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: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
---
include/linux/rhashtable.h | 35 +++++++++
lib/rhashtable.c | 162 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 197 insertions(+)
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 6d7e840..a0e5b08 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -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>
@@ -110,6 +111,7 @@ 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 {
@@ -120,9 +122,36 @@ 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);
@@ -178,6 +207,12 @@ 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) \
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 71c6aa1..69a4eb0 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -485,11 +485,15 @@ 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);
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))
@@ -813,6 +817,163 @@ 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;
+}
+
+/**
+ * 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),
@@ -885,6 +1046,7 @@ 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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