rhashtable: involve rhashtable_lookup_compare_insert routine

Introduce a new function called rhashtable_lookup_compare_insert()
which is very similar to rhashtable_lookup_insert(). But the former
makes use of users' given compare function to look for an object,
and then inserts it into hash table if found. As the entire process
of search and insertion is under protection of per bucket lock, this
can help users to avoid the involvement of extra lock.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rhashtable.h

@@ -168,7 +168,12 @@ int rhashtable_shrink(struct rhashtable *ht);
 void *rhashtable_lookup(struct rhashtable *ht, const void *key);
 void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
 				bool (*compare)(void *, void *), void *arg);
+
 bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj);
+bool rhashtable_lookup_compare_insert(struct rhashtable *ht,
+				      struct rhash_head *obj,
+				      bool (*compare)(void *, void *),
+				      void *arg);
 
 void rhashtable_destroy(struct rhashtable *ht);
 

lib/rhashtable.c

@@ -726,6 +726,43 @@ EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
  * to rhashtable_init().
  */
 bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj)
+{
+	struct rhashtable_compare_arg arg = {
+		.ht = ht,
+		.key = rht_obj(ht, obj) + ht->p.key_offset,
+	};
+
+	BUG_ON(!ht->p.key_len);
+
+	return rhashtable_lookup_compare_insert(ht, obj, &rhashtable_compare,
+						&arg);
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup_insert);
+
+/**
+ * rhashtable_lookup_compare_insert - search and insert object to hash table
+ *                                    with compare function
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @compare:	compare function, must return true on match
+ * @arg:	argument passed on to compare function
+ *
+ * Locks down the bucket chain in both the old and new table if a resize
+ * is in progress to ensure that writers can't remove from the old table
+ * and can't insert to the new table during the atomic operation of search
+ * and insertion. Searches for duplicates in both the old and new table if
+ * a resize is in progress.
+ *
+ * Lookups may occur in parallel with hashtable mutations and resizing.
+ *
+ * Will trigger an automatic deferred table resizing if the size grows
+ * beyond the watermark indicated by grow_decision() which can be passed
+ * to rhashtable_init().
+ */
+bool rhashtable_lookup_compare_insert(struct rhashtable *ht,
+				      struct rhash_head *obj,
+				      bool (*compare)(void *, void *),
+				      void *arg)
 {
 	struct bucket_table *new_tbl, *old_tbl;
 	spinlock_t *new_bucket_lock, *old_bucket_lock;
@@ -747,7 +784,8 @@ bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj)
 	if (unlikely(old_tbl != new_tbl))
 		spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
 
-	if (rhashtable_lookup(ht, rht_obj(ht, obj) + ht->p.key_offset)) {
+	if (rhashtable_lookup_compare(ht, rht_obj(ht, obj) + ht->p.key_offset,
+				      compare, arg)) {
 		success = false;
 		goto exit;
 	}
@@ -763,7 +801,7 @@ bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj)
 
 	return success;
 }
-EXPORT_SYMBOL_GPL(rhashtable_lookup_insert);
+EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert);
 
 static size_t rounded_hashtable_size(struct rhashtable_params *params)
 {