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Date: Wed, 20 Aug 2014 13:36:27 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] ioh3420: Provide a unique bus name and
 an interrupt mapping function
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To: Knut Omang <knut.omang@oracle.com>
Cc: Juan Quintela <quintela@redhat.com>, Alexey Kardashevskiy <aik@ozlabs.ru>, Marcel Apfelbaum <marcel.a@redhat.com>, qemu-devel@nongnu.org, Markus Armbruster <armbru@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>

On Wed, Aug 20, 2014 at 11:30:55AM +0200, Knut Omang wrote:
> On Wed, 2014-08-20 at 10:52 +0200, Paolo Bonzini wrote:
> > Il 20/08/2014 08:53, Knut Omang ha scritto:
> > > A unique bus name is necessary to be able to refer to each instance
> > > from the command line and monitors.
> > 
> > Is it needed?  Can't you just add id= to the -device option?
> 
> Yes, as far as I understand the problem is that the id= would work on
> the ioh3420 device itself, while what is needed here is to name the
> secondary bus of the ioh3420, which I haven't found a way to name from
> the command line.

Did you try using the device name?

For pci bridges, unless you set bus_name, bus name will
match device itself. See this code:

     * If we don't specify the name, the bus will be addressed as
     * <id>.0, where id is the device id.
     * Since PCI Bridge devices have a single bus each, we don't need
     * the index:
     * let users address the bus using the device name.
     */
    if (!br->bus_name && dev->qdev.id && *dev->qdev.id) {
            br->bus_name = dev->qdev.id;
    }



> Maybe an even better solution would be to have default names for
> everything, if not specified, from a user friendliness perspective? 
>
> I suppose this is a more general issue of sensible default values
> though, but the fact that it is easy to create devices which cannot be
> referred has caused me some confusion from time to time.
> 
> > Paolo
> 
> Thanks,
> 
> Knut