bcachefs: Improve key_visible_in_snapshot()

Delete a redundant bch2_snapshot_is_ancestor() check, and convert some
assertions to debug assertions.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/fsck.c b/fs/bcachefs/fsck.c
index e40040001ac19c3fd2978db6ac15402991b40fb0..93281b70147360a9dbc165fb8eeec74f5f7f7dfd 100644 (file)
--- a/fs/bcachefs/fsck.c
+++ b/fs/bcachefs/fsck.c
@@ -517,15 +517,14 @@ static bool key_visible_in_snapshot(struct bch_fs *c, struct snapshots_seen *see
                                    u32 id, u32 ancestor)
 {
        ssize_t i;
-       u32 top = seen->ids.nr ? seen->ids.data[seen->ids.nr - 1].equiv : 0;
 
-       BUG_ON(id > ancestor);
-       BUG_ON(!bch2_snapshot_is_equiv(c, id));
-       BUG_ON(!bch2_snapshot_is_equiv(c, ancestor));
+       EBUG_ON(id > ancestor);
+       EBUG_ON(!bch2_snapshot_is_equiv(c, id));
+       EBUG_ON(!bch2_snapshot_is_equiv(c, ancestor));
 
        /* @ancestor should be the snapshot most recently added to @seen */
-       BUG_ON(ancestor != seen->pos.snapshot);
-       BUG_ON(ancestor != top);
+       EBUG_ON(ancestor != seen->pos.snapshot);
+       EBUG_ON(ancestor != seen->ids.data[seen->ids.nr - 1].equiv);
 
        if (id == ancestor)
                return true;
@@ -533,11 +532,20 @@ static bool key_visible_in_snapshot(struct bch_fs *c, struct snapshots_seen *see
        if (!bch2_snapshot_is_ancestor(c, id, ancestor))
                return false;
 
+       /*
+        * We know that @id is a descendant of @ancestor, we're checking if
+        * we've seen a key that overwrote @ancestor - i.e. also a descendent of
+        * @ascestor and with @id as a descendent.
+        *
+        * But we already know that we're scanning IDs between @id and @ancestor
+        * numerically, since snapshot ID lists are kept sorted, so if we find
+        * an id that's an ancestor of @id we're done:
+        */
+
        for (i = seen->ids.nr - 2;
             i >= 0 && seen->ids.data[i].equiv >= id;
             --i)
-               if (bch2_snapshot_is_ancestor(c, id, seen->ids.data[i].equiv) &&
-                   bch2_snapshot_is_ancestor(c, seen->ids.data[i].equiv, ancestor))
+               if (bch2_snapshot_is_ancestor(c, id, seen->ids.data[i].equiv))
                        return false;
 
        return true;