[PATCH 12/18] qemu: capabilities: Add QEMU_CAPS_BLOCKDEV_HOSTDEV_SCSI

[Ján Tomko]

On a Thursday in 2020, Peter Krempa wrote:
>On Thu, Jul 16, 2020 at 00:16:23 +0200, Ján Tomko wrote:
>> On a Friday in 2020, Peter Krempa wrote:
>> > We want to instantiate hostdevs via -blockdev too. Add a separate
>> > capability for them for a clean transition. The new capability will be
>> > enabled when QEMU_CAPS_BLOCKDEV is present once all code is prepared.
>> >
>>
>> What is the benefit here compared to using QEMU_CAPS_BLOCKDEV directly?
>
>It encodes whether the particular VM instance was already started with
>-blockdev used for hostdevs. The benefit ... or rather necessity is that
>we need to handle cases when the VM was started with -drive differently
>on hot-unplug of the hostdev.
>
>I'd have to encode that bit of information somehow regardless of which
>approach is used to actually store it.
>
>> Seems more like a libvirt capability than a QEMU capability.
>
>It is a capability of that particular instance of the VM the same way as
>others. A VM started with pre-blockdev libvirt but modern qemu will not
>use -blockdev for hotplug after libvirt upgrade and this is exactly te
>same situation.
>

Reviewed-by: Ján Tomko <jtomko at redhat.com>

Jano
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