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
--- 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 @@
* @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 - 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 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 @@
struct rhashtable *ht, const struct bucket_table *tbl,
const void *key, const struct rhashtable_params params)
{
- /* 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;
+ unsigned hash;
- return rht_bucket_index(tbl, params.hashfn(key, key_len,
- tbl->hash_rnd));
+ /* params must be equal to ht->p if it isn't constant. */
+ 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, hash);
}
static inline unsigned int rht_head_hashfn(
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 618a3f0..798f01d 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -532,6 +532,11 @@
(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 @@
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 @@
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;