Re: A set of "standard" virtual devices?
- From: Arnd Bergmann <arnd@xxxxxxxx>
- Date: Tue, 3 Apr 2007 23:51:16 +0200
On Tuesday 03 April 2007, Jeremy Fitzhardinge wrote:
That said, something like USB is probably the best bet for this kind of
low-performance device. I think. Not that I really know anything about
USB.
USB has the disadvantage that it is more complex than PCI and requires
significantly more code to simulate on the host side.
On the plus side, I think it should be possible to implement a virtual
USB host on s390, which is not possible with PCI, but that again takes
a lot of work to implement.
One interesting aspect of the PS3 hypervisor is that some of the
low-speed interfaces are implemented as a virtual UART, meaning
something that only has read and write operations and uses an
interrupt for flow control. The implementation in
drivers/ps3/vuart.c is probably more complex than what we want
as a generic transport mechanism, but simply having a bidirectional
data stream sounds like an ideal abstraction for the "simple"
case. Some more or less obvious users of this include:
- console
- additional tty
- random
- slow network (using ppp)
- printer
- watchdog
- hid (e.g. mouse)
- system management (like ps3)
- fast network (in combination with
shared memory segment)
The transport can be hypervisor specific, e.g. there could be
a virtual PCI serial port on kvm, an hcall interface on the ps3
and a virtual CTC on s390 (kidding), while all of them can have
the same kind of hardware _behind_ the serial connection.
Arnd <><
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