From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935244AbcCPSXU (ORCPT ); Wed, 16 Mar 2016 14:23:20 -0400 Received: from mail-oi0-f52.google.com ([209.85.218.52]:35951 "EHLO mail-oi0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755137AbcCPSXS (ORCPT ); Wed, 16 Mar 2016 14:23:18 -0400 Date: Wed, 16 Mar 2016 11:23:14 -0700 From: Stephen Hemminger To: Aaron Conole Cc: netdev@vger.kernel.org, "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v2 -next 1/2] virtio: Start feature MTU support Message-ID: <20160316112314.4510d386@samsung9> In-Reply-To: <1458075853-14789-2-git-send-email-aconole@redhat.com> References: <1458075853-14789-1-git-send-email-aconole@redhat.com> <1458075853-14789-2-git-send-email-aconole@redhat.com> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Mar 2016 17:04:12 -0400 Aaron Conole wrote: > --- a/include/uapi/linux/virtio_net.h > +++ b/include/uapi/linux/virtio_net.h > @@ -55,6 +55,7 @@ > #define VIRTIO_NET_F_MQ 22 /* Device supports Receive Flow > * Steering */ > #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */ > +#define VIRTIO_NET_F_MTU 25 /* Device supports Default MTU Negotiation */ > > #ifndef VIRTIO_NET_NO_LEGACY > #define VIRTIO_NET_F_GSO 6 /* Host handles pkts w/ any GSO type */ > @@ -73,6 +74,8 @@ struct virtio_net_config { > * Legal values are between 1 and 0x8000 > */ > __u16 max_virtqueue_pairs; > + /* Default maximum transmit unit advice */ > + __u16 mtu; > } __attribute__((packed)); > > /* You can't change user visible headers without breaking ABI. This structure might be used by other user code. Also how can this work if host is using old size of structure.