From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Schmidt Subject: Re: [PATCH net] rtnetlink: fix userspace API breakage for iproute2 < v3.9.0 Date: Thu, 12 Jun 2014 16:13:09 +0200 Message-ID: <5399B575.7070604@redhat.com> References: <1401279319-29088-1-git-send-email-mschmidt@redhat.com> <20140530.174248.715408523447246496.davem@davemloft.net> <538DBDB3.7030505@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, stephen@networkplumber.org, alexander.h.duyck@intel.com, michael.riesch@omicron.at To: David Miller , Linus Torvalds Return-path: Received: from mx1.redhat.com ([209.132.183.28]:37717 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752823AbaFLON0 (ORCPT ); Thu, 12 Jun 2014 10:13:26 -0400 In-Reply-To: <538DBDB3.7030505@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On 06/03/2014 02:21 PM, Michal Schmidt wrote: > On 05/31/2014 02:42 AM, David Miller wrote: >> From: Michal Schmidt >> Date: Wed, 28 May 2014 14:15:19 +0200 >> >>> When running RHEL6 userspace on a current upstream kernel, "ip link" >>> fails to show VF information. >>> >>> The reason is a kernel<->userspace API change introduced by commit >>> 88c5b5ce5cb57 ("rtnetlink: Call nlmsg_parse() with correct header length"), >>> after which the kernel does not see iproute2's IFLA_EXT_MASK attribute >>> in the netlink request. >>> >>> iproute2 adjusted for the API change in its commit 63338dca4513 >>> ("libnetlink: Use ifinfomsg instead of rtgenmsg in rtnl_wilddump_req_filter"). >>> >>> The problem has been noticed before: >>> http://marc.info/?l=linux-netdev&m=136692296022182&w=2 >>> (Subject: Re: getting VF link info seems to be broken in 3.9-rc8) >>> >>> We can do better than tell those with old userspace to upgrade. We can >>> recognize the old iproute2 in the kernel by checking the netlink message >>> length. Even when including the IFLA_EXT_MASK attribute, its netlink >>> message is shorter than struct ifinfomsg. >>> >>> With this patch "ip link" shows VF information in both old and new >>> iproute2 versions. >>> >>> Signed-off-by: Michal Schmidt >> >> The userspace tool should be fixed on the system, rather than having the >> kernel cater to a user tool bug. >> >> I'm not applying this, sorry. > > David, > > the old version of the userspace tool did what it had to do in order to > work with a contemporary kernel. You can call that a bug, but the fact > is that it used to work that way. > > I do not see a difference between "catering to a user tool bug" and > "not breaking applications, whether we like them or not" (paraphrasing > Linus's message on this very mailing list just 10 days ago). Dave, I am sorry for harping on this, but could you please either reconsider the NAK, or explain what considerations are more important than userspace compatibility in this case? > I could understand your objection if my proposed patch could break > something else, but you are not saying that, are you? Michal