bcachefs: Fix bch2_btree_iter_peek_prev()

This makes bch2_btree_iter_peek_prev() and bch2_btree_iter_prev()
consistent with peek() and next(), w.r.t. iter->pos.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -1519,13 +1519,27 @@ void bch2_btree_iter_set_pos(struct btree_iter *iter, struct bpos new_pos)
 
 static inline bool bch2_btree_iter_advance_pos(struct btree_iter *iter)
 {
-	if (unlikely(!bkey_cmp(iter->k.p, POS_MAX)))
+	struct bpos pos = iter->k.p;
+
+	if (unlikely(!bkey_cmp(pos, POS_MAX)))
+		return false;
+
+	if (!(iter->flags & BTREE_ITER_IS_EXTENTS))
+		pos = bkey_successor(pos);
+	bch2_btree_iter_set_pos(iter, pos);
+	return true;
+}
+
+static inline bool bch2_btree_iter_rewind_pos(struct btree_iter *iter)
+{
+	struct bpos pos = bkey_start_pos(&iter->k);
+
+	if (unlikely(!bkey_cmp(pos, POS_MIN)))
 		return false;
 
-	bch2_btree_iter_set_pos(iter,
-		(iter->flags & BTREE_ITER_IS_EXTENTS)
-		? iter->k.p
-		: bkey_successor(iter->k.p));
+	if (!(iter->flags & BTREE_ITER_IS_EXTENTS))
+		pos = bkey_predecessor(pos);
+	bch2_btree_iter_set_pos(iter, pos);
 	return true;
 }
 
@@ -1619,8 +1633,7 @@ struct bkey_s_c bch2_btree_iter_peek(struct btree_iter *iter)
 	 * iter->pos should always be equal to the key we just
 	 * returned - except extents can straddle iter->pos:
 	 */
-	if (!(iter->flags & BTREE_ITER_IS_EXTENTS) ||
-	    bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0)
+	if (bkey_cmp(bkey_start_pos(k.k), iter->pos) > 0)
 		iter->pos = bkey_start_pos(k.k);
 
 	iter->uptodate = BTREE_ITER_UPTODATE;
@@ -1743,7 +1756,10 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 			return bkey_s_c_err(ret);
 
 		k = __btree_iter_peek(iter, l);
-		if (!k.k || bkey_cmp(bkey_start_pos(k.k), pos) > 0)
+		if (!k.k ||
+		    ((iter->flags & BTREE_ITER_IS_EXTENTS)
+		     ? bkey_cmp(bkey_start_pos(k.k), pos) >= 0
+		     : bkey_cmp(bkey_start_pos(k.k), pos) > 0))
 			k = __btree_iter_prev(iter, l);
 
 		if (likely(k.k))
@@ -1754,8 +1770,13 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
 	}
 
 	EBUG_ON(bkey_cmp(bkey_start_pos(k.k), pos) > 0);
-	iter->pos	= bkey_start_pos(k.k);
+
+	/* Extents can straddle iter->pos: */
+	if (bkey_cmp(k.k->p, pos) < 0)
+		iter->pos = k.k->p;
 	iter->uptodate	= BTREE_ITER_UPTODATE;
+
+	bch2_btree_iter_verify_level(iter, 0);
 	return k;
 }
 
@@ -1765,16 +1786,9 @@ struct bkey_s_c bch2_btree_iter_peek_prev(struct btree_iter *iter)
  */
 struct bkey_s_c bch2_btree_iter_prev(struct btree_iter *iter)
 {
-	struct bpos pos = bkey_start_pos(&iter->k);
-
-	EBUG_ON(btree_iter_type(iter) != BTREE_ITER_KEYS);
-	bch2_btree_iter_checks(iter);
-
-	if (unlikely(!bkey_cmp(pos, POS_MIN)))
+	if (!bch2_btree_iter_rewind_pos(iter))
 		return bkey_s_c_null;
 
-	bch2_btree_iter_set_pos(iter, bkey_predecessor(pos));
-
 	return bch2_btree_iter_peek_prev(iter);
 }
 

fs/bcachefs/fs-io.c

@@ -2454,7 +2454,7 @@ static long bchfs_fcollapse_finsert(struct bch_inode_info *inode,
 	struct address_space *mapping = inode->v.i_mapping;
 	struct bkey_buf copy;
 	struct btree_trans trans;
-	struct btree_iter *src, *dst;
+	struct btree_iter *src, *dst, *del;
 	loff_t shift, new_size;
 	u64 src_start;
 	int ret;
@@ -2524,6 +2524,7 @@ static long bchfs_fcollapse_finsert(struct bch_inode_info *inode,
 			POS(inode->v.i_ino, src_start >> 9),
 			BTREE_ITER_INTENT);
 	dst = bch2_trans_copy_iter(&trans, src);
+	del = bch2_trans_copy_iter(&trans, src);
 
 	while (1) {
 		struct disk_reservation disk_res =
@@ -2544,8 +2545,6 @@ static long bchfs_fcollapse_finsert(struct bch_inode_info *inode,
 		if (!k.k || k.k->p.inode != inode->v.i_ino)
 			break;
 
-		BUG_ON(bkey_cmp(src->pos, bkey_start_pos(k.k)));
-
 		if (insert &&
 		    bkey_cmp(k.k->p, POS(inode->v.i_ino, offset >> 9)) <= 0)
 			break;
@@ -2577,6 +2576,7 @@ static long bchfs_fcollapse_finsert(struct bch_inode_info *inode,
 		delete.k.p = copy.k->k.p;
 		delete.k.size = copy.k->k.size;
 		delete.k.p.offset -= shift >> 9;
+		bch2_btree_iter_set_pos(del, bkey_start_pos(&delete.k));
 
 		next_pos = insert ? bkey_start_pos(&delete.k) : delete.k.p;
 
@@ -2597,9 +2597,7 @@ static long bchfs_fcollapse_finsert(struct bch_inode_info *inode,
 			BUG_ON(ret);
 		}
 
-		bch2_btree_iter_set_pos(src, bkey_start_pos(&delete.k));
-
-		ret =   bch2_trans_update(&trans, src, &delete, trigger_flags) ?:
+		ret =   bch2_trans_update(&trans, del, &delete, trigger_flags) ?:
 			bch2_trans_update(&trans, dst, copy.k, trigger_flags) ?:
 			bch2_trans_commit(&trans, &disk_res,
 					  &inode->ei_journal_seq,