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

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Message-ID: <7b3f1d07-eca4-b012-c46a-e1f09bba9d6f@gmail.com>
Date:   Wed, 18 Nov 2020 11:04:50 -0700
From:   David Ahern <dsahern@...il.com>
To:     Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>,
        nicolas.dichtel@...nd.com
Cc:     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 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.