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

On Mon, Feb 15, 2021 at 09:23:32AM -0800, Xie He wrote:

On Mon, Feb 15, 2021 at 1:25 AM Leon Romanovsky [off-list ref] wrote:

quoted

quoted

+     /* 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;