+static inline int check_pos_snapshot_overwritten(struct btree_trans *trans,
+ enum btree_id id,
+ struct bpos pos)
+{
+ if (!btree_type_has_snapshots(id) ||
+ pos.snapshot == U32_MAX ||
+ !snapshot_t(trans->c, pos.snapshot)->children[0])
+ return 0;
+
+ return __check_pos_snapshot_overwritten(trans, id, pos);
+}
+
+static noinline int extent_front_merge(struct btree_trans *trans,
+ struct btree_iter *iter,
+ struct bkey_s_c k,
+ struct bkey_i **insert,
+ enum btree_update_flags flags)
+{
+ struct bch_fs *c = trans->c;
+ struct bkey_i *update;
+ int ret;
+
+ update = bch2_bkey_make_mut(trans, k);
+ ret = PTR_ERR_OR_ZERO(update);
+ if (ret)
+ return ret;
+
+ if (!bch2_bkey_merge(c, bkey_i_to_s(update), bkey_i_to_s_c(*insert)))
+ return 0;
+
+ ret = check_pos_snapshot_overwritten(trans, iter->btree_id, k.k->p) ?:
+ check_pos_snapshot_overwritten(trans, iter->btree_id, (*insert)->k.p);
+ if (ret < 0)
+ return ret;
+ if (ret)
+ return 0;
+
+ ret = bch2_btree_delete_at(trans, iter, flags);
+ if (ret)
+ return ret;
+
+ *insert = update;
+ return 0;
+}
+
+static noinline int extent_back_merge(struct btree_trans *trans,
+ struct btree_iter *iter,
+ struct bkey_i *insert,
+ struct bkey_s_c k)
+{
+ struct bch_fs *c = trans->c;
+ int ret;
+
+ ret = check_pos_snapshot_overwritten(trans, iter->btree_id, insert->k.p) ?:
+ check_pos_snapshot_overwritten(trans, iter->btree_id, k.k->p);
+ if (ret < 0)
+ return ret;
+ if (ret)
+ return 0;
+
+ bch2_bkey_merge(c, bkey_i_to_s(insert), k);
+ return 0;
+}
+
+/*
+ * When deleting, check if we need to emit a whiteout (because we're overwriting
+ * something in an ancestor snapshot)
+ */
+static int need_whiteout_for_snapshot(struct btree_trans *trans,
+ enum btree_id btree_id, struct bpos pos)
+{
+ struct btree_iter iter;
+ struct bkey_s_c k;
+ u32 snapshot = pos.snapshot;
+ int ret;
+
+ if (!bch2_snapshot_parent(trans->c, pos.snapshot))
+ return 0;
+
+ pos.snapshot++;
+
+ for_each_btree_key_norestart(trans, iter, btree_id, pos,
+ BTREE_ITER_ALL_SNAPSHOTS|
+ BTREE_ITER_NOPRESERVE, k, ret) {
+ if (!bkey_eq(k.k->p, pos))
+ break;
+
+ if (bch2_snapshot_is_ancestor(trans->c, snapshot,
+ k.k->p.snapshot)) {
+ ret = !bkey_whiteout(k.k);
+ break;
+ }
+ }
+ bch2_trans_iter_exit(trans, &iter);
+
+ return ret;
+}