#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <linux/sysctl.h>
#include <errno.h>

int _sysctl(struct __sysctl_args *args );

#define OSNAMESZ 100
void test0_osname()
{
    struct __sysctl_args args;
    char osname[OSNAMESZ];
    size_t osnamelth;
    int name[] = { CTL_KERN, KERN_OSTYPE };

    memset(&args, 0, sizeof(struct __sysctl_args));
    args.name = name;
    args.nlen = sizeof(name)/sizeof(name[0]);
    args.oldval = osname;
    args.oldlenp = &osnamelth;

    osnamelth = sizeof(osname);

    if (syscall(SYS__sysctl, &args) == -1) {
        perror("_sysctl");
        exit(EXIT_FAILURE);
    }
    printf("This machine is running %*s\n", (int)osnamelth, osname);
}

void test1_tcp_max_syn_backlog()
{
    struct __sysctl_args args;
    int var;
    size_t var_len;
    int name[] = { CTL_NET, NET_IPV4, NET_TCP_MAX_SYN_BACKLOG };

    memset(&args, 0, sizeof(struct __sysctl_args));
    args.name = name;
    args.nlen = sizeof(name)/sizeof(name[0]);
    args.oldval = &var;
    args.oldlenp = &var_len;

    if (syscall(SYS__sysctl, &args) == -1) {
        perror("_sysctl");
        exit(EXIT_FAILURE);
    }
    printf("NET_TCP_MAX_SYN_BACKLOG = %u\n", var);
}

int
main(void)
{
	test0_osname();

	test1_tcp_max_syn_backlog();

	exit(EXIT_SUCCESS);
}