netdev - Re: [PATCH net-next 11/15] sctp: add udphdr to overhead when udp

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Message-ID: <CADvbK_fL77CJ1JTj5idnEGt2Je-OdHTaJqH3Utu-WkweeYMFQQ@mail.gmail.com>
Date:   Sat, 3 Oct 2020 15:54:37 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        Neil Horman <nhorman@...driver.com>,
        Michael Tuexen <tuexen@...muenster.de>,
        Tom Herbert <therbert@...gle.com>, davem <davem@...emloft.net>
Subject: Re: [PATCH net-next 11/15] sctp: add udphdr to overhead when udp_port
 is set

On Sat, Oct 3, 2020 at 12:07 PM Marcelo Ricardo Leitner
<marcelo.leitner@...il.com> wrote:
>
> On Tue, Sep 29, 2020 at 09:49:03PM +0800, Xin Long wrote:
> > sctp_mtu_payload() is for calculating the frag size before making
> > chunks from a msg. So we should only add udphdr size to overhead
> > when udp socks are listening, as only then sctp can handling the
>                                                "handle"   ^^^^
right. :D
> > incoming sctp over udp packets and outgoing sctp over udp packets
> > will be possible.
> >
> > Note that we can't do this according to transport->encap_port, as
> > different transports may be set to different values, while the
> > chunks were made before choosing the transport, we could not be
> > able to meet all rfc6951#section-5.6 requires.
>
> I don't follow this last part. I guess you're referring to the fact
> that it won't grow back the PMTU if it is not encapsulating anymore.
> If that's it, then changelog should be different here.  As is, it
> seems it is not abiding by the RFC, but it is, as that's a 'SHOULD'.
>
> Maybe s/requires\.$/recommends./ ?
Yes, it's a "should".

What the code can only do is "the Path MTU SHOULD be increased by
the size of the UDP header" when udp listening port is disabled.