Dynamic creation and passing of IPC channels

[Tobias Stumpf]

Hello,

On Thu, 2013-12-12 at 17:57 +0100, Robert Kaiser wrote:
> Hi Björn,
> 
> Thanks for your response.
> 
> Am 12.12.2013 09:56, schrieb Björn Döbel:
> > Hi Robert,
> >
> > [..]
> > >>> Capabilities are passed around through standard IPC. The
> > >>> difference is that you don't put them into the UTCB's message
> > >>> registers but instead you out a send flexpage into the UTCB
> > >>> buffer registers. Note, that the receiver must be willing to
> > >>> receive and therefore has to add a receive flexpage on its side
> > >>> beforehand.
> > >>>
> > >>>>> Can anyone point me to some helpful documentation or maybe
> > >>>>> an example I could cannibalize to implement this
> > >>>>> (preferably in C, but C++ code would surely be helpful
> > >>>>> too)?
> > >>> Unfortunately, there's no example that does exactly what you
> > >>> want. But you might want to look at the following two:
> > >>>
> > >>> * l4/pkg/examples/libs/l4re/streammap demonstrates delegation
> > >>> of resources (memory pages in this case) from a server to a
> > >>> client. Sending cap fpages is similar - you basically replace
> > >>> Rcv_fpage::mem() with Rcv_fpage::obj() etc.
> > >>>
> > >>> * l4/pkg/examples/libs/l4re/c++/clntsrv_ns is an adaptation of
> > >>> l4/pkg/examples/clntsrv that passes capabilities the other way
> > >>> round. The client creates an IPC gate, sends it to the server
> > >>> through an L4Re namespace, and the server then obtains this
> > >>> channel and binds a server-side thread to receive messages
> > >>> through this channel.
> > > I *sort of* got this working, however there is a problem which I
> > > don't understand.
> > Would you mind sharing your example code? This would make it easier to
> > understand what's going on.
> 
> I hope it is OK to send mails with attachments to the mailing list? If
> so, you'll find my source code attached. In file client_c.c, line 85/85,
> you'll find a  commented-out ipc_receive() call followed by an
> ipc_wait() call.

I think the problem is the first parameter of ipc_receive. The parameter
specifies the object from which you would like to receive a message.

You wrote that you would like to receive a message from the IPC gate,
but IMO you have to specify the thread from which you would like to
receive a message.

Have a look on the following examples
    examples/sys/utcb-ipc/main.c
    examples/sys/aliens/main.c

Best regards,
Tobias