Linux: get CPU count without /proc or /sys

// task: get CPU count without /proc or /sys
// solution: get CPU affinity mask from PID 1

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <errno.h>

size_t get_cpu_count(void) {
    const pid_t     ack_pid = 1;
    cpu_set_t       * cs = NULL;
    cpu_set_t       * cs_t = NULL;
    const size_t    alloc_thres = 4096, reallocs_max = 10;
    size_t          cs_len = 0, reallocs = 0;
    size_t          r = 0, i = 0, k = 0;

    cs_len = alloc_thres;
    cs = malloc(cs_len);
    if (!cs) { return 0; }

    while (reallocs < reallocs_max) {
        CPU_ZERO_S(cs_len, cs);
        if (!sched_getaffinity(ack_pid, cs_len, cs)) { break; }

        if (errno != EINVAL) { goto cs_cleanup; }

        cs_len += alloc_thres;
        cs_t = realloc(cs, cs_len);
        if (!cs_t) { goto cs_cleanup; }

        cs = cs_t;
        reallocs++;
    }

    if (reallocs == reallocs_max) {
        // is it better return 0 instead of this?..
        return CPU_COUNT_S(cs_len, cs);
    }

    k = CPU_COUNT_S(cs_len, cs);
    for (i = 0; i < k; i++) {
        if (CPU_ISSET_S(i, cs_len, cs)) { r++; }
    }

cs_cleanup:
    if (cs) { free(cs); cs = NULL; }

    return r;
}

// #include <sys/sysinfo.h>

int main(void) {
    // printf("cpu count = %d\n", get_nprocs_conf());
    printf("cpu count = %ld\n", get_cpu_count());
    return 0;
}