Re: [RFC net-next 1/2] overflow: add DECLARE_FLEX() for on-stack allocs

Add DECLARE_FLEX() macro for on-stack allocations of structs with
flexible array member.

Using underlying array for on-stack storage lets us to declare known
on compile-time structures without kzalloc().

Actual usage for ice driver is in next patch of the series.

Note that "struct" kw and "*" char is moved to the caller, to both:
have shorter macro name, and have more natural type specification
in the driver code (IOW not hiding an actual type of var).

Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
---
 include/linux/overflow.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index f9b60313eaea..403b7ec120a2 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h

@@ -309,4 +309,18 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
 #define struct_size_t(type, member, count)					\
 	struct_size((type *)NULL, member, count)
 
+/**
+ * DECLARE_FLEX() - Declare an on-stack instance of structure with trailing
+ * flexible array.
+ * @type: Pointer to structure type, including "struct" keyword and "*" char.
+ * @name: Name for a (pointer) variable to create.
+ * @member: Name of the array member.
+ * @count: Number of elements in the array; must be compile-time const.
+ *
+ * Declare an instance of structure *@type with trailing flexible array.
+ */
+#define DECLARE_FLEX(type, name, member, count)					\
+	u8 name##_buf[struct_size((type)NULL, member, count)] __aligned(8) = {};\