This patch provides support for thread and process CPU time clocks in the
POSIX clock interface.  Both the existing utime and utime+stime information
(already available via getrusage et al) can be used, as well as a new
(potentially) more precise and accurate clock (which cannot distinguish user
from system time).  The clock used is that provided by the `sched_clock'
function already used internally by the scheduler.  This gives a way for
platforms to provide the highest-resolution CPU time tracking that is
available cheaply, and some already do so (such as x86 using TSC).  Because
this clock is already sampled internally by the scheduler, this new tracking
adds only the tiniest new overhead to accomplish the bookkeeping.

Some notes:

This allows per-thread clocks to be accessed only by other threads in the same
process.  The only POSIX calls that access these are defined only for
in-process use, and having this check is necessary for the userland
implementations of the POSIX clock functions to robustly refuse stale
clockid_t's in the face of potential PID reuse.

This makes no constraint on who can see whose per-process clocks.  This
information is already available for the VIRT and PROF (i.e.  utime and stime)
information via /proc.  I am open to suggestions on if/how security
constraints on who can see whose clocks should be imposed.

The SCHED clock information is now available only via clock_* syscalls.  This
means that per-thread information is not available outside the process. 
Perhaps /proc should show sched_time as well?  This would let ps et al show
this more-accurate information.

When this code is merged, it will be supported in glibc.  I have written the
support and added some test programs for glibc, which are what I mainly used
to test the new kernel code.  You can get those here:

	http://people.redhat.com/roland/glibc/kernel-cpuclocks.patchSigned-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>