[PATCH] CGroups: misc cleanups to write_string patchset

[Paul Menage]

CGroups: misc cleanups to write_string patchset

This patch contains cleanups suggested by reviewers for the recent
write_string() patchset:

- pair cgroup_lock_live_group() with cgroup_unlock() in cgroup.c for
 clarity, rather than directly unlocking cgroup_mutex.

- make the return type of cgroup_lock_live_group() a bool

- use a #define'd constant for the local buffer size in read/write functions

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

---
include/linux/cgroup.h |    4 ++--
kernel/cgroup.c        |   21 ++++++++++++---------
2 files changed, 14 insertions(+), 11 deletions(-)

Index: cws2-2.6.26-rc5-mm3/include/linux/cgroup.h
===================================================================
--- cws2-2.6.26-rc5-mm3.orig/include/linux/cgroup.h
+++ cws2-2.6.26-rc5-mm3/include/linux/cgroup.h
@@ -21,11 +21,13 @@
struct cgroupfs_root;
struct cgroup_subsys;
struct inode;
+struct cgroup;

extern int cgroup_init_early(void);
extern int cgroup_init(void);
extern void cgroup_init_smp(void);
extern void cgroup_lock(void);
+extern bool cgroup_lock_live_group(struct cgroup *cgrp);
extern void cgroup_unlock(void);
extern void cgroup_fork(struct task_struct *p);
extern void cgroup_fork_callbacks(struct task_struct *p);
@@ -295,8 +297,6 @@ int cgroup_add_files(struct cgroup *cgrp

int cgroup_is_removed(const struct cgroup *cgrp);

-int cgroup_lock_live_group(struct cgroup *cgrp);
-
int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen);

int cgroup_task_count(const struct cgroup *cgrp);
Index: cws2-2.6.26-rc5-mm3/kernel/cgroup.c
===================================================================
--- cws2-2.6.26-rc5-mm3.orig/kernel/cgroup.c
+++ cws2-2.6.26-rc5-mm3/kernel/cgroup.c
@@ -1331,10 +1331,10 @@ enum cgroup_filetype {
 * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive.
 * @cgrp: the cgroup to be checked for liveness
 *
- * Returns true (with lock held) on success, or false (with no lock
- * held) on failure.
+ * On success, returns true; the lock should be later released with
+ * cgroup_unlock(). On failure returns false with no lock held.
 */
-int cgroup_lock_live_group(struct cgroup *cgrp)
+bool cgroup_lock_live_group(struct cgroup *cgrp)
{
	mutex_lock(&cgroup_mutex);
	if (cgroup_is_removed(cgrp)) {
@@ -1351,7 +1351,7 @@ static int cgroup_release_agent_write(st
	if (!cgroup_lock_live_group(cgrp))
		return -ENODEV;
	strcpy(cgrp->root->release_agent_path, buffer);
-	mutex_unlock(&cgroup_mutex);
+	cgroup_unlock();
	return 0;
}

@@ -1362,16 +1362,19 @@ static int cgroup_release_agent_show(str
		return -ENODEV;
	seq_puts(seq, cgrp->root->release_agent_path);
	seq_putc(seq, '\n');
-	mutex_unlock(&cgroup_mutex);
+	cgroup_unlock();
	return 0;
}

+/* A buffer size big enough for numbers or short strings */
+#define CGROUP_LOCAL_BUFFER_SIZE 64 
+
static ssize_t cgroup_write_X64(struct cgroup *cgrp, struct cftype *cft,
				struct file *file,
				const char __user *userbuf,
				size_t nbytes, loff_t *unused_ppos)
{
-	char buffer[64];
+	char buffer[CGROUP_LOCAL_BUFFER_SIZE];
	int retval = 0;
	char *end;

@@ -1405,7 +1408,7 @@ static ssize_t cgroup_write_string(struc
				   const char __user *userbuf,
				   size_t nbytes, loff_t *unused_ppos)
{
-	char local_buffer[64];
+	char local_buffer[CGROUP_LOCAL_BUFFER_SIZE];
	int retval = 0;
	size_t max_bytes = cft->max_write_len;
	char *buffer = local_buffer;
@@ -1459,7 +1462,7 @@ static ssize_t cgroup_read_u64(struct cg
			       char __user *buf, size_t nbytes,
			       loff_t *ppos)
{
-	char tmp[64];
+	char tmp[CGROUP_LOCAL_BUFFER_SIZE];
	u64 val = cft->read_u64(cgrp, cft);
	int len = sprintf(tmp, "%llu\n", (unsigned long long) val);

@@ -1471,7 +1474,7 @@ static ssize_t cgroup_read_s64(struct cg
			       char __user *buf, size_t nbytes,
			       loff_t *ppos)
{
-	char tmp[64];
+	char tmp[CGROUP_LOCAL_BUFFER_SIZE];
	s64 val = cft->read_s64(cgrp, cft);
	int len = sprintf(tmp, "%lld\n", (long long) val);

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