Re: [Qemu-devel] [PULL 02/15] docs: VM Generation ID device description

[Marc-André Lureau]

Hi

On Thu, Apr 13, 2017 at 1:17 AM Marc-André Lureau <
address@hidden> wrote:

> Hi
>
> On Thu, Apr 13, 2017 at 1:03 AM Ben Warren <address@hidden> wrote:
>
> On Apr 12, 2017, at 1:47 PM, Marc-André Lureau <address@hidden>
> wrote:
>
> Hi
>
> On Thu, Apr 13, 2017 at 12:25 AM Ben Warren <address@hidden>
> wrote:
>
> On Apr 12, 2017, at 1:22 PM, Marc-André Lureau <address@hidden>
> wrote:
>
> Hi
>
> On Thu, Apr 13, 2017 at 12:17 AM Ben Warren <address@hidden>
> wrote:
>
> On Apr 12, 2017, at 1:06 PM, Marc-André Lureau <address@hidden>
> wrote:
>
> +Device Usage:
> +-------------
> +
> +The device has one property, which may be only be set using the command
> line:
> +
> +  guid - sets the value of the GUID.  A special value "auto" instructs
> +         QEMU to generate a new random GUID.
> +
> +For example:
> +
> +  QEMU  -device vmgenid,guid="324e6eaf-d1d1-4bf6-bf41-b9bb6c91fb87"
> +  QEMU  -device vmgenid,guid=auto
>
>
> The default will keep uuid to null, should it be documented? Wouldn't it
> make sense to default to auto?
>
> There is no default - you have to supply a value. It’s up to whatever
> software is managing VM lifecycle to decide what value to pass in.  Always
> setting to ‘auto’ will cause a lot of churn within Windows that may or may
> not be acceptable to your use case.
>
>
> Why would you have a vmgenid device if it's always null? Does that please
> some windows use-cases as well?
>
>
> I don’t get what you mean by this.  What device is always null?  Either
> the device is instantiated or it isn’t.  If not there, Windows will not
> find a device and I don’t know how derived objects (Invocation ID, etc.)
> are handled.
>
>
> If you start a VM without specifying guid argument, you'll always have a
> genid null uuid, event after a migration (this could have been handled by
> qemu without requiring management layer, no?). I don't understand why auto
> would create more churn than what the management layer would do by setting
> new uuid for each VM started. Could you explain?
>
> Looks like there’s a bug.  GUID should be a mandatory parameter.
>
>
> Not necessarily a bug, if the guid can be changed when starting a "new"
> VM, which I think should work.
>
> However, I didn't manage to get your driver noticing the acpi event. I
> tried to migrate/save & restore, and no vmgenid_notify kernel messages came
> out, nor notices got incremented. How did you test it?
>
>

Actually I was using an old bios, now I can change the guid and the guest
notices the change.

 { "execute": "qom-set", "arguments": { "path":
"/machine/peripheral-anon/device[1]", "property": "guid", "value": "..." } }

works, the guest noticed the change and the new value can be read. I don't
know what else would be required (except a better API) to allow QMP to
modify it.

thanks
-- 
Marc-André Lureau