Re: [libvirt] [Qemu-devel] [RFC 00/15] qmp: Report supported device types on 'query-machines'

> > Considered alternatives > ======================= > > Indirect mapping (machine => bus => device) > ------------------------------------------- > > This RFC implements a mechanism to implement ax > machine-type => supported-device-types > mapping. An alternative solution I considered was to expose an > indirect mapping: > machine-type => default-bus-types > followed by > bus-type => supported-device-types. > > But exposing only the resulting supported device-types list > imposes less restrictions on how the device and bus type > hierarchy is implemented inside QEMU. There's still a > machine-type => bus-type => device-type > mapping implemented internally, but it is an implementation > detail on the current version, and not part of the > externally-visible interface. > > The Implementation > ================== > > This add a new field to MachineClass: default_bus_types, and a > new field to BusClass: supported_device_type. Is it possible to modify a machine (setting some properties e.g. on the command line), that suddenly more devices are supported? Something like enabling an additional bus? (I assume so, because it is called "default bus types" :) )

If so, the indirect mapping could be of more benefit in the long run.

Thinking about my machine at home: I just care about the available buses. If my machine doesn't have USB, but PCI, I can buy a USB PCI card and make it support USB. Then I can happily plug in USB devices. So the "default" state might at least no longer be sufficient when wanting to plug in a USB fan on a hot summer day ;) . But, with the indirect mapping, I guess we would need yet another qmp command ... -- David