linux-kernel - Re: [PATCH net-next v4 5/5] net: hdlc

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Message-ID: <CAJht_EMgWwAdo5Z3ZMs50k5tYnFetLa=zKO6unoU2mdOuXkU5g@mail.gmail.com>
Date:   Fri, 30 Oct 2020 12:29:46 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Krzysztof Halasa <khc@...waw.pl>
Subject: Re: [PATCH net-next v4 5/5] net: hdlc_fr: Add support for any Ethertype

On Fri, Oct 30, 2020 at 9:33 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Should this still check data[5] == FR_PAD?

No, the 6th byte (data[5]) is not a padding field. It is the first
byte of the SNAP header. The original code is misleading. That is part
of the reasons why I want to fix it with this patch.

The frame format is specified in RFC 2427
(https://tools.ietf.org/html/rfc2427). We can see in Section 4.1 and
4.2 that the 6th byte is the first byte of the SNAP header.