CGroups _s64 files: add cgroups read_s64/write_s64 file methods

These patches add cgroups read_s64 and write_s64 control file methods (the
signed equivalent of read_u64/write_u64) and use them to implement the
cpu.rt_runtime_us control file in the CFS cgroup subsystem.

This patch:

These are the signed equivalents of the read_u64/write_u64 methods

Signed-off-by: Paul Menage <menage@google.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/cgroup.c

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index b5ef0c4..bd6122c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1299,14 +1299,13 @@
 	FILE_RELEASE_AGENT,
 };
 
-static ssize_t cgroup_write_u64(struct cgroup *cgrp, struct cftype *cft,
+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];
 	int retval = 0;
-	u64 val;
 	char *end;
 
 	if (!nbytes)
@@ -1318,12 +1317,17 @@
 
 	buffer[nbytes] = 0;     /* nul-terminate */
 	strstrip(buffer);
-	val = simple_strtoull(buffer, &end, 0);
-	if (*end)
-		return -EINVAL;
-
-	/* Pass to subsystem */
-	retval = cft->write_u64(cgrp, cft, val);
+	if (cft->write_u64) {
+		u64 val = simple_strtoull(buffer, &end, 0);
+		if (*end)
+			return -EINVAL;
+		retval = cft->write_u64(cgrp, cft, val);
+	} else {
+		s64 val = simple_strtoll(buffer, &end, 0);
+		if (*end)
+			return -EINVAL;
+		retval = cft->write_s64(cgrp, cft, val);
+	}
 	if (!retval)
 		retval = nbytes;
 	return retval;
@@ -1404,8 +1408,8 @@
 		return -ENODEV;
 	if (cft->write)
 		return cft->write(cgrp, cft, file, buf, nbytes, ppos);
-	if (cft->write_u64)
-		return cgroup_write_u64(cgrp, cft, file, buf, nbytes, ppos);
+	if (cft->write_u64 || cft->write_s64)
+		return cgroup_write_X64(cgrp, cft, file, buf, nbytes, ppos);
 	return -EINVAL;
 }
 
@@ -1421,6 +1425,18 @@
 	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
 }
 
+static ssize_t cgroup_read_s64(struct cgroup *cgrp, struct cftype *cft,
+			       struct file *file,
+			       char __user *buf, size_t nbytes,
+			       loff_t *ppos)
+{
+	char tmp[64];
+	s64 val = cft->read_s64(cgrp, cft);
+	int len = sprintf(tmp, "%lld\n", (long long) val);
+
+	return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
+}
+
 static ssize_t cgroup_common_file_read(struct cgroup *cgrp,
 					  struct cftype *cft,
 					  struct file *file,
@@ -1477,6 +1493,8 @@
 		return cft->read(cgrp, cft, file, buf, nbytes, ppos);
 	if (cft->read_u64)
 		return cgroup_read_u64(cgrp, cft, file, buf, nbytes, ppos);
+	if (cft->read_s64)
+		return cgroup_read_s64(cgrp, cft, file, buf, nbytes, ppos);
 	return -EINVAL;
 }