pping: Add warnings for failing to create map entry

Send a warning notifying the user that PPing failed to create a
flow/timestamp entry due to the corresponding map being full. To avoid
sending a warning for every packet, only emit warnings every
WARN_MAP_FULL_INTERVAL (which is currently hard-coded to 1s).

Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>

Author: simosund

pping/pping.c

@@ -821,6 +821,15 @@ static void print_event_json(const union pping_event *e)
 	jsonw_end_object(json_ctx);
 }
 
+static void warn_map_full(const struct map_full_event *e)
+{
+	print_ns_datetime(stderr, e->timestamp);
+	fprintf(stderr, " Warning: Unable to create %s entry for flow ",
+		e->map == PPING_MAP_FLOWSTATE ? "flow" : "timestamp");
+	print_flow_ppvizformat(stderr, &e->flow);
+	fprintf(stderr, "\n");
+}
+
 static void handle_event(void *ctx, int cpu, void *data, __u32 data_size)
 {
 	const union pping_event *e = data;
@@ -829,6 +838,9 @@ static void handle_event(void *ctx, int cpu, void *data, __u32 data_size)
 		return;
 
 	switch (e->event_type) {
+	case EVENT_TYPE_MAP_FULL:
+		warn_map_full(&e->map_event);
+		break;
 	case EVENT_TYPE_RTT:
 	case EVENT_TYPE_FLOW:
 		print_event_func(e);

pping/pping.h

@@ -14,6 +14,7 @@ typedef __u64 fixpoint64;
 /* For the event_type members of rtt_event and flow_event */
 #define EVENT_TYPE_FLOW 1
 #define EVENT_TYPE_RTT 2
+#define EVENT_TYPE_MAP_FULL 3
 
 enum __attribute__((__packed__)) flow_event_type {
 	FLOW_EVENT_NONE,
@@ -37,6 +38,11 @@ enum __attribute__((__packed__)) flow_event_source {
 	EVENT_SOURCE_USERSPACE
 };
 
+enum __attribute__((__packed__)) pping_map {
+	PPING_MAP_FLOWSTATE = 0,
+	PPING_MAP_PACKETTS
+};
+
 struct bpf_config {
 	__u64 rate_limit;
 	fixpoint64 rtt_rate;
@@ -133,10 +139,23 @@ struct flow_event {
 	__u8 reserved;
 };
 
+/*
+ * An event indicating that a new entry could not be created the map due to the
+ * map being full.
+ */
+struct map_full_event {
+	__u64 event_type;
+	__u64 timestamp;
+	struct network_tuple flow;
+	enum pping_map map;
+	__u8 reserved[3];
+};
+
 union pping_event {
 	__u64 event_type;
 	struct rtt_event rtt_event;
 	struct flow_event flow_event;
+	struct map_full_event map_event;
 };
 
 /*

pping/pping_kern.c

@@ -28,6 +28,9 @@
 // Mask for IPv6 flowlabel + traffic class -  used in fib lookup
 #define IPV6_FLOWINFO_MASK __cpu_to_be32(0x0FFFFFFF)
 
+// Emit a warning max once per second when failing to add entry to map
+#define WARN_MAP_FULL_INTERVAL 1000000000UL
+
 /*
  * This struct keeps track of the data and data_end pointers from the xdp_md or
  * __skb_buff contexts, as well as a currently parsed to position kept in nh.
@@ -78,6 +81,8 @@ struct packet_info {
 char _license[] SEC("license") = "GPL";
 // Global config struct - set from userspace
 static volatile const struct bpf_config config = {};
+static volatile __u64 last_warn_time[2] = { 0 };
+
 
 // Map definitions
 struct {
@@ -441,11 +446,35 @@ static void send_flow_event(void *ctx, struct packet_info *p_info,
 	bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &fe, sizeof(fe));
 }
 
+/*
+ * Send a map-full event for the map.
+ * Will only trigger once every WARN_MAP_FULL_INTERVAL
+ */
+static void send_map_full_event(void *ctx, struct packet_info *p_info,
+				enum pping_map map)
+{
+	struct map_full_event me;
+
+	if (p_info->time < last_warn_time[map] ||
+	    p_info->time - last_warn_time[map] < WARN_MAP_FULL_INTERVAL)
+		return;
+
+	last_warn_time[map] = p_info->time;
+
+	__builtin_memset(&me, 0, sizeof(me));
+	me.event_type = EVENT_TYPE_MAP_FULL;
+	me.timestamp = p_info->time;
+	me.flow = p_info->pid.flow;
+	me.map = map;
+
+	bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU, &me, sizeof(me));
+}
+
 /*
  * Attempt to create a new flow-state.
  * Returns a pointer to the flow_state if successful, NULL otherwise
  */
-static struct flow_state *create_flow(struct packet_info *p_info)
+static struct flow_state *create_flow(void *ctx, struct packet_info *p_info)
 {
 	struct flow_state new_state = { 0 };
 
@@ -455,8 +484,10 @@ static struct flow_state *create_flow(struct packet_info *p_info)
 					       EVENT_REASON_FIRST_OBS_PCKT;
 
 	if (bpf_map_update_elem(&flow_state, &p_info->pid.flow, &new_state,
-				BPF_NOEXIST) != 0)
+				BPF_NOEXIST) != 0) {
+		send_map_full_event(ctx, p_info, PPING_MAP_FLOWSTATE);
 		return NULL;
+	}
 
 	return bpf_map_lookup_elem(&flow_state, &p_info->pid.flow);
 }
@@ -474,7 +505,7 @@ static struct flow_state *update_flow(void *ctx, struct packet_info *p_info,
 	    !(p_info->event_type == FLOW_EVENT_CLOSING ||
 	      p_info->event_type == FLOW_EVENT_CLOSING_BOTH)) {
 		*new_flow = true;
-		f_state = create_flow(p_info);
+		f_state = create_flow(ctx, p_info);
 	}
 
 	if (!f_state)
@@ -610,8 +641,9 @@ static void pping_timestamp_packet(struct flow_state *f_state, void *ctx,
 	 */
 	f_state->last_timestamp = p_info->time;
 
-	bpf_map_update_elem(&packet_ts, &p_info->pid, &p_info->time,
-			    BPF_NOEXIST);
+	if (bpf_map_update_elem(&packet_ts, &p_info->pid, &p_info->time,
+				BPF_NOEXIST) != 0)
+		send_map_full_event(ctx, p_info, PPING_MAP_PACKETTS);
 }
 
 /*