Re: [PATCH v4 2/2] ovl: introduce new "uuid=off" option for inodes index feature

[Pavel Tikhomirov]

On 10/6/20 6:13 PM, Miklos Szeredi wrote:
> On Fri, Sep 25, 2020 at 10:35 AM Pavel Tikhomirov
> <ptikhomirov@xxxxxxxxxxxxx> wrote:
>
> > Note: In our (Virtuozzo) use case users inside a container can create
> > "regular" overlayfs mounts without any "index=" option, but we still
> > want to migrate this containers with CRIU so we set "index=on" as kernel
> > default so that all the container overlayfs mounts get support of file
> > handles automatically. With "uuid=off" we want the same thing (to be
> > able to "copy" container with uuid change) - we would set kernel default
> > so that all the container overlayfs mounts get "uuid=off" automatically.
>
> I'm not sure I buy that argument for a kernel option.   It should
> rather be a "container" option in that case, but AFAIK the kernel
> doesn't have a concept of a container.  I think this needs to be
> discussed on the relevant mailing lists.
>
> As of now mainline kernel doesn't support unprivileged overlay mounts,
> so I guess this is not an issue.  Let's just merge this without the
> kernel and the module options.

Virtuozzo kernel does have a "container" concept and we do have 
unprivileged overlay mounts to support docker inside Virtuozzo 
containers. We don't face any major issues with it. But you are right 
it's not mainstream.

Probably a normal user of mainstream kernel also might want to set 
index=on+uuid=off by default, so that all their docker containters 
automatically support inotifies and survive backing disk uuid change 
automaticaly.

I will prepare next patchset version without default.

> Thanks,
> Miklos

--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.