[PATCH 1/2] string: add mem_is_zero() helper to check if memory area is all zeros

[Jani Nikula]

Almost two thirds of the memchr_inv() usages check if the memory area is
all zeros, with no interest in where in the buffer the first non-zero
byte is located. Checking for !memchr_inv(s, 0, n) is also not very
intuitive or discoverable. Add an explicit mem_is_zero() helper for this
use case.

Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>

---

Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Andy Shevchenko <andy@xxxxxxxxxx>
---
 include/linux/string.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 60168aa2af07..3da305dab927 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -279,6 +279,18 @@ static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
 void *memchr_inv(const void *s, int c, size_t n);
 char *strreplace(char *str, char old, char new);
 
+/**
+ * mem_is_zero - Check if an area of memory is all 0's.
+ * @s: The memory area
+ * @n: The size of the area
+ *
+ * Return: True if the area of memory is all 0's.
+ */
+static inline bool mem_is_zero(const void *s, size_t n)
+{
+	return !memchr_inv(s, 0, n);
+}
+
 extern void kfree_const(const void *x);
 
 extern char *kstrdup(const char *s, gfp_t gfp) __malloc;
-- 
2.39.2