Help! (on ioctl system call)

[Randy Smith]

    I'm having problems with using the ioctl system call.  I eventually
  got a sample of the problem I'm having down to the following C program.

-----------------------------------------------------

#include <sys/ioctl.h>
#include <sgtty.h>
#include <stdio.h>
#include <sys/wait.h>

FILE *debug;

main()
{
	long me, mepg;
	int imepg;
	union wait status;

	debug = fopen("debug.file","w");
	if (!fork()) {
	   me = getpid();
	   imepg = (int) mepg = getpgrp((int)me);
	   fprintf(debug,"Me: %d, Pg: %d\n",me,mepg);
	   fflush(debug);

	   fprintf(debug,"Return from setpgrp: %d\n",setpgrp(me,me));
	   fflush(debug);

	   fprintf(debug,"Return from ioctl: %d\n",ioctl(1,TIOCSPGRP,&imepg));
	   fflush(debug);

	   fprintf(debug,"I made it (thought you'd like to know)\n");
	   fflush(debug);
	   exit(0);
	}
	fprintf(debug,"Pid from wait: %d\n",wait(&status));
	fprintf(debug,"Status code returned: %d\n",status);
}

   ------------------------------------------------------

    (forgive the sloppy last printf).

    When I copile and run this code, it hangs in the ioctl.  My debug
  file shows up (after I ^C) looking like:

--------------------------------------------------------

Me: 5567, Pg: 5566
Return from setpgrp: 0

--------------------------------------

    If I do a ps (from another terminal) while the thing is hanging, I get:

      F UID   PID  PPID CP PRI NI     ADDR  SZ  RSS WCHAN STAT TTY  TIME COMMAND
   8201 134  4098     1  0  15  0 ff8b8800  58   14     0 I    i05  0:13 -tcsh 
 408021 134  5217  4098  0  25  0 ff8c4800 202    8       T    i05  0:04 emacs 
   8001 134  5354  4098  0   5  0 ff918000  28    6 b698c I    i05  0:00 testio
   8001 134  5355  5354  0   4  0 ff954000  36    6       T    i05  0:00 testio
   8201 134  5373     1  0  15  0 ff8ed800  56   50     0 S    i13  0:11 -tcsh 
   8001 134  5462  5373 34  33  0 ff926800  70   38       R    i13  0:00 ps glx
   8001 134  5463  5373  4   1  0 ff93c800  30   10 3f944 S    i13  0:00 tee ex

 
  where testio is the name of the program, and tee and emacs should be ignored.

    Why is this call hanging on me?  I'm on a Pyramid 90x, but I got the same
  (ie. confusing enough that I couldn't tell the difference) results on a 
  VAX 750.  Suggestions from the net?

                                     -- Randy Smith

    P.S.  If the parent process doesn't wait for the child, the child EXITS
           during the ioctl.


    UUcp:  . . . ihnp4!gargoyle!sphinx!paws
    Arpa:  dvlp.dilvish%uchicago.mailnet at mit-multics.arpa
    CSnet: randy at uchicago.csnet