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

[Dongsheng Yang]

On 09/21/2015 05:44 PM, Jan Kara wrote:
> On Mon 21-09-15 17:16:49, Dongsheng Yang wrote:
>> 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.
>
> I think you are missing one thing:
>
> Assume user A has files F1 (1MB) F2 (2MB) F3 (3MB).
> User B has one file G1 (4MB).
>
> So user A uses 6 MB in total (stored in dquot for user A in dqb_curspace
> field). User B uses 4MB.
>
> Now you do "chown B F1"
>
> You need to change dq_dqb of F1 to point to user B quota structure as you
> explain, that is correct. However you also need to subtract 1MB from user
> A's total usage (which is stored in struct dquot for user A) since file F1
> no longer belongs to him. And you need to add 1 MB to user B's total usage.
>
> After this user A will have total usage of 5 MB and user B has usage of 5
> MB as well. You need to properly update the total usage of each user so
> that you can check the usage against quota limits.

But that's all done in dquot_transfer(). It dquot_decr_space(from) and
dquot_incr_space(to). Let me show the test result in my implementation.

(1). root -> 1M/2M/3M     yds ->4M

[root at atest-guest linux_compile]# ll -h /mnt/ubifs/
total 11M
-rw-r--r--. 1 root root 1.0M Sep 21 15:54 1M
-rw-r--r--. 1 root root 2.0M Sep 21 15:54 2M
-rw-r--r--. 1 root root 3.0M Sep 21 15:54 3M
-rw-r--r--. 1 yds  root 4.0M Sep 21 15:55 4M
-rw-------. 1 root root 6.0K Sep 21 15:53 aquota.group
-rw-------. 1 root root 7.0K Sep 21 15:53 aquota.user
[root at atest-guest linux_compile]# repquota -u /mnt/ubifs/
*** Report for user quotas on device /dev/ubi0_0
Block grace time: 7days; Inode grace time: 7days
                         Block limits                File limits
User            used    soft    hard  grace    used  soft  hard  grace
----------------------------------------------------------------------
root      --    6144       0       0              4     0     0
yds       --    4096       0       0              1     0     0


(2). chown yds /mnt/ubifs/1M
[root at atest-guest linux_compile]# chown yds /mnt/ubifs/1M
[root at atest-guest linux_compile]# ll -h /mnt/ubifs/
total 11M
-rw-r--r--. 1 yds  root 1.0M Sep 21 15:54 1M
-rw-r--r--. 1 root root 2.0M Sep 21 15:54 2M
-rw-r--r--. 1 root root 3.0M Sep 21 15:54 3M
-rw-r--r--. 1 yds  root 4.0M Sep 21 15:55 4M
-rw-------. 1 root root 6.0K Sep 21 15:53 aquota.group
-rw-------. 1 root root 7.0K Sep 21 15:53 aquota.user
[root at atest-guest linux_compile]# repquota -u /mnt/ubifs/
*** Report for user quotas on device /dev/ubi0_0
Block grace time: 7days; Inode grace time: 7days
                         Block limits                File limits
User            used    soft    hard  grace    used  soft  hard  grace
----------------------------------------------------------------------
root      --    5120       0       0              3     0     0
yds       --    5120       0       0              2     0     0


(3). quotacheck and check again.
[root at atest-guest linux_compile]# quotaoff /mnt/ubifs && quotacheck -u 
/mnt/ubifs/
[root at atest-guest linux_compile]# ll -h /mnt/ubifs
total 11M
-rw-r--r--. 1 yds  root 1.0M Sep 21 15:54 1M
-rw-r--r--. 1 root root 2.0M Sep 21 15:54 2M
-rw-r--r--. 1 root root 3.0M Sep 21 15:54 3M
-rw-r--r--. 1 yds  root 4.0M Sep 21 15:55 4M
-rw-------. 1 root root 6.0K Sep 21 15:53 aquota.group
-rw-------. 1 root root 7.0K Sep 21 16:00 aquota.user
[root at atest-guest linux_compile]# repquota -u /mnt/ubifs/
*** Report for user quotas on device /dev/ubi0_0
Block grace time: 7days; Inode grace time: 7days
                         Block limits                File limits
User            used    soft    hard  grace    used  soft  hard  grace
----------------------------------------------------------------------
root      --    5120       0       0              3     0     0
yds       --    5120       0       0              2     0     0

Yang
>
> 								Honza
>