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

From: David Gibson
Subject: Re: [Qemu-devel] [PATCH 5/8] pci: Replace pci_find_domain() with more general pci_root_bus_path()
Date: Fri, 24 May 2013 17:40:12 +1000
User-agent: Mutt/1.5.21 (2010-09-15)

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.

For my purposes, it doesn't much matter.  Naming the PCI root buses by
domain number makes sense for Q35, as it does for PIIX.  I've revised
my patch to add a suitable root_bus_path hook for q35.

Also, I've set up a github tree to publish this amongst other things:
Branch 'pci'.

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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