Re: [Qemu-devel] [PATCH 5/8] pci: Replace pci_find_domain() with more general pci_root_bus_path()

[Paolo Bonzini <pbonzini@redhat.com>]

Il 23/05/2013 16:57, Michael S. Tsirkin ha scritto:
> On Thu, May 23, 2013 at 04:51:17PM +0200, Paolo Bonzini wrote:
>> Il 23/05/2013 13:04, Michael S. Tsirkin ha scritto:
>>>>> Most current uses of pci_find_domain() are for error or informational
>>>>> messages, so the change in identifiers should be harmless.  The exception
>>>>> is pci_get_dev_path(), whose results form part of migration streams.  To
>>>>> maintain compatibility with old migration streams, the PIIX PCI host is
>>>>> altered to always supply "0000" for this path, which matches the old domain
>>>>> number (since the code didn't actually support domains other than 0).
>>>>>
>>>>> For the pseries (spapr) PCI bridge we use a different platform-unique
>>>>> identifier (pseries machines can routinely have dozens of PCI host
>>>>> bridges).  Theoretically that breaks migration streams, but given that we
>>>>> don't yet have migration support for pseries, it doesn't matter.
>>>>>
>>>>> Any other machines that have working migration support including PCI
>>>>> devices will need to be updated to maintain migration stream compatibility.
>>>>>
>>>>> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
>>> AFAIK PC is the only one with working migration, yes, but
>>> we have Q35 as well which can be migrated.
>>
>> Are we already supporting backwards/forwards migration with Q35?
> 
> We released 1.5 with Q35 so we better ...

We released 1.5 with Q35 migration disabled by default, IIRC to enable
it you need to remove the AHCI controller with -nodefaults.  I think
bending the rules is still reasonable.

Paolo