Add the rhashtable_replace_fast function. This replaces one object in
the table with another atomically. The hashes of the new and old objects
must be equal.
Signed-off-by: Tom Herbert <t...@herbertland.com>
---
include/linux/rhashtable.h | 82 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 82 insertions(+)
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 843ceca..77deece 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -819,4 +819,86 @@ out:
return err;
}
+/* Internal function, please use rhashtable_replace_fast() instead */
+static inline int __rhashtable_replace_fast(
+ struct rhashtable *ht, struct bucket_table *tbl,
+ struct rhash_head *obj_old, struct rhash_head *obj_new,
+ const struct rhashtable_params params)
+{
+ struct rhash_head __rcu **pprev;
+ struct rhash_head *he;
+ spinlock_t *lock;
+ unsigned int hash;
+ int err = -ENOENT;
+
+ /* Minimally, the old and new objects must have same hash
+ * (which should mean identifiers are the same).
+ */
+ hash = rht_head_hashfn(ht, tbl, obj_old, params);
+ if (hash != rht_head_hashfn(ht, tbl, obj_new, params))
+ return -EINVAL;
+
+ lock = rht_bucket_lock(tbl, hash);
+
+ spin_lock_bh(lock);
+
+ pprev = &tbl->buckets[hash];
+ rht_for_each(he, tbl, hash) {
+ if (he != obj_old) {
+ pprev = &he->next;
+ continue;
+ }
+
+ rcu_assign_pointer(obj_new->next, obj_old->next);
+ rcu_assign_pointer(*pprev, obj_new);
+ err = 0;
+ break;
+ }
+
+ spin_unlock_bh(lock);
+
+ return err;
+}
+
+/**
+ * rhashtable_replace_fast - replace an object in hash table
+ * @ht: hash table
+ * @obj_old: pointer to hash head inside object being replaced
+ * @obj_new: pointer to hash head inside object which is new
+ * @params: hash table parameters
+ *
+ * Replacing an object doesn't affect the number of elements in the hash table
+ * or bucket, so we don't need to worry about shrinking or expanding the
+ * table here.
+ *
+ * Returns zero on success, -ENOENT if the entry could not be found,
+ * -EINVAL if hash is not the same for the old and new objects.
+ */
+static inline int rhashtable_replace_fast(
+ struct rhashtable *ht, struct rhash_head *obj_old,
+ struct rhash_head *obj_new,
+ 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_replace_fast(ht, tbl, obj_old,
+ obj_new, params)) &&
+ (tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
+ ;
+
+ rcu_read_unlock();
+
+ return err;
+}
+
#endif /* _LINUX_RHASHTABLE_H */
--
2.4.6
--
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