[PATCH 1/5] cgroup: implement CFTYPE_NO_PREFIX

[Tejun Heo]

When cgroup files are created, cgroup core automatically prepends the
name of the subsystem as prefix.  This patch adds CFTYPE_NO_ which
disables the automatic prefix.  This is to work around historical
baggages and shouldn't be used for new files.

This will be used to move "cgroup.event_control" from cgroup core to
memcg.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Glauber Costa <glommer@xxxxxxxxx>
---
 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 c40e508..30d6ec4 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -405,6 +405,7 @@ enum {
 	CFTYPE_ONLY_ON_ROOT	= (1 << 0),	/* only create on root cgrp */
 	CFTYPE_NOT_ON_ROOT	= (1 << 1),	/* don't create on root cgrp */
 	CFTYPE_INSANE		= (1 << 2),	/* don't create if sane_behavior */
+	CFTYPE_NO_PREFIX	= (1 << 3),	/* (DON'T USE FOR NEW FILES) no subsys prefix */
 };
 
 #define MAX_CFTYPE_NAME		64
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index c02a288..1b87e2b 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2749,7 +2749,8 @@ static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft)
 	umode_t mode;
 	char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
 
-	if (cft->ss && !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
+	if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) &&
+	    !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) {
 		strcpy(name, cft->ss->name);
 		strcat(name, ".");
 	}
-- 
1.8.3.1

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