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