btrfs: add balance filter for stripes

Balance block groups which have the given number of stripes, defined by
a range min..max. This is useful to selectively rebalance only chunks
that do not span enough devices, applies to RAID0/10/5/6.

Signed-off-by: Gabríel Arthúr Pétursson <gabriel@system.is>
[ renamed bargs members, added to the UAPI, wrote the changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 11f13108b78b..17a94704b183 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -229,7 +229,15 @@ struct btrfs_balance_args {
                         __u32 limit_max;
                 };
         };
-        __u64 unused[7];
+
+        /*
+         * Process chunks that cross stripes_min..stripes_max devices,
+         * BTRFS_BALANCE_ARGS_STRIPES_RANGE
+         */
+        __le32 stripes_min;
+        __le32 stripes_max;
+
+        __u64 unused[6];
 } __attribute__ ((__packed__));
 
 /* report balance progress to userspace */