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Re: [Xen-devel] blktap for HVM guests without PV-on-HVM drivers

  • To: Muli Ben-Yehuda <muli@xxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Mon, 28 Jan 2008 14:03:36 +0000
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Mon, 28 Jan 2008 06:04:52 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AchhtpMa0V2xpc2pEdyKMQAX8io7RQ==
  • Thread-topic: [Xen-devel] blktap for HVM guests without PV-on-HVM drivers

On 28/1/08 13:57, "Muli Ben-Yehuda" <muli@xxxxxxxxxx> wrote:

> On Mon, Jan 28, 2008 at 01:53:06PM +0000, Keir Fraser wrote:
>> Currently qemu cannot access the PV backend driver data path. So PV
>> backends are only accessible using PV-on-HVM drivers within the HVM
>> guest.
> Thanks, good to know I wasn't missing something obvious. Are there any
> particular obstacles to fixing it, or is it a simple matter of
> programming?

It's a small matter of plumbing. There's currently no local interface to
allow dom0 userspace to get at the dom0 backend driver datapath.

Currently the only way to allow booting from a virtual disk that will later
be accessed via PV-on-HVM is to give qemu-dm direct access to the underlying
virtual-disk image (e.g., qcow or whatever) which obviously has
synchronisation issues when block requests start flying in on a completely
different data path once PV-on-HVM drivers are installed. So getting things
plumbed properly would be very nice indeed!

 -- Keir

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