rhashtable: Allow hashfn to be unset

Since every current rhashtable user uses jhash as their hash
function, the fact that jhash is an inline function causes each
user to generate a copy of its code.

This function provides a solution to this problem by allowing
hashfn to be unset.  In which case rhashtable will automatically
set it to jhash.  Furthermore, if the key length is a multiple
of 4, we will switch over to jhash2.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 1 deletions

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 618a3f00d712..798f01d64ab0 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -532,6 +532,11 @@ static size_t rounded_hashtable_size(const struct rhashtable_params *params)
 		   (unsigned long)params->min_size);
 }
 
+static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
+{
+	return jhash2(key, length, seed);
+}
+
 /**
  * rhashtable_init - initialize a new hash table
  * @ht:		hash table to be initialized
@@ -583,7 +588,7 @@ int rhashtable_init(struct rhashtable *ht,
 
 	size = HASH_DEFAULT_SIZE;
 
-	if ((!(params->key_len && params->hashfn) && !params->obj_hashfn) ||
+	if ((!params->key_len && !params->obj_hashfn) ||
 	    (params->obj_hashfn && !params->obj_cmpfn))
 		return -EINVAL;
 
@@ -610,6 +615,16 @@ int rhashtable_init(struct rhashtable *ht,
 	else
 		ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
 
+	ht->key_len = ht->p.key_len;
+	if (!params->hashfn) {
+		ht->p.hashfn = jhash;
+
+		if (!(ht->key_len & (sizeof(u32) - 1))) {
+			ht->key_len /= sizeof(u32);
+			ht->p.hashfn = rhashtable_jhash2;
+		}
+	}
+
 	tbl = bucket_table_alloc(ht, size);
 	if (tbl == NULL)
 		return -ENOMEM;