Re: [Qemu-devel] [PATCH v2 03/15] qdev: Allow device addressing via 'driver.instance'

[Markus Armbruster]

Jan Kiszka <address@hidden> writes:

> Markus Armbruster wrote:
>> Jan Kiszka <address@hidden> writes:
>> 
>>> From: Jan Kiszka <address@hidden>
>>>
>>> Extend qbus_find_dev to allow addressing of devices without an unique id
>>> via an optional per-bus instance number. The new formats are
>>> 'driver.instance' and 'alias.instance'.
>>>
>>> Signed-off-by: Jan Kiszka <address@hidden>
>>> ---
>>>  docs/qdev-device-use.txt |   12 +++++++++++-
>>>  hw/qdev.c                |   23 ++++++++++++++++++-----
>>>  2 files changed, 29 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/docs/qdev-device-use.txt b/docs/qdev-device-use.txt
>>> index 9ac1fa1..5939481 100644
>>> --- a/docs/qdev-device-use.txt
>>> +++ b/docs/qdev-device-use.txt
>>> @@ -1,6 +1,6 @@
>>>  = How to convert to -device & friends =
>>>  
>>> -=== Specifying Bus and Address on Bus ===
>>> +=== Specifying Bus, Address on Bus, and Devices ===
>>>  
>>>  In qdev, each device has a parent bus.  Some devices provide one or
>>>  more buses for children.  You can specify a device's parent bus with
>>> @@ -24,6 +24,16 @@ Furthermore, if a device only hosts a single bus, the 
>>> bus name can be
>>>  omitted in the path.  Example: /i440FX-pcihost/PIIX3 abbreviates
>>>  /i440FX-pcihost/pci.0/PIIX3/isa.0 as none of the buses has siblings.
>>>  
>>> +Existing devices can be addressed either via a unique ID if it was
>>> +assigned during creation or via the device tree path:
>>> +
>>> +/full_bus_address/driver_name[.instance_number]
>>> +    or
>>> +abbreviated_bus_address/driver_name[.instance_number]
>>> +
>>> +Example: /i440FX-pcihost/pci.0/e1000.2 addresses the second e1000
>>> +adapter on the bus 'pci.0'.
>>> +
>>>  Note: the USB device address can't be controlled at this time.
>> 
>> "instance number" isn't defined in this document.
>
> True, only implicitly via the example.
>
>> 
>> I understand the problem you're trying to solve; I've had it myself many
>> times.  But is inventing an instance number the right solution?
>> 
>> The two e1000 devices already have a perfectly fine unique identifier on
>> their bus: their bus address.  What about recognizing bus addresses in
>> paths?  Requires a suitable restriction on device names and IDs to avoid
>> ambiguity, say "start with letter".
>> 
>> qdev currently doesn't abstract bus addresses, but that's fixable.
>
> You would also have to specify unique addressing scheme to those buses
> that do not have it yet. E.g. what should be the address of a ISA bus
> device? The base of its first ioport range? But if it does not have any
> as it only injects ISA IRQs?

Hmm, instance numbers are the lesser evil in this case.

Define them properly, and make info qtree show them, and we'll be okay,
I guess.