text: /* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
  /* dbus-spawn.c Wrapper around fork/exec
   * 
   * Copyright (C) 2002, 2003, 2004  Red Hat, Inc.
   * Copyright (C) 2003 CodeFactory AB
   *
   * Licensed under the Academic Free License version 2.1
   * 
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   * 
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   *
   */
  #include "dbus-spawn.h"
  #include "dbus-sysdeps-unix.h"
  #include "dbus-internals.h"
  #include "dbus-test.h"
  #include "dbus-protocol.h"
  
  #include <unistd.h>
  #include <fcntl.h>
  #include <signal.h>
  #include <sys/wait.h>
  #include <stdlib.h>
  #ifdef HAVE_ERRNO_H
  #include <errno.h>
  #endif
  
  /**
   * @addtogroup DBusInternalsUtils
   * @{
   */
  
  /*
   * I'm pretty sure this whole spawn file could be made simpler,
   * if you thought about it a bit.
   */
  
  /**
   * Enumeration for status of a read()
   */
  typedef enum
  {
    READ_STATUS_OK,    /**< Read succeeded */
    READ_STATUS_ERROR, /**< Some kind of error */
    READ_STATUS_EOF    /**< EOF returned */
  } ReadStatus;
  
  static ReadStatus
  read_ints (int        fd,
  	   int       *buf,
  	   int        n_ints_in_buf,
  	   int       *n_ints_read,
  	   DBusError *error)
  {
    size_t bytes = 0;    
    ReadStatus retval;
    
    _DBUS_ASSERT_ERROR_IS_CLEAR (error);
  
    retval = READ_STATUS_OK;
    
    while (TRUE)
      {
        size_t chunk;
        ssize_t to_read;
  
        to_read = sizeof (int) * n_ints_in_buf - bytes;
  
        if (to_read == 0)
          break;
  
      again:
        
        chunk = read (fd,
                      ((char*)buf) + bytes,
                      to_read);
        
        if (chunk < 0 && errno == EINTR)
          goto again;
            
        if (chunk < 0)
          {
            dbus_set_error (error,
  			  DBUS_ERROR_SPAWN_FAILED,
  			  "Failed to read from child pipe (%s)",
  			  _dbus_strerror (errno));
  
            retval = READ_STATUS_ERROR;
            break;
          }
        else if (chunk == 0)
          {
            retval = READ_STATUS_EOF;
            break; /* EOF */
          }
        else /* chunk > 0 */
  	bytes += chunk;
      }
  
    *n_ints_read = (int)(bytes / sizeof(int));
  
    return retval;
  }
  
  static ReadStatus
  read_pid (int        fd,
            pid_t     *buf,
            DBusError *error)
  {
    size_t bytes = 0;    
    ReadStatus retval;
    
    _DBUS_ASSERT_ERROR_IS_CLEAR (error);
  
    retval = READ_STATUS_OK;
    
    while (TRUE)
      {
        size_t chunk;    
        ssize_t to_read;
        
        to_read = sizeof (pid_t) - bytes;
  
        if (to_read == 0)
          break;
  
      again:
        
        chunk = read (fd,
                      ((char*)buf) + bytes,
                      to_read);
        if (chunk < 0 && errno == EINTR)
          goto again;
            
        if (chunk < 0)
          {
            dbus_set_error (error,
  			  DBUS_ERROR_SPAWN_FAILED,
  			  "Failed to read from child pipe (%s)",
  			  _dbus_strerror (errno));
  
            retval = READ_STATUS_ERROR;
            break;
          }
        else if (chunk == 0)
          {
            retval = READ_STATUS_EOF;
            break; /* EOF */
          }
        else /* chunk > 0 */
  	bytes += chunk;
      }
  
    return retval;
  }
  
  /* The implementation uses an intermediate child between the main process
   * and the grandchild. The grandchild is our spawned process. The intermediate
   * child is a babysitter process; it keeps track of when the grandchild
   * exits/crashes, and reaps the grandchild.
   */
  
  /* Messages from children to parents */
  enum
  {
    CHILD_EXITED,            /* This message is followed by the exit status int */
    CHILD_FORK_FAILED,       /* Followed by errno */
    CHILD_EXEC_FAILED,       /* Followed by errno */
    CHILD_PID                /* Followed by pid_t */
  };
  
  /**
   * Babysitter implementation details
   */
  struct DBusBabysitter
  {
    int refcount; /**< Reference count */
  
    char *executable; /**< executable name to use in error messages */
    
    int socket_to_babysitter; /**< Connection to the babysitter process */
    int error_pipe_from_child; /**< Connection to the process that does the exec() */
    
    pid_t sitter_pid;  /**< PID Of the babysitter */
    pid_t grandchild_pid; /**< PID of the grandchild */
  
    DBusWatchList *watches; /**< Watches */
  
    DBusWatch *error_watch; /**< Error pipe watch */
    DBusWatch *sitter_watch; /**< Sitter pipe watch */
  
    int errnum; /**< Error number */
    int status; /**< Exit status code */
    unsigned int have_child_status : 1; /**< True if child status has been reaped */
    unsigned int have_fork_errnum : 1; /**< True if we have an error code from fork() */
    unsigned int have_exec_errnum : 1; /**< True if we have an error code from exec() */
  };
  
  static DBusBabysitter*
  _dbus_babysitter_new (void)
  {
    DBusBabysitter *sitter;
  
    sitter = dbus_new0 (DBusBabysitter, 1);
    if (sitter == NULL)
      return NULL;
  
    sitter->refcount = 1;
  
    sitter->socket_to_babysitter = -1;
    sitter->error_pipe_from_child = -1;
    
    sitter->sitter_pid = -1;
    sitter->grandchild_pid = -1;
  
    sitter->watches = _dbus_watch_list_new ();
    if (sitter->watches == NULL)
      goto failed;
    
    return sitter;
  
   failed:
    _dbus_babysitter_unref (sitter);
    return NULL;
  }
  
  /**
   * Increment the reference count on the babysitter object.
   *
   * @param sitter the babysitter
   * @returns the babysitter
   */
  DBusBabysitter *
  _dbus_babysitter_ref (DBusBabysitter *sitter)
  {
    _dbus_assert (sitter != NULL);
    _dbus_assert (sitter->refcount > 0);
    
    sitter->refcount += 1;
  
    return sitter;
  }
  
  /**
   * Decrement the reference count on the babysitter object.
   * When the reference count of the babysitter object reaches
   * zero, the babysitter is killed and the child that was being
   * babysat gets emancipated.
   *
   * @param sitter the babysitter
   */
  void
  _dbus_babysitter_unref (DBusBabysitter *sitter)
  {
    _dbus_assert (sitter != NULL);
    _dbus_assert (sitter->refcount > 0);
    
    sitter->refcount -= 1;
    if (sitter->refcount == 0)
      {      
        if (sitter->socket_to_babysitter >= 0)
          {
            /* If we haven't forked other babysitters
             * since this babysitter and socket were
             * created then this close will cause the
             * babysitter to wake up from poll with
             * a hangup and then the babysitter will
             * quit itself.
             */
            _dbus_close_socket (sitter->socket_to_babysitter, NULL);
            sitter->socket_to_babysitter = -1;
          }
  
        if (sitter->error_pipe_from_child >= 0)
          {
            _dbus_close_socket (sitter->error_pipe_from_child, NULL);
            sitter->error_pipe_from_child = -1;
          }
  
        if (sitter->sitter_pid > 0)
          {
            int status;
            int ret;
  
            /* It's possible the babysitter died on its own above 
             * from the close, or was killed randomly
             * by some other process, so first try to reap it
             */
            ret = waitpid (sitter->sitter_pid, &status, WNOHANG);
  
            /* If we couldn't reap the child then kill it, and
             * try again
             */
            if (ret == 0)
              kill (sitter->sitter_pid, SIGKILL);
  
          again:
            if (ret == 0)
              ret = waitpid (sitter->sitter_pid, &status, 0);
  
            if (ret < 0)
              {
                if (errno == EINTR)
                  goto again;
                else if (errno == ECHILD)
                  _dbus_warn ("Babysitter process not available to be reaped; should not happen\n");
                else
                  _dbus_warn ("Unexpected error %d in waitpid() for babysitter: %s\n",
                              errno, _dbus_strerror (errno));
              }
            else
              {
                _dbus_verbose ("Reaped %ld, waiting for babysitter %ld\n",
                               (long) ret, (long) sitter->sitter_pid);
                
                if (WIFEXITED (sitter->status))
                  _dbus_verbose ("Babysitter exited with status %d\n",
                                 WEXITSTATUS (sitter->status));
                else if (WIFSIGNALED (sitter->status))
                  _dbus_verbose ("Babysitter received signal %d\n",
                                 WTERMSIG (sitter->status));
                else
                  _dbus_verbose ("Babysitter exited abnormally\n");
              }
  
            sitter->sitter_pid = -1;
          }
        
        if (sitter->error_watch)
          {
            _dbus_watch_invalidate (sitter->error_watch);
            _dbus_watch_unref (sitter->error_watch);
            sitter->error_watch = NULL;
          }
  
        if (sitter->sitter_watch)
          {
            _dbus_watch_invalidate (sitter->sitter_watch);
            _dbus_watch_unref (sitter->sitter_watch);
            sitter->sitter_watch = NULL;
          }
        
        if (sitter->watches)
          _dbus_watch_list_free (sitter->watches);
  
        dbus_free (sitter->executable);
        
        dbus_free (sitter);
      }
  }
  
  static ReadStatus
  read_data (DBusBabysitter *sitter,
             int             fd)
  {
    int what;
    int got;
    DBusError error = DBUS_ERROR_INIT;
    ReadStatus r;
  
    r = read_ints (fd, &what, 1, &got, &error);
  
    switch (r)
      {
      case READ_STATUS_ERROR:
        _dbus_warn ("Failed to read data from fd %d: %s\n", fd, error.message);
        dbus_error_free (&error);
        return r;
  
      case READ_STATUS_EOF:
        return r;
  
      case READ_STATUS_OK:
        break;
      }
    
    if (got == 1)
      {
        switch (what)
          {
          case CHILD_EXITED:
          case CHILD_FORK_FAILED:
          case CHILD_EXEC_FAILED:
            {
              int arg;
              
              r = read_ints (fd, &arg, 1, &got, &error);
  
              switch (r)
                {
                case READ_STATUS_ERROR:
                  _dbus_warn ("Failed to read arg from fd %d: %s\n", fd, error.message);
                  dbus_error_free (&error);
                  return r;
                case READ_STATUS_EOF:
                  return r;
                case READ_STATUS_OK:
                  break;
                }
              
              if (got == 1)
                {
                  if (what == CHILD_EXITED)
                    {
                      sitter->have_child_status = TRUE;
                      sitter->status = arg;
                      sitter->errnum = 0;
                      _dbus_verbose ("recorded child status exited = %d signaled = %d exitstatus = %d termsig = %d\n",
                                     WIFEXITED (sitter->status), WIFSIGNALED (sitter->status),
                                     WEXITSTATUS (sitter->status), WTERMSIG (sitter->status));
                    }
                  else if (what == CHILD_FORK_FAILED)
                    {
                      sitter->have_fork_errnum = TRUE;
                      sitter->errnum = arg;
                      _dbus_verbose ("recorded fork errnum %d\n", sitter->errnum);
                    }
                  else if (what == CHILD_EXEC_FAILED)
                    {
                      sitter->have_exec_errnum = TRUE;
                      sitter->errnum = arg;
                      _dbus_verbose ("recorded exec errnum %d\n", sitter->errnum);
                    }
                }
            }
            break;
          case CHILD_PID:
            {
              pid_t pid = -1;
  
              r = read_pid (fd, &pid, &error);
              
              switch (r)
                {
                case READ_STATUS_ERROR:
                  _dbus_warn ("Failed to read PID from fd %d: %s\n", fd, error.message);
                  dbus_error_free (&error);
                  return r;
                case READ_STATUS_EOF:
                  return r;
                case READ_STATUS_OK:
                  break;
                }
              
              sitter->grandchild_pid = pid;
              
              _dbus_verbose ("recorded grandchild pid %d\n", sitter->grandchild_pid);
            }
            break;
          default:
            _dbus_warn ("Unknown message received from babysitter process\n");
            break;
          }
      }
  
    return r;
  }
  
  static void
  close_socket_to_babysitter (DBusBabysitter *sitter)
  {
    _dbus_verbose ("Closing babysitter\n");
    _dbus_close_socket (sitter->socket_to_babysitter, NULL);
    sitter->socket_to_babysitter = -1;
  }
  
  static void
  close_error_pipe_from_child (DBusBabysitter *sitter)
  {
    _dbus_verbose ("Closing child error\n");
    _dbus_close_socket (sitter->error_pipe_from_child, NULL);
    sitter->error_pipe_from_child = -1;
  }
  
  static void
  handle_babysitter_socket (DBusBabysitter *sitter,
                            int             revents)
  {
    /* Even if we have POLLHUP, we want to keep reading
     * data until POLLIN goes away; so this function only
     * looks at HUP/ERR if no IN is set.
     */
    if (revents & _DBUS_POLLIN)
      {
        _dbus_verbose ("Reading data from babysitter\n");
        if (read_data (sitter, sitter->socket_to_babysitter) != READ_STATUS_OK)
          close_socket_to_babysitter (sitter);
      }
    else if (revents & (_DBUS_POLLERR | _DBUS_POLLHUP))
      {
        close_socket_to_babysitter (sitter);
      }
  }
  
  static void
  handle_error_pipe (DBusBabysitter *sitter,
                     int             revents)
  {
    if (revents & _DBUS_POLLIN)
      {
        _dbus_verbose ("Reading data from child error\n");
        if (read_data (sitter, sitter->error_pipe_from_child) != READ_STATUS_OK)
          close_error_pipe_from_child (sitter);
      }
    else if (revents & (_DBUS_POLLERR | _DBUS_POLLHUP))
      {
        close_error_pipe_from_child (sitter);
      }
  }
  
  /* returns whether there were any poll events handled */
  static dbus_bool_t
  babysitter_iteration (DBusBabysitter *sitter,
                        dbus_bool_t     block)
  {
    DBusPollFD fds[2];
    int i;
    dbus_bool_t descriptors_ready;
  
    descriptors_ready = FALSE;
    
    i = 0;
  
    if (sitter->error_pipe_from_child >= 0)
      {
        fds[i].fd = sitter->error_pipe_from_child;
        fds[i].events = _DBUS_POLLIN;
        fds[i].revents = 0;
        ++i;
      }
    
    if (sitter->socket_to_babysitter >= 0)
      {
        fds[i].fd = sitter->socket_to_babysitter;
        fds[i].events = _DBUS_POLLIN;
        fds[i].revents = 0;
        ++i;
      }
  
    if (i > 0)
      {
        int ret;
  
        do
          {
            ret = _dbus_poll (fds, i, 0);
          }
        while (ret < 0 && errno == EINTR);
  
        if (ret == 0 && block)
          {
            do
              {
                ret = _dbus_poll (fds, i, -1);
              }
            while (ret < 0 && errno == EINTR);
          }
  
        if (ret > 0)
          {
            descriptors_ready = TRUE;
            
            while (i > 0)
              {
                --i;
                if (fds[i].fd == sitter->error_pipe_from_child)
                  handle_error_pipe (sitter, fds[i].revents);
                else if (fds[i].fd == sitter->socket_to_babysitter)
                  handle_babysitter_socket (sitter, fds[i].revents);
              }
          }
      }
  
    return descriptors_ready;
  }
  
  /**
   * Macro returns #TRUE if the babysitter still has live sockets open to the
   * babysitter child or the grandchild.
   */
  #define LIVE_CHILDREN(sitter) ((sitter)->socket_to_babysitter >= 0 || (sitter)->error_pipe_from_child >= 0)
  
  /**
   * Blocks until the babysitter process gives us the PID of the spawned grandchild,
   * then kills the spawned grandchild.
   *
   * @param sitter the babysitter object
   */
  void
  _dbus_babysitter_kill_child (DBusBabysitter *sitter)
  {
    /* be sure we have the PID of the child */
    while (LIVE_CHILDREN (sitter) &&
           sitter->grandchild_pid == -1)
      babysitter_iteration (sitter, TRUE);
  
    _dbus_verbose ("Got child PID %ld for killing\n",
                   (long) sitter->grandchild_pid);
    
    if (sitter->grandchild_pid == -1)
      return; /* child is already dead, or we're so hosed we'll never recover */
  
    kill (sitter->grandchild_pid, SIGKILL);
  }
  
  /**
   * Checks whether the child has exited, without blocking.
   *
   * @param sitter the babysitter
   */
  dbus_bool_t
  _dbus_babysitter_get_child_exited (DBusBabysitter *sitter)
  {
  
    /* Be sure we're up-to-date */
    while (LIVE_CHILDREN (sitter) &&
           babysitter_iteration (sitter, FALSE))
      ;
  
    /* We will have exited the babysitter when the child has exited */
    return sitter->socket_to_babysitter < 0;
  }
  
  /**
   * Gets the exit status of the child. We do this so implementation specific
   * detail is not cluttering up dbus, for example the system launcher code.
   * This can only be called if the child has exited, i.e. call
   * _dbus_babysitter_get_child_exited(). It returns FALSE if the child
   * did not return a status code, e.g. because the child was signaled
   * or we failed to ever launch the child in the first place.
   *
   * @param sitter the babysitter
   * @param status the returned status code
   * @returns #FALSE on failure
   */
  dbus_bool_t
  _dbus_babysitter_get_child_exit_status (DBusBabysitter *sitter,
                                          int            *status)
  {
    if (!_dbus_babysitter_get_child_exited (sitter))
      _dbus_assert_not_reached ("Child has not exited");
    
    if (!sitter->have_child_status ||
        !(WIFEXITED (sitter->status)))
      return FALSE;
  
    *status = WEXITSTATUS (sitter->status);
    return TRUE;
  }
  
  /**
   * Sets the #DBusError with an explanation of why the spawned
   * child process exited (on a signal, or whatever). If
   * the child process has not exited, does nothing (error
   * will remain unset).
   *
   * @param sitter the babysitter
   * @param error an error to fill in
   */
  void
  _dbus_babysitter_set_child_exit_error (DBusBabysitter *sitter,
                                         DBusError      *error)
  {
    if (!_dbus_babysitter_get_child_exited (sitter))
      return;
  
    /* Note that if exec fails, we will also get a child status
     * from the babysitter saying the child exited,
     * so we need to give priority to the exec error
     */
    if (sitter->have_exec_errnum)
      {
        dbus_set_error (error, DBUS_ERROR_SPAWN_EXEC_FAILED,
                        "Failed to execute program %s: %s",
                        sitter->executable, _dbus_strerror (sitter->errnum));
      }
    else if (sitter->have_fork_errnum)
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY,
                        "Failed to fork a new process %s: %s",
                        sitter->executable, _dbus_strerror (sitter->errnum));
      }
    else if (sitter->have_child_status)
      {
        if (WIFEXITED (sitter->status))
          dbus_set_error (error, DBUS_ERROR_SPAWN_CHILD_EXITED,
                          "Process %s exited with status %d",
                          sitter->executable, WEXITSTATUS (sitter->status));
        else if (WIFSIGNALED (sitter->status))
          dbus_set_error (error, DBUS_ERROR_SPAWN_CHILD_SIGNALED,
                          "Process %s received signal %d",
                          sitter->executable, WTERMSIG (sitter->status));
        else
          dbus_set_error (error, DBUS_ERROR_FAILED,
                          "Process %s exited abnormally",
                          sitter->executable);
      }
    else
      {
        dbus_set_error (error, DBUS_ERROR_FAILED,
                        "Process %s exited, reason unknown",
                        sitter->executable);
      }
  }
  
  /**
   * Sets watch functions to notify us when the
   * babysitter object needs to read/write file descriptors.
   *
   * @param sitter the babysitter
   * @param add_function function to begin monitoring a new descriptor.
   * @param remove_function function to stop monitoring a descriptor.
   * @param toggled_function function to notify when the watch is enabled/disabled
   * @param data data to pass to add_function and remove_function.
   * @param free_data_function function to be called to free the data.
   * @returns #FALSE on failure (no memory)
   */
  dbus_bool_t
  _dbus_babysitter_set_watch_functions (DBusBabysitter            *sitter,
                                        DBusAddWatchFunction       add_function,
                                        DBusRemoveWatchFunction    remove_function,
                                        DBusWatchToggledFunction   toggled_function,
                                        void                      *data,
                                        DBusFreeFunction           free_data_function)
  {
    return _dbus_watch_list_set_functions (sitter->watches,
                                           add_function,
                                           remove_function,
                                           toggled_function,
                                           data,
                                           free_data_function);
  }
  
  static dbus_bool_t
  handle_watch (DBusWatch       *watch,
                unsigned int     condition,
                void            *data)
  {
    DBusBabysitter *sitter = data;
    int revents;
    int fd;
    
    revents = 0;
    if (condition & DBUS_WATCH_READABLE)
      revents |= _DBUS_POLLIN;
    if (condition & DBUS_WATCH_ERROR)
      revents |= _DBUS_POLLERR;
    if (condition & DBUS_WATCH_HANGUP)
      revents |= _DBUS_POLLHUP;
  
    fd = dbus_watch_get_socket (watch);
  
    if (fd == sitter->error_pipe_from_child)
      handle_error_pipe (sitter, revents);
    else if (fd == sitter->socket_to_babysitter)
      handle_babysitter_socket (sitter, revents);
  
    while (LIVE_CHILDREN (sitter) &&
           babysitter_iteration (sitter, FALSE))
      ;
    
    return TRUE;
  }
  
  /** Helps remember which end of the pipe is which */
  #define READ_END 0
  /** Helps remember which end of the pipe is which */
  #define WRITE_END 1
  
  
  /* Avoids a danger in threaded situations (calling close()
   * on a file descriptor twice, and another thread has
   * re-opened it since the first close)
   */
  static int
  close_and_invalidate (int *fd)
  {
    int ret;
  
    if (*fd < 0)
      return -1;
    else
      {
        ret = _dbus_close_socket (*fd, NULL);
        *fd = -1;
      }
  
    return ret;
  }
  
  static dbus_bool_t
  make_pipe (int         p[2],
             DBusError  *error)
  {
    _DBUS_ASSERT_ERROR_IS_CLEAR (error);
    
    if (pipe (p) < 0)
      {
        dbus_set_error (error,
  		      DBUS_ERROR_SPAWN_FAILED,
  		      "Failed to create pipe for communicating with child process (%s)",
  		      _dbus_strerror (errno));
        return FALSE;
      }
  
    return TRUE;
  }
  
  static void
  do_write (int fd, const void *buf, size_t count)
  {
    size_t bytes_written;
    int ret;
    
    bytes_written = 0;
    
   again:
    
    ret = write (fd, ((const char*)buf) + bytes_written, count - bytes_written);
  
    if (ret < 0)
      {
        if (errno == EINTR)
          goto again;
        else
          {
            _dbus_warn ("Failed to write data to pipe!\n");
            exit (1); /* give up, we suck */
          }
      }
    else
      bytes_written += ret;
    
    if (bytes_written < count)
      goto again;
  }
  
  static void
  write_err_and_exit (int fd, int msg)
  {
    int en = errno;
  
    do_write (fd, &msg, sizeof (msg));
    do_write (fd, &en, sizeof (en));
    
    exit (1);
  }
  
  static void
  write_pid (int fd, pid_t pid)
  {
    int msg = CHILD_PID;
    
    do_write (fd, &msg, sizeof (msg));
    do_write (fd, &pid, sizeof (pid));
  }
  
  static void
  write_status_and_exit (int fd, int status)
  {
    int msg = CHILD_EXITED;
    
    do_write (fd, &msg, sizeof (msg));
    do_write (fd, &status, sizeof (status));
    
    exit (0);
  }
  
  static void
  do_exec (int                       child_err_report_fd,
  	 char                    **argv,
  	 char                    **envp,
  	 DBusSpawnChildSetupFunc   child_setup,
  	 void                     *user_data)
  {
  #ifdef DBUS_BUILD_TESTS
    int i, max_open;
  #endif
  
    _dbus_verbose_reset ();
    _dbus_verbose ("Child process has PID " DBUS_PID_FORMAT "\n",
                   _dbus_getpid ());
    
    if (child_setup)
      (* child_setup) (user_data);
  
  #ifdef DBUS_BUILD_TESTS
    max_open = sysconf (_SC_OPEN_MAX);
    
    for (i = 3; i < max_open; i++)
      {
        int retval;
  
        if (i == child_err_report_fd)
          continue;
        
        retval = fcntl (i, F_GETFD);
  
        if (retval != -1 && !(retval & FD_CLOEXEC))
  	_dbus_warn ("Fd %d did not have the close-on-exec flag set!\n", i);
      }
  #endif
  
    if (envp == NULL)
      {
        extern char **environ;
  
        _dbus_assert (environ != NULL);
  
        envp = environ;
      }
    
    execve (argv[0], argv, envp);
    
    /* Exec failed */
    write_err_and_exit (child_err_report_fd,
                        CHILD_EXEC_FAILED);
  }
  
  static void
  check_babysit_events (pid_t grandchild_pid,
                        int   parent_pipe,
                        int   revents)
  {
    pid_t ret;
    int status;
    
    do
      {
        ret = waitpid (grandchild_pid, &status, WNOHANG);
        /* The man page says EINTR can't happen with WNOHANG,
         * but there are reports of it (maybe only with valgrind?)
         */
      }
    while (ret < 0 && errno == EINTR);
  
    if (ret == 0)
      {
        _dbus_verbose ("no child exited\n");
        
        ; /* no child exited */
      }
    else if (ret < 0)
      {
        /* This isn't supposed to happen. */
        _dbus_warn ("unexpected waitpid() failure in check_babysit_events(): %s\n",
                    _dbus_strerror (errno));
        exit (1);
      }
    else if (ret == grandchild_pid)
      {
        /* Child exited */
        _dbus_verbose ("reaped child pid %ld\n", (long) ret);
        
        write_status_and_exit (parent_pipe, status);
      }
    else
      {
        _dbus_warn ("waitpid() reaped pid %d that we've never heard of\n",
                    (int) ret);
        exit (1);
      }
  
    if (revents & _DBUS_POLLIN)
      {
        _dbus_verbose ("babysitter got POLLIN from parent pipe\n");
      }
  
    if (revents & (_DBUS_POLLERR | _DBUS_POLLHUP))
      {
        /* Parent is gone, so we just exit */
        _dbus_verbose ("babysitter got POLLERR or POLLHUP from parent\n");
        exit (0);
      }
  }
  
  static int babysit_sigchld_pipe = -1;
  
  static void
  babysit_signal_handler (int signo)
  {
    char b = '\0';
   again:
    if (write (babysit_sigchld_pipe, &b, 1) <= 0) 
      if (errno == EINTR)
        goto again;
  }
  
  static void
  babysit (pid_t grandchild_pid,
           int   parent_pipe)
  {
    int sigchld_pipe[2];
  
    /* We don't exec, so we keep parent state, such as the pid that
     * _dbus_verbose() uses. Reset the pid here.
     */
    _dbus_verbose_reset ();
    
    /* I thought SIGCHLD would just wake up the poll, but
     * that didn't seem to work, so added this pipe.
     * Probably the pipe is more likely to work on busted
     * operating systems anyhow.
     */
    if (pipe (sigchld_pipe) < 0)
      {
        _dbus_warn ("Not enough file descriptors to create pipe in babysitter process\n");
        exit (1);
      }
  
    babysit_sigchld_pipe = sigchld_pipe[WRITE_END];
  
    _dbus_set_signal_handler (SIGCHLD, babysit_signal_handler);
    
    write_pid (parent_pipe, grandchild_pid);
  
    check_babysit_events (grandchild_pid, parent_pipe, 0);
  
    while (TRUE)
      {
        DBusPollFD pfds[2];
        
        pfds[0].fd = parent_pipe;
        pfds[0].events = _DBUS_POLLIN;
        pfds[0].revents = 0;
  
        pfds[1].fd = sigchld_pipe[READ_END];
        pfds[1].events = _DBUS_POLLIN;
        pfds[1].revents = 0;
        
        if (_dbus_poll (pfds, _DBUS_N_ELEMENTS (pfds), -1) < 0 && errno != EINTR)
          {
            _dbus_warn ("_dbus_poll() error: %s\n", strerror (errno));
            exit (1);
          }
  
        if (pfds[0].revents != 0)
          {
            check_babysit_events (grandchild_pid, parent_pipe, pfds[0].revents);
          }
        else if (pfds[1].revents & _DBUS_POLLIN)
          {
            char b;
            read (sigchld_pipe[READ_END], &b, 1);
            /* do waitpid check */
            check_babysit_events (grandchild_pid, parent_pipe, 0);
          }
      }
    
    exit (1);
  }
  
  /**
   * Spawns a new process. The executable name and argv[0]
   * are the same, both are provided in argv[0]. The child_setup
   * function is passed the given user_data and is run in the child
   * just before calling exec().
   *
   * Also creates a "babysitter" which tracks the status of the
   * child process, advising the parent if the child exits.
   * If the spawn fails, no babysitter is created.
   * If sitter_p is #NULL, no babysitter is kept.
   *
   * @param sitter_p return location for babysitter or #NULL
   * @param argv the executable and arguments
   * @param env the environment (not used on unix yet)
   * @param child_setup function to call in child pre-exec()
   * @param user_data user data for setup function
   * @param error error object to be filled in if function fails
   * @returns #TRUE on success, #FALSE if error is filled in
   */
  dbus_bool_t
  _dbus_spawn_async_with_babysitter (DBusBabysitter          **sitter_p,
                                     char                    **argv,
                                     char                    **env,
                                     DBusSpawnChildSetupFunc   child_setup,
                                     void                     *user_data,
                                     DBusError                *error)
  {
    DBusBabysitter *sitter;
    int child_err_report_pipe[2] = { -1, -1 };
    int babysitter_pipe[2] = { -1, -1 };
    pid_t pid;
    
    _DBUS_ASSERT_ERROR_IS_CLEAR (error);
  
    if (sitter_p != NULL)
      *sitter_p = NULL;
  
    sitter = NULL;
  
    sitter = _dbus_babysitter_new ();
    if (sitter == NULL)
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        return FALSE;
      }
  
    sitter->executable = _dbus_strdup (argv[0]);
    if (sitter->executable == NULL)
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        goto cleanup_and_fail;
      }
    
    if (!make_pipe (child_err_report_pipe, error))
      goto cleanup_and_fail;
  
    _dbus_fd_set_close_on_exec (child_err_report_pipe[READ_END]);
    _dbus_fd_set_close_on_exec (child_err_report_pipe[WRITE_END]);
  
    if (!_dbus_full_duplex_pipe (&babysitter_pipe[0], &babysitter_pipe[1], TRUE, error))
      goto cleanup_and_fail;
  
    _dbus_fd_set_close_on_exec (babysitter_pipe[0]);
    _dbus_fd_set_close_on_exec (babysitter_pipe[1]);
  
    /* Setting up the babysitter is only useful in the parent,
     * but we don't want to run out of memory and fail
     * after we've already forked, since then we'd leak
     * child processes everywhere.
     */
    sitter->error_watch = _dbus_watch_new (child_err_report_pipe[READ_END],
                                           DBUS_WATCH_READABLE,
                                           TRUE, handle_watch, sitter, NULL);
    if (sitter->error_watch == NULL)
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        goto cleanup_and_fail;
      }
          
    if (!_dbus_watch_list_add_watch (sitter->watches,  sitter->error_watch))
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        goto cleanup_and_fail;
      }
        
    sitter->sitter_watch = _dbus_watch_new (babysitter_pipe[0],
                                            DBUS_WATCH_READABLE,
                                            TRUE, handle_watch, sitter, NULL);
    if (sitter->sitter_watch == NULL)
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        goto cleanup_and_fail;
      }
        
    if (!_dbus_watch_list_add_watch (sitter->watches,  sitter->sitter_watch))
      {
        dbus_set_error (error, DBUS_ERROR_NO_MEMORY, NULL);
        goto cleanup_and_fail;
      }
  
    _DBUS_ASSERT_ERROR_IS_CLEAR (error);
    
    pid = fork ();
    
    if (pid < 0)
      {
        dbus_set_error (error,
  		      DBUS_ERROR_SPAWN_FORK_FAILED,
  		      "Failed to fork (%s)",
  		      _dbus_strerror (errno));
        goto cleanup_and_fail;
      }
    else if (pid == 0)
      {
        /* Immediate child, this is the babysitter process. */
        int grandchild_pid;
        
        /* Be sure we crash if the parent exits
         * and we write to the err_report_pipe
         */
        signal (SIGPIPE, SIG_DFL);
  
        /* Close the parent's end of the pipes. */
        close_and_invalidate (&child_err_report_pipe[READ_END]);
        close_and_invalidate (&babysitter_pipe[0]);
        
        /* Create the child that will exec () */
        grandchild_pid = fork ();
        
        if (grandchild_pid < 0)
  	{
  	  write_err_and_exit (babysitter_pipe[1],
  			      CHILD_FORK_FAILED);
            _dbus_assert_not_reached ("Got to code after write_err_and_exit()");
  	}
        else if (grandchild_pid == 0)
  	{
  	  do_exec (child_err_report_pipe[WRITE_END],
  		   argv,
  		   env,
  		   child_setup, user_data);
            _dbus_assert_not_reached ("Got to code after exec() - should have exited on error");
  	}
        else
  	{
            babysit (grandchild_pid, babysitter_pipe[1]);
            _dbus_assert_not_reached ("Got to code after babysit()");
  	}
      }
    else
      {      
        /* Close the uncared-about ends of the pipes */
        close_and_invalidate (&child_err_report_pipe[WRITE_END]);
        close_and_invalidate (&babysitter_pipe[1]);
  
        sitter->socket_to_babysitter = babysitter_pipe[0];
        babysitter_pipe[0] = -1;
        
        sitter->error_pipe_from_child = child_err_report_pipe[READ_END];
        child_err_report_pipe[READ_END] = -1;
  
        sitter->sitter_pid = pid;
  
        if (sitter_p != NULL)
          *sitter_p = sitter;
        else
          _dbus_babysitter_unref (sitter);
  
        dbus_free_string_array (env);
  
        _DBUS_ASSERT_ERROR_IS_CLEAR (error);
        
        return TRUE;
      }
  
   cleanup_and_fail:
  
    _DBUS_ASSERT_ERROR_IS_SET (error);
    
    close_and_invalidate (&child_err_report_pipe[READ_END]);
    close_and_invalidate (&child_err_report_pipe[WRITE_END]);
    close_and_invalidate (&babysitter_pipe[0]);
    close_and_invalidate (&babysitter_pipe[1]);
  
    if (sitter != NULL)
      _dbus_babysitter_unref (sitter);
    
    return FALSE;
  }
  
  /** @} */
  
  #ifdef DBUS_BUILD_TESTS
  
  static void
  _dbus_babysitter_block_for_child_exit (DBusBabysitter *sitter)
  {
    while (LIVE_CHILDREN (sitter))
      babysitter_iteration (sitter, TRUE);
  }
  
  static dbus_bool_t
  check_spawn_nonexistent (void *data)
  {
    char *argv[4] = { NULL, NULL, NULL, NULL };
    DBusBabysitter *sitter = NULL;
    DBusError error = DBUS_ERROR_INIT;
  
    /*** Test launching nonexistent binary */
    
    argv[0] = "/this/does/not/exist/32542sdgafgafdg";
    if (_dbus_spawn_async_with_babysitter (&sitter, argv,
                                           NULL, NULL, NULL,
                                           &error))
      {
        _dbus_babysitter_block_for_child_exit (sitter);
        _dbus_babysitter_set_child_exit_error (sitter, &error);
      }
  
    if (sitter)
      _dbus_babysitter_unref (sitter);
  
    if (!dbus_error_is_set (&error))
      {
        _dbus_warn ("Did not get an error launching nonexistent executable\n");
        return FALSE;
      }
  
    if (!(dbus_error_has_name (&error, DBUS_ERROR_NO_MEMORY) ||
          dbus_error_has_name (&error, DBUS_ERROR_SPAWN_EXEC_FAILED)))
      {
        _dbus_warn ("Not expecting error when launching nonexistent executable: %s: %s\n",
                    error.name, error.message);
        dbus_error_free (&error);
        return FALSE;
      }
  
    dbus_error_free (&error);
    
    return TRUE;
  }
  
  static dbus_bool_t
  check_spawn_segfault (void *data)
  {
    char *argv[4] = { NULL, NULL, NULL, NULL };
    DBusBabysitter *sitter = NULL;
    DBusError error = DBUS_ERROR_INIT;
  
    /*** Test launching segfault binary */
    
    argv[0] = TEST_SEGFAULT_BINARY;
    if (_dbus_spawn_async_with_babysitter (&sitter, argv,
                                           NULL, NULL, NULL,
                                           &error))
      {
        _dbus_babysitter_block_for_child_exit (sitter);
        _dbus_babysitter_set_child_exit_error (sitter, &error);
      }
  
    if (sitter)
      _dbus_babysitter_unref (sitter);
  
    if (!dbus_error_is_set (&error))
      {
        _dbus_warn ("Did not get an error launching segfaulting binary\n");
        return FALSE;
      }
  
    if (!(dbus_error_has_name (&error, DBUS_ERROR_NO_MEMORY) ||
          dbus_error_has_name (&error, DBUS_ERROR_SPAWN_CHILD_SIGNALED)))
      {
        _dbus_warn ("Not expecting error when launching segfaulting executable: %s: %s\n",
                    error.name, error.message);
        dbus_error_free (&error);
        return FALSE;
      }
  
    dbus_error_free (&error);
    
    return TRUE;
  }
  
  static dbus_bool_t
  check_spawn_exit (void *data)
  {
    char *argv[4] = { NULL, NULL, NULL, NULL };
    DBusBabysitter *sitter = NULL;
    DBusError error = DBUS_ERROR_INIT;
  
    /*** Test launching exit failure binary */
    
    argv[0] = TEST_EXIT_BINARY;
    if (_dbus_spawn_async_with_babysitter (&sitter, argv,
                                           NULL, NULL, NULL,
                                           &error))
      {
        _dbus_babysitter_block_for_child_exit (sitter);
        _dbus_babysitter_set_child_exit_error (sitter, &error);
      }
  
    if (sitter)
      _dbus_babysitter_unref (sitter);
  
    if (!dbus_error_is_set (&error))
      {
        _dbus_warn ("Did not get an error launching binary that exited with failure code\n");
        return FALSE;
      }
  
    if (!(dbus_error_has_name (&error, DBUS_ERROR_NO_MEMORY) ||
          dbus_error_has_name (&error, DBUS_ERROR_SPAWN_CHILD_EXITED)))
      {
        _dbus_warn ("Not expecting error when launching exiting executable: %s: %s\n",
                    error.name, error.message);
        dbus_error_free (&error);
        return FALSE;
      }
  
    dbus_error_free (&error);
    
    return TRUE;
  }
  
  static dbus_bool_t
  check_spawn_and_kill (void *data)
  {
    char *argv[4] = { NULL, NULL, NULL, NULL };
    DBusBabysitter *sitter = NULL;
    DBusError error = DBUS_ERROR_INIT;
  
    /*** Test launching sleeping binary then killing it */
  
    argv[0] = TEST_SLEEP_FOREVER_BINARY;
    if (_dbus_spawn_async_with_babysitter (&sitter, argv,
                                           NULL, NULL, NULL,
                                           &error))
      {
        _dbus_babysitter_kill_child (sitter);
        
        _dbus_babysitter_block_for_child_exit (sitter);
        
        _dbus_babysitter_set_child_exit_error (sitter, &error);
      }
  
    if (sitter)
      _dbus_babysitter_unref (sitter);
  
    if (!dbus_error_is_set (&error))
      {
        _dbus_warn ("Did not get an error after killing spawned binary\n");
        return FALSE;
      }
  
    if (!(dbus_error_has_name (&error, DBUS_ERROR_NO_MEMORY) ||
          dbus_error_has_name (&error, DBUS_ERROR_SPAWN_CHILD_SIGNALED)))
      {
        _dbus_warn ("Not expecting error when killing executable: %s: %s\n",
                    error.name, error.message);
        dbus_error_free (&error);
        return FALSE;
      }
  
    dbus_error_free (&error);
    
    return TRUE;
  }
  
  dbus_bool_t
  _dbus_spawn_test (const char *test_data_dir)
  {
    if (!_dbus_test_oom_handling ("spawn_nonexistent",
                                  check_spawn_nonexistent,
                                  NULL))
      return FALSE;
  
    if (!_dbus_test_oom_handling ("spawn_segfault",
                                  check_spawn_segfault,
                                  NULL))
      return FALSE;
  
    if (!_dbus_test_oom_handling ("spawn_exit",
                                  check_spawn_exit,
                                  NULL))
      return FALSE;
  
    if (!_dbus_test_oom_handling ("spawn_and_kill",
                                  check_spawn_and_kill,
                                  NULL))
      return FALSE;
    
    return TRUE;
  }
  #endif
  