Re: [Qemu-devel] [PATCH 4/7] virtio-blk: use aliases instead of duplicate qdev properties

[Peter Crosthwaite]

On Thu, May 22, 2014 at 8:32 PM, Andreas Färber <address@hidden> wrote:
> Am 22.05.2014 12:24, schrieb Stefan Hajnoczi:
>> On Thu, May 22, 2014 at 12:18 PM, Andreas Färber <address@hidden> wrote:
>>> Am 22.05.2014 00:04, schrieb Paolo Bonzini:
>>>> Il 21/05/2014 22:22, Stefan Hajnoczi ha scritto:
>>>>> virtio-blk-pci, virtio-blk-s390, and virtio-blk-ccw all duplicate the
>>>>> qdev properties of their VirtIOBlock child.  This approach does not work
>>>>> well with string or pointer properties since we must be careful about
>>>>> leaking or double-freeing them.
>>>>>
>>>>> Use the QOM alias property to forward property accesses to the
>>>>> VirtIOBlock child.  This way no duplication is necessary.
>>>>>
>>>>> Remember to stop calling virtio_blk_set_conf() so that we don't clobber
>>>>> the values already set on the VirtIOBlock instance.
>>>>
>>>> Which properties are _not_ being added?  This is probably needed for all
>>>> other virtio devices so a generic solution would be nice.
>>>
>>> "type", "realized" and the child<> property for VirtIODevice come to
>>> mind, possibly one or two more.
>>>

link<> ?

>>> If we follow a generic scheme, we could add an .instance_post_init hook
>>> for VirtIOPCIProxy iterating over all properties and blacklisting some.
>>
>> I think the trick is to alias all the qdev properties, not the QOM
>> ones.  That way we get all the explicitly declared properties and none
>> of the implicit ones.
>
> I wouldn't oppose that, but you then need to iterate over parent classes
> until you hit VirtioDeviceClass (or DeviceClass?),

IMO DeviceClass. Makes this whole alias concept non-virtio specific
and it will be more consistent with the existing qdev multi-level
property system. Add it to the qdev core for all to use:

qdev_alias_all_properties(DeviceState *target, Object *forwarder);

Or some such.

Regards,
Peter

 to avoid properties
> falling through the cracks.
>
> I just figured it easier and in line with your QMP patch to avoid
> distinguishing them in new code. But a quick solution is more important
> than futureproofness here, so I'll take or ack whatever works here.
>
> Andreas
>
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