+/*
+ * As a fallback to parsing the CPU mask in "/sys/devices/system/cpu/possible",
+ * iterate on all the folders in "/sys/devices/system/cpu" that start with
+ * "cpu" followed by an integer, keep the highest CPU id encountered during
+ * this iteration and add 1 to get a number of CPUs.
+ *
+ * Then get the value from sysconf(_SC_NPROCESSORS_CONF) as a fallback and
+ * return the highest one.
+ *
+ * On Linux, using the value from sysconf can be unreliable since the way it
+ * counts CPUs varies between C libraries and even between versions of the same
+ * library. If we used it directly, getcpu() could return a value greater than
+ * this sysconf, in which case the arrays indexed by processor would overflow.
+ *
+ * As another example, the MUSL libc implementation of the _SC_NPROCESSORS_CONF
+ * sysconf does not return the number of configured CPUs in the system but
+ * relies on the cpu affinity mask of the current task.
+ *
+ * Returns 0 or less on error.
+ */
+int get_num_possible_cpus_fallback(void)
+{
+ long max_cpuid = -1;
+
+ DIR *cpudir;
+ struct dirent *entry;
+
+ cpudir = opendir("/sys/devices/system/cpu");
+ if (cpudir == NULL)
+ goto end;
+
+ /*
+ * Iterate on all directories named "cpu" followed by an integer.
+ */
+ while ((entry = readdir(cpudir))) {
+ if (entry->d_type == DT_DIR &&
+ strncmp(entry->d_name, "cpu", 3) == 0) {
+
+ char *endptr;
+ long cpu_id;
+
+ cpu_id = strtol(entry->d_name + 3, &endptr, 10);
+ if ((cpu_id < LONG_MAX) && (endptr != entry->d_name + 3)
+ && (*endptr == '\0')) {
+ if (cpu_id > max_cpuid)
+ max_cpuid = cpu_id;
+ }
+ }
+ }
+
+ if (closedir(cpudir))
+ PERROR("closedir");
+
+ /*
+ * If the max CPU id is out of bound, set it to -1 so it results in a
+ * CPU num of 0.
+ */
+ if (max_cpuid < 0 || max_cpuid > INT_MAX)
+ max_cpuid = -1;
+
+end:
+ /*
+ * Get the sysconf value as a last resort. Keep the highest number.
+ */
+ return __max(sysconf(_SC_NPROCESSORS_CONF), max_cpuid + 1);
+}
+
+/*
+ * Get the CPU possible mask string from sysfs.
+ *
+ * buf: the buffer where the mask will be read.
+ * max_bytes: the maximum number of bytes to write in the buffer.
+ *
+ * Returns the number of bytes read or -1 on error.
+ */
+int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes)