posix/tst-fork.c

   1 /* Tests for fork.
   2    Copyright (C) 2000-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <error.h>
  21 #include <stdlib.h>
  22 #include <string.h>
  23 #include <unistd.h>
  24 #include <wait.h>
  25
  26
  27 static const char testdata[] = "This is a test";
  28 static const char testdata2[] = "And here we go again";
  29
  30
  31 int
  32 main (void)
  33 {
  34   const char *tmpdir = getenv ("TMPDIR");
  35   char buf[100];
  36   size_t tmpdirlen;
  37   char *name;
  38   int fd;
  39   pid_t pid;
  40   pid_t ppid;
  41   off_t off;
  42   int status;
  43
  44   if (tmpdir == NULL || *tmpdir == '\0')
  45     tmpdir = "/tmp";
  46   tmpdirlen = strlen (tmpdir);
  47
  48   name = (char *) malloc (tmpdirlen + strlen ("/forkXXXXXX") + 1);
  49   if (name == NULL)
  50     error (EXIT_FAILURE, errno, "cannot allocate file name");
  51
  52   mempcpy (mempcpy (name, tmpdir, tmpdirlen),
  53            "/forkXXXXXX", sizeof ("/forkXXXXXX"));
  54
  55   /* Open our test file.   */
  56   fd = mkstemp (name);
  57   if (fd == -1)
  58      error (EXIT_FAILURE, errno, "cannot open test file `%s'", name);
  59
  60   /* Make sure it gets removed.  */
  61   unlink (name);
  62
  63   /* Write some data.  */
  64   if (write (fd, testdata, strlen (testdata)) != strlen (testdata))
  65     error (EXIT_FAILURE, errno, "cannot write test data");
  66
  67   /* Get the position in the stream.  */
  68   off = lseek (fd, 0, SEEK_CUR);
  69   if (off == (off_t) -1 || off != strlen (testdata))
  70     error (EXIT_FAILURE, errno, "wrong file position");
  71
  72   /* Get the parent PID.  */
  73   ppid = getpid ();
  74
  75   /* Now fork of the process.  */
  76   pid = fork ();
  77   if (pid == 0)
  78     {
  79       /* One little test first: the PID must have changed.  */
  80       if (getpid () == ppid)
  81         error (EXIT_FAILURE, 0, "child and parent have same PID");
  82
  83       /* Test the `getppid' function.  */
  84       pid = getppid ();
  85       if (pid == (pid_t) -1 ? errno != ENOSYS : pid != ppid)
  86         error (EXIT_FAILURE, 0,
  87                "getppid returned wrong PID (%ld, should be %ld)",
  88                (long int) pid, (long int) ppid);
  89
  90       /* This is the child.  First get the position of the descriptor.  */
  91       off = lseek (fd, 0, SEEK_CUR);
  92       if (off == (off_t) -1 || off != strlen (testdata))
  93         error (EXIT_FAILURE, errno, "wrong file position in child");
  94
  95       /* Reset the position.  */
  96       if (lseek (fd, 0, SEEK_SET) != 0)
  97         error (EXIT_FAILURE, errno, "cannot reset position in child");
  98
  99       /* Read the data.  */
 100       if (read (fd, buf, sizeof buf) != strlen (testdata))
 101         error (EXIT_FAILURE, errno, "cannot read data in child");
 102
 103       /* Compare the data.  */
 104       if (memcmp (buf, testdata, strlen (testdata)) != 0)
 105         error (EXIT_FAILURE, 0, "data comparison failed in child");
 106
 107       /* Reset position again.  */
 108       if (lseek (fd, 0, SEEK_SET) != 0)
 109         error (EXIT_FAILURE, errno, "cannot reset position again in child");
 110
 111       /* Write new data.  */
 112       if (write (fd, testdata2, strlen (testdata2)) != strlen (testdata2))
 113         error (EXIT_FAILURE, errno, "cannot write new data in child");
 114
 115       /* Close the file.  This must not remove it.  */
 116       close (fd);
 117
 118       _exit (0);
 119     }
 120   else if (pid < 0)
 121     /* Something went wrong.  */
 122     error (EXIT_FAILURE, errno, "cannot fork");
 123
 124   /* Wait for the child.  */
 125   if (waitpid (pid, &status, 0) != pid)
 126     error (EXIT_FAILURE, 0, "Oops, wrong test program terminated");
 127
 128   if (WTERMSIG (status) != 0)
 129     error (EXIT_FAILURE, 0, "Child terminated incorrectly");
 130   status = WEXITSTATUS (status);
 131
 132   if (status == 0)
 133     {
 134       /* Test whether the child wrote the right data.  First test the
 135          position.  It must be the same as in the child.  */
 136       if (lseek (fd, 0, SEEK_CUR) != strlen (testdata2))
 137         error (EXIT_FAILURE, 0, "file position not changed");
 138
 139       if (lseek (fd, 0, SEEK_SET) != 0)
 140         error (EXIT_FAILURE, errno, "cannot reset file position");
 141
 142       if (read (fd, buf, sizeof buf) != strlen (testdata2))
 143         error (EXIT_FAILURE, errno, "cannot read new data");
 144
 145       if (memcmp (buf, testdata2, strlen (testdata2)) != 0)
 146         error (EXIT_FAILURE, 0, "new data not read correctly");
 147     }
 148
 149   return status;
 150 }