[dpdk-dev] [v3,3/3] doc: add private data info in crypto guide

[Abhinandan Gujjar <abhinandan.gujjar@intel.com>]

Signed-off-by: Abhinandan Gujjar <abhinandan.gujjar@intel.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>
---
 doc/guides/prog_guide/cryptodev_lib.rst | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/doc/guides/prog_guide/cryptodev_lib.rst b/doc/guides/prog_guide/cryptodev_lib.rst
index 066fe2d..b279a20 100644
--- a/doc/guides/prog_guide/cryptodev_lib.rst
+++ b/doc/guides/prog_guide/cryptodev_lib.rst
@@ -299,6 +299,33 @@ directly from the devices processed queue, and for virtual device's from a
 enqueue call.
 
 
+Private data
+~~~~~~~~~~~~
+For session-based operations, the set and get API provides a mechanism for an
+application to store and retrieve the private data information stored along with
+the crypto session.
+
+For example, suppose an application is submitting a crypto operation with a session
+associated and wants to indicate private data information which is required to be
+used after completion of the crypto operation. In this case, the application can use
+the set API to set the private data and retrieve it using get API.
+
+.. code-block:: c
+
+	int rte_cryptodev_sym_session_set_private_data(
+		struct rte_cryptodev_sym_session *sess,	void *data, uint16_t size);
+
+	void * rte_cryptodev_sym_session_get_private_data(
+		struct rte_cryptodev_sym_session *sess);
+
+
+For session-less mode, the private data information can be placed along with the
+``struct rte_crypto_op``. The ``rte_crypto_op::private_data_offset`` indicates the
+start of private data information. The offset is counted from the start of the
+rte_crypto_op including other crypto information such as the IVs (since there can
+be an IV also for authentication).
+
+
 Enqueue / Dequeue Burst APIs
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-- 
1.9.1