Re: [Qemu-ppc] [Qemu-devel] [QEMU PATCH v6 2/2] migration: migrate QTAILQ

[Jianjun Duan]

On 10/14/2016 11:39 AM, Paolo Bonzini wrote:
> 
>>> Another possibility is a macro like
>>>
>>> #define field_at_offset(base, offset, type) \
>>>    ((type) (((char *) (base)) + (offset)))
>>>
>>> so that you can do
>>>
>>>    *field_at_offset(void **, elm, (entry) + QTAILQ_NEXT_OFFSET) = NULL;
>>>    *field_at_offset(void ***, elm, (entry) + QTAILQ_PREV_OFFSET) =
>>>        *field_at_offset(void ***, head, QTAILQ_LAST_OFFSET);
>>>    **field_at_offset(void ***, head, QTAILQ_LAST_OFFSET) = (elm);
>>>    *field_at_offset(void ***, head, QTAILQ_LAST_OFFSET) =
>>>         field_at_offset(void **, elm, (entry) + QTAILQ_NEXT_OFFSET);
>>
>> The thing is that we don't know type at all. So only the offset values
>> is used. This is intended for QTAILQ of any type.
> 
> Sure, my code is identical to yours---just with more macros for readability,
> and a little more type-safe.  Another possibility:
> 
> #define QTAILQ_RAW_NEXT(elm, entry) \
>    (*field_at_offset(void **, elm, (entry) + QTAILQ_NEXT_OFFSET))
> #define QTAILQ_RAW_PREV(elm, entry) \
>    (*field_at_offset(void ***, elm, (entry) + QTAILQ_PREV_OFFSET))
> #define QTAILQ_RAW_LAST(head) \
>    (*field_at_offset(void ***, head, QTAILQ_LAST_OFFSET))
> 
>     QTAILQ_RAW_NEXT(elm, entry) = NULL;
>     QTAILQ_RAW_PREV(elm, entry) = QTAILQ_RAW_LAST(head);
>     *QTAILQ_RAW_LAST(head) = (elm);
>     QTAILQ_RAW_LAST(head) = &QTAILQ_RAW_NEXT(elm, entry);
> 

You are right. The readability can be approved.

Thanks,
Jianjun
> Thanks,
> 
> Paolo
> 
>> Thanks,
>> Jianjun
>>
>>>
>>> or something like that (note that I've always used the same type for
>>> next and last, by the way).
>>>
>>> Paolo
>>>
>>
>>
>