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

On 16.09.19 13:37, Jan Beulich wrote:

Hi, Jan

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>

Thank you.

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.



Oleksandr Tyshchenko

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