DDE Linux26 in the Hurd
christian.helmuth at genode-labs.com
Fri Jan 29 12:37:03 CET 2010
On Thu, Jan 28, 2010 at 08:28:07PM +0800, Da Zheng wrote:
> You missed my point. I understand that each driver runs in a separate program.
> The problem is that a device has to find the bus where it is located. In the
> current implementation, a driver can only scan 32 devices. If we have 33 devices
> in the system, its driver thinks there isn't such a device and fails to work.
Please, do not take the limitation to 32 devices for granted. It was
just a reasonable guess at implemenation time and is power of 2.
> So I suggest why not let the logical bus contains all devices in the system.
> Thus, the driver can always find its device no matter where the device is
> located, and we don't need an IO manager to pre-configure the logical PCI bus as
> Bjoern said, which seems quite complex.
I disagree here. In a modern OS you need access control and resource
management also on driver level, as nobody wants his VGA driver mess
with the USB host controller. The access policy to I/O resources in
our design is implemented by a special system component. This
component configures the virtual busses mentioned before, whereas each
driver gets its own virtual bus, i.e., view on the real hardware. You
may look into http://os.inf.tu-dresden.de/papers_ps/haenel-beleg.pdf.
Lukas gives a good summary of our ideas in its Architecture section.
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