#include <linux/unistd.h>
#include <linux/types.h>
#include <linux/sysctl.h>
#include <stdio.h>

_syscall1(int, _sysctl, struct __sysctl_args *, args);
int sysctl(int *name, int nlen, void *oldval, size_t *oldlenp,
    void *newval, size_t newlen)
{
  struct __sysctl_args args={name,nlen,oldval,oldlenp,newval,newlen};
  return _sysctl(&args);
}

#define SIZE(x) sizeof(x)/sizeof(x[0])
#ifndef NET_TCO_CONG_CONTROL
#define NET_TCP_CONG_CONTROL 110
#endif

int main()
{
  char oldname[100];
  size_t oldnamelen = SIZE(oldname);
  char newval[] = "reno";
  size_t newvallen = SIZE(newval);
  int name[] = { CTL_NET, NET_IPV4, NET_TCP_CONG_CONTROL };

  if (sysctl(name, SIZE(name), oldname, &oldnamelen, newval, newvallen))
    perror("sysctl");
  else
    printf("old value='%s', new value should be='%s'\n", oldname, newval);
  return 0;
}