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 <t...@kernel.org>
Cc: Glauber Costa <glom...@gmail.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 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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