获取磁盘使用率（Linux C）

#define SYS_DISK_BUFF_LEN 256
#define SYS_DISK_NAME_LEN 80
#define SYS_100_PERSENT 100
int
get_sysDiskUsage()
{
    FILE * fp;
    char filesystem[SYS_DISK_NAME_LEN],available[SYS_DISK_NAME_LEN],use[SYS_DISK_NAME_LEN],mounted[SYS_DISK_NAME_LEN],buf[SYS_DISK_BUFF_LEN]; 
    double used,blocks,used_rate;
    fp=popen("df","r");
    fgets(buf,SYS_DISK_BUFF_LEN,fp);
    double dev_total = 0,dev_used = 0;
    while(6 == fscanf(fp,"%s %lf %lf %s %s %s",filesystem,&blocks,&used,available,use,mounted))
    {
        dev_total += blocks;
        dev_used += used;
    }

    used_rate = (dev_used/dev_total)*SYS_100_PERSENT;
    pclose(fp);
    return used_rate;
}