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(ptr: 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(ptr: 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 | |