From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamal Hadi Salim Subject: Re: [PATCH iproute2 -next] ingress, clsact: don't add TCA_OPTIONS to nl msg Date: Tue, 17 May 2016 07:54:30 -0400 Message-ID: <573B0676.30500@mojatatu.com> References: <192c686bb5e277b9552fe1e5c39b14bed520dddd.1463329895.git.daniel@iogearbox.net> 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: Daniel Borkmann , stephen@networkplumber.org Return-path: Received: from mail-ig0-f195.google.com ([209.85.213.195]:34235 "EHLO mail-ig0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751779AbcEQLyj (ORCPT ); Tue, 17 May 2016 07:54:39 -0400 Received: by mail-ig0-f195.google.com with SMTP id kj7so1441136igb.1 for ; Tue, 17 May 2016 04:54:39 -0700 (PDT) In-Reply-To: <192c686bb5e277b9552fe1e5c39b14bed520dddd.1463329895.git.daniel@iogearbox.net> Sender: netdev-owner@vger.kernel.org List-ID: 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 ;-> cheers, jamal