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