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>

1 files changed, 20 insertions, 10 deletions

diff --git a/tools/testing/selftests/bpf/bpf_util.h b/tools/testing/selftests/bpf/bpf_util.h
index 315a44fa32af..84fd6f1bf33e 100644
--- a/tools/testing/selftests/bpf/bpf_util.h
+++ b/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) {
-                        printf("Failed to retrieve # possible CPUs!\n");
-                        exit(1);
-                } else if (n == 1) {
-                        end = start;
+        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 += end - start + 1;
+                        j = i + 1;
                 }
-                possible_cpus = start == 0 ? end + 1 : 0;
-                break;
         }
+
         fclose(fp);
 
         return possible_cpus;