1 #ifndef _LINUX_LIST_NULLS_H
2 #define _LINUX_LIST_NULLS_H
3
4 #include <linux/poison.h>
5 #include <linux/const.h>
6
7 /*
8 * Special version of lists, where end of list is not a NULL pointer,
9 * but a 'nulls' marker, which can have many different values.
10 * (up to 2^31 different values guaranteed on all platforms)
11 *
12 * In the standard hlist, termination of a list is the NULL pointer.
13 * In this special 'nulls' variant, we use the fact that objects stored in
14 * a list are aligned on a word (4 or 8 bytes alignment).
15 * We therefore use the last significant bit of 'ptr' :
16 * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
17 * Set to 0 : This is a pointer to some object (ptr)
18 */
19
20 struct hlist_nulls_head {
21 struct hlist_nulls_node *first;
22 };
23
24 struct hlist_nulls_node {
25 struct hlist_nulls_node *next, **pprev;
26 };
27 #define NULLS_MARKER(value) (1UL | (((long)value) << 1))
28 #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
29 ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
30
31 #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
32 /**
33 * ptr_is_a_nulls - Test if a ptr is a nulls
34 * @ptr: ptr to be tested
35 *
36 */
is_a_nulls(const struct hlist_nulls_node * ptr)37 static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
38 {
39 return ((unsigned long)ptr & 1);
40 }
41
42 /**
43 * get_nulls_value - Get the 'nulls' value of the end of chain
44 * @ptr: end of chain
45 *
46 * Should be called only if is_a_nulls(ptr);
47 */
get_nulls_value(const struct hlist_nulls_node * ptr)48 static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
49 {
50 return ((unsigned long)ptr) >> 1;
51 }
52
hlist_nulls_unhashed(const struct hlist_nulls_node * h)53 static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
54 {
55 return !h->pprev;
56 }
57
hlist_nulls_empty(const struct hlist_nulls_head * h)58 static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
59 {
60 return is_a_nulls(READ_ONCE(h->first));
61 }
62
hlist_nulls_add_head(struct hlist_nulls_node * n,struct hlist_nulls_head * h)63 static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
64 struct hlist_nulls_head *h)
65 {
66 struct hlist_nulls_node *first = h->first;
67
68 n->next = first;
69 n->pprev = &h->first;
70 h->first = n;
71 if (!is_a_nulls(first))
72 first->pprev = &n->next;
73 }
74
__hlist_nulls_del(struct hlist_nulls_node * n)75 static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
76 {
77 struct hlist_nulls_node *next = n->next;
78 struct hlist_nulls_node **pprev = n->pprev;
79
80 WRITE_ONCE(*pprev, next);
81 if (!is_a_nulls(next))
82 next->pprev = pprev;
83 }
84
hlist_nulls_del(struct hlist_nulls_node * n)85 static inline void hlist_nulls_del(struct hlist_nulls_node *n)
86 {
87 __hlist_nulls_del(n);
88 n->pprev = LIST_POISON2;
89 }
90
91 /**
92 * hlist_nulls_for_each_entry - iterate over list of given type
93 * @tpos: the type * to use as a loop cursor.
94 * @pos: the &struct hlist_node to use as a loop cursor.
95 * @head: the head for your list.
96 * @member: the name of the hlist_node within the struct.
97 *
98 */
99 #define hlist_nulls_for_each_entry(tpos, pos, head, member) \
100 for (pos = (head)->first; \
101 (!is_a_nulls(pos)) && \
102 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
103 pos = pos->next)
104
105 /**
106 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
107 * @tpos: the type * to use as a loop cursor.
108 * @pos: the &struct hlist_node to use as a loop cursor.
109 * @member: the name of the hlist_node within the struct.
110 *
111 */
112 #define hlist_nulls_for_each_entry_from(tpos, pos, member) \
113 for (; (!is_a_nulls(pos)) && \
114 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
115 pos = pos->next)
116
117 #endif
118