Question on sending capability through IPC

[Adam Lackorzynski]

On Sun Apr 01, 2012 at 15:16:24 -0500, Mai, Haohui wrote:
> I'm a little bit confused by how Fiasco.OC sending capabilities through
> IPC. Particularly, it seems that one has to pack the capability in message
> register, rather than buffer register.
> 
> Here is a code sending some capability to the client, which works with
> Fiasco.OC:
> 
> l4_utcb_t * u = l4_utcb();
> l4_utcb_mr_u(u)->mr[0] = ipc_id;
> l4_utcb_mr_u(u)->mr[1] = L4_ITEM_MAP;
> l4_utcb_mr_u(u)->mr[2] = l4_obj_fpage(cap, 0, L4_FPAGE_RWX).raw;
> l4_utcb_br_u(u)->bdr = 0;
> tag = l4_msgtag(label, 1, 1, 0);
> ipc_call(...);
> 
> Notice that the capability is assigned into mr[1] and mr[2], but not br[1]
> and br[2].
> 
> It seems that this behavior is controlled by the constructor of
> L4_snd_item_iter, at kern/l4_buf_iter.cpp:52
> 
>   explicit L4_snd_item_iter(Utcb const *utcb, unsigned offset)
>   : _buf(&utcb->values[offset]),
>     _max(&utcb->values[Utcb::Max_words]) {}
> 
> My question is that whether this is the desired behavior? I didn't find any
> specification on this.

Yes, it's the desired behaviour.



Adam
-- 
Adam                 adam at os.inf.tu-dresden.de
  Lackorzynski         http://os.inf.tu-dresden.de/~adam/