New system call and User space header file

[Sachin Gaikwad]

Hi all,

If I am adding a new system call sys_myroutine into the kernel then why is
it necessary to have header file in user space like this -

#include <unistd.h>

_syscall2(int, myroutine, int arg1, int, arg2);

What does it do when a user program calls this system call ? Can somebody
explain this to me ?

Thanks in advance,
Sachin