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

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
......@@ -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) \
......
......@@ -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 @@ exit:
}
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);
......
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