take a cpu online / offline in linux (tested on Fedora 22)

cpuenable.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/stat.h>
#include <fcntl.h>

void usage()
{
    printf("./cpuenable <online / offline> <cpu number>\n");
    exit(1);
}

int main(int argc, char **argv) {
    int ret;
    char buff[300];
    int online;
    int cpu;
    
    if (argc != 3) {
        usage();
    }
    
    cpu = atoi(argv[2]);
    
    if (!strcmp(argv[1], "online")) {
        online = 1;
    } else if (!strcmp(argv[1], "offline")) {
        online = 0;
    } else
        usage();
        
    sprintf(buff, "echo %d > /sys/device/system/cpu%d/online", online, cpu);
    
    int ret;
    
    ret = system(buff);
    if (ret != 0) {
        printf("failed to take cpu%d %s\n", cpu, argv[1]);
        return ret;
    } else
        printf("cpu%d taken %s\n", cpu, argv[1]);
    
    return 0;
}