bcachefs: fsck: Fix check_path_loop() + snapshots

A path exists in a particular snapshot: we should do the pathwalk in the
snapshot ID of the inode we started from, _not_ change snapshot ID as we
walk inodes and dirents.

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

Author: Kent Overstreet

fs/bcachefs/fsck.c

@@ -2689,19 +2689,13 @@ int bch2_check_subvolume_structure(struct bch_fs *c)
 	return ret;
 }
 
-struct pathbuf_entry {
-	u64	inum;
-	u32	snapshot;
-};
-
-typedef DARRAY(struct pathbuf_entry) pathbuf;
-
-static int bch2_bi_depth_renumber_one(struct btree_trans *trans, struct pathbuf_entry *p,
+static int bch2_bi_depth_renumber_one(struct btree_trans *trans,
+				      u64 inum, u32 snapshot,
 				      u32 new_depth)
 {
 	struct btree_iter iter;
 	struct bkey_s_c k = bch2_bkey_get_iter(trans, &iter, BTREE_ID_inodes,
-					       SPOS(0, p->inum, p->snapshot), 0);
+					       SPOS(0, inum, snapshot), 0);
 
 	struct bch_inode_unpacked inode;
 	int ret = bkey_err(k) ?:
@@ -2720,14 +2714,15 @@ static int bch2_bi_depth_renumber_one(struct btree_trans *trans, struct pathbuf_
 	return ret;
 }
 
-static int bch2_bi_depth_renumber(struct btree_trans *trans, pathbuf *path, u32 new_bi_depth)
+static int bch2_bi_depth_renumber(struct btree_trans *trans, darray_u64 *path,
+				  u32 snapshot, u32 new_bi_depth)
 {
 	u32 restart_count = trans->restart_count;
 	int ret = 0;
 
 	darray_for_each_reverse(*path, i) {
 		ret = nested_lockrestart_do(trans,
-				bch2_bi_depth_renumber_one(trans, i, new_bi_depth));
+				bch2_bi_depth_renumber_one(trans, *i, snapshot, new_bi_depth));
 		bch_err_fn(trans->c, ret);
 		if (ret)
 			break;
@@ -2738,26 +2733,19 @@ static int bch2_bi_depth_renumber(struct btree_trans *trans, pathbuf *path, u32
 	return ret ?: trans_was_restarted(trans, restart_count);
 }
 
-static bool path_is_dup(pathbuf *p, u64 inum, u32 snapshot)
-{
-	darray_for_each(*p, i)
-		if (i->inum	== inum &&
-		    i->snapshot	== snapshot)
-			return true;
-	return false;
-}
-
 static int check_path_loop(struct btree_trans *trans, struct bkey_s_c inode_k)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter inode_iter = {};
-	pathbuf path = {};
+	darray_u64 path = {};
 	struct printbuf buf = PRINTBUF;
 	u32 snapshot = inode_k.k->p.snapshot;
 	bool redo_bi_depth = false;
 	u32 min_bi_depth = U32_MAX;
 	int ret = 0;
 
+	struct bpos start = inode_k.k->p;
+
 	struct bch_inode_unpacked inode;
 	ret = bch2_inode_unpack(inode_k, &inode);
 	if (ret)
@@ -2766,9 +2754,9 @@ static int check_path_loop(struct btree_trans *trans, struct bkey_s_c inode_k)
 	while (!inode.bi_subvol) {
 		struct btree_iter dirent_iter;
 		struct bkey_s_c_dirent d;
-		u32 parent_snapshot = snapshot;
 
-		d = inode_get_dirent(trans, &dirent_iter, &inode, &parent_snapshot);
+		d = dirent_get_by_pos(trans, &dirent_iter,
+				      SPOS(inode.bi_dir, inode.bi_dir_offset, snapshot));
 		ret = bkey_err(d.s_c);
 		if (ret && !bch2_err_matches(ret, ENOENT))
 			goto out;
@@ -2786,15 +2774,10 @@ static int check_path_loop(struct btree_trans *trans, struct bkey_s_c inode_k)
 
 		bch2_trans_iter_exit(trans, &dirent_iter);
 
-		ret = darray_push(&path, ((struct pathbuf_entry) {
-			.inum		= inode.bi_inum,
-			.snapshot	= snapshot,
-		}));
+		ret = darray_push(&path, inode.bi_inum);
 		if (ret)
 			return ret;
 
-		snapshot = parent_snapshot;
-
 		bch2_trans_iter_exit(trans, &inode_iter);
 		inode_k = bch2_bkey_get_iter(trans, &inode_iter, BTREE_ID_inodes,
 					     SPOS(0, inode.bi_dir, snapshot), 0);
@@ -2816,15 +2799,22 @@ static int check_path_loop(struct btree_trans *trans, struct bkey_s_c inode_k)
 			break;
 
 		inode = parent_inode;
-		snapshot = inode_k.k->p.snapshot;
 		redo_bi_depth = true;
 
-		if (path_is_dup(&path, inode.bi_inum, snapshot)) {
+		if (darray_find(path, inode.bi_inum)) {
 			printbuf_reset(&buf);
-			prt_printf(&buf, "directory structure loop:\n");
-			darray_for_each_reverse(path, i)
-				prt_printf(&buf, "%llu:%u ", i->inum, i->snapshot);
-			prt_printf(&buf, "%llu:%u", inode.bi_inum, snapshot);
+			prt_printf(&buf, "directory structure loop in snapshot %u: ",
+				   snapshot);
+
+			ret = bch2_inum_snapshot_to_path(trans, start.offset, start.snapshot, NULL, &buf);
+			if (ret)
+				goto out;
+
+			if (c->opts.verbose) {
+				prt_newline(&buf);
+				darray_for_each(path, i)
+					prt_printf(&buf, "%llu ", *i);
+			}
 
 			if (fsck_err(trans, dir_loop, "%s", buf.buf)) {
 				ret = remove_backpointer(trans, &inode);
@@ -2844,7 +2834,7 @@ static int check_path_loop(struct btree_trans *trans, struct bkey_s_c inode_k)
 		min_bi_depth = 0;
 
 	if (redo_bi_depth)
-		ret = bch2_bi_depth_renumber(trans, &path, min_bi_depth);
+		ret = bch2_bi_depth_renumber(trans, &path, snapshot, min_bi_depth);
 out:
 fsck_err:
 	bch2_trans_iter_exit(trans, &inode_iter);