[PATCH v2 5/5] crypto/Documentation: Add crypto_pool kernel API

[Dmitry Safonov]

Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
---
 Documentation/crypto/crypto_pool.rst | 33 ++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 Documentation/crypto/crypto_pool.rst

diff --git a/Documentation/crypto/crypto_pool.rst b/Documentation/crypto/crypto_pool.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+Per-CPU pool of crypto requests
+=============
+
+Overview
+--------
+The crypto pool API manages pre-allocated per-CPU pool of crypto requests,
+providing ability to use async crypto requests on fast paths, potentially
+on atomic contexts. The allocation and initialization of the requests should
+be done before their usage as it's slow-path and may sleep.
+
+Order of operations
+-------------------
+You are required to allocate a new pool prior using it and manage its lifetime.
+You can allocate a per-CPU pool of ahash requests by ``crypto_pool_alloc_ahash()``.
+It will give you a pool id that you can use further on fast-path for hashing.
+You can increase the reference counter for an allocated pool via
+``crypto_pool_add()``. Decrease the reference counter by ``crypto_pool_release()``.
+When the refcounter hits zero, the pool is scheduled for destruction and you
+can't use the corresponding crypto pool id anymore.
+Note that ``crypto_pool_add()`` and ``crypto_pool_release()`` must be called
+only for an already existing pool and can be called in atomic contexts.
+
+``crypto_pool_get()`` disables bh and returns you back ``struct crypto_pool *``,
+which is a generic type for different crypto requests and has ``scratch`` area
+that can be used as a temporary buffer for your operation.
+
+``crypto_pool_put()`` enables bh back once you've done with your crypto
+operation.
+
+If you need to pre-allocate a bigger per-CPU ``scratch`` area for you requests,
+you can use ``crypto_pool_reserve_scratch()``.
-- 
2.39.0