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

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Message-ID: <abac619b-dec4-8179-cb59-52c8f14422a1@virtuozzo.com>
Date:   Tue, 13 Oct 2020 16:54:38 +0300
From:   Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Amir Goldstein <amir73il@...il.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] ovl: introduce new "uuid=off" option for inodes
 index feature



On 10/6/20 6:13 PM, Miklos Szeredi wrote:
> On Fri, Sep 25, 2020 at 10:35 AM Pavel Tikhomirov
> <ptikhomirov@...tuozzo.com> 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.