[PATCH v3 5/6] ovl: opt-in for per-sb io stats

[Amir Goldstein <amir73il@gmail.com>]

Traditionally, system administrators have used the iostat utility
to track the amount of io performed to a local disk filesystem.

Similar functionality is provided for NFS mounts via the nfsstat
utility that reads the NFS client's stats from /proc/pid/mountstats.

There is currently no good way for a system administrator or a
monitoring application inside a container to track the amount of io
performed via overlayfs.

Opt-in for generic io stats via /proc/pid/mountstats to provide
that functionality.

This feature depends on CONFIG_FS_IOSTATS.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/super.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 7bb0a47cb615..94ab6adebe07 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -6,6 +6,7 @@
 
 #include <uapi/linux/magic.h>
 #include <linux/fs.h>
+#include <linux/fs_iostats.h>
 #include <linux/namei.h>
 #include <linux/xattr.h>
 #include <linux/mount.h>
@@ -1979,6 +1980,10 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 	sb->s_d_op = &ovl_dentry_operations;
 
+	err = sb_iostats_init(sb);
+	if (err && err != -EOPNOTSUPP)
+		goto out;
+
 	err = -ENOMEM;
 	ofs = kzalloc(sizeof(struct ovl_fs), GFP_KERNEL);
 	if (!ofs)
-- 
2.25.1