bpf, selftests: fix handling of sparse CPU allocations

Previously, bpf_num_possible_cpus() had a bug when calculating a
number of possible CPUs in the case of sparse CPU allocations, as
it was considering only the first range or element of
/sys/devices/system/cpu/possible.

E.g. in the case of "0,2-3" (CPU 1 is not available), the function
returned 1 instead of 3.

This patch fixes the function by making it parse all CPU ranges and
elements.
Signed-off-by: Martynas Pumputis <m@lambda.lt>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/bpf_util.h

@@ -13,7 +13,7 @@ static inline unsigned int bpf_num_possible_cpus(void)
 	unsigned int start, end, possible_cpus = 0;
 	char buff[128];
 	FILE *fp;
-	int n;
+	int len, n, i, j = 0;
 
 	fp = fopen(fcpu, "r");
 	if (!fp) {
@@ -21,17 +21,27 @@ static inline unsigned int bpf_num_possible_cpus(void)
 		exit(1);
 	}
 
-	while (fgets(buff, sizeof(buff), fp)) {
-		n = sscanf(buff, "%u-%u", &start, &end);
-		if (n == 0) {
+	if (!fgets(buff, sizeof(buff), fp)) {
+		printf("Failed to read %s!\n", fcpu);
+		exit(1);
+	}
+
+	len = strlen(buff);
+	for (i = 0; i <= len; i++) {
+		if (buff[i] == ',' || buff[i] == '\0') {
+			buff[i] = '\0';
+			n = sscanf(&buff[j], "%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;
+			possible_cpus += end - start + 1;
+			j = i + 1;
 		}
+	}
+
 	fclose(fp);
 
 	return possible_cpus;