projects/linux·blob master · refs

205 lines · 6.6 KiB

1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2023 Red Hat
4 */
5
6#include "wait-queue.h"
7
8#include <linux/device-mapper.h>
9
10#include "permassert.h"
11
12#include "status-codes.h"
13
14/**
15 * vdo_waitq_enqueue_waiter() - Add a waiter to the tail end of a waitq.
16 * @waitq: The vdo_wait_queue to which to add the waiter.
17 * @waiter: The waiter to add to the waitq.
18 *
19 * The waiter must not already be waiting in a waitq.
20 */
21void vdo_waitq_enqueue_waiter(struct vdo_wait_queue *waitq, struct vdo_waiter *waiter)
22{
23 BUG_ON(waiter->next_waiter != NULL);
24
25 if (waitq->last_waiter == NULL) {
26 /*
27 * The waitq is empty, so form the initial circular list by self-linking the
28 * initial waiter.
29 */
30 waiter->next_waiter = waiter;
31 } else {
32 /* Splice the new waiter in at the end of the waitq. */
33 waiter->next_waiter = waitq->last_waiter->next_waiter;
34 waitq->last_waiter->next_waiter = waiter;
35 }
36
37 /* In both cases, the waiter we added to the list becomes the last waiter. */
38 waitq->last_waiter = waiter;
39 waitq->length += 1;
40}
41
42/**
43 * vdo_waitq_transfer_all_waiters() - Transfer all waiters from one waitq to
44 * a second waitq, emptying the first waitq.
45 * @from_waitq: The waitq containing the waiters to move.
46 * @to_waitq: The waitq that will receive the waiters from the first waitq.
47 */
48void vdo_waitq_transfer_all_waiters(struct vdo_wait_queue *from_waitq,
49 struct vdo_wait_queue *to_waitq)
50{
51 /* If the source waitq is empty, there's nothing to do. */
52 if (!vdo_waitq_has_waiters(from_waitq))
53 return;
54
55 if (vdo_waitq_has_waiters(to_waitq)) {
56 /*
57 * Both are non-empty. Splice the two circular lists together
58 * by swapping the next (head) pointers in the list tails.
59 */
60 struct vdo_waiter *from_head = from_waitq->last_waiter->next_waiter;
61 struct vdo_waiter *to_head = to_waitq->last_waiter->next_waiter;
62
63 to_waitq->last_waiter->next_waiter = from_head;
64 from_waitq->last_waiter->next_waiter = to_head;
65 }
66
67 to_waitq->last_waiter = from_waitq->last_waiter;
68 to_waitq->length += from_waitq->length;
69 vdo_waitq_init(from_waitq);
70}
71
72/**
73 * vdo_waitq_notify_all_waiters() - Notify all the entries waiting in a waitq.
74 * @waitq: The vdo_wait_queue containing the waiters to notify.
75 * @callback: The function to call to notify each waiter, or NULL to invoke the callback field
76 * registered in each waiter.
77 * @context: The context to pass to the callback function.
78 *
79 * Notifies all the entries waiting in a waitq to continue execution by invoking a callback
80 * function on each of them in turn. The waitq is copied and emptied before invoking any callbacks,
81 * and only the waiters that were in the waitq at the start of the call will be notified.
82 */
83void vdo_waitq_notify_all_waiters(struct vdo_wait_queue *waitq,
84 vdo_waiter_callback_fn callback, void *context)
85{
86 /*
87 * Copy and empty the waitq first, avoiding the possibility of an infinite
88 * loop if entries are returned to the waitq by the callback function.
89 */
90 struct vdo_wait_queue waiters;
91
92 vdo_waitq_init(&waiters);
93 vdo_waitq_transfer_all_waiters(waitq, &waiters);
94
95 /* Drain the copied waitq, invoking the callback on every entry. */
96 while (vdo_waitq_has_waiters(&waiters))
97 vdo_waitq_notify_next_waiter(&waiters, callback, context);
98}
99
100/**
101 * vdo_waitq_get_first_waiter() - Return the waiter that is at the head end of a waitq.
102 * @waitq: The vdo_wait_queue from which to get the first waiter.
103 *
104 * Return: The first (oldest) waiter in the waitq, or NULL if the waitq is empty.
105 */
106struct vdo_waiter *vdo_waitq_get_first_waiter(const struct vdo_wait_queue *waitq)
107{
108 struct vdo_waiter *last_waiter = waitq->last_waiter;
109
110 if (last_waiter == NULL) {
111 /* There are no waiters, so we're done. */
112 return NULL;
113 }
114
115 /* The waitq is circular, so the last entry links to the head of the waitq. */
116 return last_waiter->next_waiter;
117}
118
119/**
120 * vdo_waitq_dequeue_matching_waiters() - Remove all waiters that match based on the specified
121 * matching method and append them to a vdo_wait_queue.
122 * @waitq: The vdo_wait_queue to process.
123 * @waiter_match: The method to determine matching.
124 * @match_context: Contextual info for the match method.
125 * @matched_waitq: A wait_waitq to store matches.
126 */
127void vdo_waitq_dequeue_matching_waiters(struct vdo_wait_queue *waitq,
128 vdo_waiter_match_fn waiter_match,
129 void *match_context,
130 struct vdo_wait_queue *matched_waitq)
131{
132 struct vdo_wait_queue iteration_waitq;
133
134 vdo_waitq_init(&iteration_waitq);
135 vdo_waitq_transfer_all_waiters(waitq, &iteration_waitq);
136
137 while (vdo_waitq_has_waiters(&iteration_waitq)) {
138 struct vdo_waiter *waiter = vdo_waitq_dequeue_waiter(&iteration_waitq);
139
140 vdo_waitq_enqueue_waiter((waiter_match(waiter, match_context) ?
141 matched_waitq : waitq), waiter);
142 }
143}
144
145/**
146 * vdo_waitq_dequeue_waiter() - Remove the first (oldest) waiter from a waitq.
147 * @waitq: The vdo_wait_queue from which to remove the first entry.
148 *
149 * The caller will be responsible for waking the waiter by continuing its
150 * execution appropriately.
151 *
152 * Return: The first (oldest) waiter in the waitq, or NULL if the waitq is empty.
153 */
154struct vdo_waiter *vdo_waitq_dequeue_waiter(struct vdo_wait_queue *waitq)
155{
156 struct vdo_waiter *first_waiter = vdo_waitq_get_first_waiter(waitq);
157 struct vdo_waiter *last_waiter = waitq->last_waiter;
158
159 if (first_waiter == NULL)
160 return NULL;
161
162 if (first_waiter == last_waiter) {
163 /* The waitq has a single entry, so empty it by nulling the tail. */
164 waitq->last_waiter = NULL;
165 } else {
166 /*
167 * The waitq has multiple waiters, so splice the first waiter out
168 * of the circular waitq.
169 */
170 last_waiter->next_waiter = first_waiter->next_waiter;
171 }
172
173 /* The waiter is no longer in a waitq. */
174 first_waiter->next_waiter = NULL;
175 waitq->length -= 1;
176
177 return first_waiter;
178}
179
180/**
181 * vdo_waitq_notify_next_waiter() - Notify the next entry waiting in a waitq.
182 * @waitq: The vdo_wait_queue containing the waiter to notify.
183 * @callback: The function to call to notify the waiter, or NULL to invoke the callback field
184 * registered in the waiter.
185 * @context: The context to pass to the callback function.
186 *
187 * Notifies the next entry waiting in a waitq to continue execution by invoking a callback function
188 * on it after removing it from the waitq.
189 *
190 * Return: true if there was a waiter in the waitq.
191 */
192bool vdo_waitq_notify_next_waiter(struct vdo_wait_queue *waitq,
193 vdo_waiter_callback_fn callback, void *context)
194{
195 struct vdo_waiter *waiter = vdo_waitq_dequeue_waiter(waitq);
196
197 if (waiter == NULL)
198 return false;
199
200 if (callback == NULL)
201 callback = waiter->callback;
202 callback(waiter, context);
203
204 return true;
205}