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
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 */
43 static 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 */
54 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
55 {
56 return ((unsigned long)ptr) >> 1;
57 }
58
59 /**
60 * hlist_nulls_unhashed - Has node been removed and reinitialized?
61 * @h: Node to be checked
62 *
63 * Not that not all removal functions will leave a node in unhashed state.
64 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
65 * but hlist_nulls_del() does not.
66 */
67 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
68 {
69 return !h->pprev;
70 }
71
72 /**
73 * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
74 * @h: Node to be checked
75 *
76 * Not that not all removal functions will leave a node in unhashed state.
77 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
78 * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this
79 * function may be used locklessly.
80 */
81 static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
82 {
83 return !READ_ONCE(h->pprev);
84 }
85
86 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
87 {
88 return is_a_nulls(READ_ONCE(h->first));
89 }
90
91 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
92 struct hlist_nulls_head *h)
93 {
94 struct hlist_nulls_node *first = h->first;
95
96 n->next = first;
97 WRITE_ONCE(n->pprev, &h->first);
98 h->first = n;
99 if (!is_a_nulls(first))
100 WRITE_ONCE(first->pprev, &n->next);
101 }
102
103 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
104 {
105 struct hlist_nulls_node *next = n->next;
106 struct hlist_nulls_node **pprev = n->pprev;
107
108 WRITE_ONCE(*pprev, next);
109 if (!is_a_nulls(next))
110 WRITE_ONCE(next->pprev, pprev);
111 }
112
113 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
114 {
115 __hlist_nulls_del(n);
116 WRITE_ONCE(n->pprev, LIST_POISON2);
117 }
118
119 /**
120 * hlist_nulls_for_each_entry - iterate over list of given type
121 * @tpos: the type * to use as a loop cursor.
122 * @pos: the &struct hlist_node to use as a loop cursor.
123 * @head: the head for your list.
124 * @member: the name of the hlist_node within the struct.
125 *
126 */
127 #define hlist_nulls_for_each_entry(tpos, pos, head, member) \
128 for (pos = (head)->first; \
129 (!is_a_nulls(pos)) && \
130 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
131 pos = pos->next)
132
133 /**
134 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
135 * @tpos: the type * to use as a loop cursor.
136 * @pos: the &struct hlist_node to use as a loop cursor.
137 * @member: the name of the hlist_node within the struct.
138 *
139 */
140 #define hlist_nulls_for_each_entry_from(tpos, pos, member) \
141 for (; (!is_a_nulls(pos)) && \
142 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
143 pos = pos->next)
144
145 #endif
146
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