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

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Date:	Thu, 04 Dec 2014 17:21:09 +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 05/11/2014 15:23, Nicolas Dichtel a écrit :
> 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?
Any comment Eric ?


Thank you,
Nicolas
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