Dataspaces and sub-region mapping

[Daniel Waddington]

Thanks Norman.  One last question...  

If I create a class which inherits from Dataspace_capability I assume
the RPC marshalling/unmarshalling can't deal with it properly?

struct X : Genode::Dataspace_capability
{
  addr_t phys;
};

So I can avoid adding extra parameters.

Daniel

On Tue, 2013-07-02 at 08:37 +0200, Norman Feske wrote:
> Hi Daniel,
> 
> > I have a server which own as Ram_dataspace and dishes it out to client's
> > by using sub-rm attachments.
> > 
> > If I pass back to the client the Dataspace_capability for the sub-rm, am
> > I correct in saying that the client cannot get to the physical address
> > of the mapped region since this is a Dataspace not a Ram_dataspace?
> > This this case I'd need to pass it back explicitly as an extra param.
> 
> that's correct. A managed dataspace is assembled out of (potentially)
> multiply other dataspaces, each located at a different physical address
> range. As there is no single physical contiguous address range for the
> whole managed dataspace, we cannot return a meaningful value as
> 'phys_addr'. Hence, you'd need to add an extra interface for querying
> the physical address of (a portion of) the managed dataspace.
> 
> Given your description, I guess, you are using a managed dataspace to
> emulate RAM dataspace, which can be transparently revoked, or migrated
> to another physical location?
> 
> > Also, can you clarify the difference between Dataspace and Ram_dataspace
> > and how you can convert (if at all) between the two?
> 
> There is no functional difference. The dataspace type merely denotes the
> interface from where the dataspace originated from. E.g., a
> 'Rom_dataspace' originates from 'Rom_session', an 'Io_mem_dataspace'
> originates from 'Io_mem_session', etc. Because all those types are
> derived from the 'Dataspace' base type, you can use a 'static_cap_cast'
> to convert the types. E.g.,
> 
>   Ram_dataspace ram_ds_cap;
>   Dataspace     ds_cap;
>   ...
>   ds_cap = static_cap_cast<Dataspace>(ram_ds_cap);
> 
> The capability-type-casting rules are analogous to using 'static_cast'
> for C++ types. The cast function templates are located at:
> 
>   base/include/base/capability.h
> 
> Cheers
> Norman
>