145 lines
7.2 KiB
Plaintext
145 lines
7.2 KiB
Plaintext
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=pod
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=head1 NAME
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ASYNC_WAIT_CTX_new, ASYNC_WAIT_CTX_free, ASYNC_WAIT_CTX_set_wait_fd,
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ASYNC_WAIT_CTX_get_fd, ASYNC_WAIT_CTX_get_all_fds,
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ASYNC_WAIT_CTX_get_changed_fds, ASYNC_WAIT_CTX_clear_fd - functions to manage
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waiting for asynchronous jobs to complete
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=head1 SYNOPSIS
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#include <openssl/async.h>
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ASYNC_WAIT_CTX *ASYNC_WAIT_CTX_new(void);
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void ASYNC_WAIT_CTX_free(ASYNC_WAIT_CTX *ctx);
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int ASYNC_WAIT_CTX_set_wait_fd(ASYNC_WAIT_CTX *ctx, const void *key,
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OSSL_ASYNC_FD fd,
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void *custom_data,
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void (*cleanup)(ASYNC_WAIT_CTX *, const void *,
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OSSL_ASYNC_FD, void *));
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int ASYNC_WAIT_CTX_get_fd(ASYNC_WAIT_CTX *ctx, const void *key,
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OSSL_ASYNC_FD *fd, void **custom_data);
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int ASYNC_WAIT_CTX_get_all_fds(ASYNC_WAIT_CTX *ctx, OSSL_ASYNC_FD *fd,
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size_t *numfds);
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int ASYNC_WAIT_CTX_get_changed_fds(ASYNC_WAIT_CTX *ctx, OSSL_ASYNC_FD *addfd,
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size_t *numaddfds, OSSL_ASYNC_FD *delfd,
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size_t *numdelfds);
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int ASYNC_WAIT_CTX_clear_fd(ASYNC_WAIT_CTX *ctx, const void *key);
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=head1 DESCRIPTION
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For an overview of how asynchronous operations are implemented in OpenSSL see
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L<ASYNC_start_job(3)>. An ASYNC_WAIT_CTX object represents an asynchronous
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"session", i.e. a related set of crypto operations. For example in SSL terms
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this would have a one-to-one correspondence with an SSL connection.
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Application code must create an ASYNC_WAIT_CTX using the ASYNC_WAIT_CTX_new()
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function prior to calling ASYNC_start_job() (see L<ASYNC_start_job(3)>). When
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the job is started it is associated with the ASYNC_WAIT_CTX for the duration of
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that job. An ASYNC_WAIT_CTX should only be used for one ASYNC_JOB at any one
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time, but can be reused after an ASYNC_JOB has finished for a subsequent
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ASYNC_JOB. When the session is complete (e.g. the SSL connection is closed),
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application code cleans up with ASYNC_WAIT_CTX_free().
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ASYNC_WAIT_CTXs can have "wait" file descriptors associated with them. Calling
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ASYNC_WAIT_CTX_get_all_fds() and passing in a pointer to an ASYNC_WAIT_CTX in
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the B<ctx> parameter will return the wait file descriptors associated with that
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job in B<*fd>. The number of file descriptors returned will be stored in
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B<*numfds>. It is the caller's responsibility to ensure that sufficient memory
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has been allocated in B<*fd> to receive all the file descriptors. Calling
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ASYNC_WAIT_CTX_get_all_fds() with a NULL B<fd> value will return no file
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descriptors but will still populate B<*numfds>. Therefore, application code is
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typically expected to call this function twice: once to get the number of fds,
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and then again when sufficient memory has been allocated. If only one
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asynchronous engine is being used then normally this call will only ever return
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one fd. If multiple asynchronous engines are being used then more could be
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returned.
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The function ASYNC_WAIT_CTX_get_changed_fds() can be used to detect if any fds
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have changed since the last call time ASYNC_start_job() returned an ASYNC_PAUSE
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result (or since the ASYNC_WAIT_CTX was created if no ASYNC_PAUSE result has
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been received). The B<numaddfds> and B<numdelfds> parameters will be populated
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with the number of fds added or deleted respectively. B<*addfd> and B<*delfd>
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will be populated with the list of added and deleted fds respectively. Similarly
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to ASYNC_WAIT_CTX_get_all_fds() either of these can be NULL, but if they are not
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NULL then the caller is responsible for ensuring sufficient memory is allocated.
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Implementors of async aware code (e.g. engines) are encouraged to return a
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stable fd for the lifetime of the ASYNC_WAIT_CTX in order to reduce the "churn"
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of regularly changing fds - although no guarantees of this are provided to
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applications.
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Applications can wait for the file descriptor to be ready for "read" using a
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system function call such as select or poll (being ready for "read" indicates
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that the job should be resumed). If no file descriptor is made available then an
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application will have to periodically "poll" the job by attempting to restart it
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to see if it is ready to continue.
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Async aware code (e.g. engines) can get the current ASYNC_WAIT_CTX from the job
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via L<ASYNC_get_wait_ctx(3)> and provide a file descriptor to use for waiting
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on by calling ASYNC_WAIT_CTX_set_wait_fd(). Typically this would be done by an
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engine immediately prior to calling ASYNC_pause_job() and not by end user code.
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An existing association with a file descriptor can be obtained using
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ASYNC_WAIT_CTX_get_fd() and cleared using ASYNC_WAIT_CTX_clear_fd(). Both of
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these functions requires a B<key> value which is unique to the async aware
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code. This could be any unique value but a good candidate might be the
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B<ENGINE *> for the engine. The B<custom_data> parameter can be any value, and
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will be returned in a subsequent call to ASYNC_WAIT_CTX_get_fd(). The
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ASYNC_WAIT_CTX_set_wait_fd() function also expects a pointer to a "cleanup"
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routine. This can be NULL but if provided will automatically get called when
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the ASYNC_WAIT_CTX is freed, and gives the engine the opportunity to close the
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fd or any other resources. Note: The "cleanup" routine does not get called if
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the fd is cleared directly via a call to ASYNC_WAIT_CTX_clear_fd().
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An example of typical usage might be an async capable engine. User code would
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initiate cryptographic operations. The engine would initiate those operations
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asynchronously and then call ASYNC_WAIT_CTX_set_wait_fd() followed by
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ASYNC_pause_job() to return control to the user code. The user code can then
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perform other tasks or wait for the job to be ready by calling "select" or other
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similar function on the wait file descriptor. The engine can signal to the user
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code that the job should be resumed by making the wait file descriptor
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"readable". Once resumed the engine should clear the wake signal on the wait
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file descriptor.
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=head1 RETURN VALUES
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ASYNC_WAIT_CTX_new() returns a pointer to the newly allocated ASYNC_WAIT_CTX or
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NULL on error.
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ASYNC_WAIT_CTX_set_wait_fd, ASYNC_WAIT_CTX_get_fd, ASYNC_WAIT_CTX_get_all_fds,
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ASYNC_WAIT_CTX_get_changed_fds and ASYNC_WAIT_CTX_clear_fd all return 1 on
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success or 0 on error.
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=head1 NOTES
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On Windows platforms the openssl/async.h header is dependent on some
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of the types customarily made available by including windows.h. The
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application developer is likely to require control over when the latter
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is included, commonly as one of the first included headers. Therefore,
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it is defined as an application developer's responsibility to include
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windows.h prior to async.h.
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=head1 SEE ALSO
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L<crypto(7)>, L<ASYNC_start_job(3)>
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=head1 HISTORY
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ASYNC_WAIT_CTX_new(), ASYNC_WAIT_CTX_free(), ASYNC_WAIT_CTX_set_wait_fd(),
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ASYNC_WAIT_CTX_get_fd(), ASYNC_WAIT_CTX_get_all_fds(),
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ASYNC_WAIT_CTX_get_changed_fds() and ASYNC_WAIT_CTX_clear_fd()
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were added in OpenSSL 1.1.0.
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=head1 COPYRIGHT
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Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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