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

[Martin Schiller]

On 2020-11-23 11:08, Xie He wrote:
> 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.

Well, one could argue that we would have to repair these drivers, but I
don't think that will get us anywhere.

From this point of view it will be the best to handle the NETDEV_UP in
the lapb event handler and establish the link analog to the
NETDEV_CHANGE event if the carrier is UP.

> > 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.