Re: [PATCH net-next v4 2/5] net/lapb: support netdev events

[Xie He]

On Mon, Nov 23, 2020 at 1:36 AM Xie He <xie.he.0141@xxxxxxxxx> wrote:
>
> Some drivers don't support carrier status and will never change it.
> Their carrier status will always be UP. There will not be a
> NETDEV_CHANGE event.
>
> lapbether doesn't change carrier status. I also have my own virtual
> HDLC WAN driver (for testing) which also doesn't change carrier
> status.
>
> I just tested with lapbether. When I bring up the interface, there
> will only be NETDEV_PRE_UP and then NETDEV_UP. There will not be
> NETDEV_CHANGE. The carrier status is alway UP.
>
> I haven't tested whether a device can receive NETDEV_CHANGE when it is
> down. It's possible for a device driver to call netif_carrier_on when
> the interface is down. Do you know what will happen if a device driver
> calls netif_carrier_on when the interface is down?

I just did a test on lapbether and saw there would be no NETDEV_CHANGE
event when the netif is down, even if netif_carrier_on/off is called.
So we can rest assured of this part.