sys_unshare system call handler function accepts the same flags as clone
system call, checks constraints on each of the flags and invokes corresponding
unshare functions to disassociate respective process context if it was being
shared with another task.

Here is the link to a program for testing unshare system call.

http://prdownloads.sourceforge.net/audit/unshare_test.c?download

Please note that because of a problem in rmdir associated with bind mounts and
clone with CLONE_NEWNS, the test fails while trying to remove temporary test
directory.  You can remove that temporary directory by doing rmdir, twice,
from the command line.  The first will fail with EBUSY, but the second will
succeed.  I have reported the problem to Ram Pai and Al Viro with a small
program which reproduces the problem.  Al told us yesterday that he will be
looking at the problem soon.  I have tried multiple rmdirs from the
unshare_test program itself, but for some reason that is not working.  Doing
two rmdirs from command line does seem to remove the directory.
Signed-off-by: Janak Desai <janak@us.ibm.com>
Cc: Al Viro <viro@ftp.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>