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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
17struct hlist_nulls_head {
18 struct hlist_nulls_node *first;
19};
20
21struct 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 */
33static 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 */
44static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
45{
46 return ((unsigned long)ptr) >> 1;
47}
48
49static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
50{
51 return !h->pprev;
52}
53
54static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
55{
56 return is_a_nulls(h->first);
57}
58
59static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
60{
61 struct hlist_nulls_node *next = n->next;
62 struct hlist_nulls_node **pprev = n->pprev;
63 *pprev = next;
64 if (!is_a_nulls(next))
65 next->pprev = pprev;
66}
67
68/**
69 * hlist_nulls_for_each_entry - iterate over list of given type
70 * @tpos: the type * to use as a loop cursor.
71 * @pos: the &struct hlist_node to use as a loop cursor.
72 * @head: the head for your list.
73 * @member: the name of the hlist_node within the struct.
74 *
75 */
76#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
77 for (pos = (head)->first; \
78 (!is_a_nulls(pos)) && \
79 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
80 pos = pos->next)
81
82/**
83 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
84 * @tpos: the type * to use as a loop cursor.
85 * @pos: the &struct hlist_node to use as a loop cursor.
86 * @member: the name of the hlist_node within the struct.
87 *
88 */
89#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
90 for (; (!is_a_nulls(pos)) && \
91 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
92 pos = pos->next)
93
94#endif