diff mbox series

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

Message ID 20240527094320.2653177-1-jani.nikula@intel.com (mailing list archive)
State New, archived
Headers show
Series [1/2] string: add mem_is_zero() helper to check if memory area is all zeros | expand

Commit Message

Jani Nikula May 27, 2024, 9:43 a.m. UTC
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@intel.com>

---

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

Comments

Andy Shevchenko May 27, 2024, 1:27 p.m. UTC | #1
On Mon, May 27, 2024 at 12:43 PM Jani Nikula <jani.nikula@intel.com> wrote:
>
> 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.

...

> +static inline bool mem_is_zero(const void *s, size_t n)
> +{
> +       return !memchr_inv(s, 0, n);
> +}

There are potential users for the 0xff check as well. Hence the
following question:
Are we going to have a new function per byte in question, or do we
come up with a common denominator, like mem_is_all_of(mem, byte)?
Jani Nikula May 27, 2024, 2:06 p.m. UTC | #2
On Mon, 27 May 2024, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> On Mon, May 27, 2024 at 12:43 PM Jani Nikula <jani.nikula@intel.com> wrote:
>>
>> 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.
>
> ...
>
>> +static inline bool mem_is_zero(const void *s, size_t n)
>> +{
>> +       return !memchr_inv(s, 0, n);
>> +}
>
> There are potential users for the 0xff check as well. Hence the
> following question:
> Are we going to have a new function per byte in question, or do we
> come up with a common denominator, like mem_is_all_of(mem, byte)?

No. As I wrote in the commit message rationale, "Almost two thirds of
the memchr_inv() usages check if the memory area is all zeros". This is
by far the most common use case of memchr_inv().

BR,
Jani.
diff mbox series

Patch

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;