linux-kernel - [PATCH 1/1] container_of: Document container_of

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Message-Id: <20240617100825.2510728-1-sakari.ailus@linux.intel.com>
Date: Mon, 17 Jun 2024 13:08:25 +0300
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Gunthorpe <jgg@...dia.com>,
	Matthew Wilcox <willy@...radead.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>
Subject: [PATCH 1/1] container_of: Document container_of_const() is preferred

There is a warning in kerneldoc documentation of container_of() that
constness of @ptr is lost. While this is a suggestion container_of_const()
should be used instead, the vast majority of new code still uses
container_of():

$ git diff v6.8 v6.9|grep container_of\(|wc -l
788
$ git diff v6.8 v6.9|grep container_of_const|wc -l
11

Make an explicit recommendation to use container_of_const(), unless @ptr
is const but its container isn't.

Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.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..7563015ff165 100644
--- a/include/linux/container_of.h
+++ b/include/linux/container_of.h
@@ -13,7 +13,9 @@
  * @type:	the type of the container struct this is embedded in.
  * @member:	the name of the member within the struct.
  *
- * WARNING: any const qualifier of @ptr is lost.
+ * WARNING: any const qualifier of @ptr is lost. container_of() should only be
+ * used in cases where @ptr is const and its container is not and you know what
+ * you're doing. Otherwise always use container_of_const().
  */
 #define container_of(ptr, type, member) ({				\
 	void *__mptr = (void *)(ptr);					\
-- 
2.39.2