From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexey Kodanev Subject: [PATCH v2] vxlan: restore dev->mtu setting based on lower device Date: Thu, 14 Dec 2017 20:20:00 +0300 Message-ID: <1513272000-30848-1-git-send-email-alexey.kodanev@oracle.com> Cc: Stefano Brivio , Matthias Schiffer , David Miller , Junhan Yan , Jiri Benc , Hangbin Liu , Alexey Kodanev To: netdev@vger.kernel.org Return-path: Received: from aserp2130.oracle.com ([141.146.126.79]:33217 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753289AbdLNRQd (ORCPT ); Thu, 14 Dec 2017 12:16:33 -0500 Sender: netdev-owner@vger.kernel.org List-ID: Stefano Brivio says: Commit a985343ba906 ("vxlan: refactor verification and application of configuration") introduced a change in the behaviour of initial MTU setting: earlier, the MTU for a link created on top of a given lower device, without an initial MTU specification, was set to the MTU of the lower device minus headroom as a result of this path in vxlan_dev_configure(): if (!conf->mtu) dev->mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM : VXLAN_HEADROOM); which is now gone. Now, the initial MTU, in absence of a configured value, is simply set by ether_setup() to ETH_DATA_LEN (1500 bytes). This breaks userspace expectations in case the MTU of the lower device is higher than 1500 bytes minus headroom. This patch restores the previous behaviour on newlink operation. Since max_mtu can be negative and we update dev->mtu directly, also check it for valid minimum. Reported-by: Junhan Yan Fixes: a985343ba906 ("vxlan: refactor verification and application of configuration") Signed-off-by: Alexey Kodanev --- v2: Based on initial patch from Stefano Brivio: "vxlan: Restore initial MTU setting based on lower device" In this version, 'dev->mtu' is set from 'max_mtu' that already has the the needed initial MTU value based on the lower device. Plus, it is adding extra check for valid minimum of 'max_mtu'. drivers/net/vxlan.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-) diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c index 19b9cc5..1000b0e 100644 --- a/drivers/net/vxlan.c +++ b/drivers/net/vxlan.c @@ -3103,6 +3103,11 @@ static void vxlan_config_apply(struct net_device *dev, max_mtu = lowerdev->mtu - (use_ipv6 ? VXLAN6_HEADROOM : VXLAN_HEADROOM); + if (max_mtu < ETH_MIN_MTU) + max_mtu = ETH_MIN_MTU; + + if (!changelink && !conf->mtu) + dev->mtu = max_mtu; } if (dev->mtu > max_mtu) -- 1.7.1