netdev - Re: [PATCH net-next] net-loopback: allow lo dev initial state to be controlled

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Message-ID: <CAF2d9jgJZYtv3fEqB58rK+sFoT_zibvYyQdq64o6=Pgx7EY4+w@mail.gmail.com>
Date:   Wed, 18 Nov 2020 11:54:01 -0800
From:   Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>
To:     David Ahern <dsahern@...il.com>
Cc:     nicolas.dichtel@...nd.com, Ido Schimmel <idosch@...sch.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jian Yang <jianyang.kernel@...il.com>,
        David Miller <davem@...emloft.net>,
        linux-netdev <netdev@...r.kernel.org>,
        Jian Yang <jianyang@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] net-loopback: allow lo dev initial state to be controlled

On Wed, Nov 18, 2020 at 10:04 AM David Ahern <dsahern@...il.com> wrote:
>
> On 11/18/20 10:39 AM, Mahesh Bandewar (महेश बंडेवार) wrote:
> > On Wed, Nov 18, 2020 at 8:58 AM Nicolas Dichtel
> > <nicolas.dichtel@...nd.com> wrote:
> >>
> >> Le 18/11/2020 à 02:12, David Ahern a écrit :
> >> [snip]
> >>> If there is no harm in just creating lo in the up state, why not just do
> >>> it vs relying on a sysctl? It only affects 'local' networking so no real
> >>> impact to containers that do not do networking (ie., packets can't
> >>> escape). Linux has a lot of sysctl options; is this one really needed?
> >>>
> > I started with that approach but then I was informed about these
> > containers that disable networking all together including loopback.
> > Also bringing up by default would break backward compatibility hence
> > resorted to sysctl.
> >> +1
> >>
> >> And thus, it will benefit to everybody.
> >
> > Well, it benefits everyone who uses networking (most of us) inside
> > netns but would create problems for workloads that create netns to
> > disable networking. One can always disable it after creating the netns
> > but that would mean change in the workflow and it could be viewed as
> > regression.
> >
>
> Then perhaps the relevant sysctl -- or maybe netns attribute -- is
> whether to create a loopback device at all.

I'm open to ideas within the bounds of maintaining backward
compatibility. However, not able to see how we can pull it off without
creating a 'loopback' device.