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 */
is_a_nulls(const struct hlist_nulls_node * ptr)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 */
get_nulls_value(const struct hlist_nulls_node * ptr)54 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
55 {
56 return ((unsigned long)ptr) >> 1;
57 }
58
hlist_nulls_unhashed(const struct hlist_nulls_node * h)59 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
60 {
61 return !h->pprev;
62 }
63
hlist_nulls_empty(const struct hlist_nulls_head * h)64 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
65 {
66 return is_a_nulls(READ_ONCE(h->first));
67 }
68
hlist_nulls_add_head(struct hlist_nulls_node * n,struct hlist_nulls_head * h)69 static 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 WRITE_ONCE(n->pprev, &h->first);
76 h->first = n;
77 if (!is_a_nulls(first))
78 WRITE_ONCE(first->pprev, &n->next);
79 }
80
__hlist_nulls_del(struct hlist_nulls_node * n)81 static 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 WRITE_ONCE(next->pprev, pprev);
89 }
90
hlist_nulls_del(struct hlist_nulls_node * n)91 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
92 {
93 __hlist_nulls_del(n);
94 WRITE_ONCE(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