Ok, I think I figured out a proper solution, for clarity I will
reiterate the entire solution. It's a lengthy mail, but please do
read it and tell me what you guys think about it.
We want to implement a .defs file with control procedures, which can
ofcourse be independant of libchannel. The only real requirement of
the procedueres is that they have a mach_port_t parameter (like all(?)
procedures that opperate on a file.)
The control server for such a subsytem, will consist of the server
module generated from the .defs file, the corresponding stubs and a
function table struct. The function table will have a pointer for
each procedure in .defs, typically with the same signature except with
the port exchanged for a channel, and also subsystem id of the .defs
file.
The stubs jobs will be to determine which channel is implemented by
the given port, find the function table stored in the channel
associated with this subsystem and then forward the call to the right
function in the table (exchanging port and channel.)
To make this possible libchannel provides the following functions.
error_t
channel_trans_find_channel (mach_port_t port,
struct channel **channel)
Find and return in CHANNEL the channel that underlies PORT. This
function is to be implemented by the translator using libchannel.
(implementing it in channelio should be trivial as it only has one
node.)
XXX a channel_t *channel_trans_find_channel (mach_port_t) signature
might be more useful, as it can be used as a mig intrans function.
Decisions, decisions...
error_t
channel_find_control_interface (const *channel, int subsystem_id
void **ft)
Find and return in FT the function table in CHANNEL that implements
the subsystem SUBSYSTEM_ID.
A stub would then look something like this.
error_t
keyboard_S_get_mode (mach_port_t port, int *mode)
{
struct channel *channel;
struct keyboard_ft *ft;
error_t err;
err = channel_trans_find_channel (port, &channel)
if (err)
return err;
err = channel_find_control_interface (channel, KEYBOARD_SUBSYSTEM_ID,
&if)
if (err)
return err;
if (iface->get_mode)
return iface->get_mode (channel, mode)
return EOPNOTSUPP;
}
A channel will need to provide a list of demuxer functions and a
mapping from subsystem ids to function tables. The channel's class
will be repsonsible for filling these in by either providing
implementations itself or use the contents of a sub-channel's lists.
Note that the lists can not be in the class itself. For instance, a
keyboard channel can only provide a keyboard control inteface not a
mouse one, even though a mouse channel is a member of the device
class.
Finally, libchannel will provide a demuxer that uses the demuxers in
the channel. This is done simply be going through the list until a
demuxer accepts the message.
Cheers,
Fredrik
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