Re: [Xen-devel] [PATCH V3] xl: create VFB for PV guest when VNC is specified

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/12/13 11:28, Wei Liu wrote:
> On Mon, Dec 16, 2013 at 05:46:04PM +0000, Ian Campbell wrote:
> [...]
>>> Changes in V2:
>>> * use macros to reduce code duplication
>>> * vfb=[] take precedence over top level VNC options
>>> ---
>>>  tools/libxl/xl_cmdimpl.c |   89 
>>> ++++++++++++++++++++++++++++++++++++----------
>>>  1 file changed, 70 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
>>> index bd26bcc..6a22e17 100644
>>> --- a/tools/libxl/xl_cmdimpl.c
>>> +++ b/tools/libxl/xl_cmdimpl.c
>>> @@ -315,6 +315,13 @@ static void *xrealloc(void *ptr, size_t sz) {
>>>      return r;
>>>  }
>>>  
>>> +#define ARRAY_EXTEND(array,count)                                       \
>>> +    do {                                                                \
>>> +        (array) = xrealloc((array),                                     \
>>> +                           sizeof(typeof(*(array))) * ((count) + 1));   \
>> sizeof(typeof(*array)) == sizeof(*array), doesn't it?
>>
>>> +        (count) = (count) + 1;                                          \
>> (count++)
>>
>> I suppose in a macro like this it is tricky to arrange to only evaluate
>> the arguments once, since you need to read and write, but I think you
>> can arrange to evaluate array exactly once instead of 3 times and count
>> just once.
>>
> I came up with this. Is it what you asked for?
>
> #define ARRAY_EXTEND(type_ptr,ptr,type_count,count,ret)                 \
>     do {                                                                \
>         type_ptr **__ptr = &(ptr);                                      \
>         type_count *__count = &(count);                                 \
>         *__ptr = xrealloc(*__ptr,                                       \
>                           sizeof(**__ptr) * (*__count + 1));            \
>         (ret) = *__ptr + *__count;                                      \
>         (*__count)++;                                                   \
>     } while (0)
>
> Wei.

Use typeof() rather than passing the types in directly.  It is a GCC
extension, which tries its best not to evaluate its argument.

Alternatively, the __auto_type gcc keyword sould seem to do what you
want as well.

~Andrew

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