cgroups: add the trigger callback to struct cftype

Trigger callback can be used to receive a kick-up from the user space.  The
string written is ignored.

The cftype->private is used for multiplexing events.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Paul Menage <menage@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 0 deletions

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 785a01cfb49..2d1d151258c 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -243,6 +243,14 @@ struct cftype {
          */
         int (*write_s64) (struct cgroup *cgrp, struct cftype *cft, s64 val);
 
+        /*
+         * trigger() callback can be used to get some kick from the
+         * userspace, when the actual string written is not important
+         * at all. The private field can be used to determine the
+         * kick type for multiplexing.
+         */
+        int (*trigger)(struct cgroup *cgrp, unsigned int event);
+
         int (*release) (struct inode *inode, struct file *file);
 };
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 436e26f4d62..7c8cc514187 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1410,6 +1410,10 @@ static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
                 return cft->write(cgrp, cft, file, buf, nbytes, ppos);
         if (cft->write_u64 || cft->write_s64)
                 return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
+        if (cft->trigger) {
+                int ret = cft->trigger(cgrp, (unsigned int)cft->private);
+                return ret ? ret : nbytes;
+        }
         return -EINVAL;
 }