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

[Jan Kara]

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.

								Honza
-- 
Jan Kara <jack at suse.com>
SUSE Labs, CR