Re: [PATCH v2 2/3] shmem: implement user/group quota support for tmpfs

[Lukas Czerner <lczerner@redhat.com>]

On Fri, Nov 25, 2022 at 10:14:53AM +0100, Jan Kara wrote:
> On Fri 25-11-22 09:59:48, Lukas Czerner wrote:
> > On Wed, Nov 23, 2022 at 05:37:45PM +0100, Jan Kara wrote:
> > > On Mon 21-11-22 15:28:53, Lukas Czerner wrote:
> > > > Implement user and group quota support for tmpfs using system quota file
> > > > in vfsv0 quota format. Because everything in tmpfs is temporary and as a
> > > > result is lost on umount, the quota files are initialized on every
> > > > mount. This also goes for quota limits, that needs to be set up after
> > > > every mount.
> > > > 
> > > > The quota support in tmpfs is well separated from the rest of the
> > > > filesystem and is only enabled using mount option -o quota (and
> > > > usrquota and grpquota for compatibility reasons). Only quota accounting
> > > > is enabled this way, enforcement needs to be enable by regular quota
> > > > tools (using Q_QUOTAON ioctl).
> > > > 
> > > > Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> > > 
> > > ...
> > > 
> > > > diff --git a/Documentation/filesystems/tmpfs.rst b/Documentation/filesystems/tmpfs.rst
> > > > index 0408c245785e..9c4f228ef4f3 100644
> > > > --- a/Documentation/filesystems/tmpfs.rst
> > > > +++ b/Documentation/filesystems/tmpfs.rst
> > > > @@ -86,6 +86,18 @@ use up all the memory on the machine; but enhances the scalability of
> > > >  that instance in a system with many CPUs making intensive use of it.
> > > >  
> > > >  
> > > > +tmpfs also supports quota with the following mount options
> > > > +
> > > > +========  =============================================================
> > > > +quota     Quota accounting is enabled on the mount. Tmpfs is using
> > > > +          hidden system quota files that are initialized on mount.
> > > > +          Quota limits can quota enforcement can be enabled using
> > >                           ^^^ and?
> > > 
> > > > +          standard quota tools.
> > > > +usrquota  Same as quota option. Exists for compatibility reasons.
> > > > +grpquota  Same as quota option. Exists for compatibility reasons.
> > > 
> > > As we discussed with V1, I'd prefer if user & group quotas could be enabled
> > > / disabled independently. Mostly to not differ from other filesystems
> > > unnecessarily.
> > 
> > Ok, but other file systems (at least xfs and ext) differs. Mounting ext4
> > file system with quota feature with default quota option settings will
> > always enable accounting for both user and group. Mount options quota,
> > usrquota and grpquota enables enforcement; selectively with the last
> > two.
> > 
> > On xfs with no mount options quota is disabled. With quota, usrquota and
> > grpquota enforcement is enabled, again selectively with the last two.
> > 
> > And yes, with this implementation tmpfs is again different. The idea was
> > to allow enabling accounting and enforcement (with default limits)
> > selectively.
> > 
> > So how would you like the tmpfs to do it? I think having accounting only
> > can be useful and I'd like to keep it. Maybe adding qnoenforce,
> > uqnoenforce and qgnoenforce mount options, but that seems cumbersome to
> > me and enabling accounting by default seems a bit much. What do you think?
> 
> So I wanted things to be as similar to other filesystems as possible. So
> quota, usrquota, grpquota would enable quota accounting & enforcement (the
> last two selectively). If we want the possibility to enable accounting
> without enforcement that can be done by some special mount options (and
> possibly we can add them when there's user demand). Also note that there's
> always the possibility to disable quota enforcement using quota tools when
> needed. But IMHO 99% of users will want accounting & enforcement and thus
> that should be the default like with other filesystems.
> 
> 								Honza

Alright I'll do that.

Thanks!
-Lukas

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