bcachefs: skip invisible entries in empty subvolume checking

When we are checking whether a subvolume is empty in the specified snapshot,
entries that do not belong to this subvolume should be skipped.

This fixes the following case:

    $ bcachefs subvolume create ./sub
    $ cd sub
    $ bcachefs subvolume create ./sub2
    $ bcachefs subvolume snapshot . ./snap
    $ ls -a snap
    . ..
    $ rmdir snap
    rmdir: failed to remove 'snap': Directory not empty

As Kent suggested, we pass 0 in may_delete_deleted_inode() to ignore subvols
in the subvol we are checking, because inode.bi_subvol is only set on
subvolume roots, and we can't go through every inode in the subvolume and
change bi_subvol when taking a snapshot. It makes the check less strict, but
that's ok, the rest of fsck will still catch it.
Signed-off-by: Guoyu Ou <benogy@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/dirent.c

@@ -508,7 +508,7 @@ u64 bch2_dirent_lookup(struct bch_fs *c, subvol_inum dir,
 	return ret;
 }
 
-int bch2_empty_dir_snapshot(struct btree_trans *trans, u64 dir, u32 snapshot)
+int bch2_empty_dir_snapshot(struct btree_trans *trans, u64 dir, u32 subvol, u32 snapshot)
 {
 	struct btree_iter iter;
 	struct bkey_s_c k;
@@ -518,6 +518,9 @@ int bch2_empty_dir_snapshot(struct btree_trans *trans, u64 dir, u32 snapshot)
 			   SPOS(dir, 0, snapshot),
 			   POS(dir, U64_MAX), 0, k, ret)
 		if (k.k->type == KEY_TYPE_dirent) {
+			struct bkey_s_c_dirent d = bkey_s_c_to_dirent(k);
+			if (d.v->d_type == DT_SUBVOL && le32_to_cpu(d.v->d_parent_subvol) != subvol)
+				continue;
 			ret = -ENOTEMPTY;
 			break;
 		}
@@ -531,7 +534,7 @@ int bch2_empty_dir_trans(struct btree_trans *trans, subvol_inum dir)
 	u32 snapshot;
 
 	return bch2_subvolume_get_snapshot(trans, dir.subvol, &snapshot) ?:
-		bch2_empty_dir_snapshot(trans, dir.inum, snapshot);
+		bch2_empty_dir_snapshot(trans, dir.inum, dir.subvol, snapshot);
 }
 
 int bch2_readdir(struct bch_fs *c, subvol_inum inum, struct dir_context *ctx)

fs/bcachefs/dirent.h

@@ -69,7 +69,7 @@ u64 bch2_dirent_lookup(struct bch_fs *, subvol_inum,
 		       const struct bch_hash_info *,
 		       const struct qstr *, subvol_inum *);
 
-int bch2_empty_dir_snapshot(struct btree_trans *, u64, u32);
+int bch2_empty_dir_snapshot(struct btree_trans *, u64, u32, u32);
 int bch2_empty_dir_trans(struct btree_trans *, subvol_inum);
 int bch2_readdir(struct bch_fs *, subvol_inum, struct dir_context *);
 

fs/bcachefs/inode.c

@@ -1088,8 +1088,9 @@ static int may_delete_deleted_inode(struct btree_trans *trans,
 		goto out;
 
 	if (S_ISDIR(inode.bi_mode)) {
-		ret = bch2_empty_dir_snapshot(trans, pos.offset, pos.snapshot);
-		if (fsck_err_on(ret == -ENOTEMPTY, c, deleted_inode_is_dir,
+		ret = bch2_empty_dir_snapshot(trans, pos.offset, 0, pos.snapshot);
+		if (fsck_err_on(bch2_err_matches(ret, ENOTEMPTY),
+				c, deleted_inode_is_dir,
 				"non empty directory %llu:%u in deleted_inodes btree",
 				pos.offset, pos.snapshot))
 			goto delete;