Re: [PATCH v2] ext4: choose hardlimit when softlimit is larger than hardlimit in ext4_statfs_project()

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Nov 06, 2019 at 12:37:35PM +0800, Chengguang Xu wrote:
>  ---- 在 星期二, 2019-10-15 19:25:23 Jan Kara <jack@suse.cz> 撰写 ----
>  > On Tue 15-10-19 18:23:27, Chengguang Xu wrote:
>  > > Setting softlimit larger than hardlimit seems meaningless
>  > > for disk quota but currently it is allowed. In this case,
>  > > there may be a bit of comfusion for users when they run
>  > > df comamnd to directory which has project quota.
>  > > 
>  > > For example, we set 20M softlimit and 10M hardlimit of
>  > > block usage limit for project quota of test_dir(project id 123).
>  > > 
>  > > [root@hades mnt_ext4]# repquota -P -a
>  > > *** Report for project quotas on device /dev/loop0
>  > > Block grace time: 7days; Inode grace time: 7days
>  > >                         Block limits                File limits
>  > > Project         used    soft    hard  grace    used  soft  hard  grace
>  > > ----------------------------------------------------------------------
>  > >  0        --      13       0       0              2     0     0
>  > >  123      --   10237   20480   10240              5   200   100
>  > > 
>  > > The result of df command as below:
>  > > 
>  > > [root@hades mnt_ext4]# df -h test_dir
>  > > Filesystem      Size  Used Avail Use% Mounted on
>  > > /dev/loop0       20M   10M   10M  50% /home/cgxu/test/mnt_ext4
>  > > 
>  > > Even though it looks like there is another 10M free space to use,
>  > > if we write new data to diretory test_dir(inherit project id),
>  > > the write will fail with errno(-EDQUOT).
>  > > 
>  > > After this patch, the df result looks like below.
>  > > 
>  > > [root@hades mnt_ext4]# df -h test_dir
>  > > Filesystem      Size  Used Avail Use% Mounted on
>  > > /dev/loop0       10M   10M  3.0K 100% /home/cgxu/test/mnt_ext4
>  > > 
>  > > Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
>  > > ---
>  > > - Fix a bug in the limit setting logic.
>  > 
>  > Thanks for the patch! It looks good to me. You can add:
>  > 
>  > Reviewed-by: Jan Kara <jack@suse.cz>
>  > 
> 
> Hi Jan,
> 
> I have a proposal for another direction.
> Could we add a check for soft limit  in quota layer when setting the value?
> So that we could not bother with  specific file systems on statfs(). 

How do the other filesystems (e.g. xfs) behave if someone tries to set a
soft limit higher than the hard limit?

--D

> Thanks,
> Chengguang
> 
>