Oops, thanks for noticing the issue with strlen in the for loop. Changing to "int len = strlen(buff); for (i = 0; i < len; i++) <..>" should fix the issue. I'm going to re-submit the patch.

Also, I put some testing results: https://gist.github.com/brb/5369b5cfd08babb80cf2c4081dc19762

On Thu, Jan 31, 2019, at 7:25 AM, Y Song wrote:

[ My reply somehow rejected by netdev, this is to send it again. ]

On Wed, Jan 30, 2019 at 1:19 AM Martynas Pumputis [off-list ref] wrote:

quoted

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 <redacted>
---
 tools/testing/selftests/bpf/bpf_util.h | 29 +++++++++++++++++---------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/bpf/bpf_util.h b/tools/testing/selftests/bpf/bpf_util.h
index 315a44fa32af..8cab50408204 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 n, i, j = 0;

        fp = fopen(fcpu, "r");
        if (!fp) {

@@ -21,17 +21,26 @@ 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);
+       }
+
+       for (i = 0; i <= strlen(buff); i++) {
+               if (buff[i] == ',' || buff[i] == '\0') {
+                       buff[i] = '\0';

This does not sound right. For example, the cpu list "0,2-3",
you will change "," to '\0" so buffer becomes "0\02-3".
The next iteration you will get strlen(buff) = 1.
The "2-3" will be skipped.

quoted

+                       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;
--
2.20.1