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>

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 3851952..bc2488b 100644 (file)
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -19,6 +19,7 @@
 
 #include <linux/compiler.h>
 #include <linux/errno.h>
+#include <linux/jhash.h>
 #include <linux/list_nulls.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
@@ -103,7 +104,7 @@ struct rhashtable;
  * @min_size: Minimum size while shrinking
  * @nulls_base: Base value to generate nulls marker
  * @locks_mul: Number of bucket locks to allocate per cpu (default: 128)
- * @hashfn: Function to hash key
+ * @hashfn: Hash function (default: jhash2 if !(key_len % 4), or jhash)
  * @obj_hashfn: Function to hash object
  * @obj_cmpfn: Function to compare key with object
  */
@@ -125,6 +126,7 @@ struct rhashtable_params {
  * struct rhashtable - Hash table handle
  * @tbl: Bucket table
  * @nelems: Number of elements in table
+ * @key_len: Key length for hashfn
  * @p: Configuration parameters
  * @run_work: Deferred worker to expand/shrink asynchronously
  * @mutex: Mutex to protect current/future table swapping
@@ -134,6 +136,7 @@ struct rhashtable {
        struct bucket_table __rcu       *tbl;
        atomic_t                        nelems;
        bool                            being_destroyed;
+       unsigned int                    key_len;
        struct rhashtable_params        p;
        struct work_struct              run_work;
        struct mutex                    mutex;
@@ -199,13 +202,31 @@ static inline unsigned int rht_key_hashfn(
        struct rhashtable *ht, const struct bucket_table *tbl,
        const void *key, const struct rhashtable_params params)
 {
+       unsigned hash;
+
        /* params must be equal to ht->p if it isn't constant. */
-       unsigned key_len = __builtin_constant_p(params.key_len) ?
-                          (params.key_len ?: ht->p.key_len) :
-                          params.key_len;
+       if (!__builtin_constant_p(params.key_len))
+               hash = ht->p.hashfn(key, ht->key_len, tbl->hash_rnd);
+       else if (params.key_len) {
+               unsigned key_len = params.key_len;
+
+               if (params.hashfn)
+                       hash = params.hashfn(key, key_len, tbl->hash_rnd);
+               else if (key_len & (sizeof(u32) - 1))
+                       hash = jhash(key, key_len, tbl->hash_rnd);
+               else
+                       hash = jhash2(key, key_len / sizeof(u32),
+                                     tbl->hash_rnd);
+       } else {
+               unsigned key_len = ht->p.key_len;
+
+               if (params.hashfn)
+                       hash = params.hashfn(key, key_len, tbl->hash_rnd);
+               else
+                       hash = jhash(key, key_len, tbl->hash_rnd);
+       }
 
-       return rht_bucket_index(tbl, params.hashfn(key, key_len,
-                                                  tbl->hash_rnd));
+       return rht_bucket_index(tbl, hash);
 }
 
 static inline unsigned int rht_head_hashfn(

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 618a3f0..798f01d 100644 (file)
--- 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;