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Date: Mon, 14 Jun 2010 11:59:54 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH] monitor: Add force option support to pci_del
	command
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Marcos Oviedo <moviedo.maillist@gmail.com>, qemu-devel@nongnu.org

On 06/09/2010 09:27 AM, Gerd Hoffmann wrote:
>   Hi,
>
>> This make sense when you mistakenly add a pci device on a -s -S
>> scenario, like the scenario described on the following bug:
>> https://bugs.launchpad.net/qemu/+bug/544367.
>
> It doesn't IMHO.
>
>> When ACPI-based hotplug support is present on the guest and we run
>> pci_del with the force option, the hotplug events will still be
>> generated to the guest and the guest still will trigger the EJx event,
>> which will end by calling pciej_write() on qemu side. This function will
>> do nothing on a -f and pci hotplug support scenario, as the pci device
>> was previously removed by pci_del.
>
> And in case the guest wants to do anything (like flushing dirty 
> buffers) before triggering the EJx event it will horribly fail.
>
> If the guest is stopped while unplugging the device the unplug should 
> happen as soon as the guest is unpaused.

This is a case where the fundamental problem is that the pci_del command 
should block until the guest has actually responded to the request.

pci_del returning with no error and yet not having the operation 
complete is certainly a usability issue.

Regards,

Anthony Liguori

> cheers,
>   Gerd
>
>
>