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

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.