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Eric Dumazetbbaffac2008-11-16 19:37:55 -08001#ifndef _LINUX_LIST_NULLS_H
2#define _LINUX_LIST_NULLS_H
3
Ying Xuea3449de2015-01-04 15:24:35 +08004#include <linux/poison.h>
5#include <linux/const.h>
6
Eric Dumazetbbaffac2008-11-16 19:37:55 -08007/*
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};
Thomas Graff89bd6f2015-01-02 23:00:21 +010027#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
Eric Dumazetbbaffac2008-11-16 19:37:55 -080028#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
Thomas Graff89bd6f2015-01-02 23:00:21 +010029 ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
Eric Dumazetbbaffac2008-11-16 19:37:55 -080030
31#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
32/**
33 * ptr_is_a_nulls - Test if a ptr is a nulls
34 * @ptr: ptr to be tested
35 *
36 */
37static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
38{
39 return ((unsigned long)ptr & 1);
40}
41
42/**
43 * get_nulls_value - Get the 'nulls' value of the end of chain
44 * @ptr: end of chain
45 *
46 * Should be called only if is_a_nulls(ptr);
47 */
48static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
49{
50 return ((unsigned long)ptr) >> 1;
51}
52
53static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
54{
55 return !h->pprev;
56}
57
58static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
59{
Paul E. McKenney1658d352015-09-20 17:03:16 -070060 return is_a_nulls(READ_ONCE(h->first));
Eric Dumazetbbaffac2008-11-16 19:37:55 -080061}
62
Pablo Neira Ayusod219dce2009-06-13 12:28:57 +020063static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
64 struct hlist_nulls_head *h)
65{
66 struct hlist_nulls_node *first = h->first;
67
68 n->next = first;
69 n->pprev = &h->first;
70 h->first = n;
71 if (!is_a_nulls(first))
72 first->pprev = &n->next;
73}
74
Eric Dumazetbbaffac2008-11-16 19:37:55 -080075static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
76{
77 struct hlist_nulls_node *next = n->next;
78 struct hlist_nulls_node **pprev = n->pprev;
Paul E. McKenney7f5f8732015-09-18 08:45:22 -070079
80 WRITE_ONCE(*pprev, next);
Eric Dumazetbbaffac2008-11-16 19:37:55 -080081 if (!is_a_nulls(next))
82 next->pprev = pprev;
83}
84
Pablo Neira Ayusod219dce2009-06-13 12:28:57 +020085static inline void hlist_nulls_del(struct hlist_nulls_node *n)
86{
87 __hlist_nulls_del(n);
88 n->pprev = LIST_POISON2;
89}
90
Eric Dumazetbbaffac2008-11-16 19:37:55 -080091/**
92 * hlist_nulls_for_each_entry - iterate over list of given type
93 * @tpos: the type * to use as a loop cursor.
94 * @pos: the &struct hlist_node to use as a loop cursor.
95 * @head: the head for your list.
96 * @member: the name of the hlist_node within the struct.
97 *
98 */
99#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
100 for (pos = (head)->first; \
101 (!is_a_nulls(pos)) && \
102 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
103 pos = pos->next)
104
105/**
106 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
107 * @tpos: the type * to use as a loop cursor.
108 * @pos: the &struct hlist_node to use as a loop cursor.
109 * @member: the name of the hlist_node within the struct.
110 *
111 */
112#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
113 for (; (!is_a_nulls(pos)) && \
114 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
115 pos = pos->next)
116
117#endif