linux-kernel - Re: Sub volumes handling in bch2_fsck_update

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Message-ID: <51955f43-888d-40bb-9ea6-0cc4c1c40f88@arnaud-lcm.com>
Date: Wed, 23 Apr 2025 22:24:28 +0200
From: Arnaud Lecomte <contact@...aud-lcm.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: syzbot+843981bb836d699c07d1@...kaller.appspotmail.com,
 linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzkaller-bugs@...glegroups.com
Subject: Re: Sub volumes handling in bch2_fsck_update_backpointers


On 23/04/2025 19:46, Kent Overstreet wrote:
> On Wed, Apr 23, 2025 at 07:18:34PM +0200, Arnaud Lecomte wrote:
>> Would you be  okay if I try to handle it ? I am fairly new to bcachefs but I
>> am really interested to get involve into it, I like the project.
> go for it, get ktest going and join the IRC channel
>
> https://evilpiepirate.org/git/ktest.git/
Joined, I'll start tomorrow !  Thanks
>> On 23/04/2025 18:47, Kent Overstreet wrote:
>>> On Wed, Apr 23, 2025 at 05:45:31PM +0200, Arnaud Lecomte wrote:
>>>> Hey everyone, in fsck.c, we have:
>>>> /*
>>>>    * Prefer to delete the first one, since that will be the one at the wrong
>>>>    * offset:
>>>>    * return value: 0 -> delete k1, 1 -> delete k2
>>>>    */
>>>> int bch2_fsck_update_backpointers(struct btree_trans *trans,
>>>> 				  struct snapshots_seen *s,
>>>> 				  const struct bch_hash_desc desc,
>>>> 				  struct bch_hash_info *hash_info,
>>>> 				  struct bkey_i *new)
>>>> {
>>>> 	if (new->k.type != KEY_TYPE_dirent)
>>>> 		return 0;
>>>>
>>>> 	struct bkey_i_dirent *d = bkey_i_to_dirent(new);
>>>> 	struct inode_walker target = inode_walker_init();
>>>> 	int ret = 0;
>>>>
>>>> 	if (d->v.d_type == DT_SUBVOL) {
>>>> 		BUG();
>>>> 	} else {
>>>> 		ret = get_visible_inodes(trans, &target, s, le64_to_cpu(d->v.d_inum));
>>>> 		if (ret)
>>>> 			goto err;
>>>>
>>>> 		darray_for_each(target.inodes, i) {
>>>> 			i->inode.bi_dir_offset = d->k.p.offset;
>>>> 			ret = __bch2_fsck_write_inode(trans, &i->inode);
>>>> 			if (ret)
>>>> 				goto err;
>>>> 		}
>>>> 	}
>>>> err:
>>>> 	inode_walker_exit(&target);
>>>> 	return ret;
>>>> }
>>>>
>>>> What is the current state for handling subvolumes ? In someone already working on or it is something we don't want to implement
>>>> for some reasons ?
>>> This does need to be handled, I haven't started on it yet.
>>>
>>> I did just fix another subvolume root backpointers bug, which makes this
>>> one easier - now, only the newest snapshot version of a subvolume root
>>> inode needs to have a backpointer.
>>>