From: ebiederm@xmission•com (Eric W. Biederman)
To: Pavel Emelyanov <xemul@parallels•com>
Cc: Linux Netdev List <netdev@vger•kernel.org>,
David Miller <davem@davemloft•net>
Subject: Re: [PATCH 1/2] net: Allow to create links with given ifindex
Date: Tue, 31 Jul 2012 04:58:36 -0700 [thread overview]
Message-ID: <878ve0dtw3.fsf@xmission.com> (raw)
In-Reply-To: <50179F66.1000604@parallels.com> (Pavel Emelyanov's message of "Tue, 31 Jul 2012 13:03:34 +0400")
Pavel Emelyanov <xemul@parallels•com> writes:
> On 07/30/2012 02:56 PM, Eric W. Biederman wrote:
>> ebiederm@xmission•com (Eric W. Biederman) writes:
>>
>>> Pavel Emelyanov <xemul@parallels•com> writes:
>>>
>>>> Currently the RTM_NEWLINK results in -EOPNOTSUPP if the ifinfomsg->ifi_index
>>>> is not zero. I propose to allow requesting ifindices on link creation. This
>>>> is required by the checkpoint-restore to correctly restore a net namespace
>>>> (i.e. -- a container). The question what to do with pre-created devices such
>>>> as lo or sit fbdev is open, but for manually created devices this can be
>>>> solved by this patch.
>>>
>>> Have you walked through and found the locations where we still rely on
>>> ifindex being globally unique?
>>>
>>> Last time I was working in this area there were serveral places where
>>> things were indexed by just the interface index.
>>
>> If it is really safe to make ifindex per network namespace at this
>> point you can make dev_new_ifindex have a per network namespace base
>> counter, and that will fix your problems with the loopback device.
>
> Not it's not so unfortunately :(
>
> First, let's imagine that on host A the loopback device got registered as
> first device, but on host B for some reason some other device got registered
> first. In that case after migration from A to B the lo on B will have index
> equals 2. And there's no any strict requirement that lo's per net operations
> are registered first. Please, correct me if I'm wrong.
Actually there is a hard requirement that the loopback device be the
last device in a network namespace to be unregistered. We meet that
requirement by registering the loopback device first
"net/core/dev.c:net_dev_init()".
> Next. In fact, lo is not the only problem. Look at the e.g. sit versus ipgre
> fallback devices. Both gets created on netns creation and obtain whatever
> ifindices are generated for them. Even if we make ifidex per netns chances
> that sit gets registered _strictly_ before ipgre equal zero, since they are
> both modules.
True. However those fallback devices should no longer be needed,
and even if they are I think you can delete and recreate them.
Making lo the particularly interesting case.
>> Unless you have done the work to root out the last of dependencies on
>> ifindex being globally unique I think you will run into some operational
>> problems.
>
> I totally agree with that. Before doing this patch I revisited the ancient
> attempt to make ifindices per netns and checked the issues Dave and you
> discussed then -- I have looked through how the ifindices are used in the
> networking code and found no places where the system-wide uniqueness is still
> required. That's why I proposed this patch for inclusion. If you know the
> places I've missed, please let me know, I will work on it.
I took a quick look and I did not see anything. I saw places under
net/sched/ that looked a bit suspicious, and of course there are places
where we use oif and iff in some of the routing code that make we wonder
a bit. But if you have looked and if I have looked I think we are ok.
> Just an idea -- is it worth moving the possibility to have ifindidces intersect
> under CONFIG_<SOMETHING> (EXPERT/CHECKPOINT_RESTORE) to let wider audience check
> the code in real-life?
I think the best testing we are going to get diversity wise is to create
a per netns counter into dev_new_index when net-next opens up.
Having an ifindex that we can only set at netdevice creation time seems
reasonable.
Eric
next prev parent reply other threads:[~2012-07-31 11:58 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-30 4:34 [PATCH 1/2] net: Allow to create links with given ifindex Pavel Emelyanov
2012-07-30 4:36 ` [PATCH 2/2] veth: Allow to create peer link " Pavel Emelyanov
2012-07-30 10:49 ` [PATCH 1/2] net: Allow to create links " Eric W. Biederman
2012-07-30 10:56 ` Eric W. Biederman
2012-07-31 9:03 ` Pavel Emelyanov
2012-07-31 11:58 ` Eric W. Biederman [this message]
2012-07-31 13:30 ` Pavel Emelyanov
2012-08-02 10:28 ` Eric Dumazet
2012-08-02 11:09 ` Eric W. Biederman
2012-08-02 23:37 ` David Miller
2012-08-02 23:26 ` David Miller
2012-08-03 5:45 ` Eric Dumazet
2012-08-03 5:51 ` Eric Dumazet
2012-08-03 23:56 ` David Miller
2012-08-04 7:10 ` Eric Dumazet
2012-08-04 8:25 ` David Miller
2012-07-30 11:51 ` Eric Dumazet
2012-07-30 12:33 ` Eric W. Biederman
2012-07-31 9:06 ` Pavel Emelyanov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=878ve0dtw3.fsf@xmission.com \
--to=ebiederm@xmission$(echo .)com \
--cc=davem@davemloft$(echo .)net \
--cc=netdev@vger$(echo .)kernel.org \
--cc=xemul@parallels$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox