cgroup: notify ns_cgroup deprecated

The ns_cgroup will be removed very soon.  Let's warn, for this version,
ns_cgroup is deprecated.

Make ns_cgroup and clone_children exclusive.  If the clone_children is set
and the ns_cgroup is mounted, let's fail with EINVAL when the ns_cgroup
subsys is created (a printk will help the user to understand why the
creation fails).

Update the feature remove schedule file with the deprecated ns_cgroup.
Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/feature-removal-schedule.txt

@@ -526,6 +526,23 @@ Who:	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
 
 ----------------------------
 
+What:   namespace cgroup (ns_cgroup)
+When:   2.6.38
+Why:    The ns_cgroup leads to some problems:
+	* cgroup creation is out-of-control
+	* cgroup name can conflict when pids are looping
+	* it is not possible to have a single process handling
+	a lot of namespaces without falling in a exponential creation time
+	* we may want to create a namespace without creating a cgroup
+
+	The ns_cgroup is replaced by a compatibility flag 'clone_children',
+	where a newly created cgroup will copy the parent cgroup values.
+	The userspace has to manually create a cgroup and add a task to
+	the 'tasks' file.
+Who:    Daniel Lezcano <daniel.lezcano@free.fr>
+
+----------------------------
+
 What:	iwlwifi disable_hw_scan module parameters
 When:	2.6.40
 Why:	Hareware scan is the prefer method for iwlwifi devices for

kernel/ns_cgroup.c

@@ -85,6 +85,14 @@ static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
 		return ERR_PTR(-EPERM);
 	if (!cgroup_is_descendant(cgroup, current))
 		return ERR_PTR(-EPERM);
+	if (test_bit(CGRP_CLONE_CHILDREN, &cgroup->flags)) {
+		printk("ns_cgroup can't be created with parent "
+		       "'clone_children' set.\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	printk_once("ns_cgroup deprecated: consider using the "
+		    "'clone_children' flag without the ns_cgroup.\n");
 
 	ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);
 	if (!ns_cgroup)