1 #ifndef _LINUX_STDDEF_H
2 #define _LINUX_STDDEF_H
3 
4 #undef NULL
5 #if defined(__cplusplus)
6 #define NULL 0
7 #else
8 #define NULL ((void *)0)
9 #endif
10 
11 #undef offsetof
12 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
13 
14 
15 /**
16  * container_of - cast a member of a structure out to the containing structure
17  *
18  * @ptr:	the pointer to the member.
19  * @type:	the type of the container struct this is embedded in.
20  * @member:	the name of the member within the struct.
21  *
22  */
23 #define container_of(ptr, type, member) ({			\
24         const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
25         (type *)( (char *)__mptr - offsetof(type,member) );})
26 
27 /*
28  * Check at compile time that something is of a particular type.
29  * Always evaluates to 1 so you may use it easily in comparisons.
30  */
31 #define typecheck(type,x) \
32 ({	type __dummy; \
33 	typeof(x) __dummy2; \
34 	(void)(&__dummy == &__dummy2); \
35 	1; \
36 })
37 
38 
39 #endif
40