Re: [Qemu-devel] [PATCH v13 0/8] pv event interface between host and guest

[Gleb Natapov <gleb@redhat.com>]

On Wed, Mar 06, 2013 at 04:46:58PM +0800, Hu Tao wrote:
> On Sun, Mar 03, 2013 at 11:17:38AM +0200, Gleb Natapov wrote:
> > On Thu, Feb 28, 2013 at 08:13:10PM +0800, Hu Tao wrote:
> > > This series implements a new interface, kvm pv event, to notify host when
> > > some events happen in guest. Right now there is one supported event: guest
> > > panic.
> > > 
> > What other event do you have in mind? Is interface generic enough to
> > accommodate future, yet unknown, events. It allows to pass only one
> > integer specifying even type, what if additional info is needed? My be
> 
> guest crash, lockup, or warning.[1] But the first purpose is to do panic
> notification(panic event). Since at the point the guest is panicked, I
> think it's better to keep the interface as simple as possible.
> 
> [1] http://wiki.qemu.org/Features/PVCrashDetection
> 
> > stop pretending that device is generic and make it do once thing but do
> 
> you mean make the interface just do panic notification?
> 
Yes.

> > it well? For generic even passing interface (whatever it may be needed
> > for) much more powerful virtio should be used.
> > 
> > On implementation itself I do not understand why is this kvm specific.
> > The only thing that makes it so is that you hook device initialization
> > into guest kvm initialization code, but this is obviously incorrect.
> > What stops QEMU tcg or Xen from reusing the same device for the same
> > purpose except the artificial limitation in a guest.
> > 
> > Reading data from a random ioports is not how you discover platform
> > devices in 21 century (and the data you read from unassigned port is not
> > guarantied to be zero, it may depend on QEMU version), you use ACPI for
> > that and Marcelo already pointed that to you. Having little knowledge of
> > ACPI (we all do) is not a good reason to not doing it. We probably need
> > to reserve QEMU specific ACPI Plug and Play hardware ID to define our own
> 
> Do we have to request the ID from some orgnazation?
> 
A Plug and Play ID or ACPI ID can be obtained by sending e-mail to pnpid@microsoft.com.

> > devices. After that you will be able to create device with _HID(QEMU0001)
> 
> QMU0001, I think. EISA ID requires it to have only 3 letters for PNP ID.
Right, but I am not sure we need EISA ID here. Why not ACPI ID like in
the example from the spec:

Name (_HID, "MSFT0003") // Vendor-defined device

--
			Gleb.