Re: [Qemu-devel] [PATCH v4 03/23] qdev: Drop ID matching from qtree paths

[Markus Armbruster]

Jan Kiszka <address@hidden> writes:

> Markus Armbruster wrote:
>> [cc: kraxel]
>> 
>> Jan Kiszka <address@hidden> writes:
>> 
>>> From: Jan Kiszka <address@hidden>
>>>
>>> Device IDs may conflict with device names or aliases. From now on we
>>> only accept them outside qtree paths. This also makes dumping IDs in
>>> qbus_list_dev/bus obsolete.
>>>
>>> Signed-off-by: Jan Kiszka <address@hidden>
>> 
>> I don't like this at all.
>> 
>> 1. Specific problem:
>> 
>>    With the current code, multiple devices with the same driver work
>>    only if I take care: addressing by driver name gets me only the
>>    first, so I better set suitable IDs.
>> 
>>    With your patch, multiple devices with the same driver don't work, no
>>    matter what I do.
>
> [ you already found how this is resolved ]

Yes, but I don't like that the intermediate state is broken, and I don't
like the final state.

>> 2. General principle:
>> 
>>    When I set an ID, I want the system to accept that ID in all contexts
>>    where it makes sense.  Ambiguity created by badly chosen IDs is *my*
>>    problem.
>
> I disagree. IMO, QEMU should support the user to avoid such subtle
> shadowing.

IDs let me refer to my devices without having to look up ever-changing
instance numbers.  This is especially relevant when I want to do refer
to buses without using (possibly ambigious) bus names.

I want to be able to say bus=scsi-ctrl.2/scsi.0 instead of
/i440FX-pcihost/pci.0/lsi53c895a.<ever-changing-number>/scsi.0

That's much more valuable to me than a well-meant attempt at protecting
me from choosing IDs badly.

Throw in multiple PCI buses, and a "no IDs in qdev paths" law becomes
even more annoying.