Btrfs: Deal with failed writes in mirrored configurations

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 3f9a17f..a9663e92 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -90,7 +90,8 @@
 	atomic_t stripes_pending;
 	bio_end_io_t *end_io;
 	void *private;
-	int error;
+	atomic_t error;
+	int max_errors;
 	int num_stripes;
 	struct btrfs_bio_stripe stripes[];
 };