[PATCH v3 36/39] ubifs: implement ubifs_get_qsize to get quota size in ubifs

[Dongsheng Yang]

On 09/21/2015 05:13 PM, Jan Kara wrote:
> On Mon 21-09-15 12:35:01, Dongsheng Yang wrote:
>> On 09/18/2015 07:20 PM, Jan Kara wrote:
>>>> .... TBH, there is a little different with other filesystems. I did not
>>>> use the "disk" space, but the file space in ubifs quota, although dquot
>>>> means disk quota. Same with btrfs quota. If we use disk space for quota,
>>>> the most common problem from user is that: why I did not reach the limit
>>>> but I can not write any byte. COW in btrfs or out-place-updating in
>>>> ubifs makes this problem much worse.
>>>>
>>>> So I choose file space here for ubifs.
>>>
>>> OK, so these are really two separate questions. I understand your choice of
>>> using file space as the amount of space to account for quota purposes and
>>> I'm fine with that choice. Another thing is that regardless of how you
>>> decide to do quota accounting, you must maintain i_blocks / i_bytes to
>>> contain proper value because dquot_transfer() uses that information to update
>>> quota usage when inode owner is changed.
>>
>> But if we don't use i_blocks to get qsize, what we care only in
>> dquot_transter() is dquot->dq_dqb. That means, even if the i_blocks
>> is not correct in dquot_transfer() in ubifs, that's okey, because we
>> will never use this value, right?
>
> dquot_transfer() will use the value - when file F changes owner from user A
> to user B, then you need to decrement amount of space used by F from A's
> quota usage and add that amount to B's quota usage. And the amount of space
> is obtained via inode_get_bytes() which uses i_blocks and i_bytes. See
> __dquot_transfer() in fs/quota/dquot.c for details.

Yes, I see it. But if ubifs doesn't use i_blocks and i_bytes to stand
for quota size, as I mentioned I want to use i_size. Then we will never
use i_blocks. So we only need a to transfer dquot->dq_dqb values. That
means, even the i_blocks in dquot_transfer() is not correct, we don't
care it. we only need to make sure values in dquot_dq_dqb are 
transfered, such as dquot->dq_dqb->curspace for user B is equal with
i_size.

Yang


>
> 								Honza
>