Re: [PATCH v2 2/2] btrfs: automatically remove the subvolume qgroup

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/5/1 07:48, Boris Burkov 写道:
> On Wed, May 01, 2024 at 07:35:09AM +0930, Qu Wenruo wrote:
[...]
>>>
>>> I don't see how a compat bit would work here, we use them for feature
>>> compatibility and for general access to data (full or read-only). What
>>> we do with individual behavioral changes are sysfs files. They're
>>> detectable by scripts and can be also used for configuration. In this
>>> case enabling/disabling autoclean of the qgroups.
>
> This was my initial thought too, but your compat bit idea is interesting
> since it persists? I vote sysfs since it has good
> infrastructure/momentum already for similar config.

Sysfs is another way which we are already utilizing for qgroups, like
drop_subtree_threshold.

The problem is as mentioned already, it's not persistent, thus it needs
a user space daemon to set it for every fs after mount.

I'm totally fine to go sysfs for now, but I really hope to a persistent
solution.
Maybe a dedicated config tree?

Thanks,
Qu

>
>>>
>>
>> I mean the compat bit, which is fully empty now.
>>
>> The new bit would be something like BTRFS_QGROUP_AUTO_REMOVAL, with that
>> set, btrfs would auto remove any stale qgroups (for regular qgroups though).
>>
>> Without that, it would be as usual (no auto removal).
>>
>> Since this doesn't cause any on-disk change, it does not needs compat-ro
>> nor incompat.
>>
>> Thanks,
>> Qu