1/* SPDX-License-Identifier: GPL-2.0-only */
 2/*
 3 * Copyright 2023 Red Hat
 4 */
 5
 6#ifndef VDO_PRIORITY_TABLE_H
 7#define VDO_PRIORITY_TABLE_H
 8
 9#include <linux/list.h>
10
11/*
12 * A priority_table is a simple implementation of a priority queue for entries with priorities that
13 * are small non-negative integer values. It implements the obvious priority queue operations of
14 * enqueuing an entry and dequeuing an entry with the maximum priority. It also supports removing
15 * an arbitrary entry. The priority of an entry already in the table can be changed by removing it
16 * and re-enqueuing it with a different priority. All operations have O(1) complexity.
17 *
18 * The links for the table entries must be embedded in the entries themselves. Lists are used to
19 * link entries in the table and no wrapper type is declared, so an existing list entry in an
20 * object can also be used to queue it in a priority_table, assuming the field is not used for
21 * anything else while so queued.
22 *
23 * The table is implemented as an array of queues (circular lists) indexed by priority, along with
24 * a hint for which queues are non-empty. Steven Skiena calls a very similar structure a "bounded
25 * height priority queue", but given the resemblance to a hash table, "priority table" seems both
26 * shorter and more apt, if somewhat novel.
27 */
28
29struct priority_table;
30
31int __must_check vdo_make_priority_table(unsigned int max_priority,
32					 struct priority_table **table_ptr);
33
34void vdo_free_priority_table(struct priority_table *table);
35
36void vdo_priority_table_enqueue(struct priority_table *table, unsigned int priority,
37				struct list_head *entry);
38
39void vdo_reset_priority_table(struct priority_table *table);
40
41struct list_head * __must_check vdo_priority_table_dequeue(struct priority_table *table);
42
43void vdo_priority_table_remove(struct priority_table *table, struct list_head *entry);
44
45bool __must_check vdo_is_priority_table_empty(struct priority_table *table);
46
47#endif /* VDO_PRIORITY_TABLE_H */