xref: /linux/drivers/md/dm-vdo/priority-table.h (revision 6d9b262afe0ec1d6e0ef99321ca9d6b921310471)
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 
29 struct priority_table;
30 
31 int __must_check vdo_make_priority_table(unsigned int max_priority,
32 					 struct priority_table **table_ptr);
33 
34 void vdo_free_priority_table(struct priority_table *table);
35 
36 void vdo_priority_table_enqueue(struct priority_table *table, unsigned int priority,
37 				struct list_head *entry);
38 
39 void vdo_reset_priority_table(struct priority_table *table);
40 
41 struct list_head * __must_check vdo_priority_table_dequeue(struct priority_table *table);
42 
43 void vdo_priority_table_remove(struct priority_table *table, struct list_head *entry);
44 
45 bool __must_check vdo_is_priority_table_empty(struct priority_table *table);
46 
47 #endif /* VDO_PRIORITY_TABLE_H */
48