[PATCH v3 2/4] lib: implement strnstr()

[Ilias Apalodimas]

On Mon, 3 Feb 2025 at 11:12, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
> Implement library function strnstr().
> Implement strstr() using strnstr().
> Sort the includes.
>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
> v3:
>         no change
> v2:
>         no change
> ---
>  include/linux/string.h |  3 +++
>  lib/string.c           | 49 +++++++++++++++++++++++++++++-------------
>  2 files changed, 37 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index 27b2beb9ddb..d943fcce690 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -72,6 +72,9 @@ extern char * strrchr(const char *,int);
>  #ifndef __HAVE_ARCH_STRSTR
>  extern char * strstr(const char *,const char *);
>  #endif
> +#ifndef __HAVE_ARCH_STRNSTR
> +extern char *strnstr(const char *, const char *, size_t);
> +#endif
>  #ifndef __HAVE_ARCH_STRLEN
>  extern __kernel_size_t strlen(const char *);
>  #endif
> diff --git a/lib/string.c b/lib/string.c
> index feae9519f2f..691c9985692 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -16,11 +16,12 @@
>   */
>
>  #include <config.h>
> +#include <malloc.h>
> +#include <stdint.h>
>  #include <linux/compiler.h>
> +#include <linux/ctype.h>
>  #include <linux/types.h>
>  #include <linux/string.h>
> -#include <linux/ctype.h>
> -#include <malloc.h>
>
>  /**
>   * strncasecmp - Case insensitive, length-limited string comparison
> @@ -678,30 +679,48 @@ char *memdup(const void *src, size_t len)
>         return p;
>  }
>
> -#ifndef __HAVE_ARCH_STRSTR
> +#ifndef __HAVE_ARCH_STRNSTR
>  /**
> - * strstr - Find the first substring in a %NUL terminated string
> - * @s1: The string to be searched
> - * @s2: The string to search for
> + * strnstr() - find the first substring occurrence in a NUL terminated string
> + *
> + * @s1:                string to be searched
> + * @s2:                string to search for
> + * @len:       maximum number of characters in s2 to consider
> + *
> + * Return:     pointer to the first occurrence or NULL
>   */
> -char * strstr(const char * s1,const char * s2)
> +char *strnstr(const char *s1, const char *s2, size_t len)
>  {
> -       int l1, l2;
> +       size_t l1, l2;
>
> +       l1 = strnlen(s1, len);
>         l2 = strlen(s2);
> -       if (!l2)
> -               return (char *) s1;
> -       l1 = strlen(s1);
> -       while (l1 >= l2) {
> -               l1--;
> -               if (!memcmp(s1,s2,l2))
> +
> +       for (; l1 >= l2; --l1, ++s1) {
> +               if (!memcmp(s1, s2, l2))
>                         return (char *) s1;
> -               s1++;
>         }
> +
>         return NULL;
>  }
>  #endif
>
> +#ifndef __HAVE_ARCH_STRSTR
> +/**
> + * strstr() - find the first substring occurrence in a NUL terminated string
> + *
> + * @s1:                string to be searched
> + * @s2:                string to search for
> + * @len:       maximum number of characters in s2 to consider
> + *
> + * Return:     pointer to the first occurrence or NULL
> + */
> +char *strstr(const char *s1, const char *s2)
> +{
> +       return strnstr(s1, s2, SIZE_MAX);
> +}
> +#endif
> +
>  #ifndef __HAVE_ARCH_MEMCHR
>  /**
>   * memchr - Find a character in an area of memory.
> --
> 2.47.1
>

Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>