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>

---
 include/linux/cgroup.h |    8 ++++++++
 kernel/cgroup.c        |    4 ++++
 2 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 785a01c..2d1d151 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 e8e8ec4..f2d8f25 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;
 }
 
-- 
1.5.3.4

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