Re: [PATCH net] drivers/net/wan/lapbether: Added needed_tailroom

From: Willem de Bruijn
Date: Mon Aug 10 2020 - 03:32:25 EST

On Sun, Aug 9, 2020 at 7:12 PM Xie He <xie.he.0141@xxxxxxxxx> wrote:
> On Sun, Aug 9, 2020 at 1:48 AM Willem de Bruijn
> <willemdebruijn.kernel@xxxxxxxxx> wrote:
> >
> > Does this solve an actual observed bug?
> >
> > In many ways lapbeth is similar to tunnel devices. This is not common.
> Thank you for your comment!
> This doesn't solve a bug observed by me. But I think this should be
> necessary considering the logic of the code.
> Using "grep", I found that there were indeed Ethernet drivers that set
> needed_tailroom. I found it was set in these files:
> drivers/net/ethernet/sun/sunvnet.c
> drivers/net/ethernet/sun/ldmvsw.c
> Setting needed_tailroom may be necessary for this driver to run those
> Ethernet devices.

What happens when a tunnel device passes a packet to these devices?
That will also not have allocated the extra tailroom. Does that cause
a bug?