can: gw: indicate and count deleted frames due to misconfiguration

Add a statistic counter to detect deleted frames due to misconfiguration with
a new read-only CGW_DELETED netlink attribute for the CAN gateway.

Signed-off-by: Oliver Hartkopp <[e-mail]>
Signed-off-by: Marc Kleine-Budde <[e-mail]>

include/uapi/linux/can/gw.h

···
 	CGW_SRC_IF,	/* ifindex of source network interface */
 	CGW_DST_IF,	/* ifindex of destination network interface */
 	CGW_FILTER,	/* specify struct can_filter on source CAN device */
+	CGW_DELETED,	/* number of deleted CAN frames (see max_hops param) */
 	__CGW_MAX
 };
 

net/can/gw.c

···
 	struct rcu_head rcu;
 	u32 handled_frames;
 	u32 dropped_frames;
+	u32 deleted_frames;
 	struct cf_mod mod;
 	union {
 		/* CAN frame data source */
···
 
 	BUG_ON(skb->ip_summed != CHECKSUM_UNNECESSARY);
 
-	if (cgw_hops(skb) >= max_hops)
+	if (cgw_hops(skb) >= max_hops) {
+		/* indicate deleted frames due to misconfiguration */
+		gwj->deleted_frames++;
 		return;
+	}
 
 	if (!(gwj->dst.dev->flags & IFF_UP)) {
 		gwj->dropped_frames++;
···
 
 	if (gwj->dropped_frames) {
 		if (nla_put_u32(skb, CGW_DROPPED, gwj->dropped_frames) < 0)
+			goto cancel;
+	}
+
+	if (gwj->deleted_frames) {
+		if (nla_put_u32(skb, CGW_DELETED, gwj->deleted_frames) < 0)
 			goto cancel;
 	}
 
···
 
 	gwj->handled_frames = 0;
 	gwj->dropped_frames = 0;
+	gwj->deleted_frames = 0;
 	gwj->flags = r->flags;
 	gwj->gwtype = r->gwtype;