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
21 struct hlist_nulls_head {
22 struct hlist_nulls_node *first;
23 };
24
25 struct 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 */
is_a_nulls(const struct hlist_nulls_node * ptr)44 static 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 */
get_nulls_value(const struct hlist_nulls_node * ptr)55 static 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 */
hlist_nulls_unhashed(const struct hlist_nulls_node * h)68 static 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 */
hlist_nulls_unhashed_lockless(const struct hlist_nulls_node * h)82 static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
83 {
84 return !READ_ONCE(h->pprev);
85 }
86
hlist_nulls_empty(const struct hlist_nulls_head * h)87 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
88 {
89 return is_a_nulls(READ_ONCE(h->first));
90 }
91
hlist_nulls_add_head(struct hlist_nulls_node * n,struct hlist_nulls_head * h)92 static 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
__hlist_nulls_del(struct hlist_nulls_node * n)104 static 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
hlist_nulls_del(struct hlist_nulls_node * n)114 static 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
147