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(&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(&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(&n->node, &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(llist_reverse_order(n), e, &q->new) &&
122		smp_load_acquire(&q->ready) == NULL;
123}
124#endif /* LWQ_H */
125