fork.c

Glibc 2.3.2源代码(解压后有100多M)

		  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]))
		    LOSE;
		}
	      else
		{
		  /* Skip the name we use for any of our own thread ports.  */
		  mach_msg_type_number_t j;
		  for (j = 0; j < nthreads; ++j)
		    if (portnames[i] == threads[j])
		      break;
		  if (j < nthreads)
		    continue;

		  /* Copy our own send right.  */
		  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))
		LOSE;
	      if (insert == MACH_PORT_NULL)
		continue;
	      if (insert == portnames[i] &&
		  (porttypes[i] & MACH_PORT_TYPE_DEAD_NAME))
		/* This is a dead name; allocate another dead name
		   with the same name in the child.  */
	      allocate_dead_name:
		err = __mach_port_allocate_name (newtask,
						 MACH_PORT_RIGHT_DEAD_NAME,
						 portnames[i]);
	      else
		/* Insert the chosen send right into the child.  */
		err = __mach_port_insert_right (newtask,
						portnames[i],
						insert, insert_type);
	      switch (err)
		{
		case 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);
		    break;
		  }

		case KERN_INVALID_CAPABILITY:
		  /* The port just died.  It was a send right,
		     and now it's a dead name.  */
		  goto allocate_dead_name;

		default:
		  LOSE;
		  break;

		case KERN_SUCCESS:
		  /* 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)))
		    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;

      /* All state has now been copied from the parent.  It is safe to
	 resume other parent threads.  */
      resume_threads ();

      /* Create the child main user thread and signal thread.  */
      if ((err = __thread_create (newtask, &thread)) ||
	  (err = __thread_create (newtask, &sigthread)))
	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, ss->thread)) ||
	  (err = __mach_port_insert_right (newtask, ss->thread,
					   thread, MACH_MSG_TYPE_COPY_SEND)))
	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, ss->thread,
				       MACH_PORT_RIGHT_SEND,
				       thread_refs)))
	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))))
	LOSE;
      if (sigthread_refs > 1 &&
	  (err = __mach_port_mod_refs (newtask, _hurd_msgport_thread,
				       MACH_PORT_RIGHT_SEND,
				       sigthread_refs - 1)))
	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)
	  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 (_hurd_msgport_thread,
				    MACHINE_THREAD_STATE_FLAVOR,
				    (natural_t *) &state, &statecount))
	LOSE;
#if STACK_GROWTH_UP
#define THREADVAR_SPACE (__hurd_threadvar_max \
			 * sizeof *__hurd_sightread_variables)
      if (__hurd_sigthread_stack_base == 0)
	{
	  state.SP &= __hurd_threadvar_stack_mask;
	  state.SP += __hurd_threadvar_stack_offset + THREADVAR_SPACE;
	}
      else
	state.SP = __hurd_sigthread_stack_base;
#else
      if (__hurd_sigthread_stack_end == 0)
	{
	  /* The signal thread has a normal stack assigned by cthreads.
	     The threadvar_stack variables conveniently tell us how
	     to get to the highest address in the stack, just below
	     the per-thread variables.  */
	  state.SP &= __hurd_threadvar_stack_mask;
	  state.SP += __hurd_threadvar_stack_offset;
	}
      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,
				    (natural_t *) &state, statecount))
	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.  */
      _hurd_longjmp_thread_state (&state, env, 1);
      if (err = __thread_set_state (thread, MACHINE_THREAD_STATE_FLAVOR,
				    (natural_t *) &state, statecount))
	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)))
	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)))
	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);

      resume_threads ();

      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 (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 one of the (exactly) two threads in this new task, we
	 will take the task-global signals.  */
      _hurd_sigthread = ss->thread;

      /* Claim our sigstate structure and unchain the rest: the
	 threads 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.  Before we finish cleaning up,
	 we will reclaim the signal thread's sigstate structure (if
	 it had one).  */
      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;
      __mutex_unlock (&_hurd_siglock);

      /* 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));

      /* Forking clears the trace flag.  */
      __sigemptyset (&_hurdsig_traced);

      /* 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);

      /* Reclaim the signal thread's sigstate structure and free the
	 other old sigstate structures.  */
      while (oldstates != NULL)
	{
	  struct hurd_sigstate *next = oldstates->next;

	  if (oldstates->thread == _hurd_msgport_thread)
	    {
	      /* If we have a second signal state structure then we
		 must have been through here before--not good.  */
	      assert (_hurd_sigstates->next == 0);
	      _hurd_sigstates->next = oldstates;
	      oldstates->next = 0;
	    }
	  else
	    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.  */
  {
    void *const *p;
    for (p = symbol_set_first_element (_hurd_fork_locks);
	 ! symbol_set_end_p (_hurd_fork_locks, p);
	 ++p)
      __mutex_unlock (*p);
  }

  _hurd_critical_section_unlock (ss);

  return err ? __hurd_fail (err) : pid;
}
libc_hidden_def (__fork)

weak_alias (__fork, fork)