Re: New system call and User space header file

["Hareesh Nagarajan" <hareesh@xxxxxxxxxx>]

On 9/8/07, Sachin Gaikwad <sachin.kernel@xxxxxxxxx> wrote:
> 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 ?

Have a look at linux/unistd.h, _syscall2 is a macro that expands to:
  #define _syscall2(type,name,type1,arg1,type2,arg2) \
    type name(type1 arg1,type2 arg2) { return syscall(__NR_##name,
arg1, arg2); }
  #endif

And syscall() performs the actual system call.

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