add an additional async notification communication method based on callback

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Yang <yang.yang@baishancloud.com>
Signed-off-by: Ping Yu <ping.yu@intel.com>
Signed-off-by: Steven Linsell <stevenx.linsell@intel.com>

(Merged from https://github.com/openssl/openssl/pull/7573)

1 files changed, 96 insertions, 0 deletions

diff --git a/doc/man3/SSL_set_async_callback.pod b/doc/man3/SSL_set_async_callback.pod
new file mode 100644
index 0000000000..5e7f61eaf1
--- /dev/null
+++ b/doc/man3/SSL_set_async_callback.pod
@@ -0,0 +1,96 @@
+=pod
+
+=head1 NAME
+
+SSL_CTX_set_async_callback,
+SSL_CTX_set_async_callback_arg,
+SSL_set_async_callback,
+SSL_set_async_callback_arg,
+SSL_get_async_status,
+SSL_async_callback_fn
+- manage asynchronous operations
+
+=head1 SYNOPSIS
+
+=for comment multiple includes
+
+ #include <openssl/ssl.h>
+
+ typedef int (*SSL_async_callback_fn)(SSL *s, void *arg);
+ int SSL_CTX_set_async_callback(SSL_CTX *ctx, SSL_async_callback_fn callback);
+ int SSL_CTX_set_async_callback_arg(SSL_CTX *ctx, void *arg);
+ int SSL_set_async_callback(SSL *s, SSL_async_callback_fn callback);
+ int SSL_set_async_callback_arg(SSL *s, void *arg);
+ int SSL_get_async_status(SSL *s, int *status);
+
+=head1 DESCRIPTION
+
+SSL_CTX_set_async_callback() sets an asynchronous callback function. All SSL
+objects generated based on this SSL_CTX will get this callback. If an engine
+supports the callback mechanism, it will be automatically called if
+SSL_MODE_ASYNC has been set and an asynchronous capable engine completes a
+cryptography operation to notify the application to resume the paused work flow.
+
+SSL_CTX_set_async_callback_arg() sets the callback argument.
+
+SSL_set_async_callback() allows an application to set a callback in an
+asynchronous SSL object, so that when an engine completes a cryptography
+operation, the callback will be called to notify the application to resume the
+paused work flow.
+
+SSL_set_async_callback_arg() sets an argument for the SSL object when the above
+callback is called.
+
+SSL_get_async_status() returns the engine status. This function facilitates the
+communication from the engine to the application. During an SSL session,
+cryptographic operations are dispatched to an engine. The engine status is very
+useful for an application to know if the operation has been successfully
+dispatched. If the engine does not support this additional callback method,
+"ASYNC_STATUS_UNSUPPORTED" will be returned. See ASYNC_WAIT_CTX_set_status() for
+a description of all of the status values.
+
+An example of the above functions would be the following.
+1. Application sets the async callback and callback data on an SSL connection
+by calling SSL_set_async_callback().
+2. Application sets SSL_MODE_ASYNC and makes an asynchronous SSL call
+3. OpenSSL submits the asynchronous request to the engine. If a retry occurs at
+this point then the status within the ASYNC_WAIT_CTX would be set and the async
+callback function would be called (goto Step 7).
+4. The OpenSSL engine pauses the current job and returns, so that the
+application can continue processing other connections.
+5. At a future point in time (probably via a polling mechanism or via an
+interrupt) the engine will become aware that the asynchronous request has
+finished processing.
+6. The engine will call the application's callback passing the callback data as
+a parameter.
+7. The callback function should then run. Note: it is a requirement that the
+callback function is small and non-blocking as it will be run in the context of
+a polling mechanism or an interrupt.
+8. It is the application's responsibility via the callback function to schedule
+recalling the OpenSSL asynchronous function and to continue processing.
+9. The callback function has the option to check the status returned via
+SSL_get_async_status() to determine whether a retry happened instead of the
+request being submitted, allowing different processing if required.
+
+=head1 RETURN VALUES
+
+SSL_CTX_set_async_callback(), SSL_set_async_callback(),
+SSL_CTX_set_async_callback_arg(), SSL_CTX_set_async_callback_arg() and
+SSL_get_async_status() return 1 on success or 0 on error.
+
+=head1 HISTORY
+
+SSL_CTX_set_async_callback(), SSL_CTX_set_async_callback_arg(),
+SSL_set_async_callback(), SSL_set_async_callback_arg() and
+SSL_get_async_status() were first added to OpenSSL 3.0.0.
+
+=head1 COPYRIGHT
+
+Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the OpenSSL license (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut