From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [virtio-dev] Re: [RFC PATCH 1/3] qemu: virtio-bypass should
 explicitly bind to a passthrough device
Date: Thu, 5 Apr 2018 17:31:03 +0200
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Cc: Si-Wei Liu <si-wei.liu@oracle.com>, Jiri Pirko <jiri@resnulli.us>,
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To: Siwei Liu <loseweigh@gmail.com>,
        "Michael S. Tsirkin" <mst@redhat.com>
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On 04/04/2018 10:02, Siwei Liu wrote:
>> pci_bus_num is almost always a bug if not done within
>> a context of a PCI host, bridge, etc.
>>
>> In particular this will not DTRT if run before guest assigns bus
>> numbers.
>>
> I was seeking means to reserve a specific pci bus slot from drivers,
> and update the driver when guest assigns the bus number but it seems
> there's no low-hanging fruits. Because of that reason the bus_num is
> only obtained until it's really needed (during get_config) and I
> assume at that point the pci bus assignment is already done. I know
> the current one is not perfect, but we need that information (PCI
> bus:slot.func number) to name the guest device correctly.

Can you use the -device "id", and look it up as

    devices = container_get(qdev_get_machine(), "/peripheral");
    return object_resolve_path_component(devices, id);

?

Thanks,

Paolo