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

[Gal Hammer <ghammer@redhat.com>]

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 <ghammer@redhat.com>
>> ---
>>   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