Re: [PATCH v3 1/5] libxl: libxl_domain_need_memory shouldn't modify b_info

[Wei Liu <wei.liu2@citrix.com>]

On Fri, Jul 08, 2016 at 06:35:59PM +0100, Ian Jackson wrote:
> Wei Liu writes ("[PATCH v3 1/5] libxl: libxl_domain_need_memory shouldn't modify b_info"):
> > This function is used to return the memory needed for a guest. It's not
> > in a position to modify the b_info passed in (note the _setdefault
> > function).
> > 
> > Use a copy of b_info to do the calculation. Define a macro to mark the
> > change in API.
> 
> Urgh, how unpleasant.
> 
> > diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> > index 5ec4c80..65af9ee 100644
> > --- a/tools/libxl/libxl.c
> > +++ b/tools/libxl/libxl.c
> > @@ -5123,20 +5123,24 @@ int libxl_domain_need_memory(libxl_ctx *ctx, libxl_domain_build_info *b_info,
> >                               uint32_t *need_memkb)
> >  {
> >      GC_INIT(ctx);
> > +    libxl_domain_build_info tmp;
> 
> I would suggest, instead:
> 
>     int libxl_domain_need_memory(libxl_ctx *ctx,
>  -                               libxl_domain_build_info *b_info,
>  +                               const libxl_domain_build_info *b_info_in,
> ...
>  +     libxl_domain_build_info b_info[1];
> 
> If you do this then you do not need to change the bulk of the body of
> the function at all.
> 

This is a good idea.

Just that I discover there is another unpleasant fact: all the generated
copy function doesn't constify their source parameter. I will need to
write a patch to fix that first.

Wei.

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