From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: Ethernet low-level frame debugging support Date: Sun, 19 Jun 2011 13:19:44 -0700 Message-ID: <4DFE59E0.9070503@candelatech.com> References: <20110619104431.23a22fe9@opy.nosense.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Mark Smith Return-path: Received: from mail.candelatech.com ([208.74.158.172]:34677 "EHLO ns3.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754699Ab1FSUTy (ORCPT ); Sun, 19 Jun 2011 16:19:54 -0400 In-Reply-To: <20110619104431.23a22fe9@opy.nosense.org> Sender: netdev-owner@vger.kernel.org List-ID: On 06/18/2011 06:14 PM, Mark Smith wrote: > Hi, > > Firstly, I think this is a potentially quite useful feature for > networking people and that I hope it makes it into the kernel proper. > > One thing I've thought is that perhaps it might be made and named a bit > more generally, as NICs will also drop frames for other reasons other > than FCs failures e.g. runt frames. So perhaps something like "true > promiscuous" or "full promiscuous" might be a more general name, and if > it is enabled, then all NIC error checking that can be switched off is > switched off. Looking at the chipset data sheets for a few NICs that I > have / have had (netgear FA312 (natsemi ns83815), smc epic100, ne2000), > they all seem to have registers which allow switching off many if not > all of the NIC error checking settings. I called it 'save-rxerr' in ethtool...I think that is general enough? The early patch that saves the FCS just passes the 4-byte FCS up the stack. It doesn't change the ability to receive bad frames or not..that is in the later patches. > > The other thing I've thought could be useful would be to be able to > send runts by not padding the frames when they're less then 64 bytes. > I've been able to test if this is possible with the netgear FA312, as > the chipset does the padding. I connected it back to back with an > e1000e I have, switched off the chipset automatic padding on the FA312, > sent small traffic, and then saw that the e1000e's internal > rx_short_length_errors counter correspondingly increased. Of course I > can't see them with tcpdump on the e1000e because it is dropping them. Maybe the SO_NOFCS option could change to SO_DRVOPTS and take a bit-field instead of just be on/off. NOFCS could be one flag, NOPAD another, etc. That would give ability to send non-padded frames if the driver has support. Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com