=pod

=head1 NAME

OPENSSL_INIT_new, OPENSSL_INIT_set_config_filename,
OPENSSL_INIT_set_config_appname, OPENSSL_INIT_set_config_file_flags,
OPENSSL_INIT_free, OPENSSL_init_crypto, OPENSSL_cleanup, OPENSSL_atexit,
OPENSSL_thread_stop - OpenSSL initialisation
and deinitialisation functions

=head1 SYNOPSIS

 #include <openssl/crypto.h>

 void OPENSSL_cleanup(void);
 int OPENSSL_init_crypto(uint64_t opts, const OPENSSL_INIT_SETTINGS *settings);
 int OPENSSL_atexit(void (*handler)(void));
 void OPENSSL_thread_stop(void);

 OPENSSL_INIT_SETTINGS *OPENSSL_INIT_new(void);
 int OPENSSL_INIT_set_config_filename(OPENSSL_INIT_SETTINGS *init,
                                      const char* filename);
 int OPENSSL_INIT_set_config_file_flags(OPENSSL_INIT_SETTINGS *init,
                                        unsigned long flags);
 int OPENSSL_INIT_set_config_appname(OPENSSL_INIT_SETTINGS *init,
                                     const char* name);
 void OPENSSL_INIT_free(OPENSSL_INIT_SETTINGS *init);

=head1 DESCRIPTION

During normal operation OpenSSL (libcrypto) will allocate various resources at
start up that must, subsequently, be freed on close down of the library.
Additionally some resources are allocated on a per thread basis (if the
application is multi-threaded), and these resources must be freed prior to the
thread closing.

As of version 1.1.0 OpenSSL will automatically allocate all resources that it
needs so no explicit initialisation is required. Similarly it will also
automatically deinitialise as required.

However, there may be situations when explicit initialisation is desirable or
needed, for example when some nondefault initialisation is required. The
function OPENSSL_init_crypto() can be used for this purpose for
libcrypto (see also L<OPENSSL_init_ssl(3)> for the libssl
equivalent).

Numerous internal OpenSSL functions call OPENSSL_init_crypto().
Therefore, in order to perform nondefault initialisation,
OPENSSL_init_crypto() MUST be called by application code prior to
any other OpenSSL function calls.

The B<opts> parameter specifies which aspects of libcrypto should be
initialised. Valid options are:

=over 4

=item OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS

Suppress automatic loading of the libcrypto error strings. This option is
not a default option. Once selected subsequent calls to
OPENSSL_init_crypto() with the option
B<OPENSSL_INIT_LOAD_CRYPTO_STRINGS> will be ignored.

=item OPENSSL_INIT_LOAD_CRYPTO_STRINGS

Automatic loading of the libcrypto error strings. With this option the
library will automatically load the libcrypto error strings.
This option is a default option. Once selected subsequent calls to
OPENSSL_init_crypto() with the option
B<OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS> will be ignored.

=item OPENSSL_INIT_ADD_ALL_CIPHERS

With this option the library will automatically load and make available all
libcrypto ciphers. This option is a default option. Once selected subsequent
calls to OPENSSL_init_crypto() with the option
B<OPENSSL_INIT_NO_ADD_ALL_CIPHERS> will be ignored.

=item OPENSSL_INIT_ADD_ALL_DIGESTS

With this option the library will automatically load and make available all
libcrypto digests. This option is a default option. Once selected subsequent
calls to OPENSSL_init_crypto() with the option
B<OPENSSL_INIT_NO_ADD_ALL_DIGESTS> will be ignored.

=item OPENSSL_INIT_NO_ADD_ALL_CIPHERS

With this option the library will suppress automatic loading of libcrypto
ciphers. This option is not a default option. Once selected subsequent
calls to OPENSSL_init_crypto() with the option
B<OPENSSL_INIT_ADD_ALL_CIPHERS> will be ignored.

=item OPENSSL_INIT_NO_ADD_ALL_DIGESTS

With this option the library will suppress automatic loading of libcrypto
digests. This option is not a default option. Once selected subsequent
calls to OPENSSL_init_crypto() with the option
B<OPENSSL_INIT_ADD_ALL_DIGESTS> will be ignored.

=item OPENSSL_INIT_LOAD_CONFIG

With this option an OpenSSL configuration file will be automatically loaded and
used by calling OPENSSL_config(). This is not a default option for libcrypto.
As of OpenSSL 1.1.1 this is a default option for libssl (see
L<OPENSSL_init_ssl(3)> for further details about libssl initialisation). See the
description of OPENSSL_INIT_new(), below.

=item OPENSSL_INIT_NO_LOAD_CONFIG

With this option the loading of OpenSSL configuration files will be suppressed.
It is the equivalent of calling OPENSSL_no_config(). This is not a default
option.

=item OPENSSL_INIT_ASYNC

With this option the library with automatically initialise the libcrypto async
sub-library (see L<ASYNC_start_job(3)>). This is a default option.

=item OPENSSL_INIT_ENGINE_RDRAND

With this option the library will automatically load and initialise the
RDRAND engine (if available). This not a default option.

=item OPENSSL_INIT_ENGINE_DYNAMIC

With this option the library will automatically load and initialise the
dynamic engine. This not a default option.

=item OPENSSL_INIT_ENGINE_OPENSSL

With this option the library will automatically load and initialise the
openssl engine. This not a default option.

=item OPENSSL_INIT_ENGINE_CRYPTODEV

With this option the library will automatically load and initialise the
cryptodev engine (if available). This not a default option.

=item OPENSSL_INIT_ENGINE_CAPI

With this option the library will automatically load and initialise the
CAPI engine (if available). This not a default option.

=item OPENSSL_INIT_ENGINE_PADLOCK

With this option the library will automatically load and initialise the
padlock engine (if available). This not a default option.

=item OPENSSL_INIT_ENGINE_AFALG

With this option the library will automatically load and initialise the
AFALG engine. This not a default option.

=item OPENSSL_INIT_ENGINE_ALL_BUILTIN

With this option the library will automatically load and initialise all the
built in engines listed above with the exception of the openssl and afalg
engines. This not a default option.

=item OPENSSL_INIT_ATFORK

With this option the library will register its fork handlers.
See OPENSSL_fork_prepare(3) for details.

=item OPENSSL_INIT_NO_ATEXIT

By default OpenSSL will attempt to clean itself up when the process exits via an
"atexit" handler. Using this option suppresses that behaviour. This means that
the application will have to clean up OpenSSL explicitly using
OPENSSL_cleanup().

=back

Multiple options may be combined together in a single call to
OPENSSL_init_crypto(). For example:

 OPENSSL_init_crypto(OPENSSL_INIT_NO_ADD_ALL_CIPHERS
                     | OPENSSL_INIT_NO_ADD_ALL_DIGESTS, NULL);

The OPENSSL_cleanup() function deinitialises OpenSSL (both libcrypto
and libssl). All resources allocated by OpenSSL are freed. Typically there
should be no need to call this function directly as it is initiated
automatically on application exit. This is done via the standard C library
atexit() function. In the event that the application will close in a manner
that will not call the registered atexit() handlers then the application should
call OPENSSL_cleanup() directly. Developers of libraries using OpenSSL
are discouraged from calling this function and should instead, typically, rely
on auto-deinitialisation. This is to avoid error conditions where both an
application and a library it depends on both use OpenSSL, and the library
deinitialises it before the application has finished using it.

Once OPENSSL_cleanup() has been called the library cannot be reinitialised.
Attempts to call OPENSSL_init_crypto() will fail and an ERR_R_INIT_FAIL error
will be added to the error stack. Note that because initialisation has failed
OpenSSL error strings will not be available, only an error code. This code can
be put through the openssl errstr command line application to produce a human
readable error (see L<errstr(1)>).

The OPENSSL_atexit() function enables the registration of a
function to be called during OPENSSL_cleanup(). Stop handlers are
called after deinitialisation of resources local to a thread, but before other
process wide resources are freed. In the event that multiple stop handlers are
registered, no guarantees are made about the order of execution.

The OPENSSL_thread_stop() function deallocates resources associated
with the current thread. Typically this function will be called automatically by
the library when the thread exits. This should only be called directly if
resources should be freed at an earlier time, or under the circumstances
described in the NOTES section below.

The B<OPENSSL_INIT_LOAD_CONFIG> flag will load a configuration file, as with
L<CONF_modules_load_file(3)> with NULL filename and application name and the
B<CONF_MFLAGS_IGNORE_MISSING_FILE>, B<CONF_MFLAGS_IGNORE_RETURN_CODES>  and
B<CONF_MFLAGS_DEFAULT_SECTION> flags.
The filename, application name, and flags can be customized by providing a
non-null B<OPENSSL_INIT_SETTINGS> object.
The object can be allocated via B<OPENSSL_init_new()>.
The B<OPENSSL_INIT_set_config_filename()> function can be used to specify a
nondefault filename, which is copied and need not refer to persistent storage.
Similarly, OPENSSL_INIT_set_config_appname() can be used to specify a
nondefault application name.
Finally, OPENSSL_INIT_set_file_flags can be used to specify nondefault flags.
If the B<CONF_MFLAGS_IGNORE_RETURN_CODES> flag is not included, any errors in
the configuration file will cause an error return from B<OPENSSL_init_crypto>
or indirectly L<OPENSSL_init_ssl(3)>.
The object can be released with OPENSSL_INIT_free() when done.

=head1 NOTES

Resources local to a thread are deallocated automatically when the thread exits
(e.g. in a pthreads environment, when pthread_exit() is called). On Windows
platforms this is done in response to a DLL_THREAD_DETACH message being sent to
the libcrypto32.dll entry point. Some windows functions may cause threads to exit
without sending this message (for example ExitProcess()). If the application
uses such functions, then the application must free up OpenSSL resources
directly via a call to OPENSSL_thread_stop() on each thread. Similarly this
message will also not be sent if OpenSSL is linked statically, and therefore
applications using static linking should also call OPENSSL_thread_stop() on each
thread. Additionally if OpenSSL is loaded dynamically via LoadLibrary() and the
threads are not destroyed until after FreeLibrary() is called then each thread
should call OPENSSL_thread_stop() prior to the FreeLibrary() call.

On Linux/Unix where OpenSSL has been loaded via dlopen() and the application is
multi-threaded and if dlclose() is subsequently called prior to the threads
being destroyed then OpenSSL will not be able to deallocate resources associated
with those threads. The application should either call OPENSSL_thread_stop() on
each thread prior to the dlclose() call, or alternatively the original dlopen()
call should use the RTLD_NODELETE flag (where available on the platform).

=head1 RETURN VALUES

The functions OPENSSL_init_crypto, OPENSSL_atexit() and
OPENSSL_INIT_set_config_appname() return 1 on success or 0 on error.

=head1 SEE ALSO

L<OPENSSL_init_ssl(3)>

=head1 HISTORY

The OPENSSL_init_crypto(), OPENSSL_cleanup(), OPENSSL_atexit(),
OPENSSL_thread_stop(), OPENSSL_INIT_new(), OPENSSL_INIT_set_config_appname()
and OPENSSL_INIT_free() functions were added in OpenSSL 1.1.0.

=head1 COPYRIGHT

Copyright 2016-2022 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
