bcachefs: Convert bch2_dev_usrdata_drop() to for_each_btree_key2()

The new for_each_btree_key2() macro handles transaction retries,
allowing us to avoid nested transactions - which we want to avoid since
they're tricky to do completely correctly and upcoming assertions are
going to be checking for that.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_types.h

@@ -650,6 +650,11 @@ static inline bool btree_type_has_snapshots(enum btree_id id)
 	return (1 << id) & BTREE_ID_HAS_SNAPSHOTS;
 }
 
+static inline bool btree_type_has_ptrs(enum btree_id id)
+{
+	return (1 << id) & BTREE_ID_HAS_PTRS;
+}
+
 static inline bool btree_node_type_needs_gc(enum btree_node_type type)
 {
 	return BTREE_NODE_TYPE_HAS_TRIGGERS & (1U << type);

fs/bcachefs/migrate.c

@@ -35,43 +35,36 @@ static int drop_dev_ptrs(struct bch_fs *c, struct bkey_s k,
 	return 0;
 }
 
-static int __bch2_dev_usrdata_drop(struct bch_fs *c, unsigned dev_idx, int flags,
-				   enum btree_id btree_id)
+static int bch2_dev_usrdata_drop_key(struct btree_trans *trans,
+				     struct btree_iter *iter,
+				     struct bkey_s_c k,
+				     unsigned dev_idx,
+				     int flags)
 {
-	struct btree_trans trans;
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	struct bkey_buf sk;
-	int ret = 0;
-
-	bch2_bkey_buf_init(&sk);
-	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+	struct bch_fs *c = trans->c;
+	struct bkey_i *n;
+	int ret;
 
-	bch2_trans_iter_init(&trans, &iter, btree_id, POS_MIN,
-			     BTREE_ITER_PREFETCH|
-			     BTREE_ITER_ALL_SNAPSHOTS);
+	if (!bch2_bkey_has_device(k, dev_idx))
+		return 0;
 
-	while ((bch2_trans_begin(&trans),
-		(k = bch2_btree_iter_peek(&iter)).k) &&
-	       !(ret = bkey_err(k))) {
-		if (!bch2_bkey_has_device(k, dev_idx)) {
-			bch2_btree_iter_advance(&iter);
-			continue;
-		}
+	n = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
+	ret = PTR_ERR_OR_ZERO(n);
+	if (ret)
+		return ret;
 
-		bch2_bkey_buf_reassemble(&sk, c, k);
+	bkey_reassemble(n, k);
 
-		ret = drop_dev_ptrs(c, bkey_i_to_s(sk.k),
-				    dev_idx, flags, false);
+	ret = drop_dev_ptrs(c, bkey_i_to_s(n), dev_idx, flags, false);
 	if (ret)
-			break;
+		return ret;
 
 	/*
 	 * If the new extent no longer has any pointers, bch2_extent_normalize()
 	 * will do the appropriate thing with it (turning it into a
 	 * KEY_TYPE_error key, or just a discard if it was a cached extent)
 	 */
-		bch2_extent_normalize(c, bkey_i_to_s(sk.k));
+	bch2_extent_normalize(c, bkey_i_to_s(n));
 
 	/*
 	 * Since we're not inserting through an extent iterator
@@ -79,41 +72,39 @@ static int __bch2_dev_usrdata_drop(struct bch_fs *c, unsigned dev_idx, int flags
 	 * we aren't using the extent overwrite path to delete, we're
 	 * just using the normal key deletion path:
 	 */
-		if (bkey_deleted(&sk.k->k))
-			sk.k->k.size = 0;
+	if (bkey_deleted(&n->k))
+		n->k.size = 0;
 
-		ret   = bch2_btree_iter_traverse(&iter) ?:
-			bch2_trans_update(&trans, &iter, sk.k,
-					  BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?:
-			bch2_trans_commit(&trans, NULL, NULL,
-					BTREE_INSERT_NOFAIL);
+	return bch2_trans_update(trans, iter, n, BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+}
 
-		/*
-		 * don't want to leave ret == -EINTR, since if we raced and
-		 * something else overwrote the key we could spuriously return
-		 * -EINTR below:
-		 */
-		if (ret == -EINTR)
-			ret = 0;
+static int bch2_dev_usrdata_drop(struct bch_fs *c, unsigned dev_idx, int flags)
+{
+	struct btree_trans trans;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	enum btree_id id;
+	int ret = 0;
+
+	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
+
+	for (id = 0; id < BTREE_ID_NR; id++) {
+		if (!btree_type_has_ptrs(id))
+			continue;
+
+		ret = for_each_btree_key_commit(&trans, iter, id, POS_MIN,
+				BTREE_ITER_PREFETCH|BTREE_ITER_ALL_SNAPSHOTS, k,
+				NULL, NULL, BTREE_INSERT_NOFAIL,
+			bch2_dev_usrdata_drop_key(&trans, &iter, k, dev_idx, flags));
 		if (ret)
 			break;
 	}
-	bch2_trans_iter_exit(&trans, &iter);
 
 	bch2_trans_exit(&trans);
-	bch2_bkey_buf_exit(&sk, c);
-
-	BUG_ON(ret == -EINTR);
 
 	return ret;
 }
 
-static int bch2_dev_usrdata_drop(struct bch_fs *c, unsigned dev_idx, int flags)
-{
-	return  __bch2_dev_usrdata_drop(c, dev_idx, flags, BTREE_ID_extents) ?:
-		__bch2_dev_usrdata_drop(c, dev_idx, flags, BTREE_ID_reflink);
-}
-
 static int bch2_dev_metadata_drop(struct bch_fs *c, unsigned dev_idx, int flags)
 {
 	struct btree_trans trans;