Btrfs-progs: add command to get/reset device stats via ioctl

"btrfs device stats" is used to retrieve and print the device stats.
"btrfs device stats -z" is used to atomically retrieve, reset and
print the stats.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>

1 files changed, 6 insertions, 0 deletions

diff --git a/ctree.h b/ctree.h
index 1f5a795e..199f0288 100644
--- a/ctree.h
+++ b/ctree.h
@@ -1045,6 +1045,12 @@ struct btrfs_root {
 #define BTRFS_QGROUP_RELATION_KEY	246
 
 /*
+ * Persistently stores the io stats in the device tree.
+ * One key for all stats, (0, BTRFS_DEV_STATS_KEY, devid).
+ */
+#define BTRFS_DEV_STATS_KEY	249
+
+/*
  * string items are for debugging.  They just store a short string of
  * data in the FS
  */