From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: TUN/TAP: tap driver reports bogus interface speed in ethtool operations Date: Tue, 23 Jul 2013 08:49:01 -0700 Message-ID: <51EEA5ED.6080404@hp.com> References: <2F174B03-5074-4BA0-B91A-8F2F62C2B082@cygnusnetworks.de> <5192BDD6.6060703@qti.qualcomm.com> <3E916AF0-C587-443D-B653-C968A96C8751@cygnusnetworks.de> <48A2F278-A32C-47C6-AD2D-1FC15EC73B88@cygnusnetworks.de> <51E5BE27.3060207@qti.qualcomm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, David Miller , Max Krasnyansky To: Helmut Grohne Return-path: Received: from g4t0016.houston.hp.com ([15.201.24.19]:20384 "EHLO g4t0016.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933437Ab3GWPtF (ORCPT ); Tue, 23 Jul 2013 11:49:05 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 07/23/2013 06:32 AM, Helmut Grohne wrote: > > On 16.07.2013, at 23:41, Max Krasnyansky wrote: >> The patch looks fine to me (must admit that I only glanced at it). Please send it to the netdev >> mailing list netdev@vger.kernel.org, if you have't already done so. >> CC David Miller and me. > > Doing that. Now summarizing the issue for the new recipients: > > Problem: > > When querying a tap device for its speed using ethtool the tun driver reports a speed > of SPEED_10. This number is hard coded into the driver. Nowadays virtual network devices > can go way faster than that. When doing automatic bandwidth monitoring based on the > speed reported by ethtool, tap devices tend to come up as false positives. Arguably the > hard coded speed is wrong. > > Proposed solution: > > To that end I propose supporting the ETHTOOL_SSET command in addition to the already > supported ETHTOOL_GSET. It would deny setting any setting except for the bandwidth > where it would allow arbitrary values. You can find this patch attached. > > With this patch an administrator can increase the reported speed for tap devices and > keep using automatic detection of interface speeds. > > Workarounds: > > Using ethtool a detection utility can determine the driver for an interface. If the > driver matches the string "tun", the reported speed should not be used. > > Helmut > I like the idea of being able to set the reported speed for a tun/tap interface. rick jones