netdev - Re: [PATCH 0/2] bring UP loopback device at initialziation

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Message-Id: <20170705.170524.241248681076978527.davem@davemloft.net>
Date:   Wed, 05 Jul 2017 17:05:24 +0100 (WEST)
From:   David Miller <davem@...emloft.net>
To:     maheshb@...gle.com
Cc:     mahesh@...dewar.net, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, edumazet@...gle.com, ebiederm@...ssion.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH 0/2] bring UP loopback device at initialziation

From: Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>
Date: Wed, 5 Jul 2017 08:59:37 -0700

> On Wed, Jul 5, 2017 at 1:20 AM, David Miller <davem@...emloft.net> wrote:
>> From: Mahesh Bandewar <mahesh@...dewar.net>
>> Date: Tue,  4 Jul 2017 12:16:15 -0700
>>
>>> In almost every scenario the loopback device is brought UP after
>>> initialization. So there is no point of bringing up the device in
>>> DOWN state followed by device UP operation. This change exposed
>>> another issue of fib-trie initialization which is corrected in the
>>> first path.
>>
>> You use the word almost, which supports my position that someone may
>> not want this.
>>
>> I also don't see it as so much of a burdon to bring the lo device up
>> explicitly.  Systems have been having to do that since the beginning
>> of time.
>>
> Systems have only one lo device (since ages) and that is usually taken
> care at the boot time. Now with the namespaces it's not just one
> device as it's per namespace and though not much this patch will
> benefit a little. Probably we should ask a question - is it going to
> have any bad effects? I couldn't find any and my RFC patch did not get
> me any such feedback. As far as the good effects are concerned, it has
> already found a bug (another patch in this series)! Also sometime back
> I did experience weird behavior inside net-namespace if you forget to
> bring-up the loopback device. I didn't pay too much attention as
> bringing up the lo device fixed it.

You're not talking at all about why specifically you need this
(ie. your use case) when you are spinning up namespaces for users.

I do happen to know those details, but you need to talk about this
explicitly in your commit log messages and in this discussion so that
everyone else understands this as well.

Thank you.