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1/* SPDX-License-Identifier: GPL-2.0-only */
2
3#ifndef LWQ_H
4#define LWQ_H
5/*
6 * Light-weight single-linked queue built from llist
7 *
8 * Entries can be enqueued from any context with no locking.
9 * Entries can be dequeued from process context with integrated locking.
10 *
11 * This is particularly suitable when work items are queued in
12 * BH or IRQ context, and where work items are handled one at a time
13 * by dedicated threads.
14 */
15#include <linux/container_of.h>
16#include <linux/spinlock.h>
17#include <linux/llist.h>
18
19struct lwq_node {
20 struct llist_node node;
21};
22
23struct lwq {
24 spinlock_t lock;
25 struct llist_node *ready; /* entries to be dequeued */
26 struct llist_head new; /* entries being enqueued */
27};
28
29/**
30 * lwq_init - initialise a lwq
31 * @q: the lwq object
32 */
33static inline void lwq_init(struct lwq *q)
34{
35 spin_lock_init(&q->lock);
36 q->ready = NULL;
37 init_llist_head(list: &q->new);
38}
39
40/**
41 * lwq_empty - test if lwq contains any entry
42 * @q: the lwq object
43 *
44 * This empty test contains an acquire barrier so that if a wakeup
45 * is sent when lwq_dequeue returns true, it is safe to go to sleep after
46 * a test on lwq_empty().
47 */
48static inline bool lwq_empty(struct lwq *q)
49{
50 /* acquire ensures ordering wrt lwq_enqueue() */
51 return smp_load_acquire(&q->ready) == NULL && llist_empty(head: &q->new);
52}
53
54struct llist_node *__lwq_dequeue(struct lwq *q);
55/**
56 * lwq_dequeue - dequeue first (oldest) entry from lwq
57 * @q: the queue to dequeue from
58 * @type: the type of object to return
59 * @member: them member in returned object which is an lwq_node.
60 *
61 * Remove a single object from the lwq and return it. This will take
62 * a spinlock and so must always be called in the same context, typcially
63 * process contet.
64 */
65#define lwq_dequeue(q, type, member) \
66 ({ struct llist_node *_n = __lwq_dequeue(q); \
67 _n ? container_of(_n, type, member.node) : NULL; })
68
69struct llist_node *lwq_dequeue_all(struct lwq *q);
70
71/**
72 * lwq_for_each_safe - iterate over detached queue allowing deletion
73 * @_n: iterator variable
74 * @_t1: temporary struct llist_node **
75 * @_t2: temporary struct llist_node *
76 * @_l: address of llist_node pointer from lwq_dequeue_all()
77 * @_member: member in _n where lwq_node is found.
78 *
79 * Iterate over members in a dequeued list. If the iterator variable
80 * is set to NULL, the iterator removes that entry from the queue.
81 */
82#define lwq_for_each_safe(_n, _t1, _t2, _l, _member) \
83 for (_t1 = (_l); \
84 *(_t1) ? (_n = container_of(*(_t1), typeof(*(_n)), _member.node),\
85 _t2 = ((*_t1)->next), \
86 true) \
87 : false; \
88 (_n) ? (_t1 = &(_n)->_member.node.next, 0) \
89 : ((*(_t1) = (_t2)), 0))
90
91/**
92 * lwq_enqueue - add a new item to the end of the queue
93 * @n - the lwq_node embedded in the item to be added
94 * @q - the lwq to append to.
95 *
96 * No locking is needed to append to the queue so this can
97 * be called from any context.
98 * Return %true is the list may have previously been empty.
99 */
100static inline bool lwq_enqueue(struct lwq_node *n, struct lwq *q)
101{
102 /* acquire enqures ordering wrt lwq_dequeue */
103 return llist_add(new: &n->node, head: &q->new) &&
104 smp_load_acquire(&q->ready) == NULL;
105}
106
107/**
108 * lwq_enqueue_batch - add a list of new items to the end of the queue
109 * @n - the lwq_node embedded in the first item to be added
110 * @q - the lwq to append to.
111 *
112 * No locking is needed to append to the queue so this can
113 * be called from any context.
114 * Return %true is the list may have previously been empty.
115 */
116static inline bool lwq_enqueue_batch(struct llist_node *n, struct lwq *q)
117{
118 struct llist_node *e = n;
119
120 /* acquire enqures ordering wrt lwq_dequeue */
121 return llist_add_batch(new_first: llist_reverse_order(head: n), new_last: e, head: &q->new) &&
122 smp_load_acquire(&q->ready) == NULL;
123}
124#endif /* LWQ_H */
125

source code of linux/include/linux/lwq.h