Re: [Qemu-devel] [PATCH 1/3] qdev-properties.h: Explicitly set the default value for arraylen properties

[Peter Maydell <peter.maydell@linaro.org>]

On 13 July 2017 at 15:11, Markus Armbruster <armbru@redhat.com> wrote:
> Peter Maydell <peter.maydell@linaro.org> writes:
>
>> In DEFINE_PROP_ARRAY, because we use a PropertyInfo (qdev_prop_arraylen)
>> which has a .set_default_value member we will set the field to a default
>> value. That default value will be zero, by the C rule that struct
>> initialization sets unmentioned members to zero if at least one member
>> is initialized. However it's clearer to state it explicitly.
>>
>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>> ---
>> If my eyeball of the sources is correct, this is the only case we
>> have of a Property struct that uses a PropertyInfo with a non-NULL
>> .set_default_value but which doesn't explicitly set .defval.u.
>> ---
>>  include/hw/qdev-properties.h | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
>> index 0604c33..36d040c 100644
>> --- a/include/hw/qdev-properties.h
>> +++ b/include/hw/qdev-properties.h
>> @@ -110,6 +110,7 @@ extern PropertyInfo qdev_prop_arraylen;
>>                            _arrayfield, _arrayprop, _arraytype) {        \
>>          .name = (PROP_ARRAY_LEN_PREFIX _name),                          \
>>          .info = &(qdev_prop_arraylen),                                  \
>> +        .defval.u = 0,                                                  \
>>          .offset = offsetof(_state, _field)                              \
>>              + type_check(uint32_t, typeof_field(_state, _field)),       \
>>          .arrayinfo = &(_arrayprop),                                     \
>
> Hmm.
>
> .info and .defval apply to the array *length*.
> .info.set_default_value() is set_default_uint(), which uses .defval.u.
> Setting it here is correct.
>
> The array *elements* are described by .arrayinfo.  There is no
> .arraydefval, but that's okay, because .arrayinfo.set_default_value()
> doesn't get called.  Correct?

Correct. (There's no way to specify a default value for array properties.)

thanks
-- PMM