Re: [PATCH 2/4] linux/array_size.h: Add ARRAY_SIZE_OF_FIELD()

[Alejandro Colomar]

Hi Lucas,

On 2023-08-17 16:33, Lucas Segarra Fernandez wrote:
> Introduce ARRAY_SIZE_OF_FIELD() in order to get the number of elements
> of an array struct field.
> 
> Signed-off-by: Lucas Segarra Fernandez <lucas.segarra.fernandez@xxxxxxxxx>
> Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@xxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> ---
>  include/linux/array_size.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/linux/array_size.h b/include/linux/array_size.h
> index 06d7d83196ca..37dac0473b5c 100644
> --- a/include/linux/array_size.h
> +++ b/include/linux/array_size.h
> @@ -10,4 +10,12 @@
>   */
>  #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]) + __must_be_array(arr))
>  
> +/*
> + * ARRAY_SIZE_OF_FIELD - get the number of elements of an array struct field
> + *
> + * @TYPE: The structure containing the field of interest
> + * @MEMBER: The array field to be sized
> + */
> +#define ARRAY_SIZE_OF_FIELD(TYPE, MEMBER) ARRAY_SIZE((((TYPE *)0)->MEMBER))

Some comment about the name:

ARRAY_SIZE() is rather ambiguous, as there's array_size()[1], which means the
number of bytes needed to represent the array.  I suggest a name based on

-  _Lengthof()  It has been proposed to ISO C to get the number of elements
                of an array:
                <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2529.pdf>.

-  sizeof_field()  The kernel macro for the size of a struct member

So, how about lengthof_field()?


Cheers,
Alex


[1]:  The definition of array_size() is here:

$ grep -rnB10 define.array_size include/linux/overflow.h 
238-/**
239- * array_size() - Calculate size of 2-dimensional array.
240- * @a: dimension one
241- * @b: dimension two
242- *
243- * Calculates size of 2-dimensional array: @a * @b.
244- *
245- * Returns: number of bytes needed to represent the array or SIZE_MAX on
246- * overflow.
247- */
248:#define array_size(a, b)	size_mul(a, b)


> +
>  #endif  /* _LINUX_ARRAY_SIZE_H */

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