netdev - Re: [PATCH net-next RFC v3] net: hdlc_x25: Queue outgoing LAPB frames

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Date:   Mon, 15 Feb 2021 09:23:32 -0800
From:   Xie He <xie.he.0141@...il.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux X25 <linux-x25@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Martin Schiller <ms@....tdt.de>,
        Krzysztof Halasa <khc@...waw.pl>
Subject: Re: [PATCH net-next RFC v3] net: hdlc_x25: Queue outgoing LAPB frames

On Mon, Feb 15, 2021 at 1:25 AM Leon Romanovsky <leon@...nel.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.