From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756562AbcCQVUK (ORCPT ); Thu, 17 Mar 2016 17:20:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36851 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756540AbcCQVUI (ORCPT ); Thu, 17 Mar 2016 17:20:08 -0400 From: Aaron Conole To: "Michael S. Tsirkin" Cc: netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v2 -next 2/2] virtio_net: Read the advised MTU References: <1458075853-14789-1-git-send-email-aconole@redhat.com> <1458075853-14789-3-git-send-email-aconole@redhat.com> <20160316142446.GA4446@redhat.com> Date: Thu, 17 Mar 2016 17:20:05 -0400 In-Reply-To: <20160316142446.GA4446@redhat.com> (Michael S. Tsirkin's message of "Wed, 16 Mar 2016 16:24:46 +0200") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 17 Mar 2016 21:20:07 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Michael S. Tsirkin" writes: > On Tue, Mar 15, 2016 at 05:04:13PM -0400, Aaron Conole wrote: >> This patch checks the feature bit for the VIRTIO_NET_F_MTU feature. If it >> exists, read the advised MTU and use it. >> >> No proper error handling is provided for the case where a user changes the >> negotiated MTU. A future commit will add proper error handling. Instead, a >> warning is emitted if the guest changes the device MTU after previously >> being given advice. > > I don't see this as an error. Device might at best give a hint, > user/network admin always knows best. > >> >> Signed-off-by: Aaron Conole >> --- >> v2: >> * Whitespace cleanup in the last hunk >> * Code style change around the pr_warn >> * Additional test for mtu change before printing warning >> >> drivers/net/virtio_net.c | 12 ++++++++++++ >> 1 file changed, 12 insertions(+) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 767ab11..429fe01 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -146,6 +146,7 @@ struct virtnet_info { >> virtio_net_ctrl_ack ctrl_status; >> u8 ctrl_promisc; >> u8 ctrl_allmulti; >> + bool negotiated_mtu; >> }; >> >> struct padded_vnet_hdr { >> @@ -1390,8 +1391,11 @@ static const struct ethtool_ops virtnet_ethtool_ops = { >> >> static int virtnet_change_mtu(struct net_device *dev, int new_mtu) >> { >> + struct virtnet_info *vi = netdev_priv(dev); >> if (new_mtu < MIN_MTU || new_mtu > MAX_MTU) >> return -EINVAL; >> + if ((vi->negotiated_mtu) && (dev->mtu != new_mtu)) >> + pr_warn("changing mtu while the advised mtu bit exists."); > > I don't really see why are we warning here. Just drop this chunk, > as well as the flag in struct virtnet_info. Okay. I was warning because the user is changing this after telling to use something different - but if you don't think it's an error, I will drop it. Thanks so much for the review, Michael! -Aaron >> dev->mtu = new_mtu; >> return 0; >> } >> @@ -1836,6 +1840,13 @@ static int virtnet_probe(struct virtio_device *vdev) >> if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ)) >> vi->has_cvq = true; >> >> + if (virtio_has_feature(vdev, VIRTIO_NET_F_MTU)) { >> + vi->negotiated_mtu = true; >> + dev->mtu = virtio_cread16(vdev, >> + offsetof(struct virtio_net_config, >> + mtu)); >> + } >> + >> if (vi->any_header_sg) >> dev->needed_headroom = vi->hdr_len; >> >> @@ -2019,6 +2030,7 @@ static unsigned int features[] = { >> VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, >> VIRTIO_NET_F_CTRL_MAC_ADDR, >> VIRTIO_F_ANY_LAYOUT, >> + VIRTIO_NET_F_MTU, >> }; >> >> static struct virtio_driver virtio_net_driver = { >> -- >> 2.5.0