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Date: Tue, 18 Feb 2014 14:10:48 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PULL 00/20] acpi,pc,pci fixes and enhancements
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, xen-devel@lists.xensource.com, "Michael S. Tsirkin" <mst@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, armbru@redhat.com, Anthony Liguori <aliguori@amazon.com>, Anthony.Perard@citrix.com

Il 18/02/2014 13:45, Stefano Stabellini ha scritto:
> Disk unplug: hw/ide/piix.c:pci_piix3_xen_ide_unplug (see the beginning
> of the email :-P).
> It is called by hw/xen/xen_platform.c:platform_fixed_ioport_writew, in
> response to the guest writing to a magic ioport specifically to unplug
> the emulated disk.
> With this patch after the guest boots I can still access both xvda and
> sda for the same disk, leading to fs corruptions.

Ok, the last paragraph is what I was missing.

So this is dc->unplug for the PIIX3 IDE device.  Because PCI declares a 
hotplug handler, dc->unplug is not called anymore.

But unlike other dc->unplug callbacks, pci_piix3_xen_ide_unplug doesn't 
free the device, it just drops the disks underneath.  I think the 
simplest solution is to _not_ make it a dc->unplug callback at all, and 
call pci_piix3_xen_ide_unplug from unplug_disks instead of qdev_unplug. 
  qdev_unplug means "ask guest to start unplug", which is not what Xen 
wants to do here.

Paolo