lib/ccan/container_of/container_of.h

   1 #ifndef CCAN_CONTAINER_OF_H
   2 #define CCAN_CONTAINER_OF_H
   3 #include <stddef.h>
   4
   5 #include "config.h"
   6 #include <ccan/check_type/check_type.h>
   7
   8 /**
   9  * container_of - get pointer to enclosing structure
  10  * @member_ptr: pointer to the structure member
  11  * @containing_type: the type this member is within
  12  * @member: the name of this member within the structure.
  13  *
  14  * Given a pointer to a member of a structure, this macro does pointer
  15  * subtraction to return the pointer to the enclosing type.
  16  *
  17  * Example:
  18  *      struct foo {
  19  *              int fielda, fieldb;
  20  *              // ...
  21  *      };
  22  *      struct info {
  23  *              int some_other_field;
  24  *              struct foo my_foo;
  25  *      };
  26  *
  27  *      static struct info *foo_to_info(struct foo *foo)
  28  *      {
  29  *              return container_of(foo, struct info, my_foo);
  30  *      }
  31  */
  32 #define container_of(member_ptr, containing_type, member)               \
  33          ((containing_type *)                                           \
  34           ((char *)(member_ptr)                                         \
  35            - container_off(containing_type, member))                    \
  36           + check_types_match(*(member_ptr), ((containing_type *)0)->member))
  37
  38 /**
  39  * container_off - get offset to enclosing structure
  40  * @containing_type: the type this member is within
  41  * @member: the name of this member within the structure.
  42  *
  43  * Given a pointer to a member of a structure, this macro does
  44  * typechecking and figures out the offset to the enclosing type.
  45  *
  46  * Example:
  47  *      struct foo {
  48  *              int fielda, fieldb;
  49  *              // ...
  50  *      };
  51  *      struct info {
  52  *              int some_other_field;
  53  *              struct foo my_foo;
  54  *      };
  55  *
  56  *      static struct info *foo_to_info(struct foo *foo)
  57  *      {
  58  *              size_t off = container_off(struct info, my_foo);
  59  *              return (void *)((char *)foo - off);
  60  *      }
  61  */
  62 #define container_off(containing_type, member)  \
  63         offsetof(containing_type, member)
  64
  65 /**
  66  * container_of_var - get pointer to enclosing structure using a variable
  67  * @member_ptr: pointer to the structure member
  68  * @container_var: a pointer of same type as this member's container
  69  * @member: the name of this member within the structure.
  70  *
  71  * Given a pointer to a member of a structure, this macro does pointer
  72  * subtraction to return the pointer to the enclosing type.
  73  *
  74  * Example:
  75  *      static struct info *foo_to_i(struct foo *foo)
  76  *      {
  77  *              struct info *i = container_of_var(foo, i, my_foo);
  78  *              return i;
  79  *      }
  80  */
  81 #if HAVE_TYPEOF
  82 #define container_of_var(member_ptr, container_var, member) \
  83         container_of(member_ptr, typeof(*container_var), member)
  84 #else
  85 #define container_of_var(member_ptr, container_var, member)     \
  86         ((void *)((char *)(member_ptr)  -                       \
  87                   container_off_var(container_var, member)))
  88 #endif
  89
  90 /**
  91  * container_off_var - get offset of a field in enclosing structure
  92  * @container_var: a pointer to a container structure
  93  * @member: the name of a member within the structure.
  94  *
  95  * Given (any) pointer to a structure and a its member name, this
  96  * macro does pointer subtraction to return offset of member in a
  97  * structure memory layout.
  98  *
  99  */
 100 #if HAVE_TYPEOF
 101 #define container_off_var(var, member)          \
 102         container_off(typeof(*var), member)
 103 #else
 104 #define container_off_var(var, member)                  \
 105         ((char *)&(var)->member - (char *)(var))
 106 #endif
 107
 108 #endif /* CCAN_CONTAINER_OF_H */