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From: Paul Brook <paul@codesourcery.com>
Date: Thu, 17 Jun 2010 23:01:21 +0100
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Subject: [Qemu-devel] Re: RFC qdev path semantics
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To: Alex Williamson <alex.williamson@redhat.com>
Cc: chrisw@redhat.com, kvm@vger.kernel.org, Markus Armbruster <armbru@redhat.com>, qemu-devel@nongnu.org, avi@redhat.com, kraxel@redhat.com

> > ### Paul proposes to require all buses to define bus addresses.  Make
> >     one up if necessary.
> 
> That seems arbitrary and prone to breakage.  How do we handle a subtle
> change in device instantiation order and still allow migration?  If by
> code change or command line ordering my frobnitz moves from:
> 
> /i440FX-pcihost/pci.0/PIIX3/@01.0/isa.0/0
> 
> to
> 
> /i440FX-pcihost/pci.0/PIIX3/@01.0/isa.0/1

Two things are apparent here. 
(a) You've clearly misunderstood the proposals. The paths above make no sense.

(b) You've picked a particularly poor definition of device address for the ISA 
bus. We can do much better than device creation order.

> ...
> I can live with PATH/@BUS-ADDR if it's still felt that
> PATH/IDENT@BUS-ADDR isn't canonical.  What that means is that I'll
> probably code up vmstate and ramblocks to append IDENT themselves to
> keep all the goodness of having per PATH/IDENT namespaces.

As discussed elsewhere in this thread, addition of IDENT to the device path is 
neither necessary nor sufficient for migration.

I really feel like we're going round in circles here.

Paul