1 #ifndef _LINUX_LIST_NULLS_H
2 #define _LINUX_LIST_NULLS_H
3 
4 /*
5  * Special version of lists, where end of list is not a NULL pointer,
6  * but a 'nulls' marker, which can have many different values.
7  * (up to 2^31 different values guaranteed on all platforms)
8  *
9  * In the standard hlist, termination of a list is the NULL pointer.
10  * In this special 'nulls' variant, we use the fact that objects stored in
11  * a list are aligned on a word (4 or 8 bytes alignment).
12  * We therefore use the last significant bit of 'ptr' :
13  * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
14  * Set to 0 : This is a pointer to some object (ptr)
15  */
16 
17 struct hlist_nulls_head {
18 	struct hlist_nulls_node *first;
19 };
20 
21 struct hlist_nulls_node {
22 	struct hlist_nulls_node *next, **pprev;
23 };
24 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
25 	((ptr)->first = (struct hlist_nulls_node *) (1UL | (((long)nulls) << 1)))
26 
27 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
28 /**
29  * ptr_is_a_nulls - Test if a ptr is a nulls
30  * @ptr: ptr to be tested
31  *
32  */
is_a_nulls(const struct hlist_nulls_node * ptr)33 static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
34 {
35 	return ((unsigned long)ptr & 1);
36 }
37 
38 /**
39  * get_nulls_value - Get the 'nulls' value of the end of chain
40  * @ptr: end of chain
41  *
42  * Should be called only if is_a_nulls(ptr);
43  */
get_nulls_value(const struct hlist_nulls_node * ptr)44 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
45 {
46 	return ((unsigned long)ptr) >> 1;
47 }
48 
hlist_nulls_unhashed(const struct hlist_nulls_node * h)49 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
50 {
51 	return !h->pprev;
52 }
53 
hlist_nulls_empty(const struct hlist_nulls_head * h)54 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
55 {
56 	return is_a_nulls(h->first);
57 }
58 
hlist_nulls_add_head(struct hlist_nulls_node * n,struct hlist_nulls_head * h)59 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
60 					struct hlist_nulls_head *h)
61 {
62 	struct hlist_nulls_node *first = h->first;
63 
64 	n->next = first;
65 	n->pprev = &h->first;
66 	h->first = n;
67 	if (!is_a_nulls(first))
68 		first->pprev = &n->next;
69 }
70 
__hlist_nulls_del(struct hlist_nulls_node * n)71 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
72 {
73 	struct hlist_nulls_node *next = n->next;
74 	struct hlist_nulls_node **pprev = n->pprev;
75 	*pprev = next;
76 	if (!is_a_nulls(next))
77 		next->pprev = pprev;
78 }
79 
hlist_nulls_del(struct hlist_nulls_node * n)80 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
81 {
82 	__hlist_nulls_del(n);
83 	n->pprev = LIST_POISON2;
84 }
85 
86 /**
87  * hlist_nulls_for_each_entry	- iterate over list of given type
88  * @tpos:	the type * to use as a loop cursor.
89  * @pos:	the &struct hlist_node to use as a loop cursor.
90  * @head:	the head for your list.
91  * @member:	the name of the hlist_node within the struct.
92  *
93  */
94 #define hlist_nulls_for_each_entry(tpos, pos, head, member)		       \
95 	for (pos = (head)->first;					       \
96 	     (!is_a_nulls(pos)) &&					       \
97 		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
98 	     pos = pos->next)
99 
100 /**
101  * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
102  * @tpos:	the type * to use as a loop cursor.
103  * @pos:	the &struct hlist_node to use as a loop cursor.
104  * @member:	the name of the hlist_node within the struct.
105  *
106  */
107 #define hlist_nulls_for_each_entry_from(tpos, pos, member)	\
108 	for (; (!is_a_nulls(pos)) && 				\
109 		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
110 	     pos = pos->next)
111 
112 #endif
113