[PATCH v6 02/12] cgroup: implement CFTYPE_NO_PREFIX

[Lord Glauber Costa of Sealand <glommer@parallels.com>]

From: Tejun Heo <tj@kernel.org>

When cgroup files are created, cgroup core automatically prepends the
name of the subsystem as prefix.  This patch adds CFTYPE_NO_PREFIX
which disables the automatic prefix.

This will be used to deprecate cpuacct which will make cpu create and
serve the cpuacct files.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Glauber Costa <glommer@parallels.com>
---
 include/linux/cgroup.h | 1 +
 kernel/cgroup.c        | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 7d73905..7d193f9 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -277,6 +277,7 @@ struct cgroup_map_cb {
 /* cftype->flags */
 #define CFTYPE_ONLY_ON_ROOT	(1U << 0)	/* only create on root cg */
 #define CFTYPE_NOT_ON_ROOT	(1U << 1)	/* don't create on root cg */
+#define CFTYPE_NO_PREFIX	(1U << 2)	/* skip subsys prefix */
 
 #define MAX_CFTYPE_NAME		64
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4855892..2f98398 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2723,7 +2723,8 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cgroup_subsys *subsys,
 
 	simple_xattrs_init(&cft->xattrs);
 
-	if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
+	if (subsys && !(cft->flags & CFTYPE_NO_PREFIX) &&
+	    !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
 		strcpy(name, subsys->name);
 		strcat(name, ".");
 	}
-- 
1.8.1