[PATCH 2/3] memcg: put a restriction on writing memory.force_empty

[Li Zefan]

We can write whatever to memory.force_empty:

        echo 999 > memory.force_empty
        echo wow > memory.force_empty

This is odd, so let's make '1' to be the only valid value.

Signed-off-by: Li Zefan <lizf at cn.fujitsu.com>
---
 mm/memcontrol.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eb681a6..6145031 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -868,15 +868,18 @@ static ssize_t mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 				mem_cgroup_write_strategy);
 }
 
-static ssize_t mem_force_empty_write(struct cgroup *cont,
-				struct cftype *cft, struct file *file,
-				const char __user *userbuf,
-				size_t nbytes, loff_t *ppos)
+static int mem_force_empty_write(struct cgroup *cont, struct cftype *cft,
+				 u64 val)
 {
-	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
-	int ret = mem_cgroup_force_empty(mem);
-	if (!ret)
-		ret = nbytes;
+	struct mem_cgroup *mem;
+	int ret;
+
+	if (val != 1)
+		return -EINVAL;
+
+	mem = mem_cgroup_from_cont(cont);
+	ret = mem_cgroup_force_empty(mem);
+
 	return ret;
 }
 
@@ -935,7 +938,7 @@ static struct cftype mem_cgroup_files[] = {
 	},
 	{
 		.name = "force_empty",
-		.write = mem_force_empty_write,
+		.write_u64 = mem_force_empty_write,
 	},
 	{
 		.name = "stat",
-- 
1.5.4.rc3