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

[Martin Schiller]

On 2020-11-23 09:31, Xie He wrote:
> On Sun, Nov 22, 2020 at 10:55 PM Martin Schiller <ms@xxxxxxxxxx> wrote:
> > No, they aren't independent. The carrier can only be up if the device 
> > /
> > interface is UP. And as far as I can see a NETDEV_CHANGE event will 
> > also
> > only be generated on interfaces that are UP.
> >
> > So you can be sure, that if there is a NETDEV_CHANGE event then the
> > device is UP.
>
> OK. Thanks for your explanation!
>
> > I removed the NETDEV_UP handling because I don't think it makes sense
> > to implicitly try to establish layer2 (LAPB) if there is no carrier.
>
> As I understand, when the device goes up, the carrier can be either
> down or up. Right?
>
> If this is true, when a device goes up and the carrier then goes up
> after that, L2 will automatically connect, but if a device goes up and
> the carrier is already up, L2 will not automatically connect. I think
> it might be better to eliminate this difference in handling. It might
> be better to make it automatically connect in both situations, or in
> neither situations.

AFAIK the carrier can't be up before the device is up. Therefore, there
will be a NETDEV_CHANGE event after the NETDEV_UP event.

This is what I can see in my tests (with the HDLC interface).

Is the behaviour different for e.g. lapbether?

> If you want to go with the second way (auto connect in neither
> situations), the next (3rd) patch of this series might be also not
> needed.
>
> I just want to make the behavior of LAPB more consistent. I think we
> should either make LAPB auto-connect in all situations, or make LAPB
> wait for L3's instruction to connect in all situations.
>
> > And with the first X.25 connection request on that interface, it will
> > be established anyway by x25_transmit_link().
> >
> > I've tested it here with an HDLC WAN Adapter and it works as expected.
> >
> > These are also the ideal conditions for the already mentioned "on
> > demand" scenario. The only necessary change would be to call
> > x25_terminate_link() on an interface after clearing the last X.25
> > session.
> >
> > > On NETDEV_GOING_DOWN, we can also check the carrier status first and
> > > if it is down, we don't need to call lapb_disconnect_request.
> >
> > This is not necessary because lapb_disconnect_request() checks the
> > current state. And if the carrier is DOWN then the state should also 
> > be
> > LAPB_STATE_0 and so lapb_disconnect_request() does nothing.
>
> Yes, I understand. I just thought adding this check might make the
> code cleaner. But you are right.