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

[Michael S. Tsirkin]

On Thu, May 23, 2013 at 05:00:39PM +0200, Paolo Bonzini wrote:
> 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 <address@hidden>
> >>> 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

Which reminds me, does someone plan to look into fixing
migration for AHCI?

-- 
MST