Alex Williamson wrote:
quoted text
> On Fri, 2010-06-18 at 11:16 +0200, Jan Kiszka wrote:
>> Alex Williamson wrote:
>>> On Wed, 2010-06-16 at 10:23 +0200, Markus Armbruster wrote:
>>>> Alex Williamson <alex.williamson@redhat.com> writes:
>>>>
>>>>> On Tue, 2010-06-15 at 12:28 +0100, Paul Brook wrote:
>>>>>>>> Alex proposed to disambiguate by adding "identified properties of the
>>>>>>>> immediate parent bus and device" to the path component.  For PCI, these
>>>>>>>> are dev.fn.  Likewise for any other bus where devices have unambigous
>>>>>>>> bus address.  The driver name carries no information!
>>>>>>> From user POV, driver names are very handly to address a device
>>>>>>> intuitively - except for the case you have tones of devices on the same
>>>>>>> bus that are handled by the same driver. For that case we need to
>>>>>>> augment the device name with a useful per-bus ID, derived from the bus
>>>>>>> address where available, otherwise based on instance numbers.
>>>>>> This is where I think you're missing a trick. We don't need to augment the 
>>>>>> name, we just need to allow the bus id to be used instead.
>>>>> For the case of a hot remove, I agree.  If the user specifies "pci_del
>>>>> pci.0/03.0", that's completely sufficient because we don't care what's
>>>>> in that slot, just remove it.  However, I still see some use cases for
>>>>> device names in the path.  Take for example:
>>>>>
>>>>> (A): /i440FX-pcihost/pci.0/e1000.05.0
>>>>>
>>>>> vs
>>>>>
>>>>> (B): /pci.0/05.0
>>>>>
>>>>> (removing both the root bridge driver name and the device driver name)
>>>> / is the main system bus.  System bus defines no bus address at the
>>>> moment.  Therefore, you have to use the driver name i440FX-pcihost.
>>> So is the general rule "If a device's parent bus does not provide an
>>> address, print device name"?
>> What is the device name?
> 
> dev->info->name

That's for me the driver name. However, this one needs extension by an
instance number.

quoted text
> 
>>>> /i440FX-pcihost/pci.0 is the PCI bus.  PCI bus defines a bus address:
>>>> dev.fn.  Therefore, you can either use the bus address @05.0, or the
>>>> driver name e1000.
>>>>
>>>> We have "/i440FX-pcihost/pci.0/e1000" vs. "/i440FX-pcihost/pci.0/@05.0".
>>> I object to being able to use anything but an address under a bus that
>>> supports hotplug, but that aside, I think the paths for my example
>>> system look like below.  Note that anything behind and including the $
>>> is not the canonical path, that begins the free form, usage specific
>>> string, here filled by missing device names (open to suggestions other
>>> than $ here).
>> What about ":" instead of "$"? Visually more appealing IMO.
> 
> Sure, that works.
> 
>>>  Note that were isa devices do not have a bus identifier,
>>> I'm using the device name,
>> Don't understand. Why don't they have their I/O base as prefix? This is
>> inconsistent, and if we consider anything behind "$" (or ":")
>> informative, the bus address is mandatory for any device (on a bus with
>> an addressing scheme).
> 
> Not all isa devices expose an iobase property.  isa doesn't have an
> addressing scheme, it's basically a free for all of grabbing addresses
> and interrupts and hoping they don't conflict with no means to uniquely
> address a specific device.  That's why isa cards are loaded with jumpers
> so you can try to move them around.

The question is if there are ISA devices that do not use io, thus have
no such property. Paul pointed out that this might be unrealistic, and
in fact we have no such devices in QEMU so far.

quoted text
> 
>>> which I think follows the same rule as
>>> i440FX-pcihost.  Can we agree this is the goal?  Thanks,
>> It looks almost acceptable from my POV. We just need to define how to
>> get hold of devices on buses without an addressing scheme (e.g. the
>> system bus). Using the driver name is insufficient once you have > 1
>> devices of the same type. Introducing device instance numbers to those
>> buses would be straightforward IMO.
> 
> Yep, as I mentioned, I can live with instance numbers for devices that
> do not live on a hotpluggable bus.  Where will the instance number go?
> A property on the parent bus, the device, field in the DeviceState?

So far I'm generating them on the fly. We could store them in the
DeviceState if aliases based on <driver-name>.<instance-no> shall be
forbidden on hotplug buses, i.e. the instance numbers will not change
during VM lifetime. but the question is if such a restriction of alias
(even if the are unstable) wouldn't make things too much asymmetric.

Jan

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