On Mon, Jun 04, 2018 at 02:01:29PM +0100, Daniel P. Berrangé wrote: > On Mon, Jun 04, 2018 at 09:54:15AM -0300, Eduardo Habkost wrote: > > On Mon, Jun 04, 2018 at 04:38:22AM +0300, Michael S. Tsirkin wrote: > > > On Sun, Jun 03, 2018 at 12:27:49PM +0300, Marcel Apfelbaum wrote: > > > > Moving to QEMU 3.0 seems like a good opportunity for such a change. > > > > > > > > I440FX is really old and does not support modern features like IOMMU. > > > > Q35's SATA emulation is faster than pc's IDE, native PCI express hotplug > > > > is cleaner than ACPI based one and so on... > > > > > > > > Also the libvirt guys added very good support for the Q35 machine > > > > (thanks!). > > > > > > > > Management software should always specify the machine type and for the > > > > current setups, adding '-machine pc' to the command line is not such a > > > > big deal. > > > > > > > > In time the pc machine will fade out and we will probably stop adding > > > > new versions at some point. > > > > > > > > Signed-off-by: Marcel Apfelbaum <marcel.apfelb...@gmail.com> > > > > > > For command line users, I think changing the default isn't nice. > > > > > > Yes it's easy to add -machine pc but there's no documentation > > > that tells you to do so. Add to that shortcuts like -cdrom > > > stop working, hotplug needs extra bridges to work, and one > > > can see that while management tool users benefit from q35, > > > command line users will suffer. > > > > > > Can't we add a tag for management without changing the command line > > > default? How about "management-default"? "recommended"? "latest"? > > > > We could add new aliases if they are useful for management > > software, but we would need a well-defined use case and set of > > requirements+expectations for the new alias. > > I'm not convinced by the idea of adding a distinct default "for mgmt". All > the problems described wrt 'q35' vs 'pc' apply equally to management apps > as they do to humans. It just happens that one common mgmt layer (libvirt) > knows how to handle some of the complexity of q35. Other mgmt apps though > are just as likely to be hurt by the change as humans are. So effectively > the proposed "for mgmt" is actually "for libvirt >= some version", which > feels like a layering violation to me.
This means the new alias would be used only if requested explicitly by management software (not used automatically by libvirt). Taking that into account, I still don't see what exactly would be the use case here, and what exactly users can/can't expect when using the new alias. -- Eduardo
