From: Peter Rosin <peda@xxxxxxxxxx> Subject: lib/string.c: allow searching for NUL with strnchr Patch series "lib/string: search for NUL with strchr/strnchr". I noticed an inconsistency where strchr and strnchr do not behave the same with respect to the trailing NUL. strchr is standardised and the kernel function conforms, and the kernel relies on the behavior. So, naturally strchr stays as-is and strnchr is what I change. While writing a few tests to verify that my new strnchr loop was sane, I noticed that the tests for memset16/32/64 had a problem. Since it's all about the lib/string.c file I made a short series of it all... This patch (of 3): strchr considers the terminating NUL to be part of the string, and NUL can thus be searched for with that function. For consistency, do the same with strnchr. Link: http://lkml.kernel.org/r/20190506124634.6807-2-peda@xxxxxxxxxx Signed-off-by: Peter Rosin <peda@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/string.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) --- a/lib/string.c~lib-string-allow-searching-for-nul-with-strnchr +++ a/lib/string.c @@ -400,6 +400,9 @@ EXPORT_SYMBOL(strncmp); * strchr - Find the first occurrence of a character in a string * @s: The string to be searched * @c: The character to search for + * + * Note that the %NUL-terminator is considered part of the string, and can + * be searched for. */ char *strchr(const char *s, int c) { @@ -453,12 +456,18 @@ EXPORT_SYMBOL(strrchr); * @s: The string to be searched * @count: The number of characters to be searched * @c: The character to search for + * + * Note that the %NUL-terminator is considered part of the string, and can + * be searched for. */ char *strnchr(const char *s, size_t count, int c) { - for (; count-- && *s != '\0'; ++s) + while (count--) { if (*s == (char)c) return (char *)s; + if (*s++ == '\0') + break; + } return NULL; } EXPORT_SYMBOL(strnchr); _
