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

[Ian Jackson <ian.jackson@eu.citrix.com>]

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.

> +/* LIBXL_HAVE_DOMAIN_NEED_MEMORY_V2
> + *
> + * If this is defined, libxl_domain_need_memory no longer modifies
> + * passed in b_info.
> + */
> +#define LIBXL_HAVE_DOMAIN_NEED_MEMORY_V2

I suggest constifying it and

 LIBXL_HAVE_DOMAIN_NEED_MEMORY_CONST_B_INFO

Ian.

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