external/ibm-public/postfix/dist/src/util/fifo_rdwr_bug.c

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      fifo_rdwr_bug 1
   6 /* SUMMARY
   7 /*      fifo server test program
   8 /* SYNOPSIS
   9 /*      fifo_rdwr_bug
  10 /* DESCRIPTION
  11 /*      fifo_rdwr_bug creates a FIFO and opens it read-write mode.
  12 /*      On BSD/OS 3.1 select() will report that the FIFO is readable
  13 /*      even before any data is written to it. Doing an actual read
  14 /*      causes the read to block; a non-blocking read fails.
  15 /* DIAGNOSTICS
  16 /*      Problems are reported to the standard error stream.
  17 /* LICENSE
  18 /* .ad
  19 /* .fi
  20 /*      The Secure Mailer license must be distributed with this software.
  21 /* AUTHOR(S)
  22 /*      Wietse Venema
  23 /*      IBM T.J. Watson Research
  24 /*      P.O. Box 704
  25 /*      Yorktown Heights, NY 10598, USA
  26 /*--*/
  27
  28 #include <sys_defs.h>
  29 #include <sys/time.h>
  30 #include <sys/param.h>
  31 #include <sys/stat.h>
  32 #include <stdio.h>
  33 #include <fcntl.h>
  34 #include <signal.h>
  35 #include <unistd.h>
  36 #include <stdlib.h>
  37 #include <string.h>
  38
  39 #define FIFO_PATH       "test-fifo"
  40 #define perrorexit(s)   { perror(s); exit(1); }
  41
  42 static void cleanup(void)
  43 {
  44     printf("Removing fifo %s...\n", FIFO_PATH);
  45     if (unlink(FIFO_PATH))
  46         perrorexit("unlink");
  47     printf("Done.\n");
  48 }
  49
  50 int     main(int unused_argc, char **unused_argv)
  51 {
  52     struct timeval tv;
  53     fd_set  read_fds;
  54     fd_set  except_fds;
  55     int     fd;
  56
  57     (void) unlink(FIFO_PATH);
  58
  59     printf("Creating fifo %s...\n", FIFO_PATH);
  60     if (mkfifo(FIFO_PATH, 0600) < 0)
  61         perrorexit("mkfifo");
  62
  63     printf("Opening fifo %s, read-write mode...\n", FIFO_PATH);
  64     if ((fd = open(FIFO_PATH, O_RDWR, 0)) < 0) {
  65         perror("open");
  66         cleanup();
  67         exit(1);
  68     }
  69     printf("Selecting the fifo for readability...\n");
  70     FD_ZERO(&read_fds);
  71     FD_SET(fd, &read_fds);
  72     FD_ZERO(&except_fds);
  73     FD_SET(fd, &except_fds);
  74     tv.tv_sec = 1;
  75     tv.tv_usec = 0;
  76
  77     switch (select(fd + 1, &read_fds, (fd_set *) 0, &except_fds, &tv)) {
  78     case -1:
  79         perrorexit("select");
  80     default:
  81         if (FD_ISSET(fd, &read_fds)) {
  82             printf("Opening a fifo read-write makes it readable!!\n");
  83             break;
  84         }
  85     case 0:
  86         printf("The fifo is not readable, as it should be.\n");
  87         break;
  88     }
  89     cleanup();
  90     exit(0);
  91 }