Re: [Qemu-devel] [PATCH 04/14] qdev: take ownership of id pointer

[Gerd Hoffmann <kraxel@redhat.com>]

On 09/20/11 15:04, Anthony Liguori wrote:
> On 09/20/2011 01:36 AM, Gerd Hoffmann wrote:
>> On 09/19/11 18:27, Anthony Liguori wrote:
>>> On 09/19/2011 02:34 AM, Gerd Hoffmann wrote:
>>>> FYI: Keeping the pointer to the QemuOpts has one more reason: It will
>>>> free the
>>>> QemuOpts on hot-unplug, which is needed to free the id from QemuOpts
>>>> point of
>>>> view, which in turn allows to re-use the id when hot-plugging the same
>>>> (or
>>>> another) device later on.
>>>
>>> You mean, tie QemuOpts life cycle to devices life cycle
>>
>> Yes.
>>
>>> such that you
>>> cannot accidentally create a non-device QemuOpts that conflicts with the
>>> id of a device?
>>
>> Device QemuOpts have their own id namespace, so this is just about
>> conflicts
>> within devices. This ...
>>
>> device_add e1000,id=nic1
>> device_del nic1
>> device_add e1000,id=nic1
>>
>> ... will work only if you free the QemuOpts when deleting a device,
>> otherwise
>> QemuOpts will complain that nic1 is used already.
>
> But we can just verify that the id specified for qdev is unique at
> creation time and fail creation if it isn't, no?
>
> Since not all devices are assigned names via qemuopts, that seems like a
> safer approach anyway.

I think that happens anyway (didn't check the source though).

Problem is that QemuOpts wants IDs being unique too, so keep the 
QemuOpts hanging around instead of releasing them makes QemuOpts 
complain about nic1 not being unique although there isn't such a device 
in qdev space.  Oh, and not releasing the QemuOpts would also leak 
memory on each hot-unplug.

cheers,
   Gerd