linux/container_of.h: Warn about loss of constness

container_of() casts the original type to another which leads to the loss
of the const qualifier if it is not specified in the caller-provided type.
This easily leads to container_of() returning a non-const pointer to a
const struct which the C compiler does not warn about.

Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Link: https://lore.kernel.org/r/20221024111627.75183-1-sakari.ailus@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/container_of.h b/include/linux/container_of.h
index a6f242137b1168d84b27f268a125ffca47abd084..2008e9f4058c634360f952645812f9b4ac278f4d 100644 (file)
--- a/include/linux/container_of.h
+++ b/include/linux/container_of.h
@@ -13,6 +13,7 @@
  * @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.
  */
 #define container_of(ptr, type, member) ({                             \
        void *__mptr = (void *)(ptr);                                   \