/*
 * Monitoring code for network dropped packet alerts
 *
 * Copyright (C) 2009 Neil Horman <nhorman@tuxdriver.com>
 */

#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/string.h>
#include <linux/if_arp.h>
#include <linux/inetdevice.h>
#include <linux/inet.h>
#include <linux/interrupt.h>
#include <linux/netpoll.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/types.h>
#include <linux/workqueue.h>
#include <linux/netlink.h>
#include <linux/net_dropmon.h>
#include <linux/percpu.h>
#include <linux/timer.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <net/genetlink.h>
#include <net/netevent.h>

#include <trace/events/skb.h>
#include <trace/events/napi.h>

#include <asm/unaligned.h>

#define TRACE_ON 1
#define TRACE_OFF 0

static void send_dm_alert(struct work_struct *unused);


/*
 * Globals, our netlink socket pointer
 * and the work handle that will send up
 * netlink alerts
 */
static int trace_state = TRACE_OFF;
static DEFINE_MUTEX(trace_state_mutex);

struct per_cpu_dm_data {
        struct work_struct dm_alert_work;
        struct sk_buff __rcu *skb;
        atomic_t dm_hit_count;
        struct timer_list send_timer;
        int cpu;
};

struct dm_hw_stat_delta {
        struct net_device *dev;
        unsigned long last_rx;
        struct list_head list;
        struct rcu_head rcu;
        unsigned long last_drop_val;
};

static struct genl_family net_drop_monitor_family = {
        .id             = GENL_ID_GENERATE,
        .hdrsize        = 0,
        .name           = "NET_DM",
        .version        = 2,
        .maxattr        = NET_DM_CMD_MAX,
};

static DEFINE_PER_CPU(struct per_cpu_dm_data, dm_cpu_data);

static int dm_hit_limit = 64;
static int dm_delay = 1;
static unsigned long dm_hw_check_delta = 2*HZ;
static LIST_HEAD(hw_stats_list);

static void reset_per_cpu_data(struct per_cpu_dm_data *data)
{
        size_t al;
        struct net_dm_alert_msg *msg;
        struct nlattr *nla;
        struct sk_buff *skb;
        struct sk_buff *oskb = rcu_dereference_protected(data->skb, 1);

        al = sizeof(struct net_dm_alert_msg);
        al += dm_hit_limit * sizeof(struct net_dm_drop_point);
        al += sizeof(struct nlattr);

        skb = genlmsg_new(al, GFP_KERNEL);

        if (skb) {
                genlmsg_put(skb, 0, 0, &net_drop_monitor_family,
                                0, NET_DM_CMD_ALERT);
                nla = nla_reserve(skb, NLA_UNSPEC,
                                  sizeof(struct net_dm_alert_msg));
                msg = nla_data(nla);
                memset(msg, 0, al);
        } else
                schedule_work_on(data->cpu, &data->dm_alert_work);

        /*
         * Don't need to lock this, since we are guaranteed to only
         * run this on a single cpu at a time.
         * Note also that we only update data->skb if the old and new skb
         * pointers don't match.  This ensures that we don't continually call
         * synchornize_rcu if we repeatedly fail to alloc a new netlink message.
         */
        if (skb != oskb) {
                rcu_assign_pointer(data->skb, skb);

                synchronize_rcu();

                atomic_set(&data->dm_hit_count, dm_hit_limit);
        }

}

static void send_dm_alert(struct work_struct *unused)
{
        struct sk_buff *skb;
        struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);

        WARN_ON_ONCE(data->cpu != smp_processor_id());

        /*
         * Grab the skb we're about to send
         */
        skb = rcu_dereference_protected(data->skb, 1);

        /*
         * Replace it with a new one
         */
        reset_per_cpu_data(data);

        /*
         * Ship it!
         */
        if (skb)
                genlmsg_multicast(skb, 0, NET_DM_GRP_ALERT, GFP_KERNEL);

        put_cpu_var(dm_cpu_data);
}

/*
 * This is the timer function to delay the sending of an alert
 * in the event that more drops will arrive during the
 * hysteresis period.  Note that it operates under the timer interrupt
 * so we don't need to disable preemption here
 */
static void sched_send_work(unsigned long unused)
{
        struct per_cpu_dm_data *data =  &get_cpu_var(dm_cpu_data);

        schedule_work_on(smp_processor_id(), &data->dm_alert_work);

        put_cpu_var(dm_cpu_data);
}

static void trace_drop_common(struct sk_buff *skb, void *location)
{
        struct net_dm_alert_msg *msg;
        struct nlmsghdr *nlh;
        struct nlattr *nla;
        int i;
        struct sk_buff *dskb;
        struct per_cpu_dm_data *data = &get_cpu_var(dm_cpu_data);


        rcu_read_lock();
        dskb = rcu_dereference(data->skb);

        if (!dskb)
                goto out;

        if (!atomic_add_unless(&data->dm_hit_count, -1, 0)) {
                /*
                 * we're already at zero, discard this hit
                 */
                goto out;
        }

        nlh = (struct nlmsghdr *)dskb->data;
        nla = genlmsg_data(nlmsg_data(nlh));
        msg = nla_data(nla);
        for (i = 0; i < msg->entries; i++) {
                if (!memcmp(&location, msg->points[i].pc, sizeof(void *))) {
                        msg->points[i].count++;
                        atomic_inc(&data->dm_hit_count);
                        goto out;
                }
        }

        /*
         * We need to create a new entry
         */
        __nla_reserve_nohdr(dskb, sizeof(struct net_dm_drop_point));
        nla->nla_len += NLA_ALIGN(sizeof(struct net_dm_drop_point));
        memcpy(msg->points[msg->entries].pc, &location, sizeof(void *));
        msg->points[msg->entries].count = 1;
        msg->entries++;

        if (!timer_pending(&data->send_timer)) {
                data->send_timer.expires = jiffies + dm_delay * HZ;
                add_timer_on(&data->send_timer, smp_processor_id());
        }

out:
        rcu_read_unlock();
        put_cpu_var(dm_cpu_data);
        return;
}

static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
{
        trace_drop_common(skb, location);
}

static void trace_napi_poll_hit(void *ignore, struct napi_struct *napi)
{
        struct dm_hw_stat_delta *new_stat;

        /*
         * Don't check napi structures with no associated device
         */
        if (!napi->dev)
                return;

        rcu_read_lock();
        list_for_each_entry_rcu(new_stat, &hw_stats_list, list) {
                /*
                 * only add a note to our monitor buffer if:
                 * 1) this is the dev we received on
                 * 2) its after the last_rx delta
                 * 3) our rx_dropped count has gone up
                 */
                if ((new_stat->dev == napi->dev)  &&
                    (time_after(jiffies, new_stat->last_rx + dm_hw_check_delta)) &&
                    (napi->dev->stats.rx_dropped != new_stat->last_drop_val)) {
                        trace_drop_common(NULL, NULL);
                        new_stat->last_drop_val = napi->dev->stats.rx_dropped;
                        new_stat->last_rx = jiffies;
                        break;
                }
        }
        rcu_read_unlock();
}

static int set_all_monitor_traces(int state)
{
        int rc = 0;
        struct dm_hw_stat_delta *new_stat = NULL;
        struct dm_hw_stat_delta *temp;

        mutex_lock(&trace_state_mutex);

        if (state == trace_state) {
                rc = -EAGAIN;
                goto out_unlock;
        }

        switch (state) {
        case TRACE_ON:
                rc |= register_trace_kfree_skb(trace_kfree_skb_hit, NULL);
                rc |= register_trace_napi_poll(trace_napi_poll_hit, NULL);
                break;
        case TRACE_OFF:
                rc |= unregister_trace_kfree_skb(trace_kfree_skb_hit, NULL);
                rc |= unregister_trace_napi_poll(trace_napi_poll_hit, NULL);

                tracepoint_synchronize_unregister();

                /*
                 * Clean the device list
                 */
                list_for_each_entry_safe(new_stat, temp, &hw_stats_list, list) {
                        if (new_stat->dev == NULL) {
                                list_del_rcu(&new_stat->list);
                                kfree_rcu(new_stat, rcu);
                        }
                }
                break;
        default:
                rc = 1;
                break;
        }

        if (!rc)
                trace_state = state;
        else
                rc = -EINPROGRESS;

out_unlock:
        mutex_unlock(&trace_state_mutex);

        return rc;
}


static int net_dm_cmd_config(struct sk_buff *skb,
                        struct genl_info *info)
{
        return -ENOTSUPP;
}

static int net_dm_cmd_trace(struct sk_buff *skb,
                        struct genl_info *info)
{
        switch (info->genlhdr->cmd) {
        case NET_DM_CMD_START:
                return set_all_monitor_traces(TRACE_ON);
                break;
        case NET_DM_CMD_STOP:
                return set_all_monitor_traces(TRACE_OFF);
                break;
        }

        return -ENOTSUPP;
}

static int dropmon_net_event(struct notifier_block *ev_block,
                        unsigned long event, void *ptr)
{
        struct net_device *dev = ptr;
        struct dm_hw_stat_delta *new_stat = NULL;
        struct dm_hw_stat_delta *tmp;

        switch (event) {
        case NETDEV_REGISTER:
                new_stat = kzalloc(sizeof(struct dm_hw_stat_delta), GFP_KERNEL);

                if (!new_stat)
                        goto out;

                new_stat->dev = dev;
                new_stat->last_rx = jiffies;
                mutex_lock(&trace_state_mutex);
                list_add_rcu(&new_stat->list, &hw_stats_list);
                mutex_unlock(&trace_state_mutex);
                break;
        case NETDEV_UNREGISTER:
                mutex_lock(&trace_state_mutex);
                list_for_each_entry_safe(new_stat, tmp, &hw_stats_list, list) {
                        if (new_stat->dev == dev) {
                                new_stat->dev = NULL;
                                if (trace_state == TRACE_OFF) {
                                        list_del_rcu(&new_stat->list);
                                        kfree_rcu(new_stat, rcu);
                                        break;
                                }
                        }
                }
                mutex_unlock(&trace_state_mutex);
                break;
        }
out:
        return NOTIFY_DONE;
}

static struct genl_ops dropmon_ops[] = {
        {
                .cmd = NET_DM_CMD_CONFIG,
                .doit = net_dm_cmd_config,
        },
        {
                .cmd = NET_DM_CMD_START,
                .doit = net_dm_cmd_trace,
        },
        {
                .cmd = NET_DM_CMD_STOP,
                .doit = net_dm_cmd_trace,
        },
};

static struct notifier_block dropmon_net_notifier = {
        .notifier_call = dropmon_net_event
};

static int __init init_net_drop_monitor(void)
{
        struct per_cpu_dm_data *data;
        int cpu, rc;

        printk(KERN_INFO "Initializing network drop monitor service\n");

        if (sizeof(void *) > 8) {
                printk(KERN_ERR "Unable to store program counters on this arch, Drop monitor failed\n");
                return -ENOSPC;
        }

        rc = genl_register_family_with_ops(&net_drop_monitor_family,
                                           dropmon_ops,
                                           ARRAY_SIZE(dropmon_ops));
        if (rc) {
                printk(KERN_ERR "Could not create drop monitor netlink family\n");
                return rc;
        }

        rc = register_netdevice_notifier(&dropmon_net_notifier);
        if (rc < 0) {
                printk(KERN_CRIT "Failed to register netdevice notifier\n");
                goto out_unreg;
        }

        rc = 0;

        for_each_present_cpu(cpu) {
                data = &per_cpu(dm_cpu_data, cpu);
                data->cpu = cpu;
                INIT_WORK(&data->dm_alert_work, send_dm_alert);
                init_timer(&data->send_timer);
                data->send_timer.data = cpu;
                data->send_timer.function = sched_send_work;
                reset_per_cpu_data(data);
        }


        goto out;

out_unreg:
        genl_unregister_family(&net_drop_monitor_family);
out:
        return rc;
}

late_initcall(init_net_drop_monitor);