[PATCH v4 2/8] overflow: Add struct_size_with_data() and struct_data_pointer() helpers

[Andy Shevchenko]

Introduce two helper macros to calculate the size of the structure
with trailing aligned data and to retrieve the pointer to that data.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
 include/linux/overflow.h | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index bc390f026128..b93bbf1b6aaa 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -2,9 +2,10 @@
 #ifndef __LINUX_OVERFLOW_H
 #define __LINUX_OVERFLOW_H
 
+#include <linux/align.h>
 #include <linux/compiler.h>
-#include <linux/limits.h>
 #include <linux/const.h>
+#include <linux/limits.h>
 
 /*
  * We need to compute the minimum and maximum values representable in a given
@@ -337,6 +338,30 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
  */
 #define array3_size(a, b, c)	size_mul(size_mul(a, b), c)
 
+/**
+ * struct_size_with_data() - Calculate size of structure with trailing aligned data.
+ * @p: Pointer to the structure.
+ * @a: Alignment in bytes before trailing data.
+ * @s: Data size in bytes (must not be 0).
+ *
+ * Calculates size of memory needed for structure of @p followed by an
+ * aligned data of size @s.
+ *
+ * Return: number of bytes needed or SIZE_MAX on overflow.
+ */
+#define struct_size_with_data(p, a, s)	size_add(ALIGN(sizeof(*(p)), (a)), (s))
+
+/**
+ * struct_data_pointer - Calculate offset of the trailing data reserved with
+ * struct_size_with_data().
+ * @p: Pointer to the structure.
+ * @a: Alignment in bytes before trailing data.
+ *
+ * Return: offset in bytes to the trailing data reserved with
+ * struct_size_with_data().
+ */
+#define struct_data_pointer(p, a)	PTR_ALIGN((void *)((p) + 1), (a))
+
 /**
  * flex_array_size() - Calculate size of a flexible array member
  *                     within an enclosing structure.
-- 
2.43.0.rc1.1.gbec44491f096