From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Ricardo Leitner Subject: Re: [PATCH] veth: Optionally pad packets to minimum Ethernet length Date: Tue, 12 Dec 2017 16:18:17 -0200 Message-ID: <20171212181817.GB3531@localhost.localdomain> References: <1513095191-127313-1-git-send-email-eswierk@skyportsystems.com> <1513099966.26538.1.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Cc: Ed Swierk , netdev@vger.kernel.org, Benjamin Warren , Keith Holleman To: Dan Williams Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49308 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752386AbdLLSSU (ORCPT ); Tue, 12 Dec 2017 13:18:20 -0500 Content-Disposition: inline In-Reply-To: <1513099966.26538.1.camel@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Dec 12, 2017 at 11:32:46AM -0600, Dan Williams wrote: > 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? What about using some tc action (i.e. skbmod) for this? Marcelo > > 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); > >   >