Re: [Qemu-devel] [PATCH v7 09/38] libqos: Track QTestState with QVirtioBus

[Thomas Huth]

On 12.09.2017 15:28, Eric Blake wrote:
> On 09/12/2017 02:21 AM, Thomas Huth wrote:
[...]
>> I fail to see why we need a separate bus object here for each device.
>> The bus is only available one time, not multiple times, isn't it? So
>> there should also only be one bus object floating around, not multiple
>> ones... or do I miss something?
> 
> You are right that there is only one bus for the machine - the problem
> is that the object representing the bus is dynamically created on the
> fly at the point where the device is first grabbed, rather than up front
> as part of creating the machine (in other words, the device search is
> not performed on a pre-existing bus object).
> 
> Contrast qpci_device_find() (lookup based on a pre-existing bus) with
> qvirtio_mmio_init_device() (lookup that did not use a pre-existing bus);
> also note that qvirtio_pci_device_find() takes a pre-existing QPCIBus
> (since on that architecture, the QVirtioBus is itself a device on the
> QPCIBus).
> 
> I suppose that we could indeed refactor the code to require callers to
> create the QVirtioBus object up front, and then make the device lookup
> (both qvirtio_mmio_init_device() and qvirtio_pci_device_find()) take a
> QVirtioBus parameter instead of QTestState or QPCIBus.  That's slightly
> more work, but I'm happy to attempt it if you think it will be better.

At least to me, that sounds like the right way to go. I guess we might
run into other problems later if we have multiple instances of the bus
object floating around ... so sorry if this is extra work, but I'd say
let's better do it properly now instead of having to rework this again
later.

 Thomas

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