Question about signal handler.

Excuse me!
I have a question about signal handler. There is a signal handler in sigaction structure such as:

struct sigaction {
unsigned int sa_flags;
__sighandler_t sa_handler;
sigset_t sa_mask;
};

and I check the prototype of __sighandler_t is:

typedef void __signalfn_t(int);
typedef __signalfn_t __user *__sighandler_t;

I cannot find any signal mechanism that pass argument to the int parameter in signal handler. How could I utilize this int parameter?

Thanks for your favor.

Ok, I have figured out that signal identify number would be passed to the int patameter in signal handler.