[PATCH dpdk 2/2] hash: add replace API returning old data on overwrite

Robin Jarry
2026-02-12T21:33:57Z

Add rte_hash_replace_key_data() and rte_hash_replace_key_with_hash_data()
which behave like their add_key_data counterparts but return the previous
data pointer via an output parameter. On fresh insert, *old_data is set
to NULL.

When the caller provides old_data, no automatic RCU deferred free is
performed: the caller takes ownership of the old pointer and is
responsible for freeing it.

Signed-off-by: Robin Jarry <rjarry@redhat.com>
---
app/test/test_hash.c | 80 ++++++++++++++++++++++++++
doc/guides/rel_notes/release_26_03.rst | 6 ++
lib/hash/rte_cuckoo_hash.c | 42 ++++++++++++--
lib/hash/rte_hash.h | 67 +++++++++++++++++++++
4 files changed, 189 insertions(+), 6 deletions(-)

diff --git a/app/test/test_hash.c b/app/test/test_hash.c
index 56a7779e09b9..fcc02ea31205 100644
--- a/app/test/test_hash.c
+++ b/app/test/test_hash.c
@@ -2473,6 +2473,83 @@ test_hash_rcu_qsbr_replace_auto_free(void)
return ret;
}

+/*
+ * Test rte_hash_replace_key_data (explicit replace, no RCU).
+ * - Add key with data pointer (void *)1.
+ * - Replace same key with data (void *)2, verify old_data == (void *)1.
+ * - Lookup and verify data == (void *)2.
+ * - Replace with a new key (not yet inserted), verify old_data == NULL.
+ */
+static int
+test_hash_replace_key_data(void)
+{
+ struct rte_hash_parameters params = {
+ .name = "test_replace_key_data",
+ .entries = 64,
+ .key_len = sizeof(uint32_t),
+ .hash_func = NULL,
+ .hash_func_init_val = 0,
+ .socket_id = SOCKET_ID_ANY,
+ };
+ struct rte_hash *hash;
+ void *old_data = NULL;
+ void *data = NULL;
+ uint32_t key1 = 42;
+ uint32_t key2 = 99;
+ int ret = -1;
+
+ printf("\n# Running replace key data test\n");
+
+ hash = rte_hash_create(&params);
+ if (hash == NULL) {
+ printf("hash creation failed\n");
+ goto end;
+ }
+
+ /* Add key with data = (void *)1 */
+ ret = rte_hash_add_key_data(hash, &key1, (void *)(uintptr_t)1);
+ if (ret != 0) {
+ printf("failed to add key (ret=%d)\n", ret);
+ goto end;
+ }
+
+ /* Replace same key with data = (void *)2 */
+ ret = rte_hash_replace_key_data(hash, &key1, (void *)(uintptr_t)2, &old_data);
+ if (ret != 0) {
+ printf("failed to replace key (ret=%d)\n", ret);
+ goto end;
+ }
+ if (old_data != (void *)(uintptr_t)1) {
+ printf("old_data should be 0x1 but is %p\n", old_data);
+ goto end;
+ }
+
+ /* Lookup and verify data == (void *)2 */
+ ret = rte_hash_lookup_data(hash, &key1, &data);
+ if (ret < 0 || data != (void *)(uintptr_t)2) {
+ printf("lookup returned wrong data %p (ret=%d)\n", data, ret);
+ goto end;
+ }
+
+ /* Replace with a new key (not yet inserted) */
+ old_data = (void *)(uintptr_t)0xdeadbeef;
+ ret = rte_hash_replace_key_data(hash, &key2, (void *)(uintptr_t)3, &old_data);
+ if (ret != 0) {
+ printf("failed to insert new key via replace (ret=%d)\n", ret);
+ goto end;
+ }
+ if (old_data != NULL) {
+ printf("old_data should be NULL on fresh insert but is %p\n",
+ old_data);
+ goto end;
+ }
+
+end:
+ rte_hash_free(hash);
+
+ return ret;
+}
+
/*
* Do all unit and performance tests.
*/
@@ -2557,6 +2634,9 @@ test_hash(void)
if (test_hash_rcu_qsbr_replace_auto_free() < 0)
return -1;

+ if (test_hash_replace_key_data() < 0)
+ return -1;
+
return 0;
}

diff --git a/doc/guides/rel_notes/release_26_03.rst b/doc/guides/rel_notes/release_26_03.rst
index 693034bcb0d2..73418523809c 100644
--- a/doc/guides/rel_notes/release_26_03.rst
+++ b/doc/guides/rel_notes/release_26_03.rst
@@ -93,6 +93,12 @@ New Features
``rte_hash_add_key_data`` now automatically defers freeing the old data
pointer on key overwrite via the RCU defer queue.

+* **Added hash replace API.**
+
+ Added ``rte_hash_replace_key_data`` and ``rte_hash_replace_key_with_hash_data``
+ functions that return the previous data pointer on key overwrite, letting the
+ caller manage its lifecycle.
+

Removed Items
-------------
diff --git a/lib/hash/rte_cuckoo_hash.c b/lib/hash/rte_cuckoo_hash.c
index 0b979dc3be0b..039572d6eab1 100644
--- a/lib/hash/rte_cuckoo_hash.c
+++ b/lib/hash/rte_cuckoo_hash.c
@@ -1110,7 +1110,7 @@ __hash_rcu_auto_free_old_data(const struct rte_hash *h, void *old_data_val)

static inline int32_t
__rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
- hash_sig_t sig, void *data)
+ hash_sig_t sig, void *data, void **old_data)
{
uint16_t short_sig;
uint32_t prim_bucket_idx, sec_bucket_idx;
@@ -1309,7 +1309,9 @@ __rte_hash_add_key_with_hash(const struct rte_hash *h, const void *key,
return slot_id - 1;

overwrite:
- if (saved_old_data != NULL)
+ if (old_data != NULL)
+ *old_data = saved_old_data;
+ else if (saved_old_data != NULL)
__hash_rcu_auto_free_old_data(h, saved_old_data);
return ret;

@@ -1325,7 +1327,7 @@ rte_hash_add_key_with_hash(const struct rte_hash *h,
const void *key, hash_sig_t sig)
{
RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
- return __rte_hash_add_key_with_hash(h, key, sig, 0);
+ return __rte_hash_add_key_with_hash(h, key, sig, 0, NULL);
}

RTE_EXPORT_SYMBOL(rte_hash_add_key)
@@ -1333,7 +1335,7 @@ int32_t
rte_hash_add_key(const struct rte_hash *h, const void *key)
{
RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
- return __rte_hash_add_key_with_hash(h, key, rte_hash_hash(h, key), 0);
+ return __rte_hash_add_key_with_hash(h, key, rte_hash_hash(h, key), 0, NULL);
}

RTE_EXPORT_SYMBOL(rte_hash_add_key_with_hash_data)
@@ -1344,7 +1346,7 @@ rte_hash_add_key_with_hash_data(const struct rte_hash *h,
int ret;

RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);
- ret = __rte_hash_add_key_with_hash(h, key, sig, data);
+ ret = __rte_hash_add_key_with_hash(h, key, sig, data, NULL);
if (ret >= 0)
return 0;
else
@@ -1359,13 +1361,41 @@ rte_hash_add_key_data(const struct rte_hash *h, const void *key, void *data)

RETURN_IF_TRUE(((h == NULL) || (key == NULL)), -EINVAL);

- ret = __rte_hash_add_key_with_hash(h, key, rte_hash_hash(h, key), data);
+ ret = __rte_hash_add_key_with_hash(h, key, rte_hash_hash(h, key), data, NULL);
if (ret >= 0)
return 0;
else
return ret;
}

+RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_hash_replace_key_with_hash_data, 26.03)
+int
+rte_hash_replace_key_with_hash_data(const struct rte_hash *h,
+ const void *key, hash_sig_t sig,
+ void *data, void **old_data)
+{
+ int ret;
+
+ RETURN_IF_TRUE(((h == NULL) || (key == NULL) ||
+ (old_data == NULL)), -EINVAL);
+
+ *old_data = NULL;
+ ret = __rte_hash_add_key_with_hash(h, key, sig, data, old_data);
+ if (ret >= 0)
+ return 0;
+ else
+ return ret;
+}
+
+RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_hash_replace_key_data, 26.03)
+int
+rte_hash_replace_key_data(const struct rte_hash *h, const void *key,
+ void *data, void **old_data)
+{
+ return rte_hash_replace_key_with_hash_data(h, key,
+ rte_hash_hash(h, key), data, old_data);
+}
+
/* Search one bucket to find the match key - uses rw lock */
static inline int32_t
search_one_bucket_l(const struct rte_hash *h, const void *key,
diff --git a/lib/hash/rte_hash.h b/lib/hash/rte_hash.h
index e33f0aea0f5e..4a328c51501c 100644
--- a/lib/hash/rte_hash.h
+++ b/lib/hash/rte_hash.h
@@ -279,6 +279,73 @@ int32_t
rte_hash_add_key_with_hash_data(const struct rte_hash *h, const void *key,
hash_sig_t sig, void *data);

+/**
+ * Replace a key-value pair in an existing hash table, returning the previous
+ * data pointer associated with the key. If the key does not exist, it is
+ * inserted and *old_data is set to NULL.
+ *
+ * This operation is not multi-thread safe and should only be called from one
+ * thread by default. Thread safety can be enabled by setting flag during table
+ * creation.
+ *
+ * When old_data is provided, no automatic RCU deferred free is performed on
+ * overwrite; the caller takes ownership of the old pointer and is responsible
+ * for freeing it (e.g. via RCU).
+ *
+ * @param h
+ * Hash table to add the key to.
+ * @param key
+ * Key to add to the hash table.
+ * @param data
+ * Data to add to the hash table.
+ * @param old_data
+ * Output: on overwrite, set to the previous data pointer.
+ * On fresh insert, set to NULL.
+ * @return
+ * - 0 if added/replaced successfully
+ * - -EINVAL if the parameters are invalid.
+ * - -ENOSPC if there is no space in the hash for this key.
+ */
+__rte_experimental
+int
+rte_hash_replace_key_data(const struct rte_hash *h, const void *key,
+ void *data, void **old_data);
+
+/**
+ * Replace a key-value pair with a pre-computed hash value in an existing hash
+ * table, returning the previous data pointer associated with the key. If the
+ * key does not exist, it is inserted and *old_data is set to NULL.
+ *
+ * This operation is not multi-thread safe and should only be called from one
+ * thread by default. Thread safety can be enabled by setting flag during table
+ * creation.
+ *
+ * When old_data is provided, no automatic RCU deferred free is performed on
+ * overwrite; the caller takes ownership of the old pointer and is responsible
+ * for freeing it (e.g. via RCU).
+ *
+ * @param h
+ * Hash table to add the key to.
+ * @param key
+ * Key to add to the hash table.
+ * @param sig
+ * Precomputed hash value for 'key'
+ * @param data
+ * Data to add to the hash table.
+ * @param old_data
+ * Output: on overwrite, set to the previous data pointer.
+ * On fresh insert, set to NULL.
+ * @return
+ * - 0 if added/replaced successfully
+ * - -EINVAL if the parameters are invalid.
+ * - -ENOSPC if there is no space in the hash for this key.
+ */
+__rte_experimental
+int
+rte_hash_replace_key_with_hash_data(const struct rte_hash *h,
+ const void *key, hash_sig_t sig,
+ void *data, void **old_data);
+
/**
* Add a key to an existing hash table. This operation is not multi-thread safe
* and should only be called from one thread by default.
--
2.53.0