bcachefs: Flag btrees with missing data

We need this to know when we should attempt to reconstruct the snapshots
btree

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
diff --git a/fs/bcachefs/recovery.h b/fs/bcachefs/recovery.h
index 3962fd8..4bf818d 100644
--- a/fs/bcachefs/recovery.h
+++ b/fs/bcachefs/recovery.h
@@ -2,6 +2,8 @@
 #ifndef _BCACHEFS_RECOVERY_H
 #define _BCACHEFS_RECOVERY_H
 
+void bch2_btree_lost_data(struct bch_fs *, enum btree_id);
+
 int bch2_journal_replay(struct bch_fs *);
 
 int bch2_fs_recovery(struct bch_fs *);