Re: [Xen-devel] [PATCH V2 1/2] libxl: Have flexarray using the GC

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Anthony PERARD writes ("[PATCH V2 1/2] libxl: Have flexarray using the GC"):
> This patch makes the flexarray function libxl__gc aware.

> +/*
> + * It is safe to store gc in the struct because:
> + * - If it an actual gc, then the flexarray should not be used after the gc
> + *   have been freed.
> + * - If it is a NOGC, then this point to a structure embedded in libxl_ctx,
> + *   therefore will survive across several libxl calls.
> + */

Thanks, I think this explanation is correct.

> +static int gc_is_real(const libxl__gc *gc)
> +{
> +    return gc->alloc_maxsize >= 0;
> +}

You have cloned-and-hacked this from libxl_internal.c !  Instead,
either declare it in libxl_internal.h, or move it there and make it
"static inline".

> @@ -104,7 +115,8 @@ void **flexarray_contents(flexarray_t *array)
>  {
>      void **data;
>      data = array->data;
> -    free(array);
> +    if (!gc_is_real(array->gc))
> +        free(array);
>      return data;

What an odd function.  However, your patch to it seems right to me.

> diff --git a/tools/libxl/flexarray.h b/tools/libxl/flexarray.h
> index ae17f3b..aade417 100644

And the rest of the patch is mostly an impressive number of
deletions.  I won't check the semantics of each one but the style
seems plausible.

Thanks!

Ian.

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