include/linux/container_of.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_CONTAINER_OF_H
   3 #define _LINUX_CONTAINER_OF_H
   4
   5 #include <linux/build_bug.h>
   6 #include <linux/stddef.h>
   7
   8 #define typeof_member(T, m)     typeof(((T*)0)->m)
   9
  10 /**
  11  * container_of - cast a member of a structure out to the containing structure
  12  * @ptr:        the pointer to the member.
  13  * @type:       the type of the container struct this is embedded in.
  14  * @member:     the name of the member within the struct.
  15  *
  16  * WARNING: any const qualifier of @ptr is lost.
  17  */
  18 #define container_of(ptr, type, member) ({                              \
  19         void *__mptr = (void *)(ptr);                                   \
  20         static_assert(__same_type(*(ptr), ((type *)0)->member) ||       \
  21                       __same_type(*(ptr), void),                        \
  22                       "pointer type mismatch in container_of()");       \
  23         ((type *)(__mptr - offsetof(type, member))); })
  24
  25 /**
  26  * container_of_const - cast a member of a structure out to the containing
  27  *                      structure and preserve the const-ness of the pointer
  28  * @ptr:                the pointer to the member
  29  * @type:               the type of the container struct this is embedded in.
  30  * @member:             the name of the member within the struct.
  31  */
  32 #define container_of_const(ptr, type, member)                           \
  33         _Generic(ptr,                                                   \
  34                 const typeof(*(ptr)) *: ((const type *)container_of(ptr, type, member)),\
  35                 default: ((type *)container_of(ptr, type, member))      \
  36         )
  37
  38 #endif  /* _LINUX_CONTAINER_OF_H */