df75c2bfcd
While stereotyped repetitions are frowned upon in literature, they serve a useful purpose in manual pages, because it is easier for the user to find certain information if it is always presented in the same way. For that reason, this commit harmonizes the varying formulations in the HISTORY section about which functions, flags, etc. were added in which OpenSSL version. It also attempts to make the pod files more grep friendly by avoiding to insert line breaks between the symbol names and the corresponding version number in which they were introduced (wherever possible). Some punctuation and typographical errors were fixed on the way. Reviewed-by: Tim Hudson <tjh@openssl.org> (Merged from https://github.com/openssl/openssl/pull/7854)
144 lines
7.2 KiB
Text
144 lines
7.2 KiB
Text
=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 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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