On 19/11/2014 14:28, Michael S. Tsirkin wrote: > > > > qemu-2.0 -M pc-2.0 -> qemu-2.2 -M pc-2.0 > > > > what BIOS should the second qemu use? the one that existed on qemu-2.0 > > time or the one that existed on qemu-2.2 time? You can allow for > > bugfixes, but not for big changes like moving where the acpi tables were > > generated, etc, etc. > > > I really think that we should use the BIOS from qemu-2.0 era. And my > > understanding is that you defend that we should use the qemu-2.2 era > > BIOS. > > Not only that. We already do. And we don't intend to change that for 2.2.
Am I missing a part of the discussion? When we migrate, the second QEMU uses the BIOS from the first. So: qemu-2.0 -M pc-2.0 -> qemu-2.2 -M pc-2.0 uses 2.0 BIOS qemu-2.2 -M pc-2.0 -> qemu-2.0 -M pc-2.0 uses 2.2 BIOS Both should work, in general. BIOS is rarely the reason for incompatibilities. However, breakage can happen, for example I know that RHEL7 SeaBIOS does not work on RHEL6. RHEL6 SeaBIOS works on RHEL7, but it needs a couple workarounds. Shipping a separate BIOS for different machine types is unrealistic and pointless. It would also be a good terrain for bug reports, unless you also do things like "forbid creating -device megasas-gen2 on 2.1 because it was introduced in 2.2". Remember that libvirt keeps the same machine type for the whole life of a virtual machine definition, even if other parts of the hardware (e.g. disks or NICs) change. Paolo
