Re: [Qemu-devel] [PATCH v2 15/18] rtc: add a dynamic property for retrieving the date

[Anthony Liguori <aliguori@us.ibm.com>]

On 12/09/2011 05:26 AM, Kevin Wolf wrote:
> Am 02.12.2011 21:20, schrieb Anthony Liguori:
>> This really shows the power of dynamic object properties compared to qdev
>> static properties.
>>
>> This property represents a complex structure who's format is preserved over the
>> wire.  This is enabled by visitors.
>>
>> It also shows an entirely synthetic property that is not tied to device state.
>>
>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>
> There's one thing that I was hoping to find answered when I would have
> reviewed the whole series, but it hasn't happened: There is no doubt
> that dynamic properties (in the sense of being able to modify them after
> constructions) are a useful thing. But you also claim that class-based
> properties are not enough for QOM and that we need object-based ones,
> which is a requirement not immediately obvious to me.
>
> Can you provide some examples where we would explicitly need
> object-based properties?

Sure.  Any property that's dynamic needs to be object based.  A good example 
would be PCI slots.

Today, we unconditionally advertise 32 slots in our ACPI tables.  It could be 
desirable to eventually make this configurable.  So you can imagine where you 
would have an 'slot-count' property and if that was set to 16, it would result 
in 'slot[0]..slot[15]' being created.

There are other good examples too.

Regards,

Anthony Liguori

>
> Kevin
>