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
20struct hlist_nulls_head {
21	struct hlist_nulls_node *first;
22};
23
24struct 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 */
37static 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 */
48static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
49{
50	return ((unsigned long)ptr) >> 1;
51}
52
53static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
54{
55	return !h->pprev;
56}
57
58static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
59{
60	return is_a_nulls(h->first);
61}
62
63static 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
75static 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	*pprev = next;
80	if (!is_a_nulls(next))
81		next->pprev = pprev;
82}
83
84static inline void hlist_nulls_del(struct hlist_nulls_node *n)
85{
86	__hlist_nulls_del(n);
87	n->pprev = LIST_POISON2;
88}
89
90/**
91 * hlist_nulls_for_each_entry	- iterate over list of given type
92 * @tpos:	the type * to use as a loop cursor.
93 * @pos:	the &struct hlist_node to use as a loop cursor.
94 * @head:	the head for your list.
95 * @member:	the name of the hlist_node within the struct.
96 *
97 */
98#define hlist_nulls_for_each_entry(tpos, pos, head, member)		       \
99	for (pos = (head)->first;					       \
100	     (!is_a_nulls(pos)) &&					       \
101		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
102	     pos = pos->next)
103
104/**
105 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
106 * @tpos:	the type * to use as a loop cursor.
107 * @pos:	the &struct hlist_node to use as a loop cursor.
108 * @member:	the name of the hlist_node within the struct.
109 *
110 */
111#define hlist_nulls_for_each_entry_from(tpos, pos, member)	\
112	for (; (!is_a_nulls(pos)) && 				\
113		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
114	     pos = pos->next)
115
116#endif
117