Re: [PATCH bpf-next v3 1/2] bpf: add bpf_strcasecmp kfunc

[Yonghong Song <yonghong.song@linux.dev>]

On 9/2/25 2:19 AM, Rong Tao wrote:
> From: Rong Tao <rongtao@cestc.cn>
>
> bpf_strcasecmp() function performs same like bpf_strcmp() except ignoring
> the case of the characters.
>
> Signed-off-by: Rong Tao <rongtao@cestc.cn>
> ---
>   kernel/bpf/helpers.c | 68 +++++++++++++++++++++++++++++++-------------
>   1 file changed, 48 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 401b4932cc49..238fd992c786 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -3349,45 +3349,72 @@ __bpf_kfunc void __bpf_trap(void)
>    * __get_kernel_nofault instead of plain dereference to make them safe.
>    */
>   
> -/**
> - * bpf_strcmp - Compare two strings
> - * @s1__ign: One string
> - * @s2__ign: Another string
> - *
> - * Return:
> - * * %0       - Strings are equal
> - * * %-1      - @s1__ign is smaller
> - * * %1       - @s2__ign is smaller
> - * * %-EFAULT - Cannot read one of the strings
> - * * %-E2BIG  - One of strings is too large
> - * * %-ERANGE - One of strings is outside of kernel address space
> - */
> -__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
> +int __bpf_strcasecmp(const char *s1, const char *s2, bool ignore_case)

The function __bpf_strcasecmp should be a static function.

>   {
>   	char c1, c2;
>   	int i;
>   
> -	if (!copy_from_kernel_nofault_allowed(s1__ign, 1) ||
> -	    !copy_from_kernel_nofault_allowed(s2__ign, 1)) {
> +	if (!copy_from_kernel_nofault_allowed(s1, 1) ||
> +	    !copy_from_kernel_nofault_allowed(s2, 1)) {
>   		return -ERANGE;
>   	}
>   
>   	guard(pagefault)();
>   	for (i = 0; i < XATTR_SIZE_MAX; i++) {
> -		__get_kernel_nofault(&c1, s1__ign, char, err_out);
> -		__get_kernel_nofault(&c2, s2__ign, char, err_out);
> +		__get_kernel_nofault(&c1, s1, char, err_out);
> +		__get_kernel_nofault(&c2, s2, char, err_out);
> +		if (ignore_case) {
> +			c1 = tolower(c1);
> +			c2 = tolower(c2);
> +		}
>   		if (c1 != c2)
>   			return c1 < c2 ? -1 : 1;
>   		if (c1 == '\0')
>   			return 0;
> -		s1__ign++;
> -		s2__ign++;
> +		s1++;
> +		s2++;
>   	}
>   	return -E2BIG;
>   err_out:
>   	return -EFAULT;
>   }
>   
> +/**
> + * bpf_strcmp - Compare two strings
> + * @s1__ign: One string
> + * @s2__ign: Another string
> + *
> + * Return:
> + * * %0       - Strings are equal
> + * * %-1      - @s1__ign is smaller
> + * * %1       - @s2__ign is smaller
> + * * %-EFAULT - Cannot read one of the strings
> + * * %-E2BIG  - One of strings is too large
> + * * %-ERANGE - One of strings is outside of kernel address space
> + */
> +__bpf_kfunc int bpf_strcmp(const char *s1__ign, const char *s2__ign)
> +{
> +	return __bpf_strcasecmp(s1__ign, s2__ign, false);
> +}
> +
> +/**
> + * bpf_strcasecmp - Compare two strings, ignoring the case of the characters
> + * @s1__ign: One string
> + * @s2__ign: Another string
> + *
> + * Return:
> + * * %0       - Strings are equal
> + * * %-1      - @s1__ign is smaller
> + * * %1       - @s2__ign is smaller
> + * * %-EFAULT - Cannot read one of the strings
> + * * %-E2BIG  - One of strings is too large
> + * * %-ERANGE - One of strings is outside of kernel address space
> + */
> +__bpf_kfunc int bpf_strcasecmp(const char *s1__ign, const char *s2__ign)
> +{
> +	return __bpf_strcasecmp(s1__ign, s2__ign, true);
> +}
> +
>   /**
>    * bpf_strnchr - Find a character in a length limited string
>    * @s__ign: The string to be searched
> @@ -3832,6 +3859,7 @@ BTF_ID_FLAGS(func, bpf_iter_dmabuf_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
>   #endif
>   BTF_ID_FLAGS(func, __bpf_trap)
>   BTF_ID_FLAGS(func, bpf_strcmp);
> +BTF_ID_FLAGS(func, bpf_strcasecmp);
>   BTF_ID_FLAGS(func, bpf_strchr);
>   BTF_ID_FLAGS(func, bpf_strchrnul);
>   BTF_ID_FLAGS(func, bpf_strnchr);