Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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#define HLIST_NULLS_HEAD_INIT(nulls) {.first = (struct hlist_nulls_node *)NULLS_MARKER(nulls)}
32
33#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
34
35#define hlist_nulls_entry_safe(ptr, type, member) \
36 ({ typeof(ptr) ____ptr = (ptr); \
37 !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
38 })
39/**
40 * ptr_is_a_nulls - Test if a ptr is a nulls
41 * @ptr: ptr to be tested
42 *
43 */
44static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
45{
46 return ((unsigned long)ptr & 1);
47}
48
49/**
50 * get_nulls_value - Get the 'nulls' value of the end of chain
51 * @ptr: end of chain
52 *
53 * Should be called only if is_a_nulls(ptr);
54 */
55static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
56{
57 return ((unsigned long)ptr) >> 1;
58}
59
60/**
61 * hlist_nulls_unhashed - Has node been removed and reinitialized?
62 * @h: Node to be checked
63 *
64 * Not that not all removal functions will leave a node in unhashed state.
65 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
66 * but hlist_nulls_del() does not.
67 */
68static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
69{
70 return !h->pprev;
71}
72
73/**
74 * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
75 * @h: Node to be checked
76 *
77 * Not that not all removal functions will leave a node in unhashed state.
78 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
79 * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this
80 * function may be used locklessly.
81 */
82static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
83{
84 return !READ_ONCE(h->pprev);
85}
86
87static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
88{
89 return is_a_nulls(READ_ONCE(h->first));
90}
91
92static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
93 struct hlist_nulls_head *h)
94{
95 struct hlist_nulls_node *first = h->first;
96
97 n->next = first;
98 WRITE_ONCE(n->pprev, &h->first);
99 h->first = n;
100 if (!is_a_nulls(first))
101 WRITE_ONCE(first->pprev, &n->next);
102}
103
104static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
105{
106 struct hlist_nulls_node *next = n->next;
107 struct hlist_nulls_node **pprev = n->pprev;
108
109 WRITE_ONCE(*pprev, next);
110 if (!is_a_nulls(next))
111 WRITE_ONCE(next->pprev, pprev);
112}
113
114static inline void hlist_nulls_del(struct hlist_nulls_node *n)
115{
116 __hlist_nulls_del(n);
117 WRITE_ONCE(n->pprev, LIST_POISON2);
118}
119
120/**
121 * hlist_nulls_for_each_entry - iterate over list of given type
122 * @tpos: the type * to use as a loop cursor.
123 * @pos: the &struct hlist_node to use as a loop cursor.
124 * @head: the head for your list.
125 * @member: the name of the hlist_node within the struct.
126 *
127 */
128#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
129 for (pos = (head)->first; \
130 (!is_a_nulls(pos)) && \
131 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
132 pos = pos->next)
133
134/**
135 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
136 * @tpos: the type * to use as a loop cursor.
137 * @pos: the &struct hlist_node to use as a loop cursor.
138 * @member: the name of the hlist_node within the struct.
139 *
140 */
141#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
142 for (; (!is_a_nulls(pos)) && \
143 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
144 pos = pos->next)
145
146#endif