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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright 2023 Red Hat
*/
#ifndef VDO_PRIORITY_TABLE_H
#define VDO_PRIORITY_TABLE_H
#include <linux/list.h>
/*
* A priority_table is a simple implementation of a priority queue for entries with priorities that
* are small non-negative integer values. It implements the obvious priority queue operations of
* enqueuing an entry and dequeuing an entry with the maximum priority. It also supports removing
* an arbitrary entry. The priority of an entry already in the table can be changed by removing it
* and re-enqueuing it with a different priority. All operations have O(1) complexity.
*
* The links for the table entries must be embedded in the entries themselves. Lists are used to
* link entries in the table and no wrapper type is declared, so an existing list entry in an
* object can also be used to queue it in a priority_table, assuming the field is not used for
* anything else while so queued.
*
* The table is implemented as an array of queues (circular lists) indexed by priority, along with
* a hint for which queues are non-empty. Steven Skiena calls a very similar structure a "bounded
* height priority queue", but given the resemblance to a hash table, "priority table" seems both
* shorter and more apt, if somewhat novel.
*/
struct priority_table;
int __must_check vdo_make_priority_table(unsigned int max_priority,
struct priority_table **table_ptr);
void vdo_free_priority_table(struct priority_table *table);
void vdo_priority_table_enqueue(struct priority_table *table, unsigned int priority,
struct list_head *entry);
void vdo_reset_priority_table(struct priority_table *table);
struct list_head * __must_check vdo_priority_table_dequeue(struct priority_table *table);
void vdo_priority_table_remove(struct priority_table *table, struct list_head *entry);
bool __must_check vdo_is_priority_table_empty(struct priority_table *table);
#endif /* VDO_PRIORITY_TABLE_H */
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