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+/*
+ * qht.c - QEMU Hash Table, designed to scale for read-mostly workloads.
+ *
+ * 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.
+ *
+ * Assumptions:
+ * - NULL cannot be inserted/removed as a pointer value.
+ * - Trying to insert an already-existing hash-pointer pair is OK. However,
+ * it is not OK to insert into the same hash table different hash-pointer
+ * pairs that have the same pointer value, but not the hashes.
+ * - Lookups are performed under an RCU read-critical section; removals
+ * must wait for a grace period to elapse before freeing removed objects.
+ *
+ * Features:
+ * - Reads (i.e. lookups and iterators) can be concurrent with other reads.
+ * Lookups that are concurrent with writes to the same bucket will retry
+ * via a seqlock; iterators acquire all bucket locks and therefore can be
+ * concurrent with lookups and are serialized wrt writers.
+ * - Writes (i.e. insertions/removals) can be concurrent with writes to
+ * different buckets; writes to the same bucket are serialized through a lock.
+ * - Optional auto-resizing: the hash table resizes up if the load surpasses
+ * a certain threshold. Resizing is done concurrently with readers; writes
+ * are serialized with the resize operation.
+ *
+ * The key structure is the bucket, which is cacheline-sized. Buckets
+ * contain a few hash values and pointers; the u32 hash values are stored in
+ * full so that resizing is fast. Having this structure instead of directly
+ * chaining items has two advantages:
+ * - Failed lookups fail fast, and touch a minimum number of cache lines.
+ * - Resizing the hash table with concurrent lookups is easy.
+ *
+ * There are two types of buckets:
+ * 1. "head" buckets are the ones allocated in the array of buckets in qht_map.
+ * 2. all "non-head" buckets (i.e. all others) are members of a chain that
+ * starts from a head bucket.
+ * Note that the seqlock and spinlock of a head bucket applies to all buckets
+ * chained to it; these two fields are unused in non-head buckets.
+ *
+ * On removals, we move the last valid item in the chain to the position of the
+ * just-removed entry. This makes lookups slightly faster, since the moment an
+ * invalid entry is found, the (failed) lookup is over.
+ *
+ * Resizing is done by taking all bucket spinlocks (so that no other writers can
+ * race with us) and then copying all entries into a new hash map. Then, the
+ * ht->map pointer is set, and the old map is freed once no RCU readers can see
+ * it anymore.
+ *
+ * Writers check for concurrent resizes by comparing ht->map before and after
+ * acquiring their bucket lock. If they don't match, a resize has occurred
+ * while the bucket spinlock was being acquired.
+ *
+ * Related Work:
+ * - Idea of cacheline-sized buckets with full hashes taken from:
+ * David, Guerraoui & Trigonakis, "Asynchronized Concurrency:
+ * The Secret to Scaling Concurrent Search Data Structures", ASPLOS'15.
+ * - Why not RCU-based hash tables? They would allow us to get rid of the
+ * seqlock, but resizing would take forever since RCU read critical
+ * sections in QEMU take quite a long time.
+ * More info on relativistic hash tables:
+ * + Triplett, McKenney & Walpole, "Resizable, Scalable, Concurrent Hash
+ * Tables via Relativistic Programming", USENIX ATC'11.
+ * + Corbet, "Relativistic hash tables, part 1: Algorithms", @ lwn.net, 2014.
+ * https://lwn.net/Articles/612021/
+ */
+#include "qemu/osdep.h"
+#include "qemu/qht.h"
+#include "qemu/atomic.h"
+#include "qemu/rcu.h"
+
+//#define QHT_DEBUG
+
+/*
+ * We want to avoid false sharing of cache lines. Most systems have 64-byte
+ * cache lines so we go with it for simplicity.
+ *
+ * Note that systems with smaller cache lines will be fine (the struct is
+ * almost 64-bytes); systems with larger cache lines might suffer from
+ * some false sharing.
+ */
+#define QHT_BUCKET_ALIGN 64
+
+/* define these to keep sizeof(qht_bucket) within QHT_BUCKET_ALIGN */
+#if HOST_LONG_BITS == 32
+#define QHT_BUCKET_ENTRIES 6
+#else /* 64-bit */
+#define QHT_BUCKET_ENTRIES 4
+#endif
+
+enum qht_iter_type {
+ QHT_ITER_VOID, /* do nothing; use retvoid */
+ QHT_ITER_RM, /* remove element if retbool returns true */
+};
+
+struct qht_iter {
+ union {
+ qht_iter_func_t retvoid;
+ qht_iter_bool_func_t retbool;
+ } f;
+ enum qht_iter_type type;
+};
+
+/*
+ * Do _not_ use qemu_mutex_[try]lock directly! Use these macros, otherwise
+ * the profiler (QSP) will deadlock.
+ */
+static inline void qht_lock(struct qht *ht)
+{
+ if (ht->mode & QHT_MODE_RAW_MUTEXES) {
+ qemu_mutex_lock__raw(&ht->lock);
+ } else {
+ qemu_mutex_lock(&ht->lock);
+ }
+}
+
+static inline int qht_trylock(struct qht *ht)
+{
+ if (ht->mode & QHT_MODE_RAW_MUTEXES) {
+ return qemu_mutex_trylock__raw(&(ht)->lock);
+ }
+ return qemu_mutex_trylock(&(ht)->lock);
+}
+
+/* this inline is not really necessary, but it helps keep code consistent */
+static inline void qht_unlock(struct qht *ht)
+{
+ qemu_mutex_unlock(&ht->lock);
+}
+
+/*
+ * Note: reading partially-updated pointers in @pointers could lead to
+ * segfaults. We thus access them with qatomic_read/set; this guarantees
+ * that the compiler makes all those accesses atomic. We also need the
+ * volatile-like behavior in qatomic_read, since otherwise the compiler
+ * might refetch the pointer.
+ * qatomic_read's are of course not necessary when the bucket lock is held.
+ *
+ * If both ht->lock and b->lock are grabbed, ht->lock should always
+ * be grabbed first.
+ */
+struct qht_bucket {
+ QemuSpin lock;
+ QemuSeqLock sequence;
+ uint32_t hashes[QHT_BUCKET_ENTRIES];
+ void *pointers[QHT_BUCKET_ENTRIES];
+ struct qht_bucket *next;
+} QEMU_ALIGNED(QHT_BUCKET_ALIGN);
+
+QEMU_BUILD_BUG_ON(sizeof(struct qht_bucket) > QHT_BUCKET_ALIGN);
+
+/**
+ * struct qht_map - structure to track an array of buckets
+ * @rcu: used by RCU. Keep it as the top field in the struct to help valgrind
+ * find the whole struct.
+ * @buckets: array of head buckets. It is constant once the map is created.
+ * @n_buckets: number of head buckets. It is constant once the map is created.
+ * @n_added_buckets: number of added (i.e. "non-head") buckets
+ * @n_added_buckets_threshold: threshold to trigger an upward resize once the
+ * number of added buckets surpasses it.
+ *
+ * Buckets are tracked in what we call a "map", i.e. this structure.
+ */
+struct qht_map {
+ struct rcu_head rcu;
+ struct qht_bucket *buckets;
+ size_t n_buckets;
+ size_t n_added_buckets;
+ size_t n_added_buckets_threshold;
+};
+
+/* trigger a resize when n_added_buckets > n_buckets / div */
+#define QHT_NR_ADDED_BUCKETS_THRESHOLD_DIV 8
+
+static void qht_do_resize_reset(struct qht *ht, struct qht_map *new,
+ bool reset);
+static void qht_grow_maybe(struct qht *ht);
+
+#ifdef QHT_DEBUG
+
+#define qht_debug_assert(X) do { assert(X); } while (0)
+
+static void qht_bucket_debug__locked(struct qht_bucket *b)
+{
+ bool seen_empty = false;
+ bool corrupt = false;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] == NULL) {
+ seen_empty = true;
+ continue;
+ }
+ if (seen_empty) {
+ fprintf(stderr, "%s: b: %p, pos: %i, hash: 0x%x, p: %p\n",
+ __func__, b, i, b->hashes[i], b->pointers[i]);
+ corrupt = true;
+ }
+ }
+ b = b->next;
+ } while (b);
+ qht_debug_assert(!corrupt);
+}
+
+static void qht_map_debug__all_locked(struct qht_map *map)
+{
+ int i;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ qht_bucket_debug__locked(&map->buckets[i]);
+ }
+}
+#else
+
+#define qht_debug_assert(X) do { (void)(X); } while (0)
+
+static inline void qht_bucket_debug__locked(struct qht_bucket *b)
+{ }
+
+static inline void qht_map_debug__all_locked(struct qht_map *map)
+{ }
+#endif /* QHT_DEBUG */
+
+static inline size_t qht_elems_to_buckets(size_t n_elems)
+{
+ return pow2ceil(n_elems / QHT_BUCKET_ENTRIES);
+}
+
+static inline void qht_head_init(struct qht_bucket *b)
+{
+ memset(b, 0, sizeof(*b));
+ qemu_spin_init(&b->lock);
+ seqlock_init(&b->sequence);
+}
+
+static inline
+struct qht_bucket *qht_map_to_bucket(const struct qht_map *map, uint32_t hash)
+{
+ return &map->buckets[hash & (map->n_buckets - 1)];
+}
+
+/* acquire all bucket locks from a map */
+static void qht_map_lock_buckets(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ struct qht_bucket *b = &map->buckets[i];
+
+ qemu_spin_lock(&b->lock);
+ }
+}
+
+static void qht_map_unlock_buckets(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ struct qht_bucket *b = &map->buckets[i];
+
+ qemu_spin_unlock(&b->lock);
+ }
+}
+
+/*
+ * Call with at least a bucket lock held.
+ * @map should be the value read before acquiring the lock (or locks).
+ */
+static inline bool qht_map_is_stale__locked(const struct qht *ht,
+ const struct qht_map *map)
+{
+ return map != ht->map;
+}
+
+/*
+ * Grab all bucket locks, and set @pmap after making sure the map isn't stale.
+ *
+ * Pairs with qht_map_unlock_buckets(), hence the pass-by-reference.
+ *
+ * Note: callers cannot have ht->lock held.
+ */
+static inline
+void qht_map_lock_buckets__no_stale(struct qht *ht, struct qht_map **pmap)
+{
+ struct qht_map *map;
+
+ map = qatomic_rcu_read(&ht->map);
+ qht_map_lock_buckets(map);
+ if (likely(!qht_map_is_stale__locked(ht, map))) {
+ *pmap = map;
+ return;
+ }
+ qht_map_unlock_buckets(map);
+
+ /* we raced with a resize; acquire ht->lock to see the updated ht->map */
+ qht_lock(ht);
+ map = ht->map;
+ qht_map_lock_buckets(map);
+ qht_unlock(ht);
+ *pmap = map;
+ return;
+}
+
+/*
+ * Get a head bucket and lock it, making sure its parent map is not stale.
+ * @pmap is filled with a pointer to the bucket's parent map.
+ *
+ * Unlock with qemu_spin_unlock(&b->lock).
+ *
+ * Note: callers cannot have ht->lock held.
+ */
+static inline
+struct qht_bucket *qht_bucket_lock__no_stale(struct qht *ht, uint32_t hash,
+ struct qht_map **pmap)
+{
+ struct qht_bucket *b;
+ struct qht_map *map;
+
+ map = qatomic_rcu_read(&ht->map);
+ b = qht_map_to_bucket(map, hash);
+
+ qemu_spin_lock(&b->lock);
+ if (likely(!qht_map_is_stale__locked(ht, map))) {
+ *pmap = map;
+ return b;
+ }
+ qemu_spin_unlock(&b->lock);
+
+ /* we raced with a resize; acquire ht->lock to see the updated ht->map */
+ qht_lock(ht);
+ map = ht->map;
+ b = qht_map_to_bucket(map, hash);
+ qemu_spin_lock(&b->lock);
+ qht_unlock(ht);
+ *pmap = map;
+ return b;
+}
+
+static inline bool qht_map_needs_resize(const struct qht_map *map)
+{
+ return qatomic_read(&map->n_added_buckets) >
+ map->n_added_buckets_threshold;
+}
+
+static inline void qht_chain_destroy(const struct qht_bucket *head)
+{
+ struct qht_bucket *curr = head->next;
+ struct qht_bucket *prev;
+
+ qemu_spin_destroy(&head->lock);
+ while (curr) {
+ prev = curr;
+ curr = curr->next;
+ qemu_vfree(prev);
+ }
+}
+
+/* pass only an orphan map */
+static void qht_map_destroy(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ qht_chain_destroy(&map->buckets[i]);
+ }
+ qemu_vfree(map->buckets);
+ g_free(map);
+}
+
+static struct qht_map *qht_map_create(size_t n_buckets)
+{
+ struct qht_map *map;
+ size_t i;
+
+ map = g_malloc(sizeof(*map));
+ map->n_buckets = n_buckets;
+
+ map->n_added_buckets = 0;
+ map->n_added_buckets_threshold = n_buckets /
+ QHT_NR_ADDED_BUCKETS_THRESHOLD_DIV;
+
+ /* let tiny hash tables to at least add one non-head bucket */
+ if (unlikely(map->n_added_buckets_threshold == 0)) {
+ map->n_added_buckets_threshold = 1;
+ }
+
+ map->buckets = qemu_memalign(QHT_BUCKET_ALIGN,
+ sizeof(*map->buckets) * n_buckets);
+ for (i = 0; i < n_buckets; i++) {
+ qht_head_init(&map->buckets[i]);
+ }
+ return map;
+}
+
+void qht_init(struct qht *ht, qht_cmp_func_t cmp, size_t n_elems,
+ unsigned int mode)
+{
+ struct qht_map *map;
+ size_t n_buckets = qht_elems_to_buckets(n_elems);
+
+ g_assert(cmp);
+ ht->cmp = cmp;
+ ht->mode = mode;
+ qemu_mutex_init(&ht->lock);
+ map = qht_map_create(n_buckets);
+ qatomic_rcu_set(&ht->map, map);
+}
+
+/* call only when there are no readers/writers left */
+void qht_destroy(struct qht *ht)
+{
+ qht_map_destroy(ht->map);
+ memset(ht, 0, sizeof(*ht));
+}
+
+static void qht_bucket_reset__locked(struct qht_bucket *head)
+{
+ struct qht_bucket *b = head;
+ int i;
+
+ seqlock_write_begin(&head->sequence);
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] == NULL) {
+ goto done;
+ }
+ qatomic_set(&b->hashes[i], 0);
+ qatomic_set(&b->pointers[i], NULL);
+ }
+ b = b->next;
+ } while (b);
+ done:
+ seqlock_write_end(&head->sequence);
+}
+
+/* call with all bucket locks held */
+static void qht_map_reset__all_locked(struct qht_map *map)
+{
+ size_t i;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ qht_bucket_reset__locked(&map->buckets[i]);
+ }
+ qht_map_debug__all_locked(map);
+}
+
+void qht_reset(struct qht *ht)
+{
+ struct qht_map *map;
+
+ qht_map_lock_buckets__no_stale(ht, &map);
+ qht_map_reset__all_locked(map);
+ qht_map_unlock_buckets(map);
+}
+
+static inline void qht_do_resize(struct qht *ht, struct qht_map *new)
+{
+ qht_do_resize_reset(ht, new, false);
+}
+
+static inline void qht_do_resize_and_reset(struct qht *ht, struct qht_map *new)
+{
+ qht_do_resize_reset(ht, new, true);
+}
+
+bool qht_reset_size(struct qht *ht, size_t n_elems)
+{
+ struct qht_map *new = NULL;
+ struct qht_map *map;
+ size_t n_buckets;
+
+ n_buckets = qht_elems_to_buckets(n_elems);
+
+ qht_lock(ht);
+ map = ht->map;
+ if (n_buckets != map->n_buckets) {
+ new = qht_map_create(n_buckets);
+ }
+ qht_do_resize_and_reset(ht, new);
+ qht_unlock(ht);
+
+ return !!new;
+}
+
+static inline
+void *qht_do_lookup(const struct qht_bucket *head, qht_lookup_func_t func,
+ const void *userp, uint32_t hash)
+{
+ const struct qht_bucket *b = head;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (qatomic_read(&b->hashes[i]) == hash) {
+ /* The pointer is dereferenced before seqlock_read_retry,
+ * so (unlike qht_insert__locked) we need to use
+ * qatomic_rcu_read here.
+ */
+ void *p = qatomic_rcu_read(&b->pointers[i]);
+
+ if (likely(p) && likely(func(p, userp))) {
+ return p;
+ }
+ }
+ }
+ b = qatomic_rcu_read(&b->next);
+ } while (b);
+
+ return NULL;
+}
+
+static __attribute__((noinline))
+void *qht_lookup__slowpath(const struct qht_bucket *b, qht_lookup_func_t func,
+ const void *userp, uint32_t hash)
+{
+ unsigned int version;
+ void *ret;
+
+ do {
+ version = seqlock_read_begin(&b->sequence);
+ ret = qht_do_lookup(b, func, userp, hash);
+ } while (seqlock_read_retry(&b->sequence, version));
+ return ret;
+}
+
+void *qht_lookup_custom(const struct qht *ht, const void *userp, uint32_t hash,
+ qht_lookup_func_t func)
+{
+ const struct qht_bucket *b;
+ const struct qht_map *map;
+ unsigned int version;
+ void *ret;
+
+ map = qatomic_rcu_read(&ht->map);
+ b = qht_map_to_bucket(map, hash);
+
+ version = seqlock_read_begin(&b->sequence);
+ ret = qht_do_lookup(b, func, userp, hash);
+ if (likely(!seqlock_read_retry(&b->sequence, version))) {
+ return ret;
+ }
+ /*
+ * Removing the do/while from the fastpath gives a 4% perf. increase when
+ * running a 100%-lookup microbenchmark.
+ */
+ return qht_lookup__slowpath(b, func, userp, hash);
+}
+
+void *qht_lookup(const struct qht *ht, const void *userp, uint32_t hash)
+{
+ return qht_lookup_custom(ht, userp, hash, ht->cmp);
+}
+
+/*
+ * call with head->lock held
+ * @ht is const since it is only used for ht->cmp()
+ */
+static void *qht_insert__locked(const struct qht *ht, struct qht_map *map,
+ struct qht_bucket *head, void *p, uint32_t hash,
+ bool *needs_resize)
+{
+ struct qht_bucket *b = head;
+ struct qht_bucket *prev = NULL;
+ struct qht_bucket *new = NULL;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i]) {
+ if (unlikely(b->hashes[i] == hash &&
+ ht->cmp(b->pointers[i], p))) {
+ return b->pointers[i];
+ }
+ } else {
+ goto found;
+ }
+ }
+ prev = b;
+ b = b->next;
+ } while (b);
+
+ b = qemu_memalign(QHT_BUCKET_ALIGN, sizeof(*b));
+ memset(b, 0, sizeof(*b));
+ new = b;
+ i = 0;
+ qatomic_inc(&map->n_added_buckets);
+ if (unlikely(qht_map_needs_resize(map)) && needs_resize) {
+ *needs_resize = true;
+ }
+
+ found:
+ /* found an empty key: acquire the seqlock and write */
+ seqlock_write_begin(&head->sequence);
+ if (new) {
+ qatomic_rcu_set(&prev->next, b);
+ }
+ /* smp_wmb() implicit in seqlock_write_begin. */
+ qatomic_set(&b->hashes[i], hash);
+ qatomic_set(&b->pointers[i], p);
+ seqlock_write_end(&head->sequence);
+ return NULL;
+}
+
+static __attribute__((noinline)) void qht_grow_maybe(struct qht *ht)
+{
+ struct qht_map *map;
+
+ /*
+ * If the lock is taken it probably means there's an ongoing resize,
+ * so bail out.
+ */
+ if (qht_trylock(ht)) {
+ return;
+ }
+ map = ht->map;
+ /* another thread might have just performed the resize we were after */
+ if (qht_map_needs_resize(map)) {
+ struct qht_map *new = qht_map_create(map->n_buckets * 2);
+
+ qht_do_resize(ht, new);
+ }
+ qht_unlock(ht);
+}
+
+bool qht_insert(struct qht *ht, void *p, uint32_t hash, void **existing)
+{
+ struct qht_bucket *b;
+ struct qht_map *map;
+ bool needs_resize = false;
+ void *prev;
+
+ /* NULL pointers are not supported */
+ qht_debug_assert(p);
+
+ b = qht_bucket_lock__no_stale(ht, hash, &map);
+ prev = qht_insert__locked(ht, map, b, p, hash, &needs_resize);
+ qht_bucket_debug__locked(b);
+ qemu_spin_unlock(&b->lock);
+
+ if (unlikely(needs_resize) && ht->mode & QHT_MODE_AUTO_RESIZE) {
+ qht_grow_maybe(ht);
+ }
+ if (likely(prev == NULL)) {
+ return true;
+ }
+ if (existing) {
+ *existing = prev;
+ }
+ return false;
+}
+
+static inline bool qht_entry_is_last(const struct qht_bucket *b, int pos)
+{
+ if (pos == QHT_BUCKET_ENTRIES - 1) {
+ if (b->next == NULL) {
+ return true;
+ }
+ return b->next->pointers[0] == NULL;
+ }
+ return b->pointers[pos + 1] == NULL;
+}
+
+static void
+qht_entry_move(struct qht_bucket *to, int i, struct qht_bucket *from, int j)
+{
+ qht_debug_assert(!(to == from && i == j));
+ qht_debug_assert(to->pointers[i]);
+ qht_debug_assert(from->pointers[j]);
+
+ qatomic_set(&to->hashes[i], from->hashes[j]);
+ qatomic_set(&to->pointers[i], from->pointers[j]);
+
+ qatomic_set(&from->hashes[j], 0);
+ qatomic_set(&from->pointers[j], NULL);
+}
+
+/*
+ * Find the last valid entry in @orig, and swap it with @orig[pos], which has
+ * just been invalidated.
+ */
+static inline void qht_bucket_remove_entry(struct qht_bucket *orig, int pos)
+{
+ struct qht_bucket *b = orig;
+ struct qht_bucket *prev = NULL;
+ int i;
+
+ if (qht_entry_is_last(orig, pos)) {
+ orig->hashes[pos] = 0;
+ qatomic_set(&orig->pointers[pos], NULL);
+ return;
+ }
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i]) {
+ continue;
+ }
+ if (i > 0) {
+ return qht_entry_move(orig, pos, b, i - 1);
+ }
+ qht_debug_assert(prev);
+ return qht_entry_move(orig, pos, prev, QHT_BUCKET_ENTRIES - 1);
+ }
+ prev = b;
+ b = b->next;
+ } while (b);
+ /* no free entries other than orig[pos], so swap it with the last one */
+ qht_entry_move(orig, pos, prev, QHT_BUCKET_ENTRIES - 1);
+}
+
+/* call with b->lock held */
+static inline
+bool qht_remove__locked(struct qht_bucket *head, const void *p, uint32_t hash)
+{
+ struct qht_bucket *b = head;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ void *q = b->pointers[i];
+
+ if (unlikely(q == NULL)) {
+ return false;
+ }
+ if (q == p) {
+ qht_debug_assert(b->hashes[i] == hash);
+ seqlock_write_begin(&head->sequence);
+ qht_bucket_remove_entry(b, i);
+ seqlock_write_end(&head->sequence);
+ return true;
+ }
+ }
+ b = b->next;
+ } while (b);
+ return false;
+}
+
+bool qht_remove(struct qht *ht, const void *p, uint32_t hash)
+{
+ struct qht_bucket *b;
+ struct qht_map *map;
+ bool ret;
+
+ /* NULL pointers are not supported */
+ qht_debug_assert(p);
+
+ b = qht_bucket_lock__no_stale(ht, hash, &map);
+ ret = qht_remove__locked(b, p, hash);
+ qht_bucket_debug__locked(b);
+ qemu_spin_unlock(&b->lock);
+ return ret;
+}
+
+static inline void qht_bucket_iter(struct qht_bucket *head,
+ const struct qht_iter *iter, void *userp)
+{
+ struct qht_bucket *b = head;
+ int i;
+
+ do {
+ for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
+ if (b->pointers[i] == NULL) {
+ return;
+ }
+ switch (iter->type) {
+ case QHT_ITER_VOID:
+ iter->f.retvoid(b->pointers[i], b->hashes[i], userp);
+ break;
+ case QHT_ITER_RM:
+ if (iter->f.retbool(b->pointers[i], b->hashes[i], userp)) {
+ /* replace i with the last valid element in the bucket */
+ seqlock_write_begin(&head->sequence);
+ qht_bucket_remove_entry(b, i);
+ seqlock_write_end(&head->sequence);
+ qht_bucket_debug__locked(b);
+ /* reevaluate i, since it just got replaced */
+ i--;
+ continue;
+ }
+ break;
+ default:
+ g_assert_not_reached();
+ }
+ }
+ b = b->next;
+ } while (b);
+}
+
+/* call with all of the map's locks held */
+static inline void qht_map_iter__all_locked(struct qht_map *map,
+ const struct qht_iter *iter,
+ void *userp)
+{
+ size_t i;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ qht_bucket_iter(&map->buckets[i], iter, userp);
+ }
+}
+
+static inline void
+do_qht_iter(struct qht *ht, const struct qht_iter *iter, void *userp)
+{
+ struct qht_map *map;
+
+ map = qatomic_rcu_read(&ht->map);
+ qht_map_lock_buckets(map);
+ qht_map_iter__all_locked(map, iter, userp);
+ qht_map_unlock_buckets(map);
+}
+
+void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp)
+{
+ const struct qht_iter iter = {
+ .f.retvoid = func,
+ .type = QHT_ITER_VOID,
+ };
+
+ do_qht_iter(ht, &iter, userp);
+}
+
+void qht_iter_remove(struct qht *ht, qht_iter_bool_func_t func, void *userp)
+{
+ const struct qht_iter iter = {
+ .f.retbool = func,
+ .type = QHT_ITER_RM,
+ };
+
+ do_qht_iter(ht, &iter, userp);
+}
+
+struct qht_map_copy_data {
+ struct qht *ht;
+ struct qht_map *new;
+};
+
+static void qht_map_copy(void *p, uint32_t hash, void *userp)
+{
+ struct qht_map_copy_data *data = userp;
+ struct qht *ht = data->ht;
+ struct qht_map *new = data->new;
+ struct qht_bucket *b = qht_map_to_bucket(new, hash);
+
+ /* no need to acquire b->lock because no thread has seen this map yet */
+ qht_insert__locked(ht, new, b, p, hash, NULL);
+}
+
+/*
+ * Atomically perform a resize and/or reset.
+ * Call with ht->lock held.
+ */
+static void qht_do_resize_reset(struct qht *ht, struct qht_map *new, bool reset)
+{
+ struct qht_map *old;
+ const struct qht_iter iter = {
+ .f.retvoid = qht_map_copy,
+ .type = QHT_ITER_VOID,
+ };
+ struct qht_map_copy_data data;
+
+ old = ht->map;
+ qht_map_lock_buckets(old);
+
+ if (reset) {
+ qht_map_reset__all_locked(old);
+ }
+
+ if (new == NULL) {
+ qht_map_unlock_buckets(old);
+ return;
+ }
+
+ g_assert(new->n_buckets != old->n_buckets);
+ data.ht = ht;
+ data.new = new;
+ qht_map_iter__all_locked(old, &iter, &data);
+ qht_map_debug__all_locked(new);
+
+ qatomic_rcu_set(&ht->map, new);
+ qht_map_unlock_buckets(old);
+ call_rcu(old, qht_map_destroy, rcu);
+}
+
+bool qht_resize(struct qht *ht, size_t n_elems)
+{
+ size_t n_buckets = qht_elems_to_buckets(n_elems);
+ size_t ret = false;
+
+ qht_lock(ht);
+ if (n_buckets != ht->map->n_buckets) {
+ struct qht_map *new;
+
+ new = qht_map_create(n_buckets);
+ qht_do_resize(ht, new);
+ ret = true;
+ }
+ qht_unlock(ht);
+
+ return ret;
+}
+
+/* pass @stats to qht_statistics_destroy() when done */
+void qht_statistics_init(const struct qht *ht, struct qht_stats *stats)
+{
+ const struct qht_map *map;
+ int i;
+
+ map = qatomic_rcu_read(&ht->map);
+
+ stats->used_head_buckets = 0;
+ stats->entries = 0;
+ qdist_init(&stats->chain);
+ qdist_init(&stats->occupancy);
+ /* bail out if the qht has not yet been initialized */
+ if (unlikely(map == NULL)) {
+ stats->head_buckets = 0;
+ return;
+ }
+ stats->head_buckets = map->n_buckets;
+
+ for (i = 0; i < map->n_buckets; i++) {
+ const struct qht_bucket *head = &map->buckets[i];
+ const struct qht_bucket *b;
+ unsigned int version;
+ size_t buckets;
+ size_t entries;
+ int j;
+
+ do {
+ version = seqlock_read_begin(&head->sequence);
+ buckets = 0;
+ entries = 0;
+ b = head;
+ do {
+ for (j = 0; j < QHT_BUCKET_ENTRIES; j++) {
+ if (qatomic_read(&b->pointers[j]) == NULL) {
+ break;
+ }
+ entries++;
+ }
+ buckets++;
+ b = qatomic_rcu_read(&b->next);
+ } while (b);
+ } while (seqlock_read_retry(&head->sequence, version));
+
+ if (entries) {
+ qdist_inc(&stats->chain, buckets);
+ qdist_inc(&stats->occupancy,
+ (double)entries / QHT_BUCKET_ENTRIES / buckets);
+ stats->used_head_buckets++;
+ stats->entries += entries;
+ } else {
+ qdist_inc(&stats->occupancy, 0);
+ }
+ }
+}
+
+void qht_statistics_destroy(struct qht_stats *stats)
+{
+ qdist_destroy(&stats->occupancy);
+ qdist_destroy(&stats->chain);
+}