BPF : iterate all element in map

Author: 54shady

bpf/vmexit_user.c

@@ -11,14 +11,19 @@
 
 #define NR_VCPU 4
 
+#define ITERAT_ALL
+
 int main(int argc, char *argv[])
 {
 	struct bpf_link *link = NULL;
 	struct bpf_program *prog;
 	struct bpf_object *obj;
 	char filename[256];
-	int i, fd;
-	int cur, sum = 0, delta = 0;
+	int fd;
+	int cur;
+#ifdef ITERAT_ALL
+	int next_key, lookup_key;
+#else
 	/*
 	 * pstree can print out each vcpu thread id
 	 * pstree -t -p `vminfo -n demo-3 -p`
@@ -29,6 +34,9 @@ int main(int argc, char *argv[])
 	 */
 	int pids[NR_VCPU] = {3345, 3355, 3366, 3373};
 	int prev[NR_VCPU] = {0, 0, 0, 0};
+	int sum = 0, delta = 0;
+	int i;
+#endif
 
 	snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
 	obj = bpf_object__open_file(filename, NULL);
@@ -56,21 +64,36 @@ int main(int argc, char *argv[])
 		goto cleanup;
 	}
 
+	/*
+	 * iterating over elements in a BPF Map
+	 *
+	 * use `bpf_map_get_next_key` with a lookup key that doesn't exist in the map
+	 * This forces BPF to start from the beginning of the map
+	 */
 #if 1
 	fd = bpf_object__find_map_fd_by_name(obj, "my_map");
 	while (1)
 	{
+#ifdef ITERAT_ALL
+		lookup_key = -1; /* key not exsit in map */
+		while (bpf_map_get_next_key(fd, &lookup_key, &next_key) == 0)
+		{
+			bpf_map_lookup_elem(fd, &lookup_key, &cur);
+			lookup_key = next_key;
+			printf("%d:%d\n", lookup_key, cur);
+		}
+#else
 		for (i = 0; i < NR_VCPU; i++)
 		{
 			bpf_map_lookup_elem(fd, &pids[i], &cur);
 			delta = cur - prev[i];
 			sum += delta;
 			prev[i] = cur;
 		}
-
-		sleep(1);
 		printf("vmexit total: %d\n", sum);
 		sum = 0;
+#endif
+		sleep(1);
 	}
 #else
 	read_trace_pipe();