rhashtable.h 24 KB
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/*
 * Resizable, Scalable, Concurrent Hash Table
 *
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 * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
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 * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
 * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
 *
 * Code partially derived from nft_hash
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 * Rewritten with rehash code from br_multicast plus single list
 * pointer as suggested by Josh Triplett
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 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#ifndef _LINUX_RHASHTABLE_H
#define _LINUX_RHASHTABLE_H

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#include <linux/compiler.h>
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#include <linux/errno.h>
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#include <linux/jhash.h>
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#include <linux/list_nulls.h>
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#include <linux/workqueue.h>
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#include <linux/mutex.h>
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#include <linux/rcupdate.h>
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/*
 * The end of the chain is marked with a special nulls marks which has
 * the following format:
 *
 * +-------+-----------------------------------------------------+-+
 * | Base  |                      Hash                           |1|
 * +-------+-----------------------------------------------------+-+
 *
 * Base (4 bits) : Reserved to distinguish between multiple tables.
 *                 Specified via &struct rhashtable_params.nulls_base.
 * Hash (27 bits): Full hash (unmasked) of first element added to bucket
 * 1 (1 bit)     : Nulls marker (always set)
 *
 * The remaining bits of the next pointer remain unused for now.
 */
#define RHT_BASE_BITS		4
#define RHT_HASH_BITS		27
#define RHT_BASE_SHIFT		RHT_HASH_BITS

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/* Base bits plus 1 bit for nulls marker */
#define RHT_HASH_RESERVED_SPACE	(RHT_BASE_BITS + 1)

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struct rhash_head {
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	struct rhash_head __rcu		*next;
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};

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/**
 * struct bucket_table - Table of hash buckets
 * @size: Number of hash buckets
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 * @rehash: Current bucket being rehashed
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 * @hash_rnd: Random seed to fold into hash
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 * @locks_mask: Mask to apply before accessing locks[]
 * @locks: Array of spinlocks protecting individual buckets
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 * @walkers: List of active walkers
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 * @rcu: RCU structure for freeing the table
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 * @future_tbl: Table under construction during rehashing
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 * @buckets: size * hash buckets
 */
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struct bucket_table {
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	unsigned int		size;
	unsigned int		rehash;
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	u32			hash_rnd;
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	unsigned int		locks_mask;
	spinlock_t		*locks;
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	struct list_head	walkers;
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	struct rcu_head		rcu;
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	struct bucket_table __rcu *future_tbl;

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	struct rhash_head __rcu	*buckets[] ____cacheline_aligned_in_smp;
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};

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/**
 * struct rhashtable_compare_arg - Key for the function rhashtable_compare
 * @ht: Hash table
 * @key: Key to compare against
 */
struct rhashtable_compare_arg {
	struct rhashtable *ht;
	const void *key;
};

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typedef u32 (*rht_hashfn_t)(const void *data, u32 len, u32 seed);
typedef u32 (*rht_obj_hashfn_t)(const void *data, u32 seed);
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typedef int (*rht_obj_cmpfn_t)(struct rhashtable_compare_arg *arg,
			       const void *obj);
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struct rhashtable;

/**
 * struct rhashtable_params - Hash table construction parameters
 * @nelem_hint: Hint on number of elements, should be 75% of desired size
 * @key_len: Length of key
 * @key_offset: Offset of key in struct to be hashed
 * @head_offset: Offset of rhash_head in struct to be hashed
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 * @max_size: Maximum size while expanding
 * @min_size: Minimum size while shrinking
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 * @nulls_base: Base value to generate nulls marker
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 * @insecure_elasticity: Set to true to disable chain length checks
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 * @locks_mul: Number of bucket locks to allocate per cpu (default: 128)
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 * @hashfn: Hash function (default: jhash2 if !(key_len % 4), or jhash)
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 * @obj_hashfn: Function to hash object
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 * @obj_cmpfn: Function to compare key with object
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 */
struct rhashtable_params {
	size_t			nelem_hint;
	size_t			key_len;
	size_t			key_offset;
	size_t			head_offset;
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	unsigned int		max_size;
	unsigned int		min_size;
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	u32			nulls_base;
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	bool			insecure_elasticity;
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	size_t			locks_mul;
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	rht_hashfn_t		hashfn;
	rht_obj_hashfn_t	obj_hashfn;
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	rht_obj_cmpfn_t		obj_cmpfn;
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};

/**
 * struct rhashtable - Hash table handle
 * @tbl: Bucket table
 * @nelems: Number of elements in table
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 * @key_len: Key length for hashfn
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 * @elasticity: Maximum chain length before rehash
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 * @p: Configuration parameters
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 * @run_work: Deferred worker to expand/shrink asynchronously
 * @mutex: Mutex to protect current/future table swapping
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 * @lock: Spin lock to protect walker list
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 * @being_destroyed: True if table is set up for destruction
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 */
struct rhashtable {
	struct bucket_table __rcu	*tbl;
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	atomic_t			nelems;
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	bool                            being_destroyed;
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	unsigned int			key_len;
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	unsigned int			elasticity;
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	struct rhashtable_params	p;
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	struct work_struct		run_work;
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	struct mutex                    mutex;
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	spinlock_t			lock;
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};

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/**
 * struct rhashtable_walker - Hash table walker
 * @list: List entry on list of walkers
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 * @tbl: The table that we were walking over
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 */
struct rhashtable_walker {
	struct list_head list;
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	struct bucket_table *tbl;
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};

/**
 * struct rhashtable_iter - Hash table iterator, fits into netlink cb
 * @ht: Table to iterate through
 * @p: Current pointer
 * @walker: Associated rhashtable walker
 * @slot: Current slot
 * @skip: Number of entries to skip in slot
 */
struct rhashtable_iter {
	struct rhashtable *ht;
	struct rhash_head *p;
	struct rhashtable_walker *walker;
	unsigned int slot;
	unsigned int skip;
};

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static inline unsigned long rht_marker(const struct rhashtable *ht, u32 hash)
{
	return NULLS_MARKER(ht->p.nulls_base + hash);
}

#define INIT_RHT_NULLS_HEAD(ptr, ht, hash) \
	((ptr) = (typeof(ptr)) rht_marker(ht, hash))

static inline bool rht_is_a_nulls(const struct rhash_head *ptr)
{
	return ((unsigned long) ptr & 1);
}

static inline unsigned long rht_get_nulls_value(const struct rhash_head *ptr)
{
	return ((unsigned long) ptr) >> 1;
}

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static inline void *rht_obj(const struct rhashtable *ht,
			    const struct rhash_head *he)
{
	return (char *)he - ht->p.head_offset;
}

static inline unsigned int rht_bucket_index(const struct bucket_table *tbl,
					    unsigned int hash)
{
	return (hash >> RHT_HASH_RESERVED_SPACE) & (tbl->size - 1);
}

static inline unsigned int rht_key_hashfn(
	struct rhashtable *ht, const struct bucket_table *tbl,
	const void *key, const struct rhashtable_params params)
{
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	unsigned int hash;
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	/* params must be equal to ht->p if it isn't constant. */
	if (!__builtin_constant_p(params.key_len))
		hash = ht->p.hashfn(key, ht->key_len, tbl->hash_rnd);
	else if (params.key_len) {
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		unsigned int key_len = params.key_len;
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		if (params.hashfn)
			hash = params.hashfn(key, key_len, tbl->hash_rnd);
		else if (key_len & (sizeof(u32) - 1))
			hash = jhash(key, key_len, tbl->hash_rnd);
		else
			hash = jhash2(key, key_len / sizeof(u32),
				      tbl->hash_rnd);
	} else {
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		unsigned int key_len = ht->p.key_len;
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		if (params.hashfn)
			hash = params.hashfn(key, key_len, tbl->hash_rnd);
		else
			hash = jhash(key, key_len, tbl->hash_rnd);
	}

	return rht_bucket_index(tbl, hash);
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}

static inline unsigned int rht_head_hashfn(
	struct rhashtable *ht, const struct bucket_table *tbl,
	const struct rhash_head *he, const struct rhashtable_params params)
{
	const char *ptr = rht_obj(ht, he);

	return likely(params.obj_hashfn) ?
	       rht_bucket_index(tbl, params.obj_hashfn(ptr, tbl->hash_rnd)) :
	       rht_key_hashfn(ht, tbl, ptr + params.key_offset, params);
}

/**
 * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
 * @ht:		hash table
 * @tbl:	current table
 */
static inline bool rht_grow_above_75(const struct rhashtable *ht,
				     const struct bucket_table *tbl)
{
	/* Expand table when exceeding 75% load */
	return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
	       (!ht->p.max_size || tbl->size < ht->p.max_size);
}

/**
 * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
 * @ht:		hash table
 * @tbl:	current table
 */
static inline bool rht_shrink_below_30(const struct rhashtable *ht,
				       const struct bucket_table *tbl)
{
	/* Shrink table beneath 30% load */
	return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
	       tbl->size > ht->p.min_size;
}

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/**
 * rht_grow_above_100 - returns true if nelems > table-size
 * @ht:		hash table
 * @tbl:	current table
 */
static inline bool rht_grow_above_100(const struct rhashtable *ht,
				      const struct bucket_table *tbl)
{
	return atomic_read(&ht->nelems) > tbl->size;
}

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/* The bucket lock is selected based on the hash and protects mutations
 * on a group of hash buckets.
 *
 * A maximum of tbl->size/2 bucket locks is allocated. This ensures that
 * a single lock always covers both buckets which may both contains
 * entries which link to the same bucket of the old table during resizing.
 * This allows to simplify the locking as locking the bucket in both
 * tables during resize always guarantee protection.
 *
 * IMPORTANT: When holding the bucket lock of both the old and new table
 * during expansions and shrinking, the old bucket lock must always be
 * acquired first.
 */
static inline spinlock_t *rht_bucket_lock(const struct bucket_table *tbl,
					  unsigned int hash)
{
	return &tbl->locks[hash & tbl->locks_mask];
}

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#ifdef CONFIG_PROVE_LOCKING
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int lockdep_rht_mutex_is_held(struct rhashtable *ht);
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int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash);
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#else
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static inline int lockdep_rht_mutex_is_held(struct rhashtable *ht)
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{
	return 1;
}
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static inline int lockdep_rht_bucket_is_held(const struct bucket_table *tbl,
					     u32 hash)
{
	return 1;
}
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#endif /* CONFIG_PROVE_LOCKING */

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int rhashtable_init(struct rhashtable *ht,
		    const struct rhashtable_params *params);
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int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
			   struct rhash_head *obj,
			   struct bucket_table *old_tbl);
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int rhashtable_insert_rehash(struct rhashtable *ht);
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int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter);
void rhashtable_walk_exit(struct rhashtable_iter *iter);
int rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU);
void *rhashtable_walk_next(struct rhashtable_iter *iter);
void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU);

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void rhashtable_destroy(struct rhashtable *ht);
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#define rht_dereference(p, ht) \
	rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))

#define rht_dereference_rcu(p, ht) \
	rcu_dereference_check(p, lockdep_rht_mutex_is_held(ht))

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#define rht_dereference_bucket(p, tbl, hash) \
	rcu_dereference_protected(p, lockdep_rht_bucket_is_held(tbl, hash))
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#define rht_dereference_bucket_rcu(p, tbl, hash) \
	rcu_dereference_check(p, lockdep_rht_bucket_is_held(tbl, hash))

#define rht_entry(tpos, pos, member) \
	({ tpos = container_of(pos, typeof(*tpos), member); 1; })
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/**
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 * rht_for_each_continue - continue iterating over hash chain
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @head:	the previous &struct rhash_head to continue from
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
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 */
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#define rht_for_each_continue(pos, head, tbl, hash) \
	for (pos = rht_dereference_bucket(head, tbl, hash); \
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	     !rht_is_a_nulls(pos); \
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	     pos = rht_dereference_bucket((pos)->next, tbl, hash))

/**
 * rht_for_each - iterate over hash chain
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 */
#define rht_for_each(pos, tbl, hash) \
	rht_for_each_continue(pos, (tbl)->buckets[hash], tbl, hash)

/**
 * rht_for_each_entry_continue - continue iterating over hash chain
 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @head:	the previous &struct rhash_head to continue from
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 * @member:	name of the &struct rhash_head within the hashable struct.
 */
#define rht_for_each_entry_continue(tpos, pos, head, tbl, hash, member)	\
	for (pos = rht_dereference_bucket(head, tbl, hash);		\
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	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	\
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	     pos = rht_dereference_bucket((pos)->next, tbl, hash))
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/**
 * rht_for_each_entry - iterate over hash chain of given type
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 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 * @member:	name of the &struct rhash_head within the hashable struct.
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 */
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#define rht_for_each_entry(tpos, pos, tbl, hash, member)		\
	rht_for_each_entry_continue(tpos, pos, (tbl)->buckets[hash],	\
				    tbl, hash, member)
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/**
 * rht_for_each_entry_safe - safely iterate over hash chain of given type
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 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @next:	the &struct rhash_head to use as next in loop cursor.
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 * @member:	name of the &struct rhash_head within the hashable struct.
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 *
 * This hash chain list-traversal primitive allows for the looped code to
 * remove the loop cursor from the list.
 */
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#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member)	    \
	for (pos = rht_dereference_bucket((tbl)->buckets[hash], tbl, hash), \
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	     next = !rht_is_a_nulls(pos) ?				    \
		       rht_dereference_bucket(pos->next, tbl, hash) : NULL; \
	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	    \
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	     pos = next,						    \
	     next = !rht_is_a_nulls(pos) ?				    \
		       rht_dereference_bucket(pos->next, tbl, hash) : NULL)
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/**
 * rht_for_each_rcu_continue - continue iterating over rcu hash chain
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @head:	the previous &struct rhash_head to continue from
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 *
 * This hash chain list-traversal primitive may safely run concurrently with
 * the _rcu mutation primitives such as rhashtable_insert() as long as the
 * traversal is guarded by rcu_read_lock().
 */
#define rht_for_each_rcu_continue(pos, head, tbl, hash)			\
	for (({barrier(); }),						\
	     pos = rht_dereference_bucket_rcu(head, tbl, hash);		\
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	     !rht_is_a_nulls(pos);					\
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	     pos = rcu_dereference_raw(pos->next))
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/**
 * rht_for_each_rcu - iterate over rcu hash chain
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 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
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 *
 * This hash chain list-traversal primitive may safely run concurrently with
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 * the _rcu mutation primitives such as rhashtable_insert() as long as the
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 * traversal is guarded by rcu_read_lock().
 */
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#define rht_for_each_rcu(pos, tbl, hash)				\
	rht_for_each_rcu_continue(pos, (tbl)->buckets[hash], tbl, hash)

/**
 * rht_for_each_entry_rcu_continue - continue iterating over rcu hash chain
 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @head:	the previous &struct rhash_head to continue from
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 * @member:	name of the &struct rhash_head within the hashable struct.
 *
 * This hash chain list-traversal primitive may safely run concurrently with
 * the _rcu mutation primitives such as rhashtable_insert() as long as the
 * traversal is guarded by rcu_read_lock().
 */
#define rht_for_each_entry_rcu_continue(tpos, pos, head, tbl, hash, member) \
	for (({barrier(); }),						    \
	     pos = rht_dereference_bucket_rcu(head, tbl, hash);		    \
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	     (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);	    \
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	     pos = rht_dereference_bucket_rcu(pos->next, tbl, hash))
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/**
 * rht_for_each_entry_rcu - iterate over rcu hash chain of given type
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 * @tpos:	the type * to use as a loop cursor.
 * @pos:	the &struct rhash_head to use as a loop cursor.
 * @tbl:	the &struct bucket_table
 * @hash:	the hash value / bucket index
 * @member:	name of the &struct rhash_head within the hashable struct.
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 *
 * This hash chain list-traversal primitive may safely run concurrently with
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 * the _rcu mutation primitives such as rhashtable_insert() as long as the
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 * traversal is guarded by rcu_read_lock().
 */
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#define rht_for_each_entry_rcu(tpos, pos, tbl, hash, member)		\
	rht_for_each_entry_rcu_continue(tpos, pos, (tbl)->buckets[hash],\
					tbl, hash, member)
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static inline int rhashtable_compare(struct rhashtable_compare_arg *arg,
				     const void *obj)
{
	struct rhashtable *ht = arg->ht;
	const char *ptr = obj;

	return memcmp(ptr + ht->p.key_offset, arg->key, ht->p.key_len);
}

/**
 * rhashtable_lookup_fast - search hash table, inlined version
 * @ht:		hash table
 * @key:	the pointer to the key
 * @params:	hash table parameters
 *
 * Computes the hash value for the key and traverses the bucket chain looking
 * for a entry with an identical key. The first matching entry is returned.
 *
 * Returns the first entry on which the compare function returned true.
 */
static inline void *rhashtable_lookup_fast(
	struct rhashtable *ht, const void *key,
	const struct rhashtable_params params)
{
	struct rhashtable_compare_arg arg = {
		.ht = ht,
		.key = key,
	};
	const struct bucket_table *tbl;
	struct rhash_head *he;
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	unsigned int hash;
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	rcu_read_lock();

	tbl = rht_dereference_rcu(ht->tbl, ht);
restart:
	hash = rht_key_hashfn(ht, tbl, key, params);
	rht_for_each_rcu(he, tbl, hash) {
		if (params.obj_cmpfn ?
		    params.obj_cmpfn(&arg, rht_obj(ht, he)) :
		    rhashtable_compare(&arg, rht_obj(ht, he)))
			continue;
		rcu_read_unlock();
		return rht_obj(ht, he);
	}

	/* Ensure we see any new tables. */
	smp_rmb();

	tbl = rht_dereference_rcu(tbl->future_tbl, ht);
	if (unlikely(tbl))
		goto restart;
	rcu_read_unlock();

	return NULL;
}

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/* Internal function, please use rhashtable_insert_fast() instead */
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static inline int __rhashtable_insert_fast(
	struct rhashtable *ht, const void *key, struct rhash_head *obj,
	const struct rhashtable_params params)
{
	struct rhashtable_compare_arg arg = {
		.ht = ht,
		.key = key,
	};
	struct bucket_table *tbl, *new_tbl;
	struct rhash_head *head;
	spinlock_t *lock;
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	unsigned int elasticity;
	unsigned int hash;
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	int err;
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restart:
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	rcu_read_lock();

	tbl = rht_dereference_rcu(ht->tbl, ht);

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	/* All insertions must grab the oldest table containing
	 * the hashed bucket that is yet to be rehashed.
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	 */
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	for (;;) {
		hash = rht_head_hashfn(ht, tbl, obj, params);
		lock = rht_bucket_lock(tbl, hash);
		spin_lock_bh(lock);

		if (tbl->rehash <= hash)
			break;

		spin_unlock_bh(lock);
		tbl = rht_dereference_rcu(tbl->future_tbl, ht);
	}

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	new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
	if (unlikely(new_tbl)) {
		err = rhashtable_insert_slow(ht, key, obj, new_tbl);
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		if (err == -EAGAIN)
			goto slow_path;
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		goto out;
	}

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	if (unlikely(rht_grow_above_100(ht, tbl))) {
slow_path:
		spin_unlock_bh(lock);
		err = rhashtable_insert_rehash(ht);
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		rcu_read_unlock();
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		if (err)
			return err;

		goto restart;
	}
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	err = -EEXIST;
	elasticity = ht->elasticity;
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	rht_for_each(head, tbl, hash) {
600 601
		if (key &&
		    unlikely(!(params.obj_cmpfn ?
602 603 604
			       params.obj_cmpfn(&arg, rht_obj(ht, head)) :
			       rhashtable_compare(&arg, rht_obj(ht, head)))))
			goto out;
605 606
		if (!--elasticity)
			goto slow_path;
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	}

	err = 0;

	head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);

	RCU_INIT_POINTER(obj->next, head);

	rcu_assign_pointer(tbl->buckets[hash], obj);

	atomic_inc(&ht->nelems);
	if (rht_grow_above_75(ht, tbl))
		schedule_work(&ht->run_work);

out:
	spin_unlock_bh(lock);
	rcu_read_unlock();

	return err;
}

/**
 * rhashtable_insert_fast - insert object into hash table
 * @ht:		hash table
 * @obj:	pointer to hash head inside object
 * @params:	hash table parameters
 *
 * Will take a per bucket spinlock to protect against mutual mutations
 * on the same bucket. Multiple insertions may occur in parallel unless
 * they map to the same bucket lock.
 *
 * It is safe to call this function from atomic context.
 *
 * Will trigger an automatic deferred table resizing if the size grows
 * beyond the watermark indicated by grow_decision() which can be passed
 * to rhashtable_init().
 */
static inline int rhashtable_insert_fast(
	struct rhashtable *ht, struct rhash_head *obj,
	const struct rhashtable_params params)
{
	return __rhashtable_insert_fast(ht, NULL, obj, params);
}

/**
 * rhashtable_lookup_insert_fast - lookup and insert object into hash table
 * @ht:		hash table
 * @obj:	pointer to hash head inside object
 * @params:	hash table parameters
 *
 * Locks down the bucket chain in both the old and new table if a resize
 * is in progress to ensure that writers can't remove from the old table
 * and can't insert to the new table during the atomic operation of search
 * and insertion. Searches for duplicates in both the old and new table if
 * a resize is in progress.
 *
 * This lookup function may only be used for fixed key hash table (key_len
 * parameter set). It will BUG() if used inappropriately.
 *
 * It is safe to call this function from atomic context.
 *
 * Will trigger an automatic deferred table resizing if the size grows
 * beyond the watermark indicated by grow_decision() which can be passed
 * to rhashtable_init().
 */
static inline int rhashtable_lookup_insert_fast(
	struct rhashtable *ht, struct rhash_head *obj,
	const struct rhashtable_params params)
{
	const char *key = rht_obj(ht, obj);

	BUG_ON(ht->p.obj_hashfn);

	return __rhashtable_insert_fast(ht, key + ht->p.key_offset, obj,
					params);
}

/**
 * rhashtable_lookup_insert_key - search and insert object to hash table
 *				  with explicit key
 * @ht:		hash table
 * @key:	key
 * @obj:	pointer to hash head inside object
 * @params:	hash table parameters
 *
 * Locks down the bucket chain in both the old and new table if a resize
 * is in progress to ensure that writers can't remove from the old table
 * and can't insert to the new table during the atomic operation of search
 * and insertion. Searches for duplicates in both the old and new table if
 * a resize is in progress.
 *
 * Lookups may occur in parallel with hashtable mutations and resizing.
 *
 * Will trigger an automatic deferred table resizing if the size grows
 * beyond the watermark indicated by grow_decision() which can be passed
 * to rhashtable_init().
 *
 * Returns zero on success.
 */
static inline int rhashtable_lookup_insert_key(
	struct rhashtable *ht, const void *key, struct rhash_head *obj,
	const struct rhashtable_params params)
{
	BUG_ON(!ht->p.obj_hashfn || !key);

	return __rhashtable_insert_fast(ht, key, obj, params);
}

715
/* Internal function, please use rhashtable_remove_fast() instead */
716 717 718 719 720 721 722
static inline int __rhashtable_remove_fast(
	struct rhashtable *ht, struct bucket_table *tbl,
	struct rhash_head *obj, const struct rhashtable_params params)
{
	struct rhash_head __rcu **pprev;
	struct rhash_head *he;
	spinlock_t * lock;
723
	unsigned int hash;
724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795
	int err = -ENOENT;

	hash = rht_head_hashfn(ht, tbl, obj, params);
	lock = rht_bucket_lock(tbl, hash);

	spin_lock_bh(lock);

	pprev = &tbl->buckets[hash];
	rht_for_each(he, tbl, hash) {
		if (he != obj) {
			pprev = &he->next;
			continue;
		}

		rcu_assign_pointer(*pprev, obj->next);
		err = 0;
		break;
	}

	spin_unlock_bh(lock);

	return err;
}

/**
 * rhashtable_remove_fast - remove object from hash table
 * @ht:		hash table
 * @obj:	pointer to hash head inside object
 * @params:	hash table parameters
 *
 * Since the hash chain is single linked, the removal operation needs to
 * walk the bucket chain upon removal. The removal operation is thus
 * considerable slow if the hash table is not correctly sized.
 *
 * Will automatically shrink the table via rhashtable_expand() if the
 * shrink_decision function specified at rhashtable_init() returns true.
 *
 * Returns zero on success, -ENOENT if the entry could not be found.
 */
static inline int rhashtable_remove_fast(
	struct rhashtable *ht, struct rhash_head *obj,
	const struct rhashtable_params params)
{
	struct bucket_table *tbl;
	int err;

	rcu_read_lock();

	tbl = rht_dereference_rcu(ht->tbl, ht);

	/* Because we have already taken (and released) the bucket
	 * lock in old_tbl, if we find that future_tbl is not yet
	 * visible then that guarantees the entry to still be in
	 * the old tbl if it exists.
	 */
	while ((err = __rhashtable_remove_fast(ht, tbl, obj, params)) &&
	       (tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
		;

	if (err)
		goto out;

	atomic_dec(&ht->nelems);
	if (rht_shrink_below_30(ht, tbl))
		schedule_work(&ht->run_work);

out:
	rcu_read_unlock();

	return err;
}

796
#endif /* _LINUX_RHASHTABLE_H */