/*
 * 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 exection. */
        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);