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Date:   Fri, 20 Nov 2020 06:40:33 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     andrew.hendry@...il.com, davem@...emloft.net, kuba@...nel.org,
        xie.he.0141@...il.com
Cc:     linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Martin Schiller <ms@....tdt.de>
Subject: [PATCH net-next v4 2/5] net/lapb: support netdev events

This patch allows layer2 (LAPB) to react to netdev events itself and
avoids the detour via layer3 (X.25).

1. Call lapb_disconnect_request() on NETDEV_GOING_DOWN events.

2. When a NETDEV_DOWN event occur, clear all queues, enter state
   LAPB_STATE_0 and stop all timers.

3. 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>
---
 net/lapb/lapb_iface.c | 72 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/net/lapb/lapb_iface.c b/net/lapb/lapb_iface.c
index 3c03f6512c5f..52d59984fbe6 100644
--- a/net/lapb/lapb_iface.c
+++ b/net/lapb/lapb_iface.c
@@ -418,14 +418,86 @@ int lapb_data_transmit(struct lapb_cb *lapb, struct sk_buff *skb)
 	return used;
 }
 
+/* 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) {
+		switch (event) {
+		case NETDEV_GOING_DOWN:
+			lapb_disconnect_request(dev);
+			break;
+		case NETDEV_DOWN:
+			lapb = lapb_devtostruct(dev);
+			if (!lapb)
+				break;
+
+			lapb_dbg(0, "(%p) Interface down: %s\n", dev,
+				 dev->name);
+			lapb_dbg(0, "(%p) S%d -> S0\n", dev,
+				 lapb->state);
+			lapb_clear_queues(lapb);
+			lapb->state = LAPB_STATE_0;
+			lapb->n2count   = 0;
+			lapb_stop_t1timer(lapb);
+			lapb_stop_t2timer(lapb);
+			break;
+		case NETDEV_CHANGE:
+			lapb = lapb_devtostruct(dev);
+			if (!lapb)
+				break;
+
+			if (!netif_carrier_ok(dev)) {
+				lapb_dbg(0, "(%p) Carrier lost: %s\n", dev,
+					 dev->name);
+				lapb_dbg(0, "(%p) S%d -> S0\n", dev,
+					 lapb->state);
+				lapb_clear_queues(lapb);
+				lapb->state = LAPB_STATE_0;
+				lapb->n2count   = 0;
+				lapb_stop_t1timer(lapb);
+				lapb_stop_t2timer(lapb);
+			} else {
+				lapb_dbg(0, "(%p): Carrier detected: %s\n",
+					 dev, dev->name);
+				if (lapb->mode & LAPB_DCE) {
+					lapb_start_t1timer(lapb);
+				} else {
+					if (lapb->state == LAPB_STATE_0) {
+						lapb->state = LAPB_STATE_1;
+						lapb_establish_data_link(lapb);
+					}
+				}
+			}
+			break;
+		}
+	}
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block lapb_dev_notifier = {
+	.notifier_call = lapb_device_event,
+};
+
 static int __init lapb_init(void)
 {
+	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>");
-- 
2.20.1

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