Re: [Qemu-devel] [PATCH V15 1/5] docs: vm generation id device's description

[Gal Hammer]

On 27/04/2015 16:55, Michael S. Tsirkin wrote:
> On Mon, Apr 27, 2015 at 02:19:47PM +0300, Gal Hammer wrote:
> > Signed-off-by: Gal Hammer <address@hidden>
> > ---
> >   docs/specs/vmgenid.txt | 35 +++++++++++++++++++++++++++++++++++
> >   1 file changed, 35 insertions(+)
> >   create mode 100644 docs/specs/vmgenid.txt
> >
> > diff --git a/docs/specs/vmgenid.txt b/docs/specs/vmgenid.txt
> > new file mode 100644
> > index 0000000..86ce6ab
> > --- /dev/null
> > +++ b/docs/specs/vmgenid.txt
> > @@ -0,0 +1,35 @@
> > +VIRTUAL MACHINE GENERATION ID
> > +=============================
> > +
> > +Copyright (C) 2014 Red Hat, Inc.
>
> It's 2015, isn't it?
>
> > +
> > +This work is licensed under the terms of the GNU GPL, version 2 or later.
> > +See the COPYING file in the top-level directory.
> > +
> > +===
> > +
> > +The VM generation ID (vmgenid) device is an emulated device which
> > +exposes a 128-bit, cryptographically random, integer value identifier.
>
> The value is up to user, let's not claim it's cryptographically random.

I'll add a sentence that clear this issue.

> > +This allows management applications (e.g. libvirt) to notify the guest
> > +operating system when the virtual machine is executed with a different
> > +configuration (e.g. snapshot execution or creation from a template).
> > +
> > +This is specified on the web at: http://go.microsoft.com/fwlink/?LinkId=260709
> > +
> > +---
> > +
> > +The vmgenid device is a sysbus device with the following ACPI ID:
> > +"QEMU0002".
>
> No one is expected to locate it using that ID, right?

Nope. According to the specs the device should be identified through its 
_CID and/or _DDN names.

> > +
> > +The device adds a "vmgenid.uuid" property, which can be modified using
> > +the -global command line argument or the QMP interface.
> > +
> > +The device uses a fixed memory resource: 0xfedf0000-0xfedf000f to store
> > +the GUID's buffer.
> > +
> > +According to the specification, any change to the GUID executes an
> > +ACPI notification. The vmgenid device triggers the GPE._E00 which
> > +executes the ACPI Notify operation.
> > +
> > +Although not specified in Microsoft's document, it is assumed that the
> > +device is expected to use the little-endian system.
> > --
> > 2.1.0