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Commit f2dba9c6 authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
Browse files

rhashtable: Introduce rhashtable_walk_* 



Some existing rhashtable users get too intimate with it by walking
the buckets directly.  This prevents us from easily changing the
internals of rhashtable.

This patch adds the helpers rhashtable_walk_init/exit/start/next/stop
which will replace these custom walkers.

They are meant to be usable for both procfs seq_file walks as well
as walking by a netlink dump.  The iterator structure should fit
inside a netlink dump cb structure, with at least one element to
spare.

Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 28134a53

include/linux/rhashtable.h

+35 −0
Original line number Diff line number Diff line
@@ -18,6 +18,7 @@ 
#ifndef _LINUX_RHASHTABLE_H

#define _LINUX_RHASHTABLE_H



#include <linux/compiler.h>

#include <linux/list_nulls.h>

#include <linux/workqueue.h>

#include <linux/mutex.h>
@@ -111,6 +112,7 @@ struct rhashtable_params { 
 * @p: Configuration parameters

 * @run_work: Deferred worker to expand/shrink asynchronously

 * @mutex: Mutex to protect current/future table swapping

 * @walkers: List of active walkers

 * @being_destroyed: True if table is set up for destruction

 */

struct rhashtable {
@@ -121,9 +123,36 @@ struct rhashtable { 
	struct rhashtable_params	p;

	struct work_struct		run_work;

	struct mutex                    mutex;

	struct list_head		walkers;

	bool                            being_destroyed;

};



/**

 * struct rhashtable_walker - Hash table walker

 * @list: List entry on list of walkers

 * @resize: Resize event occured

 */

struct rhashtable_walker {

	struct list_head list;

	bool resize;

};



/**

 * 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;

};



static inline unsigned long rht_marker(const struct rhashtable *ht, u32 hash)

{

	return NULLS_MARKER(ht->p.nulls_base + hash);
@@ -179,6 +208,12 @@ bool rhashtable_lookup_compare_insert(struct rhashtable *ht, 
				      bool (*compare)(void *, void *),

				      void *arg);



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);



void rhashtable_destroy(struct rhashtable *ht);



#define rht_dereference(p, ht) \

lib/rhashtable.c

+163 −0
Original line number Diff line number Diff line
@@ -484,6 +484,7 @@ static void rht_deferred_worker(struct work_struct *work) 
{

	struct rhashtable *ht;

	struct bucket_table *tbl;

	struct rhashtable_walker *walker;



	ht = container_of(work, struct rhashtable, run_work);

	mutex_lock(&ht->mutex);
@@ -492,6 +493,9 @@ static void rht_deferred_worker(struct work_struct *work) 


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



	list_for_each_entry(walker, &ht->walkers, list)

		walker->resize = true;



	if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))

		rhashtable_expand(ht);

	else if (ht->p.shrink_decision && ht->p.shrink_decision(ht, tbl->size))
@@ -822,6 +826,164 @@ bool rhashtable_lookup_compare_insert(struct rhashtable *ht, 
}

EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert);



/**

 * rhashtable_walk_init - Initialise an iterator

 * @ht:		Table to walk over

 * @iter:	Hash table Iterator

 *

 * This function prepares a hash table walk.

 *

 * Note that if you restart a walk after rhashtable_walk_stop you

 * may see the same object twice.  Also, you may miss objects if

 * there are removals in between rhashtable_walk_stop and the next

 * call to rhashtable_walk_start.

 *

 * For a completely stable walk you should construct your own data

 * structure outside the hash table.

 *

 * This function may sleep so you must not call it from interrupt

 * context or with spin locks held.

 *

 * You must call rhashtable_walk_exit if this function returns

 * successfully.

 */

int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)

{

	iter->ht = ht;

	iter->p = NULL;

	iter->slot = 0;

	iter->skip = 0;



	iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);

	if (!iter->walker)

		return -ENOMEM;



	mutex_lock(&ht->mutex);

	list_add(&iter->walker->list, &ht->walkers);

	mutex_unlock(&ht->mutex);



	return 0;

}

EXPORT_SYMBOL_GPL(rhashtable_walk_init);



/**

 * rhashtable_walk_exit - Free an iterator

 * @iter:	Hash table Iterator

 *

 * This function frees resources allocated by rhashtable_walk_init.

 */

void rhashtable_walk_exit(struct rhashtable_iter *iter)

{

	mutex_lock(&iter->ht->mutex);

	list_del(&iter->walker->list);

	mutex_unlock(&iter->ht->mutex);

	kfree(iter->walker);

}

EXPORT_SYMBOL_GPL(rhashtable_walk_exit);



/**

 * rhashtable_walk_start - Start a hash table walk

 * @iter:	Hash table iterator

 *

 * Start a hash table walk.  Note that we take the RCU lock in all

 * cases including when we return an error.  So you must always call

 * rhashtable_walk_stop to clean up.

 *

 * Returns zero if successful.

 *

 * Returns -EAGAIN if resize event occured.  Note that the iterator

 * will rewind back to the beginning and you may use it immediately

 * by calling rhashtable_walk_next.

 */

int rhashtable_walk_start(struct rhashtable_iter *iter)

{

	rcu_read_lock();



	if (iter->walker->resize) {

		iter->slot = 0;

		iter->skip = 0;

		iter->walker->resize = false;

		return -EAGAIN;

	}



	return 0;

}

EXPORT_SYMBOL_GPL(rhashtable_walk_start);



/**

 * rhashtable_walk_next - Return the next object and advance the iterator

 * @iter:	Hash table iterator

 *

 * Note that you must call rhashtable_walk_stop when you are finished

 * with the walk.

 *

 * Returns the next object or NULL when the end of the table is reached.

 *

 * Returns -EAGAIN if resize event occured.  Note that the iterator

 * will rewind back to the beginning and you may continue to use it.

 */

void *rhashtable_walk_next(struct rhashtable_iter *iter)

{

	const struct bucket_table *tbl;

	struct rhashtable *ht = iter->ht;

	struct rhash_head *p = iter->p;

	void *obj = NULL;



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



	if (p) {

		p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);

		goto next;

	}



	for (; iter->slot < tbl->size; iter->slot++) {

		int skip = iter->skip;



		rht_for_each_rcu(p, tbl, iter->slot) {

			if (!skip)

				break;

			skip--;

		}



next:

		if (!rht_is_a_nulls(p)) {

			iter->skip++;

			iter->p = p;

			obj = rht_obj(ht, p);

			goto out;

		}



		iter->skip = 0;

	}



	iter->p = NULL;



out:

	if (iter->walker->resize) {

		iter->p = NULL;

		iter->slot = 0;

		iter->skip = 0;

		iter->walker->resize = false;

		return ERR_PTR(-EAGAIN);

	}



	return obj;

}

EXPORT_SYMBOL_GPL(rhashtable_walk_next);



/**

 * rhashtable_walk_stop - Finish a hash table walk

 * @iter:	Hash table iterator

 *

 * Finish a hash table walk.

 */

void rhashtable_walk_stop(struct rhashtable_iter *iter)

{

	rcu_read_unlock();

	iter->p = NULL;

}

EXPORT_SYMBOL_GPL(rhashtable_walk_stop);



static size_t rounded_hashtable_size(struct rhashtable_params *params)

{

	return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
@@ -894,6 +1056,7 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params) 
	memset(ht, 0, sizeof(*ht));

	mutex_init(&ht->mutex);

	memcpy(&ht->p, params, sizeof(*params));

	INIT_LIST_HEAD(&ht->walkers);



	if (params->locks_mul)

		ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);