Re: [Xen-devel] [PATCH V4 5/8] xen/common: Introduce xrealloc_flex_struct() helper macros

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.09.2019 17:35, Oleksandr Tyshchenko wrote:
> --- a/xen/include/xen/xmalloc.h
> +++ b/xen/include/xen/xmalloc.h
> @@ -35,6 +35,15 @@
>  #define xzalloc_array(_type, _num) \
>      ((_type *)_xzalloc_array(sizeof(_type), __alignof__(_type), _num))
>  
> +/* Allocate space for a structure with a flexible array of typed objects. */
> +#define xmalloc_flex_struct(type, field, nr) \
> +    (type *)_xmalloc(offsetof(type, field[nr]), __alignof__(type))
> +
> +/* Re-allocate space for a structure with a flexible array of typed objects. 
> */
> +#define xrealloc_flex_struct(ptr, field, nr)                          \
> +    (typeof(ptr))_xrealloc(ptr, offsetof(typeof(*(ptr)), field[nr]),  \
> +                           __alignof__(typeof(*(ptr))))

With the missing parentheses around the entire constructs added
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

I'd like to note though that it sort of feels as if this notation
isn't going to provide maximum flexibility. I therefore wonder
whether the last two parameters shouldn't be combined, resulting
in an invocation like

    ptr = xmalloc_flex_struct(struct s, field[5]);

But I realize this would allow for (more; I'll reply to patch 6
in a minute) abuse, so this wouldn't be a clear win.

Jan

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