Btrfs-progs: add support for device replace procedure

This is the user mode part of the device replace patch series.

The command group "btrfs replace" is added with three commands:
- btrfs replace start srcdev|srcdevid targetdev [-Bfr] mount_point
- btrfs replace status mount_point [-1]
- btrfs replace cancel mount_point

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

1 files changed, 6 insertions, 0 deletions

diff --git a/ctree.h b/ctree.h
index 199f0288..4da0af57 100644
--- a/ctree.h
+++ b/ctree.h
@@ -1051,6 +1051,12 @@ struct btrfs_root {
 #define BTRFS_DEV_STATS_KEY	249
 
 /*
+ * Persistently stores the device replace state in the device tree.
+ * The key is built like this: (0, BTRFS_DEV_REPLACE_KEY, 0).
+ */
+#define BTRFS_DEV_REPLACE_KEY	250
+
+/*
  * string items are for debugging.  They just store a short string of
  * data in the FS
  */