结构体成员取结构体头指针
list_entry->container_of->offsetof
344 /*
345 list_entry - get the struct for this entry
346 @ptr: the &struct list_head pointer.
347 @type: the type of the struct this is embedded in.
348 @member: the name of the list_struct within the struct.
349 /
350 #define list_entry(ptr, type, member) \
351 container_of(ptr, type, member)
684 /*
685 container_of - cast a member of a structure out to the containing structure
686 @ptr: the pointer to the member.
687 @type: the type of the container struct this is embedded in.
688 @member: the name of the member within the struct.
689
690 /
691 #define container_of(ptr, type, member) ({ \
692 const typeof( ((type )0)->member ) __mptr = (ptr); \
693 (type )( (char *)__mptr - offsetof(type,member) );})
Linux/include/linux/stddef.h
1 #ifndef _LINUX_STDDEF_H
2 #define _LINUX_STDDEF_H
3
4 #include <linux/compiler.h>
5
6 #ifdef KERNEL
7
8 #undef NULL
9 #define NULL ((void )0)
10
11 enum {
12 false = 0,
13 true = 1
14 };
15
16 #undef offsetof
17 #ifdef compiler_offsetof
18 #define offsetof(TYPE,MEMBER) compiler_offsetof(TYPE,MEMBER)
19 #else
20 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE )0)->MEMBER)
21 #endif
22 #endif / KERNEL /
23
24 #endif
25
__compiler_offsetof(TYPE,MEMBER)就和gcc的原子操作实现一样，也是编译器built-in