drop_monitor: Expose tail drop counter

Previous patch made the length of the per-CPU skb drop list
configurable. Expose a counter that shows how many packets could not be
enqueued to this list.

This allows users determine the desired queue length.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 101 insertions, 0 deletions

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index eb3c34d69ea9..39e094907391 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -51,12 +51,18 @@ static int trace_state = TRACE_OFF;
  */
 static DEFINE_MUTEX(net_dm_mutex);
 
+struct net_dm_stats {
+        u64 dropped;
+        struct u64_stats_sync syncp;
+};
+
 struct per_cpu_dm_data {
         spinlock_t              lock;   /* Protects 'skb' and 'send_timer' */
         struct sk_buff          *skb;
         struct sk_buff_head     drop_queue;
         struct work_struct      dm_alert_work;
         struct timer_list       send_timer;
+        struct net_dm_stats     stats;
 };
 
 struct dm_hw_stat_delta {
@@ -300,6 +306,9 @@ static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
 
 unlock_free:
         spin_unlock_irqrestore(&data->drop_queue.lock, flags);
+        u64_stats_update_begin(&data->stats.syncp);
+        data->stats.dropped++;
+        u64_stats_update_end(&data->stats.syncp);
         consume_skb(nskb);
 }
 
@@ -732,6 +741,93 @@ free_msg:
         return rc;
 }
 
+static void net_dm_stats_read(struct net_dm_stats *stats)
+{
+        int cpu;
+
+        memset(stats, 0, sizeof(*stats));
+        for_each_possible_cpu(cpu) {
+                struct per_cpu_dm_data *data = &per_cpu(dm_cpu_data, cpu);
+                struct net_dm_stats *cpu_stats = &data->stats;
+                unsigned int start;
+                u64 dropped;
+
+                do {
+                        start = u64_stats_fetch_begin_irq(&cpu_stats->syncp);
+                        dropped = cpu_stats->dropped;
+                } while (u64_stats_fetch_retry_irq(&cpu_stats->syncp, start));
+
+                stats->dropped += dropped;
+        }
+}
+
+static int net_dm_stats_put(struct sk_buff *msg)
+{
+        struct net_dm_stats stats;
+        struct nlattr *attr;
+
+        net_dm_stats_read(&stats);
+
+        attr = nla_nest_start(msg, NET_DM_ATTR_STATS);
+        if (!attr)
+                return -EMSGSIZE;
+
+        if (nla_put_u64_64bit(msg, NET_DM_ATTR_STATS_DROPPED,
+                              stats.dropped, NET_DM_ATTR_PAD))
+                goto nla_put_failure;
+
+        nla_nest_end(msg, attr);
+
+        return 0;
+
+nla_put_failure:
+        nla_nest_cancel(msg, attr);
+        return -EMSGSIZE;
+}
+
+static int net_dm_stats_fill(struct sk_buff *msg, struct genl_info *info)
+{
+        void *hdr;
+        int rc;
+
+        hdr = genlmsg_put(msg, info->snd_portid, info->snd_seq,
+                          &net_drop_monitor_family, 0, NET_DM_CMD_STATS_NEW);
+        if (!hdr)
+                return -EMSGSIZE;
+
+        rc = net_dm_stats_put(msg);
+        if (rc)
+                goto nla_put_failure;
+
+        genlmsg_end(msg, hdr);
+
+        return 0;
+
+nla_put_failure:
+        genlmsg_cancel(msg, hdr);
+        return -EMSGSIZE;
+}
+
+static int net_dm_cmd_stats_get(struct sk_buff *skb, struct genl_info *info)
+{
+        struct sk_buff *msg;
+        int rc;
+
+        msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+        if (!msg)
+                return -ENOMEM;
+
+        rc = net_dm_stats_fill(msg, info);
+        if (rc)
+                goto free_msg;
+
+        return genlmsg_reply(msg, info);
+
+free_msg:
+        nlmsg_free(msg);
+        return rc;
+}
+
 static int dropmon_net_event(struct notifier_block *ev_block,
                              unsigned long event, void *ptr)
 {
@@ -799,6 +895,10 @@ static const struct genl_ops dropmon_ops[] = {
                 .cmd = NET_DM_CMD_CONFIG_GET,
                 .doit = net_dm_cmd_config_get,
         },
+        {
+                .cmd = NET_DM_CMD_STATS_GET,
+                .doit = net_dm_cmd_stats_get,
+        },
 };
 
 static int net_dm_nl_pre_doit(const struct genl_ops *ops,
@@ -865,6 +965,7 @@ static int __init init_net_drop_monitor(void)
                 data = &per_cpu(dm_cpu_data, cpu);
                 spin_lock_init(&data->lock);
                 skb_queue_head_init(&data->drop_queue);
+                u64_stats_init(&data->stats.syncp);
         }
 
         goto out;