text: /*
   * Linux network device link state notification
   *
   * Author:
   *     Stefan Rompf <sux@loplof.de>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License
   * as published by the Free Software Foundation; either version
   * 2 of the License, or (at your option) any later version.
   *
   */
  
  #include <linux/module.h>
  #include <linux/netdevice.h>
  #include <linux/if.h>
  #include <net/sock.h>
  #include <net/pkt_sched.h>
  #include <linux/rtnetlink.h>
  #include <linux/jiffies.h>
  #include <linux/spinlock.h>
  #include <linux/workqueue.h>
  #include <linux/bitops.h>
  #include <asm/types.h>
  
  
  enum lw_bits {
  	LW_URGENT = 0,
  };
  
  static unsigned long linkwatch_flags;
  static unsigned long linkwatch_nextevent;
  
  static void linkwatch_event(struct work_struct *dummy);
  static DECLARE_DELAYED_WORK(linkwatch_work, linkwatch_event);
  
  static LIST_HEAD(lweventlist);
  static DEFINE_SPINLOCK(lweventlist_lock);
  
  static unsigned char default_operstate(const struct net_device *dev)
  {
  	if (!netif_carrier_ok(dev))
  		return (dev->ifindex != dev->iflink ?
  			IF_OPER_LOWERLAYERDOWN : IF_OPER_DOWN);
  
  	if (netif_dormant(dev))
  		return IF_OPER_DORMANT;
  
  	return IF_OPER_UP;
  }
  
  
  static void rfc2863_policy(struct net_device *dev)
  {
  	unsigned char operstate = default_operstate(dev);
  
  	if (operstate == dev->operstate)
  		return;
  
  	write_lock_bh(&dev_base_lock);
  
  	switch(dev->link_mode) {
  	case IF_LINK_MODE_DORMANT:
  		if (operstate == IF_OPER_UP)
  			operstate = IF_OPER_DORMANT;
  		break;
  
  	case IF_LINK_MODE_DEFAULT:
  	default:
  		break;
  	}
  
  	dev->operstate = operstate;
  
  	write_unlock_bh(&dev_base_lock);
  }
  
  
  static bool linkwatch_urgent_event(struct net_device *dev)
  {
  	return netif_running(dev) && netif_carrier_ok(dev) &&
  		qdisc_tx_changing(dev);
  }
  
  
  static void linkwatch_add_event(struct net_device *dev)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&lweventlist_lock, flags);
  	if (list_empty(&dev->link_watch_list)) {
  		list_add_tail(&dev->link_watch_list, &lweventlist);
  		dev_hold(dev);
  	}
  	spin_unlock_irqrestore(&lweventlist_lock, flags);
  }
  
  
  static void linkwatch_schedule_work(int urgent)
  {
  	unsigned long delay = linkwatch_nextevent - jiffies;
  
  	if (test_bit(LW_URGENT, &linkwatch_flags))
  		return;
  
  	/* Minimise down-time: drop delay for up event. */
  	if (urgent) {
  		if (test_and_set_bit(LW_URGENT, &linkwatch_flags))
  			return;
  		delay = 0;
  	}
  
  	/* If we wrap around we'll delay it by at most HZ. */
  	if (delay > HZ)
  		delay = 0;
  
  	/*
  	 * This is true if we've scheduled it immeditately or if we don't
  	 * need an immediate execution and it's already pending.
  	 */
  	if (schedule_delayed_work(&linkwatch_work, delay) == !delay)
  		return;
  
  	/* Don't bother if there is nothing urgent. */
  	if (!test_bit(LW_URGENT, &linkwatch_flags))
  		return;
  
  	/* It's already running which is good enough. */
  	if (!__cancel_delayed_work(&linkwatch_work))
  		return;
  
  	/* Otherwise we reschedule it again for immediate execution. */
  	schedule_delayed_work(&linkwatch_work, 0);
  }
  
  
  static void linkwatch_do_dev(struct net_device *dev)
  {
  	/*
  	 * Make sure the above read is complete since it can be
  	 * rewritten as soon as we clear the bit below.
  	 */
  	smp_mb__before_clear_bit();
  
  	/* We are about to handle this device,
  	 * so new events can be accepted
  	 */
  	clear_bit(__LINK_STATE_LINKWATCH_PENDING, &dev->state);
  
  	rfc2863_policy(dev);
  	if (dev->flags & IFF_UP) {
  		if (netif_carrier_ok(dev))
  			dev_activate(dev);
  		else
  			dev_deactivate(dev);
  
  		netdev_state_change(dev);
  	}
  	dev_put(dev);
  }
  
  static void __linkwatch_run_queue(int urgent_only)
  {
  	struct net_device *dev;
  	LIST_HEAD(wrk);
  
  	/*
  	 * Limit the number of linkwatch events to one
  	 * per second so that a runaway driver does not
  	 * cause a storm of messages on the netlink
  	 * socket.  This limit does not apply to up events
  	 * while the device qdisc is down.
  	 */
  	if (!urgent_only)
  		linkwatch_nextevent = jiffies + HZ;
  	/* Limit wrap-around effect on delay. */
  	else if (time_after(linkwatch_nextevent, jiffies + HZ))
  		linkwatch_nextevent = jiffies;
  
  	clear_bit(LW_URGENT, &linkwatch_flags);
  
  	spin_lock_irq(&lweventlist_lock);
  	list_splice_init(&lweventlist, &wrk);
  
  	while (!list_empty(&wrk)) {
  
  		dev = list_first_entry(&wrk, struct net_device, link_watch_list);
  		list_del_init(&dev->link_watch_list);
  
  		if (urgent_only && !linkwatch_urgent_event(dev)) {
  			list_add_tail(&dev->link_watch_list, &lweventlist);
  			continue;
  		}
  		spin_unlock_irq(&lweventlist_lock);
  		linkwatch_do_dev(dev);
  		spin_lock_irq(&lweventlist_lock);
  	}
  
  	if (!list_empty(&lweventlist))
  		linkwatch_schedule_work(0);
  	spin_unlock_irq(&lweventlist_lock);
  }
  
  void linkwatch_forget_dev(struct net_device *dev)
  {
  	unsigned long flags;
  	int clean = 0;
  
  	spin_lock_irqsave(&lweventlist_lock, flags);
  	if (!list_empty(&dev->link_watch_list)) {
  		list_del_init(&dev->link_watch_list);
  		clean = 1;
  	}
  	spin_unlock_irqrestore(&lweventlist_lock, flags);
  	if (clean)
  		linkwatch_do_dev(dev);
  }
  
  
  /* Must be called with the rtnl semaphore held */
  void linkwatch_run_queue(void)
  {
  	__linkwatch_run_queue(0);
  }
  
  
  static void linkwatch_event(struct work_struct *dummy)
  {
  	rtnl_lock();
  	__linkwatch_run_queue(time_after(linkwatch_nextevent, jiffies));
  	rtnl_unlock();
  }
  
  
  void linkwatch_fire_event(struct net_device *dev)
  {
  	bool urgent = linkwatch_urgent_event(dev);
  
  	if (!test_and_set_bit(__LINK_STATE_LINKWATCH_PENDING, &dev->state)) {
  		linkwatch_add_event(dev);
  	} else if (!urgent)
  		return;
  
  	linkwatch_schedule_work(urgent);
  }
  EXPORT_SYMBOL(linkwatch_fire_event);
  