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Re: [Qemu-block] [Qemu-devel] Behavior of QMP "query-block"

From: Kevin Wolf
Subject: Re: [Qemu-block] [Qemu-devel] Behavior of QMP "query-block"
Date: Fri, 26 May 2017 22:02:32 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 26.05.2017 um 18:55 hat John Snow geschrieben:
> On 05/26/2017 07:40 AM, Kevin Wolf wrote:
> > There is one completely crazy thing that Xen does with respect to disks.
> > Instead of having support for their PV disks (i.e. virtio-blk, just
> > different) in the BIOS, they add _both_ an IDE disk and a PV disk to the
> > VM, so that the bootloader or non-PV-aware guest OSes can access the IDE
> > disk, for which they most certainly do have drivers. As soon as a driver
> > for the PV disk is loaded, however, that driver calls a hypervisor
> > function that removes all the IDE disks from the VM and leaves only the
> > PV ones there, so that the PV-aware guest doesn't see two same disks.
> > 
> > I suspect that what you're seeing initially is the IDE disks, and when
> > the PV driver is loaded, they disappear.
> Sure, but does that mean that you'd see *no* block devices via a query
> afterwards?

I believe xen_disk creates an anonymous BlockBackend, so it wouldn't
appear in 'info block'. Though remembering that Xen does weird things is
enough for me, I don't really want to know all the details that I am
lucky enough to have forgotten. And trust me, neither do you.


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