linux-kernel - Re: [PATCH net-next 3/4] flow_dissector: extract more ICMP information

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Date:   Wed, 23 Oct 2019 12:53:37 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     Simon Horman <simon.horman@...ronome.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        "David S . Miller" <davem@...emloft.net>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Paul Blakey <paulb@...lanox.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 3/4] flow_dissector: extract more ICMP information

On Wed, Oct 23, 2019 at 12:00 PM Simon Horman
<simon.horman@...ronome.com> wrote:
> On Mon, Oct 21, 2019 at 10:09:47PM +0200, Matteo Croce wrote:
> > +     switch (ih->type) {
> > +     case ICMP_ECHO:
> > +     case ICMP_ECHOREPLY:
> > +     case ICMP_TIMESTAMP:
> > +     case ICMP_TIMESTAMPREPLY:
> > +     case ICMPV6_ECHO_REQUEST:
> > +     case ICMPV6_ECHO_REPLY:
> > +             /* As we use 0 to signal that the Id field is not present,
> > +              * avoid confusion with packets without such field
> > +              */
> > +             key_icmp->id = ih->un.echo.id ? : 1;
>
> Its not obvious to me why the kernel should treat id-zero as a special
> value if it is not special on the wire.
>
> Perhaps a caller who needs to know if the id is present can
> check the ICMP type as this code does, say using a helper.
>

Hi,

The problem is that the 0-0 Type-Code pair identifies the echo replies.
So instead of adding a bool is_present value I hardcoded the info in
the ID field making it always non null, at the expense of a possible
collision, which is harmless.


--
Matteo Croce
per aspera ad upstream