Forking and catching SIGCHLD, si_pid always contains 0.

[Jesus Sanchez]

Hi, using 4.6 release.

    I'm doing some code on process forking and catching signals on
OpenBSD. My interest here is to catch the SIGCHLD signal and do things
with the pid which sended the signal on the function called to treat it.

    As said in "Advanced Programming in the Unix Environment" book, when
calling a sigaction function there is a siginfo_t * with data about the
process sending the signal. On this struct, the member int si_pid
contains the PID of the process sending the signal. I tried in a very
simple code to obtain the PID of the child process but si_pid member
always contains 0 when I print it, and don't know what's wrong with it.

    I included a very simple source code to try this with the mail, what
I'm missing?

Google didn't helped at all.

Thanks for your time.
-J
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

/* this func is called when SIGCHLD is received */
void mysigaction(int nsig, siginfo_t * info , void *nothing){

   /* print some info values */
        printf("info->si_pid: %d info->si_code: %d info->si_status: %d --\n",
                        info->si_pid , (*info). si_code, (*info).si_status);
        printf("nsig: %d\n",nsig);

        return ;
}

int main(){

        struct sigaction myaction;
        myaction.sa_sigaction=mysigaction;
        myaction.sa_flags=SA_SIGINFO ;
   /* use sa_sigaction instead sa_handler to
    * have siginfo_t * values */

        sigaction(SIGCHLD,&myaction,(void*)NULL);

        int pid=fork();
        if (pid > 0 ) { // father
                printf("father, child pid is:  %d\n",pid);
                wait(NULL);
        }

        if (pid == 0){ // son
                printf("son, getpid() returns: %d\n",getpid());
                exit(0);
        }

        return 0;
}