Date:	Mon, 4 Jun 2012 15:56:15 +0200
From:	Jan Kara <jack@...e.cz>
To:	Jeff Liu <jeff.liu@...cle.com>
Cc:	Jan Kara <jack@...e.cz>, Serge Hallyn <serge.hallyn@...onical.com>,
	tytso@....edu, containers@...ts.linux-foundation.org,
	david@...morbit.com, hch@...radead.org, bpm@....com,
	christopher.jones@...cle.com, linux-fsdevel@...r.kernel.org,
	cgroups@...r.kernel.org, tm@....ma, linux-ext4@...r.kernel.org,
	chris.mason@...cle.com, tinguely@....com
Subject: Re: container disk quota

On Mon 04-06-12 21:35:06, Jeff Liu wrote:
> On 06/04/2012 05:42 PM, Jan Kara wrote:
> 
> > On Mon 04-06-12 12:46:49, Jeff Liu wrote:
> >> On 06/04/2012 10:57 AM, Serge Hallyn wrote:
> >>> Quoting Jeff Liu (jeff.liu@...cle.com):
> >>>> Hi Serge,
> >>>>
> >>>> On 06/02/2012 12:04 AM, Serge Hallyn wrote:
> >>>>
> >>>>> Quoting Jan Kara (jack@...e.cz):
> >>>>>>   Hello,
> >>>>>>
> >>>>>> On Wed 30-05-12 22:58:54, jeff.liu@...cle.com wrote:
> >>>>>>> According to glauber's comments regarding container disk quota, it should be binded to mount
> >>>>>>> namespace rather than cgroup.
> >>>>>>>
> >>>>>>> Per my try out, it works just fine by combining with userland quota utilitly in this way.
> >>>>>>> However, they are something has to be done at user tools too IMHO.
> >>>>>>>
> >>>>>>> Currently, the patchset is in very initial phase, I'd like to post it early to seek more
> >>>>>>> feedbacks from you guys.
> >>>>>>>
> >>>>>>> Hopefully I can clarify my ideas clearly.
> >>>>>>   So what I miss in this introductory email is some highlevel description
> >>>>>> like what is the desired functionality you try to implement and what is it
> >>>>>> good for. Looking at the examples below, it seems you want to be able to
> >>>>>> set quota limits for namespace-uid (and also namespace-gid???) pairs, am I
> >>>>>> right?
> >>>>>>
> >>>>>>   If yes, then I would like to understand one thing: When writing to a
> >>>>>> file, used space is accounted to the owner of the file. Now how do we
> >>>>>> determine owning namespace? Do you implicitely assume that only processes
> >>>>>> from one namespace will be able to access the file?
> >>>>>>
> >>>>>> 								Honza
> >>>>>
> >>>>> Not having looked closely at the original patchset, let me ask - is this
> >>>>> feature going to be a freebie with Eric's usernamespace patches?
> >>>>
> >>>> It we can reach a consensus to bind quota on mount namespace for
> >>>> container or other things maybe.
> >>>> I think it definitely should depends on user namespace.
> >>>>
> >>>>>
> >>>>> There, a container can be started in its own user namespace.  It's uid
> >>>>> 1000 will be mapped to something like 1101000 on the host.  So the actual
> >>>>> uid against who the quota is counted is 1101000.  In another container,
> >>>>> uid 1000 will be mapped to 1201000, and again quota will be counted against
> >>>>> 1201000.
> >>>>
> >>>> Is it also an implications that we can examine do container quota or not
> >>>> based on the uid/gid number?
> >>>
> >>> I'm sorry I don't understand the question.
> >>
> >> Sorry for my poor english.
> >>
> >>>
> >>> As an attempt at an answer:  the quota code wouldn't change at all.  We would
> >>> simply exploit the fact that uid 1000 in container1 has a real uid of 101100,
> >>> which is different from the real uid 102100 assigned to uid 1000 in container2
> >>> and from real uid 1000 (uid 1000 on the host).
> >>
> >> In that case, looks we only need to figure out how to let quota tools
> >> works at container.
> >> I'll build a new kernel with user_ns to give a try.
> >   GETQUOTA or SETQUOTA quotactls should work just fine inside a container
> > (for those quota-tools just need access to /proc/mounts). QUOTAON should
> > also work for e.g. XFS or ext4 with hidden quota files. When quota files
> > are visible in fs namespace (as for ext3 or so), things would be a bit
> > tricky because they won't be possibly visible from container and QUOTAON
> > needs that.
> 
> I still think if we can cache container dquot on memory to make this
> feature as simple as possible. :)
  Sorry, I don't understand. Quota structures are cached in memory. Also
what would be simpler if you also do some caching in a container?

> And also, quotacheck is the major issue I have faced previously, since we need a reasonable approach to calculate
> and save the current inodes/blocks usage firstly.
  Yes, quotacheck inside a container is a problem. But similarly as with
quotaon(8), I think such global operation should rather be done outside.
 
> > Also with QUOTAON there is the principial problem that quotas either are or
> > are not enabled for the whole filesystem.
> 
> IMHO, we could supply uid/gid quota for the whole filesystem only(i.e,
> the "/" rootfs), and we can support project quota among sub-directories
> in the future if possible.
> 
> > So probably the only reasonable
> > choice when you would like to supporot quotas in the container would be to
> > have quotas enabled all the time, and inside the container, you would just
> > set some quota limits or you won't...
> 
> I remember that ext4 has already supported quota as the first class,
> looks we can consider container quota same to that.
> 
> So we can ignore the quotacheck step, only focus on quota limits setup
> inside container?
  Yes, that would be my suggestion.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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