On Tue, Apr 25, 2006 at 07:28:54PM -0400, Jonathan S. Shapiro wrote:
> > > > A user logs in to a terminal, and his session receives the
> > > > corresponding capabilities. One of them will be for the usb bus,
> > > > where he can register any device driver he wants....
> > >
> > > Are the device drivers (D) provided by the operating system or the
> > > user?
> > By the user. The idea is that you can bring your own driver for your
> > device, and don't need the system administrator to install it in order to
> > use your device. I'd expect a Hurd system to be able to do that. :-)
> A large (and increasing) number of drivers have access to physical DMA.
> As a result, letting the user bring their own drivers is exactly
> equivalent to letting them install their own OS.
Obviously user-provided drivers cannot be allowed to do that directly (but
they may do it through calls to the framework). However, for user-provided
drivers I was thinking about devices that the users brings with him. There it
would be the bus driver (usb, firewire) which does the DMA calls, and the
actual driver just talks to the bus driver.
An exception is (I think) pcmcia, which is so "directly" wired to the machine
that it would do the DMA itself. For this, user drivers will be slower than
system drivers due to the indirection. But I still like it to be possible for
the user to use his own drivers. :-)
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