Kevin Lawton wrote:
>
> A couple quick thoughts on this special guest OS driver interface...
>
> There will be a need for such drivers for multiple devices, if we want to get the
>most out of plex86. Video, disk,
> network card, etc... Thus we should define a simple and generic interface from the
>guest to the host.
that sounds ok to me
> For efficiency and simplicity, it is most beneficial if the guest OS driver uses a
>memory buffer which is locked
> down in guest memory, so we don't have to worry about page faults. I'm thinking the
>driver writes a packet
> of information, to this memory buffer, and passes some information regarding the
>location of that packet via IO ports. This tells
> the VM where to find the packet, and it can then redirect this info to the
>corresponding host user
> code which handles the data.
>
> We might have a packet like this:
>
> - Packet physical address
>
> - Magic Number
> - Packet length (not including header)
> - Channel ID (in case there are multiple data channels for a device)
> - Return buffer address (if needed)
> - Return buffer size (if needed)
> - Data (driver specific)
>
> The guest driver would tell the VM about this packet by a single dword write,
>specifying the address of the packet itself. The
> magic number in the packet would double check this is meant for our interface.
I assume we would have some kind of "register callback" functions and
the Channel ID will be used to call the correct "device" function?
it might be "better" to specify as less as possible in the packet
(enough to identify the channel id, since for different types of
devices, each may have their own requirements of buffers, etc)... it's
probably better to let the "device callback" handle this kind of
information.
> The question is what kind of addresses to use. If the guest could specify physical
>addresses, that would simplify things.
then it's probably the best way to implement some testing code.
> If we specify linear addresses, then each host user space driver component will need
>to call a function to do the translation
> from linear --> physical memory, so that it can access the guest's phy memory.
is there a specific advantage of using the linear address?
--
Best regards,
Jeroen Janssen
+++
The Patrician relaxed, in a way which only then drew gentle attention to
the foregoing moment of tension.
-- (Terry Pratchett, Men At Arms)
+++
