selftests/bpf: Make bpf_util work on uniprocessor systems

The current implementation fails to work on uniprocessor systems.
Fix the parser to also handle the uniprocessor case.
Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/bpf/bpf_util.h

@@ -12,6 +12,7 @@ static inline unsigned int bpf_num_possible_cpus(void)
 	unsigned int start, end, possible_cpus = 0;
 	char buff[128];
 	FILE *fp;
+	int n;
 
 	fp = fopen(fcpu, "r");
 	if (!fp) {
@@ -20,17 +21,17 @@ static inline unsigned int bpf_num_possible_cpus(void)
 	}
 
 	while (fgets(buff, sizeof(buff), fp)) {
-		if (sscanf(buff, "%u-%u", &start, &end) == 2) {
+		n = sscanf(buff, "%u-%u", &start, &end);
+		if (n == 0) {
+			printf("Failed to retrieve # possible CPUs!\n");
+			exit(1);
+		} else if (n == 1) {
+			end = start;
+		}
 		possible_cpus = start == 0 ? end + 1 : 0;
 		break;
 	}
-	}
-
 	fclose(fp);
-	if (!possible_cpus) {
-		printf("Failed to retrieve # possible CPUs!\n");
-		exit(1);
-	}
 
 	return possible_cpus;
 }