Re: [Qemu-devel] Re: [PATCH 07/11] eeprom93xx: Use the new hack macro to avoid duplicate field names

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/23/2011 04:58 AM, Juan Quintela wrote:
> Anthony Liguori<aliguori@us.ibm.com>  wrote:
>> I don't fully understand this hack business but we need field to be unique so..
>>
>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>> ---
>>   hw/eeprom93xx.c |    2 +-
>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/hw/eeprom93xx.c b/hw/eeprom93xx.c
>> index cfa695d..f1d75ec 100644
>> --- a/hw/eeprom93xx.c
>> +++ b/hw/eeprom93xx.c
>> @@ -114,7 +114,7 @@ static const VMStateInfo vmstate_hack_uint16_from_uint8 = {
>>   };
>>
>>   #define VMSTATE_UINT16_HACK_TEST(_f, _s, _t)                           \
>> -    VMSTATE_SINGLE_TEST(_f, _s, _t, 0, vmstate_hack_uint16_from_uint8, uint16_t)
>> +    VMSTATE_SINGLE_TEST_HACK(_f, _s, _t, 0, vmstate_hack_uint16_from_uint8, uint16_t)
>>
>>   static bool is_old_eeprom_version(void *opaque, int version_id)
>>   {
> After the fact, we need to promote it as "full types".
>
> Basically it is needed when we sent a field with a different size that
> we use it on the struct.
>
> if we have
>
> struct FOOState {
>         int32_t bar;
> ....
> }
>
> and it is sent as
>
> VMSTATE_INT8(bar, ....)
>
> In this case, I went through the whole device, checed that int8_t was
> enough and did the change.
>
> But if we have:
>
> struct FOOState {
>         int8_t bar;
> ....
> }
>
> and it is sent as
>
> VMSTATE_INT32(bar, ....)
>
> Then it is not trivial :-(
>
> We change FOOState to int32 or we break migration format.  Here is where
> the _HACK suffix appeared.
>
> I thought it was not going to be needed a lot, but there are several
> devices that just sent everything over the wire as uint32, independently
> of its type.

Could we get away with just doing:

VMSTATE_UNUSED(3),
VMSTATE_UINT8(bar, ...),

That's fully compatible on the wire and seems to be a clearer expression 
of exactly what the problem is.

Regards,

Anthony Liguori

> Later, Juan.
>