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

[Andreas Färber]

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.
>>
>> 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?), 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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