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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Dec 17, 2013 at 11:36:29AM +0000, Andrew Cooper wrote:
> 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.
> 

Oh I thought typeof((count)) always evaluates its argument, good to
know. ;-)

Wei.

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

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