__fork.c

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		{
		  insert = MACH_PORT_NULL;
		  record_refs = &sigthread_refs;
		  /* Allocate a dead name right as a placeholder.  */
		  if (err = __mach_port_allocate_name
		      (newtask, MACH_PORT_RIGHT_DEAD_NAME, portnames[i]))
		    goto lose;
		}
	      else
		{
		  /* Skip the name we use for any of our own thread ports.  */
		  unsigned int j;
		  for (j = 0; j < nthreads; ++j)
		    if (portnames[i] == threads[j])
		      break;
		  if (j < nthreads)
		    continue;

		  insert = portnames[i];
		}
	      /* Find out how many user references we have for
		 the send right with this name.  */
	      if (err = __mach_port_get_refs (__mach_task_self (),
					      portnames[i],
					      MACH_PORT_RIGHT_SEND,
					      record_refs ?: &refs))
		goto lose;
	      if (insert == MACH_PORT_NULL)
		continue;
	      /* Insert the chosen send right into the child.  */
	      err = __mach_port_insert_right (newtask,
					      portnames[i],
					      insert,
					      MACH_MSG_TYPE_COPY_SEND);
	      if (err == KERN_NAME_EXISTS)
		{
		  /* It already has a send right under this name (?!).
		     Well, it starts out with a send right for its task
		     port, and inherits the bootstrap and exception ports
		     from us.  */
		  mach_port_t childport;
		  mach_msg_type_name_t poly;
		  assert (__mach_port_extract_right (newtask, portnames[i],
						     MACH_MSG_TYPE_COPY_SEND,
						     &childport, &poly) == 0 &&
			  childport == insert &&
			  __mach_port_deallocate (__mach_task_self (),
						  childport) == 0);
		}
	      else if (err)
		goto lose;
	      /* Give the child as many user references as we have.  */
	      if (refs > 1 &&
		  (err = __mach_port_mod_refs (newtask,
					       portnames[i],
					       MACH_PORT_RIGHT_SEND,
					       refs - 1)))
		goto lose;
	    }
	}

      /* Unlock the standard port cells.  The child must unlock its own
	 copies too.  */
      for (i = 0; i < _hurd_nports; ++i)
	__spin_unlock (&_hurd_ports[i].lock);
      ports_locked = 0;

      /* Unlock the signal state.  The child must unlock its own copy too.  */
      unlockss ();

      /* Create the child main user thread and signal thread.  */
      if ((err = __thread_create (newtask, &thread)) ||
	  (err = __thread_create (newtask, &sigthread)))
	goto lose;

      /* Insert send rights for those threads.  We previously allocated
         dead name rights with the names we want to give the thread ports
         in the child as placeholders.  Now deallocate them so we can use
         the names.  */
      if ((err = __mach_port_deallocate (newtask, thread_self)) ||
	  (err = __mach_port_insert_right (newtask, thread_self,
					   thread, MACH_MSG_TYPE_COPY_SEND)))
	goto lose;
      /* We have one extra user reference created at the beginning of this
	 function, accounted for by mach_port_names (and which will thus be
	 accounted for in the child below).  This extra right gets consumed
	 in the child by the store into _hurd_sigthread in the child fork.  */
      if (thread_refs > 1 &&
	  (err = __mach_port_mod_refs (newtask, thread_self,
				       MACH_PORT_RIGHT_SEND,
				       thread_refs - 1)))
	goto lose;
      if ((_hurd_msgport_thread != MACH_PORT_NULL) /* Let user have none.  */
	  && ((err = __mach_port_deallocate (newtask, _hurd_msgport_thread)) ||
	      (err = __mach_port_insert_right (newtask, _hurd_msgport_thread,
					       sigthread,
					       MACH_MSG_TYPE_COPY_SEND))))
	goto lose;
      if (sigthread_refs > 1 &&
	  (err = __mach_port_mod_refs (newtask, _hurd_msgport_thread,
				       MACH_PORT_RIGHT_SEND,
				       sigthread_refs - 1)))
	goto lose;

      /* This seems like a convenient juncture to copy the proc server's
	 idea of what addresses our argv and envp are found at from the
	 parent into the child.  Since we happen to know that the child
	 shares our memory image, it is we who should do this copying.  */
      {
	vm_address_t argv, envp;
	err = (__USEPORT (PROC, __proc_get_arg_locations (port, &argv, &envp))
	       ?: __proc_set_arg_locations (newproc, argv, envp));
	if (err)
	  goto lose;
      }
	    
      /* Set the child signal thread up to run the msgport server function
	 using the same signal thread stack copied from our address space.
	 We fetch the state before longjmp'ing it so that miscellaneous
	 registers not affected by longjmp (such as i386 segment registers)
	 are in their normal default state.  */
      statecount = MACHINE_THREAD_STATE_COUNT;
      if (err = __thread_get_state (sigthread, MACHINE_THREAD_STATE_FLAVOR,
				    (int *) &state, &statecount))
	goto lose;
#if STACK_GROWTH_UP
      state.SP = __hurd_sigthread_stack_base;
#else
      state.SP = __hurd_sigthread_stack_end;
#endif      
      MACHINE_THREAD_STATE_SET_PC (&state,
				   (unsigned long int) _hurd_msgport_receive);
      if (err = __thread_set_state (sigthread, MACHINE_THREAD_STATE_FLAVOR,
				    (int *) &state, statecount))
	goto lose;
      /* We do not thread_resume SIGTHREAD here because the child
	 fork needs to do more setup before it can take signals.  */

      /* Set the child user thread up to return 1 from the setjmp above.  */
      if (err = __thread_get_state (thread, MACHINE_THREAD_STATE_FLAVOR,
				    (int *) &state, &statecount))
	goto lose;
      _hurd_longjmp_thread_state (&state, env, 1);
      if (err = __thread_set_state (thread, MACHINE_THREAD_STATE_FLAVOR,
				    (int *) &state, statecount))
	goto lose;

      /* Get the PID of the child from the proc server.  We must do this
	 before calling proc_child below, because at that point any
	 authorized POSIX.1 process may kill the child task with SIGKILL.  */
      if (err = __USEPORT (PROC, __proc_task2pid (port, newtask, &pid)))
	goto lose;

      /* Register the child with the proc server.  It is important that
	 this be that last thing we do before starting the child thread
	 running.  Once proc_child has been done for the task, it appears
	 as a POSIX.1 process.  Any errors we get must be detected before
	 this point, and the child must have a message port so it responds
	 to POSIX.1 signals.  */
      if (err = __USEPORT (PROC, __proc_child (port, newtask)))
	goto lose;

      /* This must be the absolutely last thing we do; we can't assume that
	 the child will remain alive for even a moment once we do this.  We
	 ignore errors because we have committed to the fork and are not
	 allowed to return them after the process becomes visible to
	 POSIX.1 (which happened right above when we called proc_child).  */
      (void) __thread_resume (thread);

    lose:
      if (ports_locked)
	for (i = 0; i < _hurd_nports; ++i)
	  __spin_unlock (&_hurd_ports[i].lock);

      if (newtask != MACH_PORT_NULL)
	{
	  if (err)
	    __task_terminate (newtask);
	  __mach_port_deallocate (__mach_task_self (), newtask);
	}
      if (thread != MACH_PORT_NULL)
	__mach_port_deallocate (__mach_task_self (), thread);
      if (sigthread != MACH_PORT_NULL)
	__mach_port_deallocate (__mach_task_self (), sigthread);
      if (newproc != MACH_PORT_NULL)
	__mach_port_deallocate (__mach_task_self (), newproc);
      if (thread_self != MACH_PORT_NULL)
	__mach_port_deallocate (__mach_task_self (), thread_self);

      if (portnames)
	__vm_deallocate (__mach_task_self (),
			 (vm_address_t) portnames,
			 nportnames * sizeof (*portnames));
      if (porttypes)
	__vm_deallocate (__mach_task_self (),
			 (vm_address_t) porttypes,
			 nporttypes * sizeof (*porttypes));
      if (threads)
	{
	  for (i = 0; i < nthreads; ++i)
	    __mach_port_deallocate (__mach_task_self (), threads[i]);
	  __vm_deallocate (__mach_task_self (),
			   (vm_address_t) threads,
			   nthreads * sizeof (*threads));
	}

      /* Run things that want to run in the parent to restore it to
	 normality.  Usually prepare hooks and parent hooks are
	 symmetrical: the prepare hook arrests state in some way for the
	 fork, and the parent hook restores the state for the parent to
	 continue executing normally.  */
      RUN_HOOK (_hurd_fork_parent_hook, ());
    }
  else
    {
      struct hurd_sigstate *oldstates;

      /* We are the child task.  Unlock the standard port cells, which were
         locked in the parent when we copied its memory.  The parent has
         inserted send rights with the names that were in the cells then.  */
      for (i = 0; i < _hurd_nports; ++i)
	__spin_unlock (&_hurd_ports[i].lock);

      /* We are the only thread in this new task, so we will
	 take the task-global signals.  */
      _hurd_sigthread = thread_self;

      /* Unchain the sigstate structures for threads that existed in the
	 parent task but don't exist in this task (the child process).
	 Delay freeing them until later because some of the further setup
	 and unlocking might be required for free to work.  */
      oldstates = _hurd_sigstates;
      if (oldstates == ss)
	oldstates = ss->next;
      else
	{
	  while (_hurd_sigstates->next != ss)
	    _hurd_sigstates = _hurd_sigstates->next;
	  _hurd_sigstates->next = ss->next;
	}
      ss->next = NULL;
      _hurd_sigstates = ss;

      /* Unlock our copies of the signal state locks.  */
      unlockss ();

      /* Fetch our new process IDs from the proc server.  No need to
	 refetch our pgrp; it is always inherited from the parent (so
	 _hurd_pgrp is already correct), and the proc server will send us a
	 proc_newids notification when it changes.  */
      err = __USEPORT (PROC, __proc_getpids (port, &_hurd_pid, &_hurd_ppid,
					     &_hurd_orphaned));

      /* Run things that want to run in the child task to set up.  */
      RUN_HOOK (_hurd_fork_child_hook, ());

      /* Set up proc server-assisted fault recovery for the signal thread.  */
      _hurdsig_fault_init ();

      /* Start the signal thread listening on the message port.  */
      if (!err)
	err = __thread_resume (_hurd_msgport_thread);

      /* Free the old sigstate structures.  */
      while (oldstates != NULL)
	{
	  struct hurd_sigstate *next = oldstates->next;
	  free (oldstates);
	  oldstates = next;
	}
      /* XXX what to do if we have any errors here? */

      pid = 0;
    }

  /* Unlock things we locked before creating the child task.
     They are locked in both the parent and child tasks.  */
  for (i = 0; i < _hurd_fork_locks.n; ++i)
    __mutex_unlock (_hurd_fork_locks.locks[i]);

  return err ? __hurd_fail (err) : pid;
}