[PATCH]Futex doc.

[ffrederick]

Hi,
     Someone could help me having a complete futex doc ?
Here's a first version :

Regards,
Fabian

Documentation for futexes               kernel version 2.6.0-test6
        (c) 2003 Fabian Frederick <ffrederick@xxxxxxxxxxxxxxxxxxxxx>

Note : Based on user man page by Bert Hubert - Comments by Jamie Lokier.

===============================================================================

This file contains documentation for Fast Userspace Mutexes.
For complete authors list and sources you can read /kernel/futex.c

===============================================================================

What's a mutex ?

Mutex stands for mutual exclusion.In other words, it helps synchronizing processes
against shared memory access for instance.

Futex is basically a counter whose value is atomically updated in userland.
Any concurrent access will be managed in kernel space.

3 futex types exist :

	-shared
	-private
	-both

===============================================================================

Linux implementation

You can find POSIX mutex adaptation through futexes.User point of view and 
documentation can be found at http://ds9a.nl/futex-manpages/

Futex interface is sys_futex syscall.Here are recognized operations:

	-FUTEX_WAIT    : Wait a process to up futex.
	-FUTEX_WAKE    : Wake up all futex waiters.
	-FUTEX_FD      : Associate a file descriptor to futex
	-FUTEX_REQUEUE : Requeue all waiters hashed on one physical page to another
                         physical page.



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