linux-kernel - Sub volumes handling in bch2_fsck_update

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Message-ID: <20250423154531.376838-1-contact@arnaud-lcm.com>
Date: Wed, 23 Apr 2025 17:45:31 +0200
From: Arnaud Lecomte <contact@...aud-lcm.com>
To: syzbot+843981bb836d699c07d1@...kaller.appspotmail.com
Cc: kent.overstreet@...ux.dev,
	linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Sub volumes handling in bch2_fsck_update_backpointers

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 ?

Regards,
Arnaud