From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752832AbeAZJ2j (ORCPT ); Fri, 26 Jan 2018 04:28:39 -0500 Received: from mail-wr0-f169.google.com ([209.85.128.169]:40445 "EHLO mail-wr0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752521AbeAZJ2g (ORCPT ); Fri, 26 Jan 2018 04:28:36 -0500 X-Google-Smtp-Source: AH8x22402N6PAW5dQAQRgpGCg/SoA3pL+CsYMaQepIAq6kNj776G41Qwu67ii3JXb7s/zoG3PuFY6A== Reply-To: nicolas.dichtel@6wind.com Subject: Re: [PATCH net-next 0/3 V1] rtnetlink: enable IFLA_IF_NETNSID for RTM_{DEL,SET}LINK References: <20180124142634.17766-1-christian.brauner@ubuntu.com> <20180124173515.5ae2bc05@redhat.com> <20180125233043.66ff08c2@redhat.com> <3b916ec7-3aca-13a7-7a48-7a7e8822e488@6wind.com> <20180126093629.142e2a74@redhat.com> To: Jiri Benc Cc: Christian Brauner , netdev@vger.kernel.org, ebiederm@xmission.com, davem@davemloft.net, dsahern@gmail.com, fw@strlen.de, daniel@iogearbox.net, lucien.xin@gmail.com, mschiffer@universe-factory.net, jakub.kicinski@netronome.com, vyasevich@gmail.com, linux-kernel@vger.kernel.org, w.bumiller@proxmox.com, Christian Brauner From: Nicolas Dichtel Organization: 6WIND Message-ID: <011a90c5-03a6-14da-d12c-d3ef4316e756@6wind.com> Date: Fri, 26 Jan 2018 10:28:31 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180126093629.142e2a74@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 26/01/2018 à 09:36, Jiri Benc a écrit : > On Fri, 26 Jan 2018 00:34:51 +0100, Nicolas Dichtel wrote: >> Why meaningful? The user knows that the answer is like if if was done in another >> netns. It enables to have only one netlink socket instead of one per netns. But >> the code using it will be the same. > > Because you can't use it to query the linked interface. You can't even > use it as an opaque value to track interfaces (netnsid+ifindex) because > netnsids are not unique across net name spaces. You can easily have two > interfaces that have all the ifindex, ifname, netnsid (and basically > everything else) identical but being completely different interfaces. Yes, the user have to map those info correctly. And this complexifies the (user) code a lot. > That's really not helpful. > >> I fear that with your approach, it will results to a lot of complexity in the >> kernel. > > The complexity is (at least partly) already there. It's an inevitable > result of the design decision to have relative identifiers. Yes, you're right. My approach moves the complexity to the user, which make this feature hard to use. > > I agree that we should think about how to make this easy to implement. > I like your idea of doing this somehow generically. Perhaps it's > possible to do while keeping the netnsids valid in the caller's netns? Yes. I agree that it will be a lot easier to use if the conversion is done in the kernel. And having a generic mechanism will also help a lot to use it. > >> What is really missing for me, is a way to get a fd from an nsid. The user >> should be able to call RTM_GETNSID with an fd and a nsid and the kernel performs >> the needed operations so that the fd points to the corresponding netns. > > That's what I was missing, too. I even looked into implementing it. But > opening a fd on behalf of the process and returning it over netlink is a > wrong thing to do. Netlink messages can get lost. Then you have a fd > leak you can do nothing about. Yes, I also looked at this ;-) > > Given that we have netnsids used for so much stuff already (like > NETLINK_LISTEN_ALL_NSID) you need to track them anyway. And if you need > to track them, why bother with another identifier? It would be better > if netnsid can be used universally for anything. Then there will be no > need for the conversion. I like this idea a lot. So the missing part is a setns() using the nsid ;-) Regards, Nicolas