linux-kernel - Re: [PATCH v4 2/7] kernel.h: Split out container_of() and typeof

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Date:   Thu, 07 Oct 2021 09:27:38 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-media@...r.kernel.org
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        jic23@...nel.org, linux@...musvillemoes.dk,
        Thorsten Leemhuis <regressions@...mhuis.info>
Subject: Re: [PATCH v4 2/7] kernel.h: Split out container_of() and
 typeof_member() macros

On Thu, 2021-10-07 at 18:44 +0300, Andy Shevchenko wrote:
> kernel.h is being used as a dump for all kinds of stuff for a long time.
> Here is the attempt cleaning it up by splitting out container_of() and
> typeof_member() macros.
> 
> For time being include new header back to kernel.h to avoid twisted
> indirected includes for existing users.

IMO: this new file is missing 2 #include directives.

> diff --git a/include/linux/container_of.h b/include/linux/container_of.h
[]
> @@ -0,0 +1,37 @@
> +/* SPDX-License-Identifier: GPL-2.0 */

And trivially: I'd prefer GPL-2.0-only

> +#ifndef _LINUX_CONTAINER_OF_H
> +#define _LINUX_CONTAINER_OF_H
> +
> +#define typeof_member(T, m)	typeof(((T*)0)->m)
> +
> +/**
> + * container_of - cast a member of a structure out to the containing structure
> + * @ptr:	the pointer to the member.
> + * @type:	the type of the container struct this is embedded in.
> + * @member:	the name of the member within the struct.
> + *
> + */
> +#define container_of(ptr, type, member) ({				\
> +	void *__mptr = (void *)(ptr);					\
> +	BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) &&	\
> +			 !__same_type(*(ptr), void),			\
> +			 "pointer type mismatch in container_of()");	\

This is not a self-contained header as it requires
#include <linux/build_bug.h>
which should be at the top of this file.

> +	((type *)(__mptr - offsetof(type, member))); })
> +
> +/**
> + * container_of_safe - cast a member of a structure out to the containing structure
> + * @ptr:	the pointer to the member.
> + * @type:	the type of the container struct this is embedded in.
> + * @member:	the name of the member within the struct.
> + *
> + * If IS_ERR_OR_NULL(ptr), ptr is returned unchanged.
> + */
> +#define container_of_safe(ptr, type, member) ({				\
> +	void *__mptr = (void *)(ptr);					\
> +	BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) &&	\
> +			 !__same_type(*(ptr), void),			\
> +			 "pointer type mismatch in container_of()");	\
> +	IS_ERR_OR_NULL(__mptr) ? ERR_CAST(__mptr) :			\
> +		((type *)(__mptr - offsetof(type, member))); })

And this requires

#include <linux/err.h>

> +
> +#endif	/* _LINUX_CONTAINER_OF_H */