netdev - Re: [PATCH iproute2 -next] ingress, clsact: don't add TCA

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Date:	Mon, 16 May 2016 11:22:37 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	jhs@...atatu.com, tgraf@...g.ch, netdev@...r.kernel.org
Subject: Re: [PATCH iproute2 -next] ingress, clsact: don't add TCA_OPTIONS
 to nl msg

On Sun, 15 May 2016 18:36:03 +0200
Daniel Borkmann <daniel@...earbox.net> 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 <daniel@...earbox.net>
> ---
>  tc/q_clsact.c  | 1 -
>  tc/q_ingress.c | 1 -
>  2 files changed, 2 deletions(-)

Applied to net-next