RE: [PATCH 2/2] ata_piix: defer disks to the Hyper-V drivers by default

[KY Srinivasan <kys@microsoft.com>]

> -----Original Message-----
> From: Alan Cox [mailto:alan@lxorguk.ukuu.org.uk]
> Sent: Saturday, April 14, 2012 12:02 PM
> To: Andy Whitcroft
> Cc: Jeff Garzik; linux-ide@vger.kernel.org; linux-kernel@vger.kernel.org; KY
> Srinivasan; Mike Sterling
> Subject: Re: [PATCH 2/2] ata_piix: defer disks to the Hyper-V drivers by default
> 
> O> +#ifdef CONFIG_X86
> > +	/* On Hyper-V hypervisors the disks are exposed on both the emulated
> > +	 * SATA controller and on the paravirtualised drivers.  The CD/DVD
> > +	 * devices are only exposed on the emulated controller.  Request we
> > +	 * ignore ATA devices on this host.
> > +	 */
> > +	if (prefer_ms_hyperv && x86_hyper == &x86_hyper_ms_hyperv) {
> > +		host->flags |= ATA_HOST_IGNORE_ATA;
> > +		dev_info(&pdev->dev, "Hyper-V hypervisor detected, ignoring
> ATA disks\n");
> > +	}
> > +#endif
> 
> Does hyper-v not set its own unique and identifable pci
> subvendor/subdevice ?

Number of elements of the virtual BIOS we present the guest can be used
to detect that we are running on Hyper-V. Additionally, we are exporting state based
on CPU detection which is what Andy is using here. As far as I know these are the only
ways to detect that we are running on Hyper-V. 

Regards,

K. Y
> 
> Alan
> 
>