summaryrefslogtreecommitdiff
path: root/include/linux/list_nulls.h
blob: fa6e8471bd2278f939b7084bd1b2655ef253df71 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_LIST_NULLS_H
#define _LINUX_LIST_NULLS_H

#include <linux/poison.h>
#include <linux/const.h>

/*
 * Special version of lists, where end of list is not a NULL pointer,
 * but a 'nulls' marker, which can have many different values.
 * (up to 2^31 different values guaranteed on all platforms)
 *
 * In the standard hlist, termination of a list is the NULL pointer.
 * In this special 'nulls' variant, we use the fact that objects stored in
 * a list are aligned on a word (4 or 8 bytes alignment).
 * We therefore use the last significant bit of 'ptr' :
 * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
 * Set to 0 : This is a pointer to some object (ptr)
 */

struct hlist_nulls_head {
	struct hlist_nulls_node *first;
};

struct hlist_nulls_node {
	struct hlist_nulls_node *next, **pprev;
};
#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
	((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))

#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)

#define hlist_nulls_entry_safe(ptr, type, member) \
	({ typeof(ptr) ____ptr = (ptr); \
	   !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
	})
/**
 * ptr_is_a_nulls - Test if a ptr is a nulls
 * @ptr: ptr to be tested
 *
 */
static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
{
	return ((unsigned long)ptr & 1);
}

/**
 * get_nulls_value - Get the 'nulls' value of the end of chain
 * @ptr: end of chain
 *
 * Should be called only if is_a_nulls(ptr);
 */
static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
{
	return ((unsigned long)ptr) >> 1;
}

/**
 * hlist_nulls_unhashed - Has node been removed and reinitialized?
 * @h: Node to be checked
 *
 * Not that not all removal functions will leave a node in unhashed state.
 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
 * but hlist_nulls_del() does not.
 */
static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
{
	return !h->pprev;
}

/**
 * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
 * @h: Node to be checked
 *
 * Not that not all removal functions will leave a node in unhashed state.
 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
 * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
 * function may be used locklessly.
 */
static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
{
	return !READ_ONCE(h->pprev);
}

static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
{
	return is_a_nulls(READ_ONCE(h->first));
}

static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
					struct hlist_nulls_head *h)
{
	struct hlist_nulls_node *first = h->first;

	n->next = first;
	WRITE_ONCE(n->pprev, &h->first);
	h->first = n;
	if (!is_a_nulls(first))
		WRITE_ONCE(first->pprev, &n->next);
}

static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
{
	struct hlist_nulls_node *next = n->next;
	struct hlist_nulls_node **pprev = n->pprev;

	WRITE_ONCE(*pprev, next);
	if (!is_a_nulls(next))
		WRITE_ONCE(next->pprev, pprev);
}

static inline void hlist_nulls_del(struct hlist_nulls_node *n)
{
	__hlist_nulls_del(n);
	WRITE_ONCE(n->pprev, LIST_POISON2);
}

/**
 * hlist_nulls_for_each_entry	- iterate over list of given type
 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct hlist_node to use as a loop cursor.
 * @head:	the head for your list.
 * @member:	the name of the hlist_node within the struct.
 *
 */
#define hlist_nulls_for_each_entry(tpos, pos, head, member)		       \
	for (pos = (head)->first;					       \
	     (!is_a_nulls(pos)) &&					       \
		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
	     pos = pos->next)

/**
 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct hlist_node to use as a loop cursor.
 * @member:	the name of the hlist_node within the struct.
 *
 */
#define hlist_nulls_for_each_entry_from(tpos, pos, member)	\
	for (; (!is_a_nulls(pos)) && 				\
		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
	     pos = pos->next)

#endif