/*
* Copyright (C) 2016, Emilio G. Cota <cota@braap.org>
*
* License: GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
#ifndef QEMU_QHT_H
#define QEMU_QHT_H
#include "qemu/seqlock.h"
#include "qemu/thread.h"
#include "qemu/qdist.h"
struct qht {
struct qht_map *map;
QemuMutex lock; /* serializes setters of ht->map */
unsigned int mode;
};
/**
* struct qht_stats - Statistics of a QHT
* @head_buckets: number of head buckets
* @used_head_buckets: number of non-empty head buckets
* @entries: total number of entries
* @chain: frequency distribution representing the number of buckets in each
* chain, excluding empty chains.
* @occupancy: frequency distribution representing chain occupancy rate.
* Valid range: from 0.0 (empty) to 1.0 (full occupancy).
*
* An entry is a pointer-hash pair.
* Each bucket can host several entries.
* Chains are chains of buckets, whose first link is always a head bucket.
*/
struct qht_stats {
size_t head_buckets;
size_t used_head_buckets;
size_t entries;
struct qdist chain;
struct qdist occupancy;
};
typedef bool (*qht_lookup_func_t)(const void *obj, const void *userp);
typedef void (*qht_iter_func_t)(struct qht *ht, void *p, uint32_t h, void *up);
#define QHT_MODE_AUTO_RESIZE 0x1 /* auto-resize when heavily loaded */
/**
* qht_init - Initialize a QHT
* @ht: QHT to be initialized
* @n_elems: number of entries the hash table should be optimized for.
* @mode: bitmask with OR'ed QHT_MODE_*
*/
void qht_init(struct qht *ht, size_t n_elems, unsigned int mode);
/**
* qht_destroy - destroy a previously initialized QHT
* @ht: QHT to be destroyed
*
* Call only when there are no readers/writers left.
*/
void qht_destroy(struct qht *ht);
/**
* qht_insert - Insert a pointer into the hash table
* @ht: QHT to insert to
* @p: pointer to be inserted
* @hash: hash corresponding to @p
*
* Attempting to insert a NULL @p is a bug.
* Inserting the same pointer @p with different @hash values is a bug.
*
* In case of successful operation, smp_wmb() is implied before the pointer is
* inserted into the hash table.
*
* Returns true on success.
* Returns false if the @p-@hash pair already exists in the hash table.
*/
bool qht_insert(struct qht *ht, void *p, uint32_t hash);
/**
* qht_lookup - Look up a pointer in a QHT
* @ht: QHT to be looked up
* @func: function to compare existing pointers against @userp
* @userp: pointer to pass to @func
* @hash: hash of the pointer to be looked up
*
* Needs to be called under an RCU read-critical section.
*
* smp_read_barrier_depends() is implied before the call to @func.
*
* The user-provided @func compares pointers in QHT against @userp.
* If the function returns true, a match has been found.
*
* Returns the corresponding pointer when a match is found.
* Returns NULL otherwise.
*/
void *qht_lookup(struct qht *ht, qht_lookup_func_t func, const void *userp,
uint32_t hash);
/**
* qht_remove - remove a pointer from the hash table
* @ht: QHT to remove from
* @p: pointer to be removed
* @hash: hash corresponding to @p
*
* Attempting to remove a NULL @p is a bug.
*
* Just-removed @p pointers cannot be immediately freed; they need to remain
* valid until the end of the RCU grace period in which qht_remove() is called.
* This guarantees that concurrent lookups will always compare against valid
* data.
*
* Returns true on success.
* Returns false if the @p-@hash pair was not found.
*/
bool qht_remove(struct qht *ht, const void *p, uint32_t hash);
/**
* qht_reset - reset a QHT
* @ht: QHT to be reset
*
* All entries in the hash table are reset. No resizing is performed.
*
* If concurrent readers may exist, the objects pointed to by the hash table
* must remain valid for the existing RCU grace period -- see qht_remove().
* See also: qht_reset_size()
*/
void qht_reset(struct qht *ht);
/**
* qht_reset_size - reset and resize a QHT
* @ht: QHT to be reset and resized
* @n_elems: number of entries the resized hash table should be optimized for.
*
* Returns true if the resize was necessary and therefore performed.
* Returns false otherwise.
*
* If concurrent readers may exist, the objects pointed to by the hash table
* must remain valid for the existing RCU grace period -- see qht_remove().
* See also: qht_reset(), qht_resize().
*/
bool qht_reset_size(struct qht *ht, size_t n_elems);
/**
* qht_resize - resize a QHT
* @ht: QHT to be resized
* @n_elems: number of entries the resized hash table should be optimized for
*
* Returns true on success.
* Returns false if the resize was not necessary and therefore not performed.
* See also: qht_reset_size().
*/
bool qht_resize(struct qht *ht, size_t n_elems);
/**
* qht_iter - Iterate over a QHT
* @ht: QHT to be iterated over
* @func: function to be called for each entry in QHT
* @userp: additional pointer to be passed to @func
*
* Each time it is called, user-provided @func is passed a pointer-hash pair,
* plus @userp.
*/
void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp);
/**
* qht_statistics_init - Gather statistics from a QHT
* @ht: QHT to gather statistics from
* @stats: pointer to a &struct qht_stats to be filled in
*
* Does NOT need to be called under an RCU read-critical section,
* since it does not dereference any pointers stored in the hash table.
*
* When done with @stats, pass the struct to qht_statistics_destroy().
* Failing to do this will leak memory.
*/
void qht_statistics_init(struct qht *ht, struct qht_stats *stats);
/**
* qht_statistics_destroy - Destroy a &struct qht_stats
* @stats: &struct qht_stats to be destroyed
*
* See also: qht_statistics_init().
*/
void qht_statistics_destroy(struct qht_stats *stats);
#endif /* QEMU_QHT_H */
