Re: [PATCH] bcachefs: skip invisible entries in empty subvolume checking

[Guoyu Ou <benogy@gmail.com>]

On Sat, Feb 10, 2024 at 05:56:15PM -0500, Kent Overstreet wrote:
> On Sat, Feb 10, 2024 at 10:06:37PM +0800, Guoyu Ou wrote:
> > 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
> >
> > Signed-off-by: Guoyu Ou <benogy@gmail.com>
>
> So that's an interesting corner case - can you add a ktest test for it?
> https://evilpiepirate.org/git/ktest.git/
>
> If you're not using it yet, please jump on IRC and ask if you run into
> any issues getting it going;
>
> There's an issue with your fix: in may_delete_deleted_inode(), you're
> getting the subvol from inode.bi_subvol.
>
> That's incorrect, because bi_subvol is only set on subvolume roots,
> because we can't go through every inode in the subvolume and change
> bi_subvol when taking a snapshot.
>
> You're doing it right in bch2_empty_dir_trans(), which is the path that
> matters more; may_delete_deleted_inode() is only checking "did this
> filesystem get borked".
>
> I would just pass in 0 from may_delete_deleted_inode(), and then have
> empty_dir_snapshot() ignore DT_SUBVOL dirents when subvol == 0. It makes
> the check less strict, but that's ok, the rest of fsck will still catch
> it.

Got it. I will add a new test case and update this patch later.

>
> > ---
> >  fs/bcachefs/dirent.c | 7 +++++--
> >  fs/bcachefs/dirent.h | 2 +-
> >  fs/bcachefs/inode.c  | 2 +-
> >  3 files changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/bcachefs/dirent.c b/fs/bcachefs/dirent.c
> > index 4ae1e9f002a0..82c5bff01411 100644
> > --- a/fs/bcachefs/dirent.c
> > +++ b/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)
> > diff --git a/fs/bcachefs/dirent.h b/fs/bcachefs/dirent.h
> > index 21ffeb78f02e..aeb8207ca9f2 100644
> > --- a/fs/bcachefs/dirent.h
> > +++ b/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 *);
> >
> > diff --git a/fs/bcachefs/inode.c b/fs/bcachefs/inode.c
> > index 086f0090b03a..8f85d0132cc2 100644
> > --- a/fs/bcachefs/inode.c
> > +++ b/fs/bcachefs/inode.c
> > @@ -1088,7 +1088,7 @@ 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);
> > +		ret = bch2_empty_dir_snapshot(trans, pos.offset, inode.bi_subvol, pos.snapshot);
> >  		if (fsck_err_on(ret == -ENOTEMPTY, c, deleted_inode_is_dir,
> >  				"non empty directory %llu:%u in deleted_inodes btree",
> >  				pos.offset, pos.snapshot))
> > --
> > 2.43.0
> >