Re: [Xen-devel] Detecting PV drivers

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 4 Apr 2013, Jon Ludlam wrote:
> Hi,
> 
> I'm trying find out the best way of detecting whether PV drivers have 
> loaded in an HVM guest. For example, this is so we can decide whether or 
> not to wait for a response from the guest when suspending.
> 
> I think the best way of doing this is to find out whether the hypercall 
> page has been populated or not, as this is the first thing that any PV 
> drivers will have to do, but I don't know how to detect this, or even if 
> this is possible - is there any way of finding this out?
> 
> At the moment we're currently thinking of looking at status of the 
> callback IRQ, which is the second thing that the Citrix PV drivers 
> currently do, but I'm not sure about any other drivers. Would this be a 
> reasonable thing to do if we can't detect the hypercall page?

This is exactly what libxl does right now, see:

tools/libxl/libxl_dom.c:libxl__domain_suspend_common_callback

Libxl also checks the state of HVM_PARAM_ACPI_S_STATE.

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