[PATCH -next 1/2] string.h: Introduce memset_range() for wiping members

[Xiu Jianfeng]

Motivated by memset_after() and memset_startat(), introduce a new helper,
memset_range() that takes the target struct instance, the byte to write,
and two member names where zeroing should start and end.

Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
---
 include/linux/string.h | 20 ++++++++++++++++++++
 lib/memcpy_kunit.c     | 12 ++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index b6572aeca2f5..7f19863253f2 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -291,6 +291,26 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
 	       sizeof(*(obj)) - offsetof(typeof(*(obj)), member));	\
 })
 
+/**
+ * memset_range - Set a value ranging from member1 to member2, boundary included.
+ *
+ * @obj: Address of target struct instance
+ * @v: Byte value to repeatedly write
+ * @member1: struct member to start writing at
+ * @member2: struct member where writing should stop
+ *
+ */
+#define memset_range(obj, v, member_1, member_2)			\
+({									\
+	u8 *__ptr = (u8 *)(obj);					\
+	typeof(v) __val = (v);						\
+	BUILD_BUG_ON(offsetof(typeof(*(obj)), member_1) >		\
+		     offsetof(typeof(*(obj)), member_2));		\
+	memset(__ptr + offsetof(typeof(*(obj)), member_1), __val,	\
+	       offsetofend(typeof(*(obj)), member_2) -			\
+	       offsetof(typeof(*(obj)), member_1));			\
+})
+
 /**
  * str_has_prefix - Test if a string has a given prefix
  * @str: The string to test
diff --git a/lib/memcpy_kunit.c b/lib/memcpy_kunit.c
index 62f8ffcbbaa3..0dd800412455 100644
--- a/lib/memcpy_kunit.c
+++ b/lib/memcpy_kunit.c
@@ -229,6 +229,13 @@ static void memset_test(struct kunit *test)
 			  0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79, 0x79,
 			},
 	};
+	struct some_bytes range = {
+		.data = { 0x30, 0x30, 0x30, 0x30, 0x81, 0x81, 0x81, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			  0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30, 0x30,
+			},
+	};
 	struct some_bytes dest = { };
 	int count, value;
 	u8 *ptr;
@@ -269,6 +276,11 @@ static void memset_test(struct kunit *test)
 	dest = control;
 	memset_startat(&dest, 0x79, four);
 	compare("memset_startat()", dest, startat);
+
+	/* Verify memset_range() */
+	dest = control;
+	memset_range(&dest, 0x81, two, three);
+	compare("memset_range()", dest, range);
 #undef TEST_OP
 }
 
-- 
2.17.1