1b2441318SGreg Kroah-Hartman /* SPDX-License-Identifier: GPL-2.0 */
2bbaffacaSEric Dumazet #ifndef _LINUX_LIST_NULLS_H
3bbaffacaSEric Dumazet #define _LINUX_LIST_NULLS_H
4bbaffacaSEric Dumazet
5a3449dedSYing Xue #include <linux/poison.h>
6a3449dedSYing Xue #include <linux/const.h>
7a3449dedSYing Xue
8bbaffacaSEric Dumazet /*
9bbaffacaSEric Dumazet * Special version of lists, where end of list is not a NULL pointer,
10bbaffacaSEric Dumazet * but a 'nulls' marker, which can have many different values.
11bbaffacaSEric Dumazet * (up to 2^31 different values guaranteed on all platforms)
12bbaffacaSEric Dumazet *
13bbaffacaSEric Dumazet * In the standard hlist, termination of a list is the NULL pointer.
14bbaffacaSEric Dumazet * In this special 'nulls' variant, we use the fact that objects stored in
15bbaffacaSEric Dumazet * a list are aligned on a word (4 or 8 bytes alignment).
16bbaffacaSEric Dumazet * We therefore use the last significant bit of 'ptr' :
17bbaffacaSEric Dumazet * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
18bbaffacaSEric Dumazet * Set to 0 : This is a pointer to some object (ptr)
19bbaffacaSEric Dumazet */
20bbaffacaSEric Dumazet
21bbaffacaSEric Dumazet struct hlist_nulls_head {
22bbaffacaSEric Dumazet struct hlist_nulls_node *first;
23bbaffacaSEric Dumazet };
24bbaffacaSEric Dumazet
25bbaffacaSEric Dumazet struct hlist_nulls_node {
26bbaffacaSEric Dumazet struct hlist_nulls_node *next, **pprev;
27bbaffacaSEric Dumazet };
28f89bd6f8SThomas Graf #define NULLS_MARKER(value) (1UL | (((long)value) << 1))
29bbaffacaSEric Dumazet #define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
30f89bd6f8SThomas Graf ((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
31bbaffacaSEric Dumazet
32bbaffacaSEric Dumazet #define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
334fe84359SAlexei Starovoitov
344fe84359SAlexei Starovoitov #define hlist_nulls_entry_safe(ptr, type, member) \
354fe84359SAlexei Starovoitov ({ typeof(ptr) ____ptr = (ptr); \
364fe84359SAlexei Starovoitov !is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
374fe84359SAlexei Starovoitov })
38bbaffacaSEric Dumazet /**
39bbaffacaSEric Dumazet * ptr_is_a_nulls - Test if a ptr is a nulls
40bbaffacaSEric Dumazet * @ptr: ptr to be tested
41bbaffacaSEric Dumazet *
42bbaffacaSEric Dumazet */
is_a_nulls(const struct hlist_nulls_node * ptr)43bbaffacaSEric Dumazet static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
44bbaffacaSEric Dumazet {
45bbaffacaSEric Dumazet return ((unsigned long)ptr & 1);
46bbaffacaSEric Dumazet }
47bbaffacaSEric Dumazet
48bbaffacaSEric Dumazet /**
49bbaffacaSEric Dumazet * get_nulls_value - Get the 'nulls' value of the end of chain
50bbaffacaSEric Dumazet * @ptr: end of chain
51bbaffacaSEric Dumazet *
52bbaffacaSEric Dumazet * Should be called only if is_a_nulls(ptr);
53bbaffacaSEric Dumazet */
get_nulls_value(const struct hlist_nulls_node * ptr)54bbaffacaSEric Dumazet static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
55bbaffacaSEric Dumazet {
56bbaffacaSEric Dumazet return ((unsigned long)ptr) >> 1;
57bbaffacaSEric Dumazet }
58bbaffacaSEric Dumazet
59*02b99b38SPaul E. McKenney /**
60*02b99b38SPaul E. McKenney * hlist_nulls_unhashed - Has node been removed and reinitialized?
61*02b99b38SPaul E. McKenney * @h: Node to be checked
62*02b99b38SPaul E. McKenney *
63*02b99b38SPaul E. McKenney * Not that not all removal functions will leave a node in unhashed state.
64*02b99b38SPaul E. McKenney * For example, hlist_del_init_rcu() leaves the node in unhashed state,
65*02b99b38SPaul E. McKenney * but hlist_nulls_del() does not.
66*02b99b38SPaul E. McKenney */
hlist_nulls_unhashed(const struct hlist_nulls_node * h)67bbaffacaSEric Dumazet static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
68bbaffacaSEric Dumazet {
69bbaffacaSEric Dumazet return !h->pprev;
70bbaffacaSEric Dumazet }
71bbaffacaSEric Dumazet
72*02b99b38SPaul E. McKenney /**
73*02b99b38SPaul E. McKenney * hlist_nulls_unhashed_lockless - Has node been removed and reinitialized?
74*02b99b38SPaul E. McKenney * @h: Node to be checked
75*02b99b38SPaul E. McKenney *
76*02b99b38SPaul E. McKenney * Not that not all removal functions will leave a node in unhashed state.
77*02b99b38SPaul E. McKenney * For example, hlist_del_init_rcu() leaves the node in unhashed state,
78*02b99b38SPaul E. McKenney * but hlist_nulls_del() does not. Unlike hlist_nulls_unhashed(), this
79*02b99b38SPaul E. McKenney * function may be used locklessly.
80*02b99b38SPaul E. McKenney */
hlist_nulls_unhashed_lockless(const struct hlist_nulls_node * h)81*02b99b38SPaul E. McKenney static inline int hlist_nulls_unhashed_lockless(const struct hlist_nulls_node *h)
82*02b99b38SPaul E. McKenney {
83*02b99b38SPaul E. McKenney return !READ_ONCE(h->pprev);
84*02b99b38SPaul E. McKenney }
85*02b99b38SPaul E. McKenney
hlist_nulls_empty(const struct hlist_nulls_head * h)86bbaffacaSEric Dumazet static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
87bbaffacaSEric Dumazet {
881658d35eSPaul E. McKenney return is_a_nulls(READ_ONCE(h->first));
89bbaffacaSEric Dumazet }
90bbaffacaSEric Dumazet
hlist_nulls_add_head(struct hlist_nulls_node * n,struct hlist_nulls_head * h)91d219dce7SPablo Neira Ayuso static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
92d219dce7SPablo Neira Ayuso struct hlist_nulls_head *h)
93d219dce7SPablo Neira Ayuso {
94d219dce7SPablo Neira Ayuso struct hlist_nulls_node *first = h->first;
95d219dce7SPablo Neira Ayuso
96d219dce7SPablo Neira Ayuso n->next = first;
97860c8802SPaul E. McKenney WRITE_ONCE(n->pprev, &h->first);
98d219dce7SPablo Neira Ayuso h->first = n;
99d219dce7SPablo Neira Ayuso if (!is_a_nulls(first))
100860c8802SPaul E. McKenney WRITE_ONCE(first->pprev, &n->next);
101d219dce7SPablo Neira Ayuso }
102d219dce7SPablo Neira Ayuso
__hlist_nulls_del(struct hlist_nulls_node * n)103bbaffacaSEric Dumazet static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
104bbaffacaSEric Dumazet {
105bbaffacaSEric Dumazet struct hlist_nulls_node *next = n->next;
106bbaffacaSEric Dumazet struct hlist_nulls_node **pprev = n->pprev;
1077f5f873cSPaul E. McKenney
1087f5f873cSPaul E. McKenney WRITE_ONCE(*pprev, next);
109bbaffacaSEric Dumazet if (!is_a_nulls(next))
110860c8802SPaul E. McKenney WRITE_ONCE(next->pprev, pprev);
111bbaffacaSEric Dumazet }
112bbaffacaSEric Dumazet
hlist_nulls_del(struct hlist_nulls_node * n)113d219dce7SPablo Neira Ayuso static inline void hlist_nulls_del(struct hlist_nulls_node *n)
114d219dce7SPablo Neira Ayuso {
115d219dce7SPablo Neira Ayuso __hlist_nulls_del(n);
116860c8802SPaul E. McKenney WRITE_ONCE(n->pprev, LIST_POISON2);
117d219dce7SPablo Neira Ayuso }
118d219dce7SPablo Neira Ayuso
119bbaffacaSEric Dumazet /**
120bbaffacaSEric Dumazet * hlist_nulls_for_each_entry - iterate over list of given type
121bbaffacaSEric Dumazet * @tpos: the type * to use as a loop cursor.
122bbaffacaSEric Dumazet * @pos: the &struct hlist_node to use as a loop cursor.
123bbaffacaSEric Dumazet * @head: the head for your list.
124bbaffacaSEric Dumazet * @member: the name of the hlist_node within the struct.
125bbaffacaSEric Dumazet *
126bbaffacaSEric Dumazet */
127bbaffacaSEric Dumazet #define hlist_nulls_for_each_entry(tpos, pos, head, member) \
128bbaffacaSEric Dumazet for (pos = (head)->first; \
129bbaffacaSEric Dumazet (!is_a_nulls(pos)) && \
130bbaffacaSEric Dumazet ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
131bbaffacaSEric Dumazet pos = pos->next)
132bbaffacaSEric Dumazet
133bbaffacaSEric Dumazet /**
134bbaffacaSEric Dumazet * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
135bbaffacaSEric Dumazet * @tpos: the type * to use as a loop cursor.
136bbaffacaSEric Dumazet * @pos: the &struct hlist_node to use as a loop cursor.
137bbaffacaSEric Dumazet * @member: the name of the hlist_node within the struct.
138bbaffacaSEric Dumazet *
139bbaffacaSEric Dumazet */
140bbaffacaSEric Dumazet #define hlist_nulls_for_each_entry_from(tpos, pos, member) \
141bbaffacaSEric Dumazet for (; (!is_a_nulls(pos)) && \
142bbaffacaSEric Dumazet ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
143bbaffacaSEric Dumazet pos = pos->next)
144bbaffacaSEric Dumazet
145bbaffacaSEric Dumazet #endif
146