cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time

Alter the ss->can_attach and ss->attach functions to be able to deal with
a whole threadgroup at a time, for use in cgroup_attach_proc.  (This is a
pre-patch to cgroup-procs-writable.patch.)

Currently, new mode of the attach function can only tell the subsystem
about the old cgroup of the threadgroup leader.  No subsystem currently
needs that information for each thread that's being moved, but if one were
to be added (for example, one that counts tasks within a group) this bit
would need to be reworked a bit to tell the subsystem the right
information.

[hidave.darkstar@gmail.com: fix build]
Signed-off-by: Ben Blum <bblum@google.com>
Signed-off-by: Paul Menage <menage@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Matt Helsley <matthltc@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Dave Young <hidave.darkstar@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 3ac78a2f4b5a..b62bb9294d0c 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -425,10 +425,11 @@ struct cgroup_subsys {
                                                   struct cgroup *cgrp);
         int (*pre_destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
         void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
-        int (*can_attach)(struct cgroup_subsys *ss,
-                          struct cgroup *cgrp, struct task_struct *tsk);
+        int (*can_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
+                          struct task_struct *tsk, bool threadgroup);
         void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
-                        struct cgroup *old_cgrp, struct task_struct *tsk);
+                        struct cgroup *old_cgrp, struct task_struct *tsk,
+                        bool threadgroup);
         void (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
         void (*exit)(struct cgroup_subsys *ss, struct task_struct *task);
         int (*populate)(struct cgroup_subsys *ss,