1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_LIST_NULLS_H
3#define _LINUX_LIST_NULLS_H
4
5#include <linux/poison.h>
6#include <linux/const.h>
7
8/*
9 * Special version of lists, where end of list is not a NULL pointer,
10 * but a 'nulls' marker, which can have many different values.
11 * (up to 2^31 different values guaranteed on all platforms)
12 *
13 * In the standard hlist, termination of a list is the NULL pointer.
14 * In this special 'nulls' variant, we use the fact that objects stored in
15 * a list are aligned on a word (4 or 8 bytes alignment).
16 * We therefore use the last significant bit of 'ptr' :
17 * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
18 * Set to 0 : This is a pointer to some object (ptr)
19 */
20
21struct hlist_nulls_head {
22 struct hlist_nulls_node *first;
23};
24
25struct hlist_nulls_node {
26 struct hlist_nulls_node *next, **pprev;
27};
28#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
29#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
30 ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
31
32#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
33
34#define hlist_nulls_entry_safe(ptr, type, member) \
35 ({ typeof(ptr) ____ptr = (ptr); \
36 !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
37 })
38/**
39 * ptr_is_a_nulls - Test if a ptr is a nulls
40 * @ptr: ptr to be tested
41 *
42 */
43static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
44{
45 return ((unsigned long)ptr & 1);
46}
47
48/**
49 * get_nulls_value - Get the 'nulls' value of the end of chain
50 * @ptr: end of chain
51 *
52 * Should be called only if is_a_nulls(ptr);
53 */
54static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
55{
56 return ((unsigned long)ptr) >> 1;
57}
58
59static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
60{
61 return !h->pprev;
62}
63
64static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
65{
66 return is_a_nulls(READ_ONCE(h->first));
67}
68
69static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
70 struct hlist_nulls_head *h)
71{
72 struct hlist_nulls_node *first = h->first;
73
74 n->next = first;
75 n->pprev = &h->first;
76 h->first = n;
77 if (!is_a_nulls(first))
78 first->pprev = &n->next;
79}
80
81static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
82{
83 struct hlist_nulls_node *next = n->next;
84 struct hlist_nulls_node **pprev = n->pprev;
85
86 WRITE_ONCE(*pprev, next);
87 if (!is_a_nulls(next))
88 next->pprev = pprev;
89}
90
91static inline void hlist_nulls_del(struct hlist_nulls_node *n)
92{
93 __hlist_nulls_del(n);
94 n->pprev = LIST_POISON2;
95}
96
97/**
98 * hlist_nulls_for_each_entry - iterate over list of given type
99 * @tpos: the type * to use as a loop cursor.
100 * @pos: the &struct hlist_node to use as a loop cursor.
101 * @head: the head for your list.
102 * @member: the name of the hlist_node within the struct.
103 *
104 */
105#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
106 for (pos = (head)->first; \
107 (!is_a_nulls(pos)) && \
108 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
109 pos = pos->next)
110
111/**
112 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
113 * @tpos: the type * to use as a loop cursor.
114 * @pos: the &struct hlist_node to use as a loop cursor.
115 * @member: the name of the hlist_node within the struct.
116 *
117 */
118#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
119 for (; (!is_a_nulls(pos)) && \
120 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
121 pos = pos->next)
122
123#endif
124