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References: <20210215072703.43952-1-xie.he.0141@gmail.com> <YCo96zjXHyvKpbUM@unreal>
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From:   Xie He <xie.he.0141@gmail.com>
Date:   Mon, 15 Feb 2021 09:23:32 -0800
Message-ID: <CAJht_EOQBDdwa0keS9XTKZgXE44_b5cHJt=fFaKy-wFDpe6iaw@mail.gmail.com>
Subject: Re: [PATCH net-next RFC v3] net: hdlc_x25: Queue outgoing LAPB frames
To:     Leon Romanovsky <leon@kernel.org>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Linux X25 <linux-x25@vger.kernel.org>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Martin Schiller <ms@dev.tdt.de>,
        Krzysztof Halasa <khc@pm.waw.pl>
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On Mon, Feb 15, 2021 at 1:25 AM Leon Romanovsky <leon@kernel.org> wrote:
>
> > +     /* When transmitting data:
> > +      * first we'll remove a pseudo header of 1 byte,
> > +      * then the LAPB module will prepend an LAPB header of at most 3 bytes.
> > +      */
> > +     dev->needed_headroom = 3 - 1;
>
> 3 - 1 = 2
>
> Thanks

Actually this is intentional. It makes the numbers more meaningful.

The compiler should automatically generate the "2" so there would be
no runtime penalty.