OverlaysFS offline tools

[Amir Goldstein]

On Wed, Jan 8, 2020 at 4:06 PM Vivek Goyal <vgoyal at redhat.com> wrote:
>
> On Wed, Jan 08, 2020 at 09:27:12AM +0200, Amir Goldstein wrote:
> > [-fsdevel,+containers]
> >
> > > On Thu, Apr 18, 2019 at 1:58 PM StuartIanNaylor <rolyantrauts at gmail.com> wrote:
> > > >
> > > > Apols to ask here but are there any tools for overlayFS?
> > > >
> > > > https://github.com/kmxz/overlayfs-tools is just about the only thing I
> > > > can find.
> > >
> > > There is also https://github.com/hisilicon/overlayfs-progs which
> > > can check and fix overlay layers, but it hasn't been updated in a while.
> > >
> >
> > Hi Vivek (and containers folks),
> >
> > Stuart has pinged me on https://github.com/StuartIanNaylor/zram-config/issues/4
> > to ask about the status of overlayfs offline tools.
> >
> > Quoting my answer here for visibility to more container developers:
> >
> > I have been involved with implementing many overlayfs features in the
> > kernel in the
> > past couple of years (redirect_dir,index,nfs_export,xino,metacopy).
> > All of these features bring benefits to end users, but AFAIK, they are
> > all still disabled
> > by default in containers runtimes (?) because lack of tools support
> > (e.g. migration
> > /import/export). I cannot force anyone to use the new overlayfs
> > features nor to write
> > offline tools support for them.
> >
> > So how can we improve this situation?
> >
> > If the problem is development resources then I've had great experience
> > in the past
> > with OSS internship programs like Google summer of code (GSoC):
> > Organizations, such as Redhat or mobyproject.org, can participate in the program
> > by posting proposals for open source projects.
> > Developers, such as myself, volunteer to mentors projects and students apply
> > to work on them.
> >
> > IIRC, the timeline for GSoC for project proposals in around April. Applying as
> > an organization could be before that.
> >
> > Vivek, since you are the only developer I know involved in containers runtime
> > projects I am asking you, but really its a question for all container developers
> > out there.
> >
> > Are you aware of missing features in containers that could be met by filling the
> > gaps with overlayfs offline tools?
>
> CCing Dan Walsh as he is taking care of podman and often I hear some of
> the the complaints from him w.r.t what he thinks is missing. This is
> not necessarily related to overlayfs offline tools.
>
> - Unpriviliged mounting of overlayfs.
>
>   He wants to launch containers unpriviliged and hence wants to be able
>   to mount overlayfs without being root in init_user_ns. I think Miklos
>   posted some patches for that but not much progress after that.
>
>   https://patchwork.kernel.org/cover/11212091/
>
> - shiftfs
>
>   As of now they are relying on doing chown of the image but will really
>   like to see the ability to shift uid/gids using shiftfs or using
>   VFS layer solution.
>
> - Overlayfs redirect_dir is not compatible with image building
>
>   redirect_dir is not compatible with image building and I think that's
>   one reason that its not used by default. And as metacopy is dependent
>   on redirect_dir, its not used by default as well. It can be used for
>   running containers though, but one needs to know that in advacnce.
>
>   So it will be good if that's fixed with redirect_dir and metacopy
>   features and then there is higher chance that these features are
>   enabled by default.
>
>   Miklos had some ides on how to tackle the issue of getting diff
>   correctly with redirect_dir enabled.
>
>   https://www.spinics.net/lists/linux-unionfs/msg06969.html
>

FYI, I have been playing with kmxz's overlay (offline tools).
It's a nice little tool :)
Adding "awareness" to redirect and metacopy was easy [1].

It should be easy to add support for command "export"
that does what Miklos suggested in order to migrate an image with
metacopy/redirect.

As a first step, command "vacuum" (or a new one) could be run
on layers to check if layers are already portable and then the
heavy weight "export" is not needed.

>   Having said that, I think Dan Walsh has enabled metacopy by default
>   in podman in certain configurations (for running containers and not
>   for building images).
>

I submitted a talk proposal to plumbers containers track about
enabling overlayfs features in container runtimes [2].

The last time I brought up this topic [3] the discussion quickly shifted
to the hot shiftfs (pun intended) and the same thing happened with this
thread about offline tools [4].
Please resist the temptation to do that again!
I realize shiftfs and userns overlay are high priority features for containers.
I trust they will gets their own talk on containers track.

Vivek,

It would be great if you could co-author this talk with me, although
it is intended to be more of a round table discussion anyway.
The main idea is to exchange knowledge between overlayfs users
and overlayfs developers.

Thanks,
Amir.

[1] https://github.com/amir73il/overlayfs-tools/commits/metacopy
[2] https://linuxplumbersconf.org/event/7/abstracts/601/
[3] https://lore.kernel.org/linux-unionfs/CAOQ4uxiQEpofdS97kxnii8LtVW2QiKAGvjjaH0Px-Bj3eHVCFA@mail.gmail.com/
[4] https://lore.kernel.org/linux-unionfs/70a7e65d-40a5-7940-0d4d-14cdbfef39bd@redhat.com/