Re: [PATCH v8 6/8] mm/util: Deduplicate code in {kstrdup,kstrndup,kmemdup_nul}

[Alejandro Colomar <alx@kernel.org>]

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On Wed, Aug 28, 2024 at 11:03:19AM GMT, Yafang Shao wrote:
> These three functions follow the same pattern. To deduplicate the code,
> let's introduce a common helper __kmemdup_nul().
> 
> Suggested-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Simon Horman <horms@kernel.org>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Alejandro Colomar <alx@kernel.org>
> ---

Reviewed-by: Alejandro Colomar <alx@kernel.org>

Cheers,
Alex

>  mm/util.c | 68 ++++++++++++++++++++++---------------------------------
>  1 file changed, 27 insertions(+), 41 deletions(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 9a77a347c385..42714fe13e24 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -45,33 +45,41 @@ void kfree_const(const void *x)
>  EXPORT_SYMBOL(kfree_const);
>  
>  /**
> - * kstrdup - allocate space for and copy an existing string
> - * @s: the string to duplicate
> + * __kmemdup_nul - Create a NUL-terminated string from @s, which might be unterminated.
> + * @s: The data to copy
> + * @len: The size of the data, not including the NUL terminator
>   * @gfp: the GFP mask used in the kmalloc() call when allocating memory
>   *
> - * Return: newly allocated copy of @s or %NULL in case of error
> + * Return: newly allocated copy of @s with NUL-termination or %NULL in
> + * case of error
>   */
> -noinline
> -char *kstrdup(const char *s, gfp_t gfp)
> +static __always_inline char *__kmemdup_nul(const char *s, size_t len, gfp_t gfp)
>  {
> -	size_t len;
>  	char *buf;
>  
> -	if (!s)
> +	/* '+1' for the NUL terminator */
> +	buf = kmalloc_track_caller(len + 1, gfp);
> +	if (!buf)
>  		return NULL;
>  
> -	len = strlen(s) + 1;
> -	buf = kmalloc_track_caller(len, gfp);
> -	if (buf) {
> -		memcpy(buf, s, len);
> -		/* During memcpy(), the string might be updated to a new value,
> -		 * which could be longer than the string when strlen() is
> -		 * called. Therefore, we need to add a NUL termimator.
> -		 */
> -		buf[len - 1] = '\0';
> -	}
> +	memcpy(buf, s, len);
> +	/* Ensure the buf is always NUL-terminated, regardless of @s. */
> +	buf[len] = '\0';
>  	return buf;
>  }
> +
> +/**
> + * kstrdup - allocate space for and copy an existing string
> + * @s: the string to duplicate
> + * @gfp: the GFP mask used in the kmalloc() call when allocating memory
> + *
> + * Return: newly allocated copy of @s or %NULL in case of error
> + */
> +noinline
> +char *kstrdup(const char *s, gfp_t gfp)
> +{
> +	return s ? __kmemdup_nul(s, strlen(s), gfp) : NULL;
> +}
>  EXPORT_SYMBOL(kstrdup);
>  
>  /**
> @@ -106,19 +114,7 @@ EXPORT_SYMBOL(kstrdup_const);
>   */
>  char *kstrndup(const char *s, size_t max, gfp_t gfp)
>  {
> -	size_t len;
> -	char *buf;
> -
> -	if (!s)
> -		return NULL;
> -
> -	len = strnlen(s, max);
> -	buf = kmalloc_track_caller(len+1, gfp);
> -	if (buf) {
> -		memcpy(buf, s, len);
> -		buf[len] = '\0';
> -	}
> -	return buf;
> +	return s ? __kmemdup_nul(s, strnlen(s, max), gfp) : NULL;
>  }
>  EXPORT_SYMBOL(kstrndup);
>  
> @@ -192,17 +188,7 @@ EXPORT_SYMBOL(kvmemdup);
>   */
>  char *kmemdup_nul(const char *s, size_t len, gfp_t gfp)
>  {
> -	char *buf;
> -
> -	if (!s)
> -		return NULL;
> -
> -	buf = kmalloc_track_caller(len + 1, gfp);
> -	if (buf) {
> -		memcpy(buf, s, len);
> -		buf[len] = '\0';
> -	}
> -	return buf;
> +	return s ? __kmemdup_nul(s, len, gfp) : NULL;
>  }
>  EXPORT_SYMBOL(kmemdup_nul);
>  
> -- 
> 2.43.5
> 

-- 
<https://www.alejandro-colomar.es/>

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