linux-kernel - Re: [PATCH] linux/container

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Message-ID: <ZONIFMSmLZMeFPOY@smile.fi.intel.com>
Date:   Mon, 21 Aug 2023 14:18:44 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Alejandro Colomar <alx@...nel.org>
Cc:     qat-linux@...el.com, Alejandro Colomar <alx.manpages@...il.com>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Lucas Segarra Fernandez <lucas.segarra.fernandez@...el.com>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>
Subject: Re: [PATCH] linux/container_of.h: Add memberof()

On Sun, Aug 20, 2023 at 09:52:22PM +0200, Alejandro Colomar wrote:
> On 2023-08-18 10:46, Andy Shevchenko wrote:
> > On Fri, Aug 18, 2023 at 01:28:42PM +0800, Herbert Xu wrote:
> >> On Thu, Aug 17, 2023 at 04:33:17PM +0200, Lucas Segarra Fernandez wrote:

...

> Many xxxof_{member,field}() macros make use of the same construction to
> refer to a member of a struct without needing a variable of the
> structure type.
> 
> memberof(T, m) simplifies all of those, avoids possible mistakes in
> repetition, adds a meaningful name to the construction, and improves
> readability by avoiding too many parentheses together.
> 
> It uses a compound literal, which should optimized out by the compiler.
> It's a bit simpler to read than the dereference of a casted null
> pointer, due to having less parentheses in the implementation.
> 
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: Lucas Segarra Fernandez <lucas.segarra.fernandez@...el.com>
> Cc: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
> Signed-off-by: Alejandro Colomar <alx.manpages@...il.com>
> ---
>  include/linux/container_of.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/container_of.h b/include/linux/container_of.h
> index 713890c867be..5e762025c780 100644
> --- a/include/linux/container_of.h
> +++ b/include/linux/container_of.h
> @@ -5,7 +5,9 @@
>  #include <linux/build_bug.h>
>  #include <linux/stddef.h>
>  
> -#define typeof_member(T, m)	typeof(((T*)0)->m)
> +
> +#define memberof(T, member)  ((T){}.member)

I'm not sure. This seems to me utilization of compound literal, while above
uses direct struct member pointer calculations.

> +#define typeof_member(T, m)  typeof(memberof(T, m))

-- 
With Best Regards,
Andy Shevchenko