netdev - Re: [PATCH net-next v6 2/5] net/lapb: support netdev events

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Date:   Wed, 25 Nov 2020 13:49:25 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Martin Schiller <ms@....tdt.de>
Cc:     andrew.hendry@...il.com, davem@...emloft.net,
        xie.he.0141@...il.com, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 2/5] net/lapb: support netdev events

On Tue, 24 Nov 2020 10:39:35 +0100 Martin Schiller wrote:
> This patch allows layer2 (LAPB) to react to netdev events itself and
> avoids the detour via layer3 (X.25).
> 
> 1. Establish layer2 on NETDEV_UP events, if the carrier is already up.
> 
> 2. Call lapb_disconnect_request() on NETDEV_GOING_DOWN events to signal
>    the peer that the connection will go down.
>    (Only when the carrier is up.)
> 
> 3. When a NETDEV_DOWN event occur, clear all queues, enter state
>    LAPB_STATE_0 and stop all timers.
> 
> 4. The NETDEV_CHANGE event makes it possible to handle carrier loss and
>    detection.
> 
>    In case of Carrier Loss, clear all queues, enter state LAPB_STATE_0
>    and stop all timers.
> 
>    In case of Carrier Detection, we start timer t1 on a DCE interface,
>    and on a DTE interface we change to state LAPB_STATE_1 and start
>    sending SABM(E).
> 
> Signed-off-by: Martin Schiller <ms@....tdt.de>

> +/* Handle device status changes. */
> +static int lapb_device_event(struct notifier_block *this, unsigned long event,
> +			     void *ptr)
> +{
> +	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
> +	struct lapb_cb *lapb;
> +
> +	if (!net_eq(dev_net(dev), &init_net))
> +		return NOTIFY_DONE;
> +
> +	if (dev->type == ARPHRD_X25) {

Flip condition, save indentation.

	if (dev->type != ARPHRD_X25)
		return NOTIFY_DONE;

You can also pull out of all the cases:

	lapb = lapb_devtostruct(dev);
	if (!lapb)
		return NOTIFY_DONE;

right?

> +		switch (event) {
> +		case NETDEV_UP:
> +			lapb_dbg(0, "(%p) Interface up: %s\n", dev,
> +				 dev->name);
> +
> +			if (netif_carrier_ok(dev)) {
> +				lapb = lapb_devtostruct(dev);
> +				if (!lapb)
> +					break;

>  static int __init lapb_init(void)
>  {
> +	register_netdevice_notifier(&lapb_dev_notifier);

This can fail, so:

	return register_netdevice_notifier(&lapb_dev_notifier);

>  	return 0;
>  }
>  
>  static void __exit lapb_exit(void)
>  {
>  	WARN_ON(!list_empty(&lapb_list));
> +
> +	unregister_netdevice_notifier(&lapb_dev_notifier);
>  }
>  
>  MODULE_AUTHOR("Jonathan Naylor <g4klx@...lx.demon.co.uk>");