From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH] Work around dhclient brokenness (v2) Date: Tue, 19 Aug 2008 17:16:15 +0300 Message-ID: <48AAD5AF.1070204@qumranet.com> References: <1219155040-27953-1-git-send-email-aliguori@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Mark McLoughlin , Rusty Russell , Herbert Xu To: Anthony Liguori Return-path: Received: from il.qumranet.com ([212.179.150.194]:12815 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752161AbYHSOQQ (ORCPT ); Tue, 19 Aug 2008 10:16:16 -0400 In-Reply-To: <1219155040-27953-1-git-send-email-aliguori@us.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Anthony Liguori wrote: > With the latest GSO/csum offload patches, any guest using an unpatched version > of dhclient (any Ubuntu guest, for instance), will no longer be able to get > a DHCP address. > > dhclient is actually at fault here. It uses AF_PACKET to receive DHCP responses > but does not check auxdata to see if the packet has a valid csum. This causes > it to throw out the DHCP responses it gets from the virtio interface as there > is not a valid checksum. > > Fedora has carried a patch to fix their dhclient (it's needed for Xen too) but > this patch has not made it into a release of dhclient. AFAIK, the patch is in > the dhclient CVS but I cannot confirm since their CVS is not public. > > This patch, suggested by Rusty, looks for UDP packets (of a normal MTU) and > explicitly adds a checksum to them if they are missing one. > > This allows unpatched dhclients to continue to work without needing to update > the guest kernels. > > Since v1, we refined the search criteria to only consider packets originating > from a DHCP server. I also added a comment to note that we should disable this > routine when we introduce zero copy. > Applied, thanks. -- error compiling committee.c: too many arguments to function