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

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Message-ID: <20201119205633.6775c072@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Thu, 19 Nov 2020 20:56:33 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Mahesh Bandewar (महेश बंडेवार) " <maheshb@...gle.com>
Cc:     nicolas.dichtel@...nd.com, David Ahern <dsahern@...il.com>,
        Ido Schimmel <idosch@...sch.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 Thu, 19 Nov 2020 19:55:08 -0800 Mahesh Bandewar (महेश बंडेवार) wrote:
> On Thu, Nov 19, 2020 at 12:03 AM Nicolas Dichtel
> > Le 18/11/2020 à 18:39, Mahesh Bandewar (महेश बंडेवार) a écrit :  
> > > 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.  
> > The networking is very limited with only a loopback. Do you have some real use
> > case in mind?  
> 
> My use cases all use networking but I think principally we cannot
> break backward compatibility, right?
> Jakub, WDYT?

Do you have more details on what the use cases are that expect no
networking?

TBH I don't get the utility of this knob. If you want to write vaguely
portable software you have to assume the knob won't be useful, because
either (a) kernel may be old, or (b) you shouldn't assume to own the
sysctls and this is a global one (what if an application spawns that
expects legacy behavior?)

And if you have to check for those two things you're gonna write more
code than just ifuping lo would be.

Maybe you can shed some more light on how it makes life at Google
easier for you? Or someone else can enlighten me?

I don't have much practical experience with namespaces, but the more 
I think about it the more pointless it seems.