// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Linux network device link state notification
 *
 * Author:
 *     Stefan Rompf <sux@loplof.de>
 */

#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 <linux/types.h>

#include "dev.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 int default_operstate(const struct net_device *dev)
{
        if (netif_testing(dev))
                return IF_OPER_TESTING;

        /* Some uppers (DSA) have additional sources for being down, so
         * first check whether lower is indeed the source of its down state.
         */
        if (!netif_carrier_ok(dev)) {
                struct net_device *peer;
                int iflink;

                /* If called from netdev_run_todo()/linkwatch_sync_dev(),
                 * dev_net(dev) can be already freed, and RTNL is not held.
                 */
                if (dev->reg_state <= NETREG_REGISTERED)
                        iflink = dev_get_iflink(dev);
                else
                        iflink = dev->ifindex;

                if (iflink == dev->ifindex)
                        return IF_OPER_DOWN;

                ASSERT_RTNL();
                peer = __dev_get_by_index(dev_net(dev), iflink);
                if (!peer)
                        return IF_OPER_DOWN;

                return netif_carrier_ok(peer) ? IF_OPER_DOWN :
                                                IF_OPER_LOWERLAYERDOWN;
        }

        if (netif_dormant(dev))
                return IF_OPER_DORMANT;

        return IF_OPER_UP;
}

static void rfc2863_policy(struct net_device *dev)
{
        unsigned int operstate = default_operstate(dev);

        if (operstate == READ_ONCE(dev->operstate))
                return;

        switch(dev->link_mode) {
        case IF_LINK_MODE_TESTING:
                if (operstate == IF_OPER_UP)
                        operstate = IF_OPER_TESTING;
                break;

        case IF_LINK_MODE_DORMANT:
                if (operstate == IF_OPER_UP)
                        operstate = IF_OPER_DORMANT;
                break;
        case IF_LINK_MODE_DEFAULT:
        default:
                break;
        }

        WRITE_ONCE(dev->operstate, operstate);
}


void linkwatch_init_dev(struct net_device *dev)
{
        /* Handle pre-registration link state changes */
        if (!netif_carrier_ok(dev) || netif_dormant(dev) ||
            netif_testing(dev))
                rfc2863_policy(dev);
}


static bool linkwatch_urgent_event(struct net_device *dev)
{
        if (!netif_running(dev))
                return false;

        if (dev->ifindex != dev_get_iflink(dev))
                return true;

        if (netif_is_lag_port(dev) || netif_is_lag_master(dev))
                return true;

        return 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);
                netdev_hold(dev, &dev->linkwatch_dev_tracker, GFP_ATOMIC);
        }
        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;

        /*
         * If urgent, schedule immediate execution; otherwise, don't
         * override the existing timer.
         */
        if (test_bit(LW_URGENT, &linkwatch_flags))
                mod_delayed_work(system_dfl_wq, &linkwatch_work, 0);
        else
                queue_delayed_work(system_dfl_wq, &linkwatch_work, delay);
}


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_atomic();

        /* 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);

                netif_state_change(dev);
        }
}

static void __linkwatch_run_queue(int urgent_only)
{
#define MAX_DO_DEV_PER_LOOP     100

        int do_dev = MAX_DO_DEV_PER_LOOP;
        /* Use a local list here since we add non-urgent
         * events back to the global one when called with
         * urgent_only=1.
         */
        LIST_HEAD(wrk);

        /* Give urgent case more budget */
        if (urgent_only)
                do_dev += MAX_DO_DEV_PER_LOOP;

        /*
         * 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) && do_dev > 0) {
                struct net_device *dev;

                dev = list_first_entry(&wrk, struct net_device, link_watch_list);
                list_del_init(&dev->link_watch_list);

                if (!netif_device_present(dev) ||
                    (urgent_only && !linkwatch_urgent_event(dev))) {
                        list_add_tail(&dev->link_watch_list, &lweventlist);
                        continue;
                }
                /* We must free netdev tracker under
                 * the spinlock protection.
                 */
                netdev_tracker_free(dev, &dev->linkwatch_dev_tracker);
                spin_unlock_irq(&lweventlist_lock);
                netdev_lock_ops(dev);
                linkwatch_do_dev(dev);
                netdev_unlock_ops(dev);
                /* Use __dev_put() because netdev_tracker_free() was already
                 * called above. Must be after netdev_unlock_ops() to prevent
                 * netdev_run_todo() from freeing the device while still in use.
                 */
                __dev_put(dev);
                do_dev--;
                spin_lock_irq(&lweventlist_lock);
        }

        /* Add the remaining work back to lweventlist */
        list_splice_init(&wrk, &lweventlist);

        if (!list_empty(&lweventlist))
                linkwatch_schedule_work(0);
        spin_unlock_irq(&lweventlist_lock);
}

static bool linkwatch_clean_dev(struct net_device *dev)
{
        unsigned long flags;
        bool clean = false;

        spin_lock_irqsave(&lweventlist_lock, flags);
        if (!list_empty(&dev->link_watch_list)) {
                list_del_init(&dev->link_watch_list);
                clean = true;
                /* We must release netdev tracker under
                 * the spinlock protection.
                 */
                netdev_tracker_free(dev, &dev->linkwatch_dev_tracker);
        }
        spin_unlock_irqrestore(&lweventlist_lock, flags);

        return clean;
}

void __linkwatch_sync_dev(struct net_device *dev)
{
        netdev_ops_assert_locked(dev);

        if (linkwatch_clean_dev(dev)) {
                linkwatch_do_dev(dev);
                /* Use __dev_put() because netdev_tracker_free() was already
                 * called inside linkwatch_clean_dev().
                 */
                __dev_put(dev);
        }
}

void linkwatch_sync_dev(struct net_device *dev)
{
        if (linkwatch_clean_dev(dev)) {
                netdev_lock_ops(dev);
                linkwatch_do_dev(dev);
                netdev_unlock_ops(dev);
                /* Use __dev_put() because netdev_tracker_free() was already
                 * called inside linkwatch_clean_dev().
                 */
                __dev_put(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);