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