From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Emelyanov Subject: Re: [PATCH][NETNS] Make ifindex generation per-namespace Date: Wed, 10 Oct 2007 12:55:32 +0400 Message-ID: <470C9384.9050102@openvz.org> References: <470B71CD.3000706@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: David Miller , Linux Netdev List , devel@openvz.org To: "Eric W. Biederman" Return-path: Received: from sacred.ru ([62.205.161.221]:34646 "EHLO sacred.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751871AbXJJI6N (ORCPT ); Wed, 10 Oct 2007 04:58:13 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Eric W. Biederman wrote: > Pavel Emelyanov writes: > >> Currently indexes for netdevices come sequentially one by >> one, and the same stays true even for devices that are >> created for namespaces. >> >> Side effects of this are: >> * lo device has not 1 index in a namespace. This may break >> some userspace that relies on it (and AFAIR something >> really broke in OpenVZ VEs without this); > > As it happens lo hasn't been registered first for some time > so it hasn't had ifindex of 1 in the normal kernel. > >> * after some time namespaces will have devices with indexes >> like 1000000 os similar. This might be confusing for a >> human (tools will not mind). > > Only if we wind up creating that many devices. Nope. Create and destroy new net ns for 10000 times and you'll get it. >> So move the (currently "global" and static) ifindex variable >> on the struct net, making the indexes allocation look more >> like on a standalone machine. >> >> Moreover - when we have indexes intersect between namespaces, >> we may catch more BUGs in the future related to "wrong device >> was found for a given index". > > Not yet. > > I know there are several data structures internal to the kernel that > are indexed by ifindex, and not struct net_device *. There is the > iflink field in struct net_device. We need a way to refer to network > devices in other namespaces in rtnetlink in an unambiguous way. I > don't see any real problems with a global ifindex assignment until > we start migrating applications. > > So please hold off on this until the kernel has been audited and > we have removed all of the uses of ifindex that assume ifindex is > global, that we can find. Ok. > Right now a namespace local ifindex seems to be just asking for > trouble. You said the same about caching the global pid on the task_struct, but looks like you were wrong ;) Just kidding. > Eric > >