[RFC/PATCH 8/8]: CGroup Files: Convert res_counter_write() to be a cgroups write_string() handler

[menage]

Currently read_counter_write() is a raw file handler even though it's
ultimately taking a number, since in some cases it wants to
pre-process the string when converting it to a number.

This patch converts res_counter_write() from a raw file handler to a
write_string() handler; this allows some of the boilerplate
copying/locking/checking to be removed, and simplies the cleanup path,
since these functions are now performed by the cgroups framework.

Signed-off-by: Paul Menage <menage@xxxxxxxxxx>

---
 include/linux/res_counter.h |    4 ++--
 kernel/res_counter.c        |   36 +++++++++---------------------------
 mm/memcontrol.c             |   11 +++++------
 3 files changed, 16 insertions(+), 35 deletions(-)

Index: cgroup-2.6.25-mm1/include/linux/res_counter.h
===================================================================
--- cgroup-2.6.25-mm1.orig/include/linux/res_counter.h
+++ cgroup-2.6.25-mm1/include/linux/res_counter.h
@@ -63,8 +63,8 @@ u64 res_counter_read_u64(struct res_coun
 ssize_t res_counter_read(struct res_counter *counter, int member,
 		const char __user *buf, size_t nbytes, loff_t *pos,
 		int (*read_strategy)(unsigned long long val, char *s));
-ssize_t res_counter_write(struct res_counter *counter, int member,
-		const char __user *buf, size_t nbytes, loff_t *pos,
+int res_counter_write(struct res_counter *counter, int member,
+		char *buffer,
 		int (*write_strategy)(char *buf, unsigned long long *val));
 
 /*
Index: cgroup-2.6.25-mm1/kernel/res_counter.c
===================================================================
--- cgroup-2.6.25-mm1.orig/kernel/res_counter.c
+++ cgroup-2.6.25-mm1/kernel/res_counter.c
@@ -102,44 +102,26 @@ u64 res_counter_read_u64(struct res_coun
 	return *res_counter_member(counter, member);
 }
 
-ssize_t res_counter_write(struct res_counter *counter, int member,
-		const char __user *userbuf, size_t nbytes, loff_t *pos,
-		int (*write_strategy)(char *st_buf, unsigned long long *val))
+int res_counter_write(
+	struct res_counter *counter, int member,
+	char *buf,
+	int (*write_strategy)(char *st_buf, unsigned long long *val))
 {
-	int ret;
-	char *buf, *end;
+	char *end;
 	unsigned long flags;
 	unsigned long long tmp, *val;
 
-	buf = kmalloc(nbytes + 1, GFP_KERNEL);
-	ret = -ENOMEM;
-	if (buf == NULL)
-		goto out;
-
-	buf[nbytes] = '\0';
-	ret = -EFAULT;
-	if (copy_from_user(buf, userbuf, nbytes))
-		goto out_free;
-
-	ret = -EINVAL;
-
-	strstrip(buf);
 	if (write_strategy) {
-		if (write_strategy(buf, &tmp)) {
-			goto out_free;
-		}
+		if (write_strategy(buf, &tmp))
+			return -EINVAL;
 	} else {
 		tmp = simple_strtoull(buf, &end, 10);
 		if (*end != '\0')
-			goto out_free;
+			return -EINVAL;
 	}
 	spin_lock_irqsave(&counter->lock, flags);
 	val = res_counter_member(counter, member);
 	*val = tmp;
 	spin_unlock_irqrestore(&counter->lock, flags);
-	ret = nbytes;
-out_free:
-	kfree(buf);
-out:
-	return ret;
+	return 0;
 }
Index: cgroup-2.6.25-mm1/mm/memcontrol.c
===================================================================
--- cgroup-2.6.25-mm1.orig/mm/memcontrol.c
+++ cgroup-2.6.25-mm1/mm/memcontrol.c
@@ -848,13 +848,12 @@ static u64 mem_cgroup_read(struct cgroup
 				    cft->private);
 }
 
-static ssize_t mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
-				struct file *file, const char __user *userbuf,
-				size_t nbytes, loff_t *ppos)
+static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
+			    char *buffer)
 {
 	return res_counter_write(&mem_cgroup_from_cont(cont)->res,
-				cft->private, userbuf, nbytes, ppos,
-				mem_cgroup_write_strategy);
+				 cft->private, buffer,
+				 mem_cgroup_write_strategy);
 }
 
 static int mem_cgroup_reset(struct cgroup *cont, unsigned int event)
@@ -929,7 +928,7 @@ static struct cftype mem_cgroup_files[] 
 	{
 		.name = "limit_in_bytes",
 		.private = RES_LIMIT,
-		.write = mem_cgroup_write,
+		.write_string = mem_cgroup_write,
 		.read_u64 = mem_cgroup_read,
 	},
 	{

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