1=pod
2
3=head1 NAME
4
5OSSL_LIB_CTX, OSSL_LIB_CTX_new, OSSL_LIB_CTX_new_from_dispatch,
6OSSL_LIB_CTX_new_child, OSSL_LIB_CTX_free, OSSL_LIB_CTX_load_config,
7OSSL_LIB_CTX_get0_global_default, OSSL_LIB_CTX_set0_default
8- OpenSSL library context
9
10=head1 SYNOPSIS
11
12 #include <openssl/crypto.h>
13
14 typedef struct ossl_lib_ctx_st OSSL_LIB_CTX;
15
16 OSSL_LIB_CTX *OSSL_LIB_CTX_new(void);
17 OSSL_LIB_CTX *OSSL_LIB_CTX_new_from_dispatch(const OSSL_CORE_HANDLE *handle,
18                                              const OSSL_DISPATCH *in);
19 OSSL_LIB_CTX *OSSL_LIB_CTX_new_child(const OSSL_CORE_HANDLE *handle,
20                                      const OSSL_DISPATCH *in);
21 int OSSL_LIB_CTX_load_config(OSSL_LIB_CTX *ctx, const char *config_file);
22 void OSSL_LIB_CTX_free(OSSL_LIB_CTX *ctx);
23 OSSL_LIB_CTX *OSSL_LIB_CTX_get0_global_default(void);
24 OSSL_LIB_CTX *OSSL_LIB_CTX_set0_default(OSSL_LIB_CTX *ctx);
25
26=head1 DESCRIPTION
27
28B<OSSL_LIB_CTX> is an internal OpenSSL library context type.
29Applications may allocate their own, but may also use NULL to use
30a default context with functions that take an B<OSSL_LIB_CTX>
31argument.
32
33When a non default library context is in use care should be taken with
34multi-threaded applications to properly clean up thread local resources before
35the OSSL_LIB_CTX is freed.
36See L<OPENSSL_thread_stop_ex(3)> for more information.
37
38OSSL_LIB_CTX_new() creates a new OpenSSL library context.
39
40OSSL_LIB_CTX_new_from_dispatch() creates a new OpenSSL library context
41initialised to use callbacks from the OSSL_DISPATCH structure. This is primarily
42useful for provider authors. The I<handle> and dispatch structure arguments
43passed should be the same ones as passed to a provider's
44OSSL_provider_init function. Some OpenSSL functions, such as
45L<BIO_new_from_core_bio(3)>, require the library context to be created in this
46way in order to work.
47
48OSSL_LIB_CTX_new_child() is only useful to provider authors and does the same
49thing as OSSL_LIB_CTX_new_from_dispatch() except that it additionally links the
50new library context to the application library context. The new library context
51is a full library context in its own right, but will have all the same providers
52available to it that are available in the application library context (without
53having to reload them). If the application loads or unloads providers from the
54application library context then this will be automatically mirrored in the
55child library context.
56
57In addition providers that are not loaded in the parent library context can be
58explicitly loaded into the child library context independently from the parent
59library context. Providers loaded independently in this way will not be mirrored
60in the parent library context and will not be affected if the parent library
61context subsequently loads the same provider.
62
63A provider may call the function L<OSSL_PROVIDER_load(3)> with the child library
64context as required. If the provider already exists due to it being mirrored
65from the parent library context then it will remain available and its reference
66count will be increased. If L<OSSL_PROVIDER_load(3)> is called in this way then
67L<OSSL_PROVIDER_unload(3)> should be subsequently called to decrement the
68reference count. L<OSSL_PROVIDER_unload(3)> must not be called for a provider in
69the child library context that did not have an earlier L<OSSL_PROVIDER_load(3)>
70call for that provider in that child library context.
71
72In addition to providers, a child library context will also mirror the default
73properties (set via L<EVP_set_default_properties(3)>) from the parent library
74context. If L<EVP_set_default_properties(3)> is called directly on a child
75library context then the new properties will override anything from the parent
76library context and mirroring of the properties will stop.
77
78When OSSL_LIB_CTX_new_child() is called from within the scope of a provider's
79B<OSSL_provider_init> function the currently initialising provider is not yet
80available in the application's library context and therefore will similarly not
81yet be available in the newly constructed child library context. As soon as the
82B<OSSL_provider_init> function returns then the new provider is available in the
83application's library context and will be similarly mirrored in the child
84library context.
85
86OSSL_LIB_CTX_load_config() loads a configuration file using the given C<ctx>.
87This can be used to associate a library context with providers that are loaded
88from a configuration.
89
90OSSL_LIB_CTX_free() frees the given I<ctx>, unless it happens to be the
91default OpenSSL library context.
92
93OSSL_LIB_CTX_get0_global_default() returns a concrete (non NULL) reference to
94the global default library context.
95
96OSSL_LIB_CTX_set0_default() sets the default OpenSSL library context to be
97I<ctx> in the current thread.  The previous default library context is
98returned.  Care should be taken by the caller to restore the previous
99default library context with a subsequent call of this function. If I<ctx> is
100NULL then no change is made to the default library context, but a pointer to
101the current library context is still returned. On a successful call of this
102function the returned value will always be a concrete (non NULL) library
103context.
104
105Care should be taken when changing the default library context and starting
106async jobs (see L<ASYNC_start_job(3)>), as the default library context when
107the job is started will be used throughout the lifetime of an async job, no
108matter how the calling thread makes further default library context changes
109in the mean time.  This means that the calling thread must not free the
110library context that was the default at the start of the async job before
111that job has finished.
112
113=head1 RETURN VALUES
114
115OSSL_LIB_CTX_new(), OSSL_LIB_CTX_get0_global_default() and
116OSSL_LIB_CTX_set0_default() return a library context pointer on success, or NULL
117on error.
118
119OSSL_LIB_CTX_free() doesn't return any value.
120
121=head1 HISTORY
122
123All of the functions described on this page were added in OpenSSL 3.0.
124
125=head1 COPYRIGHT
126
127Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved.
128
129Licensed under the Apache License 2.0 (the "License").  You may not use
130this file except in compliance with the License.  You can obtain a copy
131in the file LICENSE in the source distribution or at
132L<https://www.openssl.org/source/license.html>.
133
134=cut
135