Markus Armbruster wrote:
> Jan Kiszka <jan.kis...@web.de> writes:
>
>> Luiz Capitulino wrote:
>>> On Sun, 23 May 2010 12:59:19 +0200
>>> Jan Kiszka <jan.kis...@web.de> wrote:
>>>
>>>> From: Jan Kiszka <jan.kis...@siemens.com>
>>>>
>>>> Allow to specify the device to be removed via device_del not only by ID
>>>> but also by its full or abbreviated qtree path. For this purpose,
>>>> qdev_find is introduced which combines walking the qtree with searching
>>>> for device IDs if required.
>>> [...]
>>>
>>>> Arguments:
>>>>
>>>> -- "id": the device's ID (json-string)
>>>> +- "path": the device's qtree path or unique ID (json-string)
>>>>
>>>> Example:
>>>>
>>>> --> { "execute": "device_del", "arguments": { "id": "net1" } }
>>>> +-> { "execute": "device_del", "arguments": { "path": "net1" } }
>>> Doesn't seem like a good change to me, besides being incompatible[1] we
>>> shouldn't overload arguments this way in QMP as overloading leads to
>>> interface degradation (harder to use, understand, maintain).
>> It's not overloaded, think of an ID as a (weak) symbolic link in the
>> qtree filesystem. The advantage of basing everything on top of full or
>> abbreviated qtree paths is that IDs are not always assigned, paths are.
>
> As long as your patch doesn't change the interpretation of IDs, we can
> keep the old name.
>
> The recent review of QMP documentation may lead to a "clean up bad
> names" flag day. One more wouldn't make it worse, I guess.
>
>>> Maybe we could have both arguments as optional, but one must be passed.
>> This would at least require some way to keep the proposed unified path
>> specification for the human monitor (having separate arguments there is
>> really unhandy).
>
> Correct.
>
> It would be nice to have device_del support paths in addition to IDs.
> I'd expect management tools to slap IDs on everything, so they won't
> care, but human users do.
>
> As far as I know, we have two places where we let the user name a node
> in the qtree: device_add bus=X and device_del X. The former names a
> bus, the latter a device. But both are nodes in the same tree, so
> consistency is in order.
>
> Only devices have user-specified IDs. Buses have names assigned by the
> system. Unique names, hopefully.
...but not necessarily. The bus name device_add accepts can also be a
full, thus unambiguous path.
>
> If the user doesn't specify a device ID, the driver name is used
> instead. If you put multiple instances of the same device on the same
> bus, they have the *same* path. For instance, here's a snippet of info
> qtree after adding two usb-mouse:
>
> dev: piix3-usb-uhci, id ""
> bus-prop: addr = 01.2
> bus-prop: romfile = <null>
> bus-prop: rombar = 1
> class USB controller, addr 00:01.2, pci id 8086:7020 (sub 1af4:1100)
> bar 4: i/o at 0xffffffffffffffff [0x1e]
> bus: usb.0
> type USB
> dev: usb-hub, id ""
> addr 0.0, speed 12, name QEMU USB Hub, attached
> dev: usb-mouse, id "no2"
> addr 0.0, speed 12, name QEMU USB Mouse, attached
> dev: usb-mouse, id ""
> addr 0.0, speed 12, name QEMU USB Mouse, attached
>
> Both devices have the same full path
> /i440FX-pcihost/pci.0/piix3-usb-uhci/usb.0/usb-mouse
> Which one does your code pick? Shouldn't it refuse to pick?
Patch 3 of this series resolves this as follows:
usb-mouse[.0] -> first listed instance
usb-mouse.1 -> second instance
...
We should probably include this numbering in the qtree dump, I guess.
>
> By the way, you *can* put '/' in IDs. I call that a bug.
Even if we prevent this, IDs can still collide with abbreviated device
or bus paths. Therefore I give paths precedence over IDs in patch 4.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
