[pups] screen 3.9.9 vs. 2.11BSD write() to fifo and/or select() on socket - TUHS

13 Feb 2002

Would someone please advise me about fifos and sockets in 2.11BSD?  I'm having 
trouble porting screen 3.9.9, the multiplexing terminal emulator, to 2.11BSD 
because of them.  I'm running Mr. Schultz's 2.11BSD with all patches up to 
#442 on Mr. Brandt's p11 emulator version 2.9.  FWIW, I have INET in my kernel 
but I've ifconfig-ed only lo0.

screen's configure complains that it finds no usable fifo or socket.

The fifo test portion of the configure script fails when writing to the fifo.  
The write() returns -1 and sets errno == 79, "Inappropriate file type or 
format".  This happens when I run the test as root, as I must in order to use 
mknod() to create the fifo.  See fifotest.c, below.

screen can use sockets instead of fifos.  That portion of the configure script 
fails as well.  It fails in that it does not return from the select() on the 
socket until the alarm goes off.  See socketstest.c, below.

/* fifotest.c */
#include "confdefs.h"
#include <sys/errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
/*
#ifndef O_NONBLOCK
#define O_NONBLOCK O_NDELAY
#endif
#ifndef S_IFIFO
#define S_IFIFO 0010000
#endif
*/
char *fin = "/tmp/conftest254";

main()
{
  struct stat stb;
  int f;

  (void)alarm(5);
#ifdef POSIX
  if (mkfifo(fin, 0777)) {
#else
  if (mknod(fin, S_IFIFO|0777, 0)) {
#endif
printf("mknod failed\n");
perror("mknod");
    exit(1);
    }
  if (stat(fin, &stb) || (stb.st_mode & S_IFIFO) != S_IFIFO) {
  printf("stat failed\n");
    exit(1);
    }
  close(0);
#ifdef __386BSD__
  /*
   * The next test fails under 386BSD, but screen works using fifos.
   * Fifos in O_RDWR mode are only used for the BROKEN_PIPE case and for
   * the select() configuration test.
   */
  exit(0);
#endif
  if (open(fin, O_RDONLY | O_NONBLOCK)) {
    printf("open #1 failed\n");
    exit(1);
    }
  if (fork() == 0)
    {
      printf("f0\n");
      close(0);
      if (open(fin, O_WRONLY | O_NONBLOCK)) {
        printf("f0 open #2 failed\n");
        exit(1);
        }
      close(0);
      if (open(fin, O_WRONLY | O_NONBLOCK)) {
        printf("f0 open #3 failed\n");
        exit(1);
        }
      if (write(0, "TEST", 4) == -1) { /* FAILS HERE */
        printf("f0 write failed %d\n", errno);
        perror("write");
        exit(1);
        }
      exit(0);
    }
  printf("f1\n");
  f = 1;
  if (select(1, &f, 0, 0, 0) == -1) {
    printf("f1 select failed\n");
    exit(1);
    }
  exit(0);
}

/* socketstest.c */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <fcntl.h>

char *son = "/tmp/conftest254";

main()
{
  int s1, s2, s3, l;
  struct sockaddr_un a;

  (void)alarm(5);
  if ((s1 = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
    perror("socket");
    exit(1);
    }
  a.sun_family = AF_UNIX;
  strcpy(a.sun_path, son);
  (void) unlink(son);
  if (bind(s1, (struct sockaddr *) &a, strlen(son)+2) == -1) {
    perror("bind");
    exit(1);
    }
  if (listen(s1, 2)) {
    perror("listen");
    exit(1);
    }
  if (fork() == 0)
    {
      if ((s2 = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
        perror("f0 socket");
        kill(getppid(), 3);
        }
      (void)connect(s2, (struct sockaddr *)&a, strlen(son) + 2);
      if (write(s2, "HELLO", 5) == -1) {
        perror("f0 write");
        kill(getppid(), 3);
        }
      exit(0);
    }
  l = sizeof(a);
  if (close(0) == -1) {
    perror("close");
  }

  if (accept(s1, &a, &l)) {
    perror("accept");
    exit(1);
    }
  l = 1;
  if (select(1, &l, 0, 0, 0) == -1) { /* DOESN'T RETURN BEFORE SIG_ALARM */
    perror("select");
    exit(1);
    }
  exit(0);
}

-- 
David Talmage (talmage(a)cmf.nrl.navy.mil)
ITT Industries, Advanced Engineering & Sciences,
Advanced Technology Group