netdev - [RFC net-next 1/2] overflow: add DECLARE

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Date: Tue,  1 Aug 2023 13:19:22 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Kees Cook <keescook@...omium.org>
Cc: Jacob Keller <jacob.e.keller@...el.com>,
	intel-wired-lan@...ts.osuosl.org,
	netdev@...r.kernel.org,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>
Subject: [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@...el.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 *@...e with trailing flexible array.
+ */
+#define DECLARE_FLEX(type, name, member, count)					\
+	u8 name##_buf[struct_size((type)NULL, member, count)] __aligned(8) = {};\
+	type name = (type)&name##_buf
+
 #endif /* __LINUX_OVERFLOW_H */
-- 
2.38.1