netdev - Re: [PATCH net-next v4 0/4] netns: allow to identify peer netns

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Message-ID: <545A32C4.7070108@6wind.com>
Date:	Wed, 05 Nov 2014 15:23:00 +0100
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	netdev@...r.kernel.org, containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	davem@...emloft.net, stephen@...workplumber.org,
	akpm@...ux-foundation.org, luto@...capital.net,
	cwang@...pensource.com
Subject: Re: [PATCH net-next v4 0/4] netns: allow to identify peer netns

Le 31/10/2014 20:14, Eric W. Biederman a écrit :
> Nicolas Dichtel <nicolas.dichtel@...nd.com> writes:
>
>> Le 30/10/2014 19:41, Eric W. Biederman a écrit :
>>> Nicolas Dichtel <nicolas.dichtel@...nd.com> writes:
>>>
>>>> The goal of this serie is to be able to multicast netlink messages with an
>>>> attribute that identify a peer netns.
>>>> This is needed by the userland to interpret some informations contained in
>>>> netlink messages (like IFLA_LINK value, but also some other attributes in case
>>>> of x-netns netdevice (see also
>>>> http://thread.gmane.org/gmane.linux.network/315933/focus=316064 and
>>>> http://thread.gmane.org/gmane.linux.kernel.containers/28301/focus=4239)).
>>>>
>>>> Ids of peer netns are set by userland via a new genl messages. These ids are
>>>> stored per netns and are local (ie only valid in the netns where they are set).
>>>> To avoid allocating an int for each peer netns, I use idr_for_each() to retrieve
>>>> the id of a peer netns. Note that it will be possible to add a table (struct net
>>>> -> id) later to optimize this lookup if needed.
>>>>
>>>> Patch 1/4 introduces the netlink API mechanism to set and get these ids.
>>>> Patch 2/4 and 3/4 implements an example of how to use these ids in rtnetlink
>>>> messages. And patch 4/4 shows that the netlink messages can be symetric between
>>>> a GET and a SET.
>>>>
>>>> iproute2 patches are available, I can send them on demand.
>>>
>>> A quick reply.  I think this patchset is in the right general direction.
>>> There are some oddball details that seem odd/awkward to me such as using
>>> genetlink instead of rtnetlink to get and set the ids, and not having
>>> ids if they are not set (that feels like a maintenance/usability challenge).
>> No problem to use rtnetlink, in fact, I hesitated.
>>
>> For the second point, I'm not sure to follow you: how to have an id, which will
>> not break migration, without asking the user to set it?
>
> We have that situtation with ifindex already.  Basically the thought is
> to allow an id to be set, but also allow an id to be auto-generated if
> we use an namespace without an id being set.
If my understanding is correct, the difference is that we want to hide some
netns.
Do you think we can generate an id for each netns that does not have one and
relying on the fact that this id has no meaning unless you have a netns file
descriptor that allow you to get the id of this netns?


Regards,
Nicolas
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