bpf: selftests: handle 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 <[email protected]>

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

tools/testing/selftests/bpf/bpf_util.h +1 -6

index 315a44fa32af..8cab50408204 100644
@@ -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);

tools/testing/selftests/bpf/bpf_util.h +10 -3

+                       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

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

Quoted 39 lines · Martynas Pumputis

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 <[email protected]>

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

tools/testing/selftests/bpf/bpf_util.h +1 -6

index 315a44fa32af..8cab50408204 100644
@@ -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);

tools/testing/selftests/bpf/bpf_util.h static inline unsigned int bpf_num_possible_cpus(void) · line 31

Quoted 10 lines

tools/testing/selftests/bpf/bpf_util.h +8 -2

-               } 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 20 lines

tools/testing/selftests/bpf/bpf_util.h +10 -3

+                       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