From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55680) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dELVU-0003uH-2z for qemu-devel@nongnu.org; Fri, 26 May 2017 16:06:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dELVT-0007oi-3g for qemu-devel@nongnu.org; Fri, 26 May 2017 16:06:44 -0400 Date: Fri, 26 May 2017 16:06:30 -0400 From: Konrad Rzeszutek Wilk Message-ID: <20170526200630.GA3609@char.us.oracle.com> References: <539d9960-d554-032f-3e88-b2531743a0a1@redhat.com> <20170526114023.GI7211@noname.str.redhat.com> <4626709f-2af0-ae9e-089d-089c918cfe44@redhat.com> <20170526200232.GA4340@noname.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170526200232.GA4340@noname.redhat.com> Subject: Re: [Qemu-devel] [Qemu-block] Behavior of QMP "query-block" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: John Snow , Bruno Alvisio , qemu-devel@nongnu.org, Qemu-block On Fri, May 26, 2017 at 10:02:32PM +0200, Kevin Wolf wrote: > 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 Not hypervisor. It calls the PCI device which is emulated in QEMU. That "unplugs" the IDE. > > > 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. Keep in mind that PV drivers are kernel drivers. Unless the qdisk driver is used - and then you should see that as well. > > Kevin >