hash: retrieve a key given its position

The function rte_hash_get_key_with_position is added in this patch.
As the position returned when adding a key is frequently used as an
offset into an array of user data, this function performs the operation
of retrieving a key given this offset.

A possible use case would be to delete a key from the hash table when
its entry in the array of data has certain value. For instance, the key
could be a flow 5-tuple, and the value stored in the array a time
stamp.

Signed-off-by: Juan Antonio Montesinos <juan.antonio.montesinos.delgado@ericsson.com>
Signed-off-by: Yari Adan Petralanda <yari.adan.petralanda@ericsson.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>

app/test/test_hash.c

@@ -420,6 +420,46 @@ static int test_add_update_delete(void)
 	return 0;
 }
 
+/*
+ * Sequence of operations for retrieving a key with its position
+ *
+ *  - create table
+ *  - add key
+ *  - get the key with its position: hit
+ *  - delete key
+ *  - try to get the deleted key: miss
+ *
+ */
+static int test_hash_get_key_with_position(void)
+{
+	struct rte_hash *handle = NULL;
+	int pos, expectedPos, result;
+	void *key;
+
+	ut_params.name = "hash_get_key_w_pos";
+	handle = rte_hash_create(&ut_params);
+	RETURN_IF_ERROR(handle == NULL, "hash creation failed");
+
+	pos = rte_hash_add_key(handle, &keys[0]);
+	print_key_info("Add", &keys[0], pos);
+	RETURN_IF_ERROR(pos < 0, "failed to add key (pos0=%d)", pos);
+	expectedPos = pos;
+
+	result = rte_hash_get_key_with_position(handle, pos, &key);
+	RETURN_IF_ERROR(result != 0, "error retrieving a key");
+
+	pos = rte_hash_del_key(handle, &keys[0]);
+	print_key_info("Del", &keys[0], pos);
+	RETURN_IF_ERROR(pos != expectedPos,
+			"failed to delete key (pos0=%d)", pos);
+
+	result = rte_hash_get_key_with_position(handle, pos, &key);
+	RETURN_IF_ERROR(result != -ENOENT, "non valid key retrieved");
+
+	rte_hash_free(handle);
+	return 0;
+}
+
 /*
  * Sequence of operations for find existing hash table
  *
@@ -1442,6 +1482,8 @@ test_hash(void)
 		return -1;
 	if (test_hash_add_delete_jhash_3word() < 0)
 		return -1;
+	if (test_hash_get_key_with_position() < 0)
+		return -1;
 	if (test_hash_find_existing() < 0)
 		return -1;
 	if (test_add_update_delete() < 0)

lib/librte_hash/rte_cuckoo_hash.c

@@ -877,6 +877,26 @@ rte_hash_del_key(const struct rte_hash *h, const void *key)
 	return __rte_hash_del_key_with_hash(h, key, rte_hash_hash(h, key));
 }
 
+int
+rte_hash_get_key_with_position(const struct rte_hash *h, const int32_t position,
+			       void **key)
+{
+	RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
+
+	struct rte_hash_key *k, *keys = h->key_store;
+	k = (struct rte_hash_key *) ((char *) keys + (position + 1) *
+				     h->key_entry_size);
+	*key = k->key;
+
+	if (position !=
+	    __rte_hash_lookup_with_hash(h, *key, rte_hash_hash(h, *key),
+					NULL)) {
+		return -ENOENT;
+	}
+
+	return 0;
+}
+
 /* Lookup bulk stage 0: Prefetch input key */
 static inline void
 lookup_stage0(unsigned *idx, uint64_t *lookup_mask,

lib/librte_hash/rte_hash.h

@@ -271,6 +271,24 @@ rte_hash_del_key(const struct rte_hash *h, const void *key);
 int32_t
 rte_hash_del_key_with_hash(const struct rte_hash *h, const void *key, hash_sig_t sig);
 
+/**
+ * Find a key in the hash table given the position.
+ * This operation is multi-thread safe.
+ *
+ * @param h
+ *   Hash table to get the key from.
+ * @param position
+ *   Position returned when the key was inserted.
+ * @param key
+ *   Output containing a pointer to the key
+ * @return
+ *   - 0 if retrieved successfully
+ *   - EINVAL if the parameters are invalid.
+ *   - ENOENT if no valid key is found in the given position.
+ */
+int
+rte_hash_get_key_with_position(const struct rte_hash *h, const int32_t position,
+			       void **key);
 
 /**
  * Find a key-value pair in the hash table.

lib/librte_hash/rte_hash_version.map

@@ -38,3 +38,10 @@ DPDK_2.2 {
 	rte_hash_set_cmp_func;
 
 } DPDK_2.1;
+
+DPDK_16.07 {
+	global:
+
+	rte_hash_get_key_with_position;
+
+} DPDK_2.2;