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/next/end 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 | 44 +++++++++++++++++++++
lib/rhashtable.c | 91 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 135 insertions(+)
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 6d7e840..b03b375 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>
@@ -123,6 +124,22 @@ struct rhashtable {
bool being_destroyed;
};
+/**
+ * struct rhashtable_iter - Hash table iterator
+ * @ht: Table to iterate through
+ * @p: Current pointer
+ * @lock: Slot lock
+ * @slot: Current slot
+ * @skip: Number of entries to skip in slot
+ */
+struct rhashtable_iter {
+ struct rhashtable *ht;
+ struct rhash_head *p;
+ spinlock_t *lock;
+ 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 +195,33 @@ bool rhashtable_lookup_compare_insert(struct rhashtable *ht,
bool (*compare)(void *, void *),
void *arg);
+/**
+ * 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.
+ */
+static inline void rhashtable_walk_init(struct rhashtable *ht,
+ struct rhashtable_iter *iter)
+{
+ iter->ht = ht;
+ iter->p = NULL;
+ iter->slot = 0;
+ iter->skip = 0;
+}
+
+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..d51fb06 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -813,6 +813,97 @@ exit:
}
EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert);
+/**
+ * rhashtable_walk_start - Start a hash table walk
+ * @iter: Hash table iterator
+ *
+ * Start a hash table walk.
+ *
+ * Returns zero if successful. Returns -EINTR if we couldn't
+ * obtain the resize lock.
+ */
+int rhashtable_walk_start(struct rhashtable_iter *iter)
+{
+ struct rhashtable *ht = iter->ht;
+ int err;
+
+ err = mutex_lock_interruptible(&ht->mutex);
+ rcu_read_lock();
+
+ if (!err)
+ mutex_unlock(&ht->mutex);
+
+ return err;
+}
+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.
+ */
+void *rhashtable_walk_next(struct rhashtable_iter *iter)
+{
+ const struct bucket_table *tbl;
+ struct rhashtable *ht = iter->ht;
+ struct rhash_head *p = iter->p;
+
+ tbl = rht_dereference_rcu(ht->tbl, ht);
+
+ if (p) {
+ p = rht_dereference_bucket(p->next, tbl, iter->slot);
+ goto next;
+ }
+
+ for (; iter->slot < tbl->size; iter->slot++) {
+ int skip = iter->skip;
+
+ iter->lock = bucket_lock(tbl, iter->slot);
+ spin_lock_bh(iter->lock);
+
+ rht_for_each(p, tbl, iter->slot) {
+ if (!skip)
+ break;
+ skip--;
+ }
+
+next:
+ if (!rht_is_a_nulls(p)) {
+ iter->skip++;
+ iter->p = p;
+ return rht_obj(ht, p);
+ }
+ spin_unlock_bh(iter->lock);
+
+ iter->skip = 0;
+ }
+
+ iter->p = NULL;
+ return NULL;
+}
+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)
+{
+ if (iter->p)
+ spin_unlock_bh(iter->lock);
+
+ 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),
--
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