drop_monitor: Add basic infrastructure for hardware drops

Export a function that can be invoked in order to report packets that
were dropped by the underlying hardware along with metadata.

Subsequent patches will add support for the different alert modes.

Signed-off-by: Ido Schimmel <[e-mail]>
Acked-by: Jiri Pirko <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

MAINTAINERS

···
 W:	https://fedorahosted.org/dropwatch/
 F:	net/core/drop_monitor.c
 F:	include/uapi/linux/net_dropmon.h
+F:	include/net/drop_monitor.h
 
 NETWORKING DRIVERS
 M:	"David S. Miller" <[e-mail]>

include/net/drop_monitor.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _NET_DROP_MONITOR_H_
+#define _NET_DROP_MONITOR_H_
+
+#include <linux/ktime.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+
+/**
+ * struct net_dm_hw_metadata - Hardware-supplied packet metadata.
+ * @trap_group_name: Hardware trap group name.
+ * @trap_name: Hardware trap name.
+ * @input_dev: Input netdevice.
+ */
+struct net_dm_hw_metadata {
+	const char *trap_group_name;
+	const char *trap_name;
+	struct net_device *input_dev;
+};
+
+#if IS_ENABLED(CONFIG_NET_DROP_MONITOR)
+void net_dm_hw_report(struct sk_buff *skb,
+		      const struct net_dm_hw_metadata *hw_metadata);
+#else
+static inline void
+net_dm_hw_report(struct sk_buff *skb,
+		 const struct net_dm_hw_metadata *hw_metadata)
+{
+}
+#endif
+
+#endif /* _NET_DROP_MONITOR_H_ */

net/core/drop_monitor.c

···
 #include <linux/bitops.h>
 #include <linux/slab.h>
 #include <linux/module.h>
+#include <net/drop_monitor.h>
 #include <net/genetlink.h>
 #include <net/netevent.h>
 
···
  * netlink alerts
  */
 static int trace_state = TRACE_OFF;
+static bool monitor_hw;
 
 /* net_dm_mutex
  *
···
 	void (*napi_poll_probe)(void *ignore, struct napi_struct *napi,
 				int work, int budget);
 	void (*work_item_func)(struct work_struct *work);
+	void (*hw_probe)(struct sk_buff *skb,
+			 const struct net_dm_hw_metadata *hw_metadata);
 };
 
 struct net_dm_skb_cb {
···
 	rcu_read_unlock();
 }
 
+static void
+net_dm_hw_summary_probe(struct sk_buff *skb,
+			const struct net_dm_hw_metadata *hw_metadata)
+{
+}
+
 static const struct net_dm_alert_ops net_dm_alert_summary_ops = {
 	.kfree_skb_probe	= trace_kfree_skb_hit,
 	.napi_poll_probe	= trace_napi_poll_hit,
 	.work_item_func		= send_dm_alert,
+	.hw_probe		= net_dm_hw_summary_probe,
 };
 
 static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
···
 		net_dm_packet_report(skb);
 }
 
+static void
+net_dm_hw_packet_probe(struct sk_buff *skb,
+		       const struct net_dm_hw_metadata *hw_metadata)
+{
+}
+
 static const struct net_dm_alert_ops net_dm_alert_packet_ops = {
 	.kfree_skb_probe	= net_dm_packet_trace_kfree_skb_hit,
 	.napi_poll_probe	= net_dm_packet_trace_napi_poll_hit,
 	.work_item_func		= net_dm_packet_work,
+	.hw_probe		= net_dm_hw_packet_probe,
 };
 
 static const struct net_dm_alert_ops *net_dm_alert_ops_arr[] = {
 	[NET_DM_ALERT_MODE_SUMMARY]	= &net_dm_alert_summary_ops,
 	[NET_DM_ALERT_MODE_PACKET]	= &net_dm_alert_packet_ops,
 };
+
+void net_dm_hw_report(struct sk_buff *skb,
+		      const struct net_dm_hw_metadata *hw_metadata)
+{
+	if (!monitor_hw)
+		return;
+
+	net_dm_alert_ops_arr[net_dm_alert_mode]->hw_probe(skb, hw_metadata);
+}
+EXPORT_SYMBOL_GPL(net_dm_hw_report);
 
 static int net_dm_trace_on_set(struct netlink_ext_ack *extack)
 {