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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: Thu, 23 May 2013 22:21:09 +1000
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, May 23, 2013 at 02:04:08PM +0300, Michael S. Tsirkin wrote:
> On Thu, May 09, 2013 at 10:31:09AM +1000, David Gibson wrote:
> > pci_find_domain() is used in a number of places where we want an id for a
> > whole PCI domain (i.e. the subtree under a PCI root bus).  The trouble is
> > that many platforms may support multiple independent host bridges with no
> > hardware supplied notion of domain number.
> > 
> > This patch, therefore, replaces calls to pci_find_domain() with calls to
> > a new pci_root_bus_path() returning a string.  The new call is implemented
> > in terms of a new callback in the host bridge class, so it can be defined
> > in some way that's well defined for the platform.  When no callback is
> > available we fall back on the qbus name.
> > 
> > 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.

Good point, I'll add a similar hook to q35.

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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