netdev - Re: [RFC PATCH net-next v2 0/5] netns: allow to identify peer netns

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Message-ID: <8761g2nurx.fsf@x220.int.ebiederm.org>
Date:	Thu, 02 Oct 2014 12:20:18 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	nicolas.dichtel@...nd.com
Cc:	Andy Lutomirski <luto@...capital.net>,
	Network Development <netdev@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: [RFC PATCH net-next v2 0/5] netns: allow to identify peer netns

Nicolas Dichtel <nicolas.dichtel@...nd.com> writes:

> Le 29/09/2014 20:43, Eric W. Biederman a écrit :
>> Nicolas Dichtel <nicolas.dichtel@...nd.com> writes:
>>
>>> Le 26/09/2014 20:57, Eric W. Biederman a écrit :
>>>> Andy Lutomirski <luto@...capital.net> writes:
>>>>
>>>>> On Fri, Sep 26, 2014 at 11:10 AM, Eric W. Biederman
>>>>> <ebiederm@...ssion.com> wrote:
>>>>>> I see two ways to go with this.
>>>>>>
>>>>>> - A per network namespace table to that you can store ids for ``peer''
>>>>>>     network namespaces.  The table would need to be populated manually by
>>>>>>     the likes of ip netns add.
>>>>>>
>>>>>>     That flips the order of assignment and makes this idea solid.
>>> I have a preference for this solution, because it allows to have a full
>>> broadcast messages. When you have a lot of network interfaces (> 10k),
>>> it saves a lot of time to avoid another request to get all informations.
>>
>> My practical question is how often does it happen that we care?
> In fact, I don't think that scenarii with a lot of netns have a full mesh of
> x-netns interfaces. It will be more one "link" netns with the physical
> interface and all other with one interface with the link part in this "link"
> netns. Hence, only one nsid is needing in each netns.

I will buy that a full mesh is unlikely.  

For people doing simulations anything physical has a limited number of
links.

For people wanting all to all connectivity setting up an internal
macvlan (or the equivalent) is likely much simpler and more efficient
that a full mesh.

So the question in my mind is how do we create these identifiers at need
(when we create the cross network namespace links) instead of at network
namespace creation time.  I don't see an answer to that in your patches,
and perhaps it obvious.

Eric
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