Re: [Qemu-devel] [PATCH 2/3] qdev: support properties which don't set a default value

[Peter Maydell]

On 13 July 2017 at 18:10, Markus Armbruster <address@hidden> wrote:
> Peter Maydell <address@hidden> writes:
>
>> On 12 July 2017 at 12:22, Markus Armbruster <address@hidden> wrote:
>>> Peter Maydell <address@hidden> writes:
>>>
>>>> In some situations it's useful to have a qdev property which doesn't
>>>> automatically set its default value when qdev_property_add_static is
>>>> called (for instance when the default value is not constant).
>>>>
>>>> Support this by adding a flag to the Property struct indicating
>>>> whether to set the default value.  This replaces the existing test
>>>> for whether the PorpertyInfo set_default_value function pointer is
>>>
>>> PropertyInfo
>>>
>>>> NULL, and we set the .set_default field to true for all those cases
>>>> of struct Property which use a PropertyInfo with a non-NULL
>>>> set_default_value, so behaviour remains the same as before.
>>>>
>>>> We define two new macros DEFINE_PROP_SIGNED_NODEFAULT and
>>>> DEFINE_PROP_UNSIGNED_NODEFAULT, to cover the most plausible use cases
>>>> of wanting to set an integer property with no default value.
>>>
>>> Your text makes me wonder what is supposed to set the default value
>>> then.  Glancing ahead to PATCH 3, it looks like method instance_init()
>>> is.  Can you think of a scenario where something else sets it?
>>
>> OK, proposed extra paragraph for commit message:
>>
>> This gives us the semantics of:
>>  * if .set_default is true and .info->set_default_value is not NULL,
>>    then .defval is used as the the default value of the property
>
> If I read your patch correctly, then this should be "if .set_default is
> true, then .info->set_default_value() must not be null, and .defval is
> used ..."

Yes.

thanks
-- PMM