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

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Date:   Wed, 5 Jul 2017 10:50:37 -0700
From:   Mahesh Bandewar (महेश बंडेवार) 
        <maheshb@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     mahesh@...dewar.net, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, Eric Dumazet <edumazet@...gle.com>,
        ebiederm@...ssion.com, linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 0/2] bring UP loopback device at initialziation

On Wed, Jul 5, 2017 at 9:05 AM, David Miller <davem@...emloft.net> wrote:
> 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.
>
Well, I can make this commit message long-winded but most of the (so
called) issues are well known and I thought I wont add any additional
value repeating them here hence kept it simple. I can spin up the next
rev with the long-winded commit message. ;)

> Thank you.