RE: [PATCH dpdk v2 3/3] hash: add replace API returning old data on overwrite

Konstantin Ananyev
2026-03-04T11:44:16Z

>
> 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 f487b3b725dd..cf957de55288 100644
> --- a/lib/hash/rte_cuckoo_hash.c
> +++ b/lib/hash/rte_cuckoo_hash.c
> @@ -1106,7 +1106,7 @@ __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;
> @@ -1305,7 +1305,9 @@ __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;
>
> @@ -1321,7 +1323,7 @@ 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)
> @@ -1329,7 +1331,7 @@ 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)
> @@ -1340,7 +1342,7 @@ 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
> @@ -1355,13 +1357,41 @@ 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.
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev@huawei.com>

> 2.53.0
>