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

[Dongsheng Yang]

On 09/23/2015 03:42 PM, Jan Kara wrote:
> On Mon 21-09-15 19:02:30, Dongsheng Yang wrote:
>> 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.
>
> Yes, dquot_decr_space(transfer_from[cnt], cur_space) and
> dquot_incr_space(transfer_to[cnt], cur_space) are the functions changing
> usage. However have a look at what cur_space is. It is set as:
>
> cur_space = inode_get_bytes(inode);
>
> and inode_get_bytes() is:
>
> ret = (((loff_t)inode->i_blocks) << 9) + inode->i_bytes;
>
> So for dquot_transfer() to work correctly, filesystem has to properly
> maintain i_blocks and i_bytes.

Oh, my mistake. you are right. We have to maintain i_blocks for quota
then. will update it.

Yang
>
>> (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
>
> Yes, this case is working because quota code updated i_blocks properly when
> creating files. But if you do not set i_blocks when reading inodes
> (which seems to be the case) I expect the following would not work:
>
> mount -t ubifs -o usrjquota=aquota.user,jqfmt=vfsv0 <dev> /mnt
> quotacheck -vu /mnt
> quotaon -vu /mnt
> dd if=/dev/zero of=file1 bs=1M count=1
> # Umount fs to prune cached information
> umount /mnt
> mount -t ubifs -o usrjquota=aquota.user,jqfmt=vfsv0 <dev> /mnt
> quotaon -vu /mnt
> chown yds /mnt/file1
> repquota -u /mnt/
>
> Now unless you set i_blocks when reading inode, yds would not be accounted
> for 1 MB /mnt/file1 is using...
>
> 								Honza
>