ipc: introduce message queue copy feature
authorStanislav Kinsbursky <skinsbursky@parallels.com>
Fri, 4 Jan 2013 23:34:55 +0000 (15:34 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 5 Jan 2013 00:11:45 +0000 (16:11 -0800)
commit4a674f34ba04a002244edaf891b5da7fc1473ae8
tree14544a5d49b4a218bac3f5995503c8e208735cef
parentf9dd87f4738c7555aca2cdf8cb2b2326cafb0cad
ipc: introduce message queue copy feature

This patch is required for checkpoint/restore in userspace.

c/r requires some way to get all pending IPC messages without deleting
them from the queue (checkpoint can fail and in this case tasks will be
resumed, so queue have to be valid).

To achive this, new operation flag MSG_COPY for sys_msgrcv() system call
was introduced.  If this flag was specified, then mtype is interpreted as
number of the message to copy.

If MSG_COPY is set, then kernel will allocate dummy message with passed
size, and then use new copy_msg() helper function to copy desired message
(instead of unlinking it from the queue).

Notes:

1) Return -ENOSYS if MSG_COPY is specified, but
   CONFIG_CHECKPOINT_RESTORE is not set.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
include/uapi/linux/msg.h
ipc/msg.c
ipc/msgutil.c
ipc/util.h