Re: How to clone a port right

[Carl Fredrik Hammar]

Hi,

On Tue, Jul 07, 2009 at 09:24:27PM +0300, Sergiu Ivanov wrote:
>   /* Opens the port on which to set the mountee.  */
>   error_t
>     open_port (int flags, mach_port_t * underlying,
>                mach_msg_type_name_t * underlying_type, task_t task,
>                void *cookie)
>   {
>     err = 0;
> 
>     /* Create a port to `np`.  */
>     newpi = netfs_make_protid
>       (netfs_make_peropen (np, flags, NULL), user);
>     if (!newpi)
>       {
>         iohelp_free_iouser (user);
>         return errno;
>       }
> 
>     *underlying = underlying_port = ports_get_send_right (newpi);
>     *underlying_type = MACH_MSG_TYPE_COPY_SEND;
> 
>     ports_port_deref (newpi);
> 
>     return err;
>   }                             /*open_port */
> 
> [...]
>
> Now the question: can the reason for such failure be the fact that the
> port right stored in underlying_node is used both in unionmount and in
> the mountee?  If so, is there a way to clone the port right?

This issue has been resolved in IRC, but I'll answer the question
for the record.  The port right is copied by mach_msg, if its type
is MACH_MSG_TYPE_COPY_SEND.  And this is the type you passed in
UNDERLYING_TYPE, so it is copied.  To move it you use ..._MOVE_SEND,
you can also create a send right from a receive right with ..._MAKE_SEND.

Regards,
  Fredrik