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1#ifndef _LINUX_LIST_NULLS_H
2#define _LINUX_LIST_NULLS_H
3
4#include <linux/poison.h>
5#include <linux/const.h>
6
7/*
8 * Special version of lists, where end of list is not a NULL pointer,
9 * but a 'nulls' marker, which can have many different values.
10 * (up to 2^31 different values guaranteed on all platforms)
11 *
12 * In the standard hlist, termination of a list is the NULL pointer.
13 * In this special 'nulls' variant, we use the fact that objects stored in
14 * a list are aligned on a word (4 or 8 bytes alignment).
15 * We therefore use the last significant bit of 'ptr' :
16 * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
17 * Set to 0 : This is a pointer to some object (ptr)
18 */
19
20struct hlist_nulls_head {
21 struct hlist_nulls_node *first;
22};
23
24struct hlist_nulls_node {
25 struct hlist_nulls_node *next, **pprev;
26};
27#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
28#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
29 ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
30
31#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
32
33#define hlist_nulls_entry_safe(ptr, type, member) \
34 ({ typeof(ptr) ____ptr = (ptr); \
35 !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
36 })
37/**
38 * ptr_is_a_nulls - Test if a ptr is a nulls
39 * @ptr: ptr to be tested
40 *
41 */
42static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
43{
44 return ((unsigned long)ptr & 1);
45}
46
47/**
48 * get_nulls_value - Get the 'nulls' value of the end of chain
49 * @ptr: end of chain
50 *
51 * Should be called only if is_a_nulls(ptr);
52 */
53static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
54{
55 return ((unsigned long)ptr) >> 1;
56}
57
58static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
59{
60 return !h->pprev;
61}
62
63static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
64{
65 return is_a_nulls(READ_ONCE(h->first));
66}
67
68static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
69 struct hlist_nulls_head *h)
70{
71 struct hlist_nulls_node *first = h->first;
72
73 n->next = first;
74 n->pprev = &h->first;
75 h->first = n;
76 if (!is_a_nulls(first))
77 first->pprev = &n->next;
78}
79
80static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
81{
82 struct hlist_nulls_node *next = n->next;
83 struct hlist_nulls_node **pprev = n->pprev;
84
85 WRITE_ONCE(*pprev, next);
86 if (!is_a_nulls(next))
87 next->pprev = pprev;
88}
89
90static inline void hlist_nulls_del(struct hlist_nulls_node *n)
91{
92 __hlist_nulls_del(n);
93 n->pprev = LIST_POISON2;
94}
95
96/**
97 * hlist_nulls_for_each_entry - iterate over list of given type
98 * @tpos: the type * to use as a loop cursor.
99 * @pos: the &struct hlist_node to use as a loop cursor.
100 * @head: the head for your list.
101 * @member: the name of the hlist_node within the struct.
102 *
103 */
104#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
105 for (pos = (head)->first; \
106 (!is_a_nulls(pos)) && \
107 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
108 pos = pos->next)
109
110/**
111 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
112 * @tpos: the type * to use as a loop cursor.
113 * @pos: the &struct hlist_node to use as a loop cursor.
114 * @member: the name of the hlist_node within the struct.
115 *
116 */
117#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
118 for (; (!is_a_nulls(pos)) && \
119 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
120 pos = pos->next)
121
122#endif