Re: about btrfs quota issues

[Arne Jansen <sensille@gmx.net>]

On 11.03.2013 15:15, Wang Shilong wrote:
> 
> <snip>
> 
>>> The worst thing is that i don't think users can master this magic
>>> concept very well.
>>
>> Normally users don't need very sophisticated scenarios. In fact, they
>> don't even need higher level quota groups, the basic tracking is
>> enough. In this case, everything just works as expected for the user.
>> If you start creating and assigning qgroups manually, prepare to handle
>> the complexity.
>>
> Considering this case:
> 
> a subvolume related to a user, we limit the space by limiting every subvolume
> qgroup, but  we also want to limit  the total space all the users can use. So we create
> a parent qgroup(1/1 for example) and assign all subvolume group to this parent group.
> 
> The above case is regularly used i think, What's more, many snapshots may be done.
> So  i think what i am concerning is not a corner case..

So you just missed to assign the new subvolume to 1/1 by using -i on
snapshot creation.

-Arne

> 
> Thanks,
> Wang
>>
>>>
>>>>
>>>>> If so, i think it really confusing and too complex for users to do
>>>>> such work, is't it?...
>>>>
>>>> It is complex. That is why I always point anyone asking to do some work
>>>> on btrfs or qgroups to writing an enhanced interface to simplify this
>>>> task for the user. I don't think the kernel should handle this.
>>>> And that's why I took the effort to write a pdf to explain the
>>>> concepts :)
>>>
>>> I don't have any  good ideas about this yet..
>>>
>>>> But the current interface is not only complex, it also is very powerful.
>>>> You can solve problems with it that no other quota system I know of can
>>>> solve.
>>>>
>>>>>
>>>>> BTW, i have a question about the function btrfs_qgroup_inherit(),
>>>>> when copying exclusive value from src_qgroup to dst_qgroup:
>>>>>
>>>>>      dst_qgroup->exclusive = src_qgroup->exclusive + level_size
>>>>>
>>>>> while copying referenced value from src_qgroup to dot_qgroup:
>>>>>
>>>>>      dst_qgroup->referenced = src_qgroup->referenced -level_size
>>>>>
>>>>> I can't really figure out...~_~
>>>>
>>>> level_size is just a small correction for the space the tree root
>>>> occupies. The tree root is never shared between sub volumes.
>>>
>>> O.K. I  got it..
>>>
>>> Thanks,
>>> Wang
>>>
>>>>
>>>> -Arne
>>>>
>>>>>
>>>>> Thanks,
>>>>> Wang
>>>>
>>>
>>
>