list_nulls.h

  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
 21struct hlist_nulls_head {
 22	struct hlist_nulls_node *first;
 23};
 24
 25struct 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#define HLIST_NULLS_HEAD_INIT(nulls) {.first = (struct hlist_nulls_node *)NULLS_MARKER(nulls)}
 32
 33#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
 34
 35#define hlist_nulls_entry_safe(ptr, type, member) \
 36	({ typeof(ptr) ____ptr = (ptr); \
 37	   !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
 38	})
 39/**
 40 * ptr_is_a_nulls - Test if a ptr is a nulls
 41 * @ptr: ptr to be tested
 42 *
 43 */
 44static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
 45{
 46	return ((unsigned long)ptr & 1);
 47}
 48
 49/**
 50 * get_nulls_value - Get the 'nulls' value of the end of chain
 51 * @ptr: end of chain
 52 *
 53 * Should be called only if is_a_nulls(ptr);
 54 */
 55static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
 56{
 57	return ((unsigned long)ptr) >> 1;
 58}
 59
 60/**
 61 * hlist_nulls_unhashed - Has node been removed and reinitialized?
 62 * @h: Node to be checked
 63 *
 64 * Not that not all removal functions will leave a node in unhashed state.
 65 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
 66 * but hlist_nulls_del() does not.
 67 */
 68static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
 69{
 70	return !h->pprev;
 71}
 72
 73/**
 74 * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
 75 * @h: Node to be checked
 76 *
 77 * Not that not all removal functions will leave a node in unhashed state.
 78 * For example, hlist_del_init_rcu() leaves the node in unhashed state,
 79 * but hlist_nulls_del() does not.  Unlike hlist_nulls_unhashed(), this
 80 * function may be used locklessly.
 81 */
 82static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
 83{
 84	return !READ_ONCE(h->pprev);
 85}
 86
 87static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
 88{
 89	return is_a_nulls(READ_ONCE(h->first));
 90}
 91
 92static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
 93					struct hlist_nulls_head *h)
 94{
 95	struct hlist_nulls_node *first = h->first;
 96
 97	n->next = first;
 98	WRITE_ONCE(n->pprev, &h->first);
 99	h->first = n;
100	if (!is_a_nulls(first))
101		WRITE_ONCE(first->pprev, &n->next);
102}
103
104static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
105{
106	struct hlist_nulls_node *next = n->next;
107	struct hlist_nulls_node **pprev = n->pprev;
108
109	WRITE_ONCE(*pprev, next);
110	if (!is_a_nulls(next))
111		WRITE_ONCE(next->pprev, pprev);
112}
113
114static inline void hlist_nulls_del(struct hlist_nulls_node *n)
115{
116	__hlist_nulls_del(n);
117	WRITE_ONCE(n->pprev, LIST_POISON2);
118}
119
120/**
121 * hlist_nulls_for_each_entry	- iterate over list of given type
122 * @tpos:	the type * to use as a loop cursor.
123 * @pos:	the &struct hlist_node to use as a loop cursor.
124 * @head:	the head for your list.
125 * @member:	the name of the hlist_node within the struct.
126 *
127 */
128#define hlist_nulls_for_each_entry(tpos, pos, head, member)		       \
129	for (pos = (head)->first;					       \
130	     (!is_a_nulls(pos)) &&					       \
131		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
132	     pos = pos->next)
133
134/**
135 * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
136 * @tpos:	the type * to use as a loop cursor.
137 * @pos:	the &struct hlist_node to use as a loop cursor.
138 * @member:	the name of the hlist_node within the struct.
139 *
140 */
141#define hlist_nulls_for_each_entry_from(tpos, pos, member)	\
142	for (; (!is_a_nulls(pos)) && 				\
143		({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
144	     pos = pos->next)
145
146#endif