From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Williams Subject: Re: [PATCH] veth: Optionally pad packets to minimum Ethernet length Date: Tue, 12 Dec 2017 11:32:46 -0600 Message-ID: <1513099966.26538.1.camel@redhat.com> References: <1513095191-127313-1-git-send-email-eswierk@skyportsystems.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Cc: Benjamin Warren , Keith Holleman To: Ed Swierk , netdev@vger.kernel.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46242 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752432AbdLLRcv (ORCPT ); Tue, 12 Dec 2017 12:32:51 -0500 In-Reply-To: <1513095191-127313-1-git-send-email-eswierk@skyportsystems.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 2017-12-12 at 08:13 -0800, Ed Swierk wrote: > Most physical Ethernet devices pad short packets to the minimum > length > of 64 bytes (including FCS) on transmit. It can be useful to simulate > this behavior when debugging a problem that results from it (such as > incorrect L4 checksum calculation). > > Padding is unnecessary for most applications so leave it off by > default. Enable padding only when the otherwise unused IFF_AUTOMEDIA > flag is set (e.g. by writing 0x5003 to flags in sysfs). This seems like a weird overload of AUTOMEDIA, which no other driver uses for this purpose. Seems like the only other user of AUTOMEDIA is 8390/etherh.c for some 10BaseT/10Base2 stuff. I'm not sure what the interface should be, but perhaps a sysfs attribute would be better than overloading IFF_AUTOMEDIA? Dan > Signed-off-by: Ed Swierk > --- >  drivers/net/veth.c | 6 ++++++ >  1 file changed, 6 insertions(+) > > diff --git a/drivers/net/veth.c b/drivers/net/veth.c > index f5438d0978ca..292029bf4bb2 100644 > --- a/drivers/net/veth.c > +++ b/drivers/net/veth.c > @@ -111,6 +111,12 @@ static netdev_tx_t veth_xmit(struct sk_buff > *skb, struct net_device *dev) >   goto drop; >   } >   > + if (unlikely(dev->flags & IFF_AUTOMEDIA)) { > + /* if eth_skb_pad returns an error the skb was freed > */ > + if (eth_skb_pad(skb)) > + goto drop; > + } > + >   if (likely(dev_forward_skb(rcv, skb) == NET_RX_SUCCESS)) { >   struct pcpu_vstats *stats = this_cpu_ptr(dev- > >vstats); >