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;