I've been working on a patch that is a roll up of Andrew Morton's patch, and
also of some work by Nick Pollitt to use a prctl() interface to the
cpus_allowed bitmask.  It also includes a new bitmask 'launch_policy' which
allows a process to set a launch policy which is used to determine it's
childrens' cpus_allowed bitmasks prior to launch.

The patch is against 2.4.10.  It can be found on
http://sourceforge.com/projects/lse and I'll also attatch the most recent
version below.

Robert,
	There are two reasons not to use the cpus_online_map.
	1. It isn't (or at least wasn't as of 2.4.10) available on all architectures.
	2. If cpus are added, or removed, the bitmask the user originally requested is
effectively ignored.  ie: if the user tries to set cpus_allowed to 0x0000ffff
and we mask that against the current online map (0x00000003 in your example),
and then another cpu comes online, the cpus_allowed bitmask will not be updated
to reflect this change.

Ingo,
	I'm going to look into using the set-affinity patch you posted with my patch. 
I also agree that /proc is not the best way to access this data, but I *do*
believe it is *a* good way.  I think that having both interfaces (/proc and a
syscall) gives us the best of both worlds.

Enjoy!

-matt

P.S.-please CC any replies, as I'm not on the list.