > Would it not be appropriate either to do a documentation or to remove it ?
>
> Adding documentation, yes.

I also recently added two futex op codes which need to be added to the 
man page, but they are documented in Documentation/futex-requeue-pi.txt. 
  Documentation/pi-futex.txt documents the FUTEX_(UN)LOCK_PI opcodes 
which aren't in the man pages either.

--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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