Add DEFINE_FLEX() macro for on-stack allocations of structs with
flexible array member.
Add also const_flex_size() macro, that reads size of structs
allocated by DEFINE_FLEX().
Using underlying array for on-stack storage lets us to declare
known-at-compile-time structures without kzalloc().
Actual usage for ice driver is in following patches of the series.
Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
---
v1: change macro name; add macro for size read;
accept struct type instead of ptr to it; change alignment;
---
include/linux/overflow.h | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index f9b60313eaea..21a4410799eb 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -309,4 +309,31 @@ 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)
+/**
+ * DEFINE_FLEX() - Define a zeroed, on-stack, instance of @type structure with
+ * a trailing flexible array member.
+ *
+ * @type: structure type name, including "struct" keyword.
+ * @name: Name for a variable to define.
+ * @member: Name of the array member.
+ * @count: Number of elements in the array; must be compile-time const.
+ */
+#define DEFINE_FLEX(type, name, member, count) \
+ union { \
+ u8 bytes[struct_size_t(type, member, count)]; \
+ type obj; \
+ } name##_u __aligned(_Alignof(type)) = {}; \
+ type *name = (type *)&name##_u
+
+/**
+ * const_flex_size() - Get size of on-stack instance of structure with
+ * a trailing flexible array member.
+ *
+ * @name: Name of the variable, the one defined by DEFINE_FLEX() macro above.
+ *
+ * Get size of @name, which is equivalent to struct_size(name, array, count),
+ * but does not require (repeating) last two arguments.
+ */
+#define const_flex_size(name) __builtin_object_size(name, 1)
+
#endif /* __LINUX_OVERFLOW_H */--
2.40.1