drop_monitor: Allow user to start monitoring hardware drops

Drop monitor has start and stop commands, but so far these were only
used to start and stop monitoring of software drops.

Now that drop monitor can also monitor hardware drops, we should allow
the user to control these as well.

Do that by adding SW and HW flags to these commands. If no flag is
specified, then only start / stop monitoring software drops. This is
done in order to maintain backward-compatibility with existing user
space applications.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/net_dropmon.h

@@ -90,6 +90,8 @@ enum net_dm_attr {
 	NET_DM_ATTR_HW_ENTRIES,			/* nested */
 	NET_DM_ATTR_HW_ENTRY,			/* nested */
 	NET_DM_ATTR_HW_TRAP_COUNT,		/* u32 */
+	NET_DM_ATTR_SW_DROPS,			/* flag */
+	NET_DM_ATTR_HW_DROPS,			/* flag */
 
 	__NET_DM_ATTR_MAX,
 	NET_DM_ATTR_MAX = __NET_DM_ATTR_MAX - 1

net/core/drop_monitor.c

@@ -952,13 +952,82 @@ static const struct net_dm_alert_ops *net_dm_alert_ops_arr[] = {
 void net_dm_hw_report(struct sk_buff *skb,
 		      const struct net_dm_hw_metadata *hw_metadata)
 {
+	rcu_read_lock();
+
 	if (!monitor_hw)
-		return;
+		goto out;
 
 	net_dm_alert_ops_arr[net_dm_alert_mode]->hw_probe(skb, hw_metadata);
+
+out:
+	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(net_dm_hw_report);
 
+static int net_dm_hw_monitor_start(struct netlink_ext_ack *extack)
+{
+	const struct net_dm_alert_ops *ops;
+	int cpu;
+
+	if (monitor_hw) {
+		NL_SET_ERR_MSG_MOD(extack, "Hardware monitoring already enabled");
+		return -EAGAIN;
+	}
+
+	ops = net_dm_alert_ops_arr[net_dm_alert_mode];
+
+	if (!try_module_get(THIS_MODULE)) {
+		NL_SET_ERR_MSG_MOD(extack, "Failed to take reference on module");
+		return -ENODEV;
+	}
+
+	for_each_possible_cpu(cpu) {
+		struct per_cpu_dm_data *hw_data = &per_cpu(dm_hw_cpu_data, cpu);
+		struct net_dm_hw_entries *hw_entries;
+
+		INIT_WORK(&hw_data->dm_alert_work, ops->hw_work_item_func);
+		timer_setup(&hw_data->send_timer, sched_send_work, 0);
+		hw_entries = net_dm_hw_reset_per_cpu_data(hw_data);
+		kfree(hw_entries);
+	}
+
+	monitor_hw = true;
+
+	return 0;
+}
+
+static void net_dm_hw_monitor_stop(struct netlink_ext_ack *extack)
+{
+	int cpu;
+
+	if (!monitor_hw)
+		NL_SET_ERR_MSG_MOD(extack, "Hardware monitoring already disabled");
+
+	monitor_hw = false;
+
+	/* After this call returns we are guaranteed that no CPU is processing
+	 * any hardware drops.
+	 */
+	synchronize_rcu();
+
+	for_each_possible_cpu(cpu) {
+		struct per_cpu_dm_data *hw_data = &per_cpu(dm_hw_cpu_data, cpu);
+		struct sk_buff *skb;
+
+		del_timer_sync(&hw_data->send_timer);
+		cancel_work_sync(&hw_data->dm_alert_work);
+		while ((skb = __skb_dequeue(&hw_data->drop_queue))) {
+			struct net_dm_hw_metadata *hw_metadata;
+
+			hw_metadata = NET_DM_SKB_CB(skb)->hw_metadata;
+			net_dm_hw_metadata_free(hw_metadata);
+			consume_skb(skb);
+		}
+	}
+
+	module_put(THIS_MODULE);
+}
+
 static int net_dm_trace_on_set(struct netlink_ext_ack *extack)
 {
 	const struct net_dm_alert_ops *ops;
@@ -1153,14 +1222,61 @@ static int net_dm_cmd_config(struct sk_buff *skb,
 	return 0;
 }
 
+static int net_dm_monitor_start(bool set_sw, bool set_hw,
+				struct netlink_ext_ack *extack)
+{
+	bool sw_set = false;
+	int rc;
+
+	if (set_sw) {
+		rc = set_all_monitor_traces(TRACE_ON, extack);
+		if (rc)
+			return rc;
+		sw_set = true;
+	}
+
+	if (set_hw) {
+		rc = net_dm_hw_monitor_start(extack);
+		if (rc)
+			goto err_monitor_hw;
+	}
+
+	return 0;
+
+err_monitor_hw:
+	if (sw_set)
+		set_all_monitor_traces(TRACE_OFF, extack);
+	return rc;
+}
+
+static void net_dm_monitor_stop(bool set_sw, bool set_hw,
+				struct netlink_ext_ack *extack)
+{
+	if (set_hw)
+		net_dm_hw_monitor_stop(extack);
+	if (set_sw)
+		set_all_monitor_traces(TRACE_OFF, extack);
+}
+
 static int net_dm_cmd_trace(struct sk_buff *skb,
 			struct genl_info *info)
 {
+	bool set_sw = !!info->attrs[NET_DM_ATTR_SW_DROPS];
+	bool set_hw = !!info->attrs[NET_DM_ATTR_HW_DROPS];
+	struct netlink_ext_ack *extack = info->extack;
+
+	/* To maintain backward compatibility, we start / stop monitoring of
+	 * software drops if no flag is specified.
+	 */
+	if (!set_sw && !set_hw)
+		set_sw = true;
+
 	switch (info->genlhdr->cmd) {
 	case NET_DM_CMD_START:
-		return set_all_monitor_traces(TRACE_ON, info->extack);
+		return net_dm_monitor_start(set_sw, set_hw, extack);
 	case NET_DM_CMD_STOP:
-		return set_all_monitor_traces(TRACE_OFF, info->extack);
+		net_dm_monitor_stop(set_sw, set_hw, extack);
+		return 0;
 	}
 
 	return -EOPNOTSUPP;
@@ -1392,6 +1508,8 @@ static const struct nla_policy net_dm_nl_policy[NET_DM_ATTR_MAX + 1] = {
 	[NET_DM_ATTR_ALERT_MODE] = { .type = NLA_U8 },
 	[NET_DM_ATTR_TRUNC_LEN] = { .type = NLA_U32 },
 	[NET_DM_ATTR_QUEUE_LEN] = { .type = NLA_U32 },
+	[NET_DM_ATTR_SW_DROPS]	= {. type = NLA_FLAG },
+	[NET_DM_ATTR_HW_DROPS]	= {. type = NLA_FLAG },
 };
 
 static const struct genl_ops dropmon_ops[] = {