[PATCH 9/9] bcachefs: peek_prev_min(): Search forwards for extents, snapshots

[Kent Overstreet <kent.overstreet@linux.dev>]

With extents and snapshots, for slightly different reasons, we may have
to search forwards to find a key that compares equal to iter->pos (i.e.
a key that peek_prev() should return, as it returns keys <= iter->pos).

peek_slot() does this, and is an easy way to fix this case.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
 fs/bcachefs/btree_iter.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c
index 6bb2eb388c1b..d22c212bb4e6 100644
--- a/fs/bcachefs/btree_iter.c
+++ b/fs/bcachefs/btree_iter.c
@@ -2564,6 +2564,21 @@ static struct bkey_s_c __bch2_btree_iter_peek_prev(struct btree_iter *iter, stru
  */
 struct bkey_s_c bch2_btree_iter_peek_prev_min(struct btree_iter *iter, struct bpos end)
 {
+	if ((iter->flags & (BTREE_ITER_is_extents|BTREE_ITER_filter_snapshots)) &&
+	   !bkey_eq(iter->pos, POS_MAX)) {
+		/*
+		 * bkey_start_pos(), for extents, is not monotonically
+		 * increasing until after filtering for snapshots:
+		 *
+		 * Thus, for extents we need to search forward until we find a
+		 * real visible extents - easiest to just use peek_slot() (which
+		 * internally uses peek() for extents)
+		 */
+		struct bkey_s_c k = bch2_btree_iter_peek_slot(iter);
+		if (bkey_err(k) || !bkey_deleted(k.k))
+			return k;
+	}
+
 	struct btree_trans *trans = iter->trans;
 	struct bpos search_key = iter->pos;
 	struct bkey_s_c k;
@@ -2579,9 +2594,6 @@ struct bkey_s_c bch2_btree_iter_peek_prev_min(struct btree_iter *iter, struct bp
 		goto out_no_locked;
 	}
 
-	if (iter->flags & BTREE_ITER_filter_snapshots)
-		search_key.snapshot = U32_MAX;
-
 	while (1) {
 		k = __bch2_btree_iter_peek_prev(iter, search_key);
 		if (unlikely(!k.k))
-- 
2.45.2