From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [Lxc-users] Bad checksums and lost packets with macvlan on dummy Date: Tue, 01 Mar 2011 21:04:42 +0100 Message-ID: <4D6D515A.8060707@free.fr> References: <20110221150710.GA5651@nord.niifaq.ru> <4D6282DB.2080204@free.fr> <20110221153421.GA6602@nord.niifaq.ru> <4D628DC3.9000400@free.fr> <20110223170512.GA10277@nord.niifaq.ru> <4D6A6A5F.4030707@free.fr> <1298836236.8726.109.camel@edumazet-laptop> <4D6AB578.3010704@free.fr> <1298879114.8726.131.camel@edumazet-laptop> <4D6CF4A8.6000205@free.fr> <4D6D2402.6020705@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , Andrian Nord , lxc-users@lists.sourceforge.net, Linux Netdev List To: Patrick McHardy Return-path: Received: from smtp5-g21.free.fr ([212.27.42.5]:60647 "EHLO smtp5-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757193Ab1CAUEw (ORCPT ); Tue, 1 Mar 2011 15:04:52 -0500 In-Reply-To: <4D6D2402.6020705@trash.net> Sender: netdev-owner@vger.kernel.org List-ID: On 03/01/2011 05:51 PM, Patrick McHardy wrote: > On 01.03.2011 14:29, Daniel Lezcano wrote: >> On 02/28/2011 08:45 AM, Eric Dumazet wrote: >>>> In the normal case, dummy0 is supposed to drop the packets. But with >>>> macvlan these packets are broadcasted to the other macvlan ports, so no >>>> checksum is computed when the packets are transmitted between macvlan1 >>>> and macvlan2. >>> So where frames get bad checksums ? >>> >>> In this "bridge" mode, I suspect the broadcast is done _before_ sending >>> frame to dummy, so maybe macvlan should not inherit from lowerdev in >>> this particular case ? >> Hi Eric, >> >> yes, you are right, the packets are sent before. >> >> In the 'macvlan_queue_xmit', the code checks the dev is in 'bridge' >> mode. If so, it looks if there is a destination port for the packet and >> then calls the 'forward' callback which is 'dev_forward_skb'. >> >> I was able to reproduce the same problem with qemu and an emulated >> 'e1000' card instead of dummy0. The packets are dropped too. >> >> Patrick, do you have any suggestions to fix this ? > Since the frames are only looped back locally, I suppose the easiest > fix would be to mark them with CHECKSUM_UNNECESSARY. Alternatively > we need to complete the checksum manually, similar to what > dev_hard_start_xmit() does. That sounds very simple to fix, maybe too much simple :) I did the following change: --- drivers/net/macvlan.c | 1 + 1 file changed, 1 insertion(+) Index: linux-next/drivers/net/macvlan.c =================================================================== --- linux-next.orig/drivers/net/macvlan.c +++ linux-next/drivers/net/macvlan.c @@ -222,6 +222,7 @@ static int macvlan_queue_xmit(struct sk_ if (vlan->mode == MACVLAN_MODE_BRIDGE) { const struct ethhdr *eth = (void *)skb->data; + skb->ip_summed = CHECKSUM_UNNECESSARY; /* send to other bridge ports directly */ if (is_multicast_ether_addr(eth->h_dest)) { and that fixed the problem. Do you think it is acceptable ? Thanks -- Daniel