From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH iproute2 -next] ingress, clsact: don't add TCA_OPTIONS to nl msg Date: Tue, 17 May 2016 15:10:42 +0200 Message-ID: <573B1852.4000703@iogearbox.net> References: <192c686bb5e277b9552fe1e5c39b14bed520dddd.1463329895.git.daniel@iogearbox.net> <573B0676.30500@mojatatu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: tgraf@suug.ch, netdev@vger.kernel.org To: Jamal Hadi Salim , stephen@networkplumber.org Return-path: Received: from www62.your-server.de ([213.133.104.62]:37938 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643AbcEQNKs (ORCPT ); Tue, 17 May 2016 09:10:48 -0400 In-Reply-To: <573B0676.30500@mojatatu.com> Sender: netdev-owner@vger.kernel.org List-ID: On 05/17/2016 01:54 PM, Jamal Hadi Salim wrote: > On 16-05-15 12:36 PM, Daniel Borkmann wrote: >> In ingress and clsact qdisc TCA_OPTIONS are ignored, since it's >> parameterless. In tc, we add an empty addattr_l(... TCA_OPTIONS, >> NULL, 0) to the netlink message nevertheless. This has the >> side effect that when someone tries a 'tc qdisc replace' and >> already an existing such qdisc is present, tc fails with >> EINVAL here. >> >> Reason is that in the kernel, this invokes qdisc_change() when >> such requested qdisc is already present. When TCA_OPTIONS are >> passed to modify parameters, it looks whether qdisc implements >> .change() callback, and if not present (like in both cases here) >> it returns with error. Rather than adding an empty stub to the >> kernel that ignores TCA_OPTIONS again, just don't add TCA_OPTIONS >> to the netlink message in the first place. >> >> Before: >> >> # tc qdisc replace dev foo clsact # first try >> # tc qdisc replace dev foo clsact # second one >> RTNETLINK answers: Invalid argument >> >> After: >> >> # tc qdisc replace dev foo clsact >> # tc qdisc replace dev foo clsact >> # tc qdisc replace dev foo clsact >> >> Signed-off-by: Daniel Borkmann > > Acked-by: Jamal Hadi Salim > > I see need for correctness but was curious of use case > that made you even look at this ;-> Sure, wanted to use this in a script that is called when some event arrives and the error 'Invalid argument' looked quite weird to me (... would have understood -ENOTSUPP ;)), which then led me looking into whether clsact code is correct or not, but it eventually turned out that the api code throws that error when TCA_OPTIONS are present, but no .change() callback, so motivation was to make sure clsact is fine and to improve usability there for the replace command. Thanks, Daniel