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

[Leon Romanovsky]

On Mon, Feb 15, 2021 at 09:23:32AM -0800, Xie He wrote:
> On Mon, Feb 15, 2021 at 1:25 AM Leon Romanovsky <leon@xxxxxxxxxx> 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.

If you want it intentional, write it in the comment.

/* When transmitting data, we will need extra 2 bytes headroom,
 * which are 3 bytes of LAPB header minus one byte of pseudo header.
 */
 dev->needed_headroom = 2;