Re: [Xen-devel] Qemu upstream drive question

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-02-16 at 10:53 +0000, Daniel Castro wrote:
> Hello All,
> 
> When a HVM guest is started upstream qemu presents the emulated drives
> as PCI devices or ata drives?

> If more than drive is present how can I know which drive is which in xenstore?

Emulated devices do not appear in xenstore.

Some PV devices may have an emulated equivalent but the rule of thumb is
that an OS should only use either PV or Emulated devices and not mix and
match.

In Linux we implement this by requiring that the emulated devices are
unplugged before we will use the PV path.

In principal you can infer which Emulated device might matches a PV
device, the file docs/misc/vbd-interface.txt in the xen tree gives some
hints about this, but basically PV disks 0..3 can correspond to the
first four IDE devices (primary-master, primary-slave, secondary-master
& secondary-slave).

I presume you are asking in the context of SeaBIOS. In that context you
could argue against unplugging because the guest OS may want to use
emulated devices, however I would suggest that for simplicity for time
being you just unplug the emulated devices before you enable the PV
path.

Ian.



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