include/sys/containerof.h

   1 /*
   2  * This file and its contents are supplied under the terms of the
   3  * Common Development and Distribution License ("CDDL"), version 1.0.
   4  * You may only use this file in accordance with the terms of version
   5  * 1.0 of the CDDL.
   6  *
   7  * A full copy of the text of the CDDL should have accompanied this
   8  * source.  A copy of the CDDL is also available via the Internet at
   9  * http://www.illumos.org/license/CDDL.
  10  */
  11
  12 /*
  13  * Copyright 2017 Toomas Soome <tsoome@me.com>
  14  */
  15
  16 #ifndef _SYS_CONTAINEROF_H
  17 #define _SYS_CONTAINEROF_H
  18
  19 /*
  20  * __containerof macro for private use in illumos.
  21  *
  22  * __containerof(ptr, type, member) will return pointer to the data
  23  * structure of given type, calculated based on the offset of 'member'
  24  * in the structure 'type'.
  25  *
  26  * For this macro to work, we should be certain of the pointer type.
  27  */
  28
  29 #include <sys/stddef.h>
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 #if !defined(__containerof)
  36
  37 /*
  38  * The extension to support statements and declarations in expressions,
  39  * https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html, is available
  40  * in gcc >= 3.1.
  41  * We perform the assignment below to try and provide additional type safety.
  42  */
  43 #if (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
  44 #define __containerof(m, s, name) (                                     \
  45 {                                                                       \
  46         const volatile __typeof(((s *)0)->name) *__m = (m);             \
  47         (void *)((uintptr_t)__m - (uintptr_t)offsetof(s, name));        \
  48 })
  49 #else
  50 #define __containerof(m, s, name)                       \
  51         (void *)((uintptr_t)(m) - (uintptr_t)offsetof(s, name))
  52 #endif
  53 #endif
  54
  55 #ifdef __cplusplus
  56 }
  57 #endif
  58
  59 #endif /* _SYS_CONTAINEROF_H */