=pod

=head1 NAME

ossl_provider_find, ossl_provider_new, ossl_provider_up_ref,
ossl_provider_free,
ossl_provider_set_fallback, ossl_provider_set_module_path,
ossl_provider_add_parameter,
ossl_provider_activate, ossl_provider_available,
ossl_provider_ctx,
ossl_provider_forall_loaded,
ossl_provider_name, ossl_provider_dso,
ossl_provider_module_name, ossl_provider_module_path,
ossl_provider_library_context,
ossl_provider_teardown, ossl_provider_gettable_params,
ossl_provider_get_params, ossl_provider_query_operation
- internal provider routines

=head1 SYNOPSIS

 #include "internal/provider.h"

 OSSL_PROVIDER *ossl_provider_find(OPENSSL_CTX *libctx, const char *name,
                                   int noconfig);
 OSSL_PROVIDER *ossl_provider_new(OPENSSL_CTX *libctx, const char *name,
                                  ossl_provider_init_fn *init_function
                                  int noconfig);
 int ossl_provider_up_ref(OSSL_PROVIDER *prov);
 void ossl_provider_free(OSSL_PROVIDER *prov);

 /* Setters */
 int ossl_provider_set_fallback(OSSL_PROVIDER *prov);
 int ossl_provider_set_module_path(OSSL_PROVIDER *prov, const char *path);
 int ossl_provider_add_parameter(OSSL_PROVIDER *prov, const char *name,
                                 const char *value);

 /* Load and initialize the Provider */
 int ossl_provider_activate(OSSL_PROVIDER *prov);
 /* Check if provider is available */
 int ossl_provider_available(OSSL_PROVIDER *prov);

 /* Return pointer to the provider's context */
 void *ossl_provider_ctx(const OSSL_PROVIDER *prov);

 /* Iterate over all loaded providers */
 int ossl_provider_forall_loaded(OPENSSL_CTX *,
                                 int (*cb)(OSSL_PROVIDER *provider,
                                           void *cbdata),
                                 void *cbdata);

 /* Getters for other library functions */
 const char *ossl_provider_name(OSSL_PROVIDER *prov);
 const DSO *ossl_provider_dso(OSSL_PROVIDER *prov);
 const char *ossl_provider_module_name(OSSL_PROVIDER *prov);
 const char *ossl_provider_module_path(OSSL_PROVIDER *prov);
 OPENSSL_CTX *ossl_provider_library_context(const OSSL_PROVIDER *prov);

 /* Thin wrappers around calls to the provider */
 void ossl_provider_teardown(const OSSL_PROVIDER *prov);
 const OSSL_PARAM *ossl_provider_gettable_params(const OSSL_PROVIDER *prov);
 int ossl_provider_get_params(const OSSL_PROVIDER *prov, OSSL_PARAM params[]);
 const OSSL_ALGORITHM *ossl_provider_query_operation(const OSSL_PROVIDER *prov,
                                                     int operation_id,
                                                     int *no_cache);

=head1 DESCRIPTION

I<OSSL_PROVIDER> is a type that holds all the necessary information
to handle a provider, regardless of if it's built in to the
application or the OpenSSL libraries, or if it's a loadable provider
module.
Instances of this type are commonly referred to as "provider objects".

A provider object is always stored in a set of provider objects
in the library context.

Provider objects are reference counted.

Provider objects are initially inactive, i.e. they are only recorded
in the store, but are not used.
They are activated with the first call to ossl_provider_activate(),
and are inactivated when ossl_provider_free() has been called as many
times as ossl_provider_activate() has.

=head2 Functions

ossl_provider_find() finds an existing provider object in the provider
object store by I<name>.
The config file will be automatically loaded unless I<noconfig> is set.
Typically I<noconfig> should be 0.
We set I<noconfig> to 1 only when calling these functions while processing a
config file in order to avoid recursively attempting to load the file.
The provider object it finds has its reference count incremented.

ossl_provider_new() creates a new provider object named I<name> and
stores it in the provider object store, unless there already is one
there with the same name.
If there already is one with the same name, it's returned with its
reference count incremented.
The config file will be automatically loaded unless I<noconfig> is set.
Typically I<noconfig> should be 0.
We set I<noconfig> to 1 only when calling these functions while processing a
config file in order to avoid recursively attempting to load the file.
The reference count of a newly created provider object will always
be 2; one for being added to the store, and one for the returned
reference.
If I<init_function> is NULL, the provider is assumed to be a
dynamically loadable module, with the symbol B<OSSL_provider_init> as
its initialisation function.
If I<init_function> isn't NULL, the provider is assumed to be built
in, with I<init_function> being the pointer to its initialisation
function.
For further description of the initialisation function, see the
description of ossl_provider_activate() below.

ossl_provider_up_ref() increments the provider object I<prov>'s
reference count.

ossl_provider_free() decrements the provider object I<prov>'s
reference count; if it drops below 2, the provider object is assumed
to have fallen out of use and will be deactivated (its I<teardown>
function is called); if it drops down to zero, I<prov> is assumed to
have been taken out of the store, and the associated module will be
unloaded if one was loaded, and I<prov> itself will be freed.

ossl_provider_set_fallback() marks an available provider I<prov> as
fallback.
Note that after this call, the provider object pointer that was
used can simply be dropped, but not freed.

ossl_provider_set_module_path() sets the module path to load the
provider module given the provider object I<prov>.
This will be used in preference to automatically trying to figure out
the path from the provider name and the default module directory (more
on this in L</NOTES>).

ossl_provider_library_context() returns the library context the given
provider I<prov> is registered in.

ossl_provider_add_parameter() adds a global parameter for the provider
to retrieve as it sees fit.
The parameters are a combination of I<name> and I<value>, and the
provider will use the name to find the value it wants.
Only text parameters can be given, and it's up to the provider to
interpret them.

ossl_provider_activate() "activates" the provider for the given
provider object I<prov>.
What "activates" means depends on what type of provider object it
is:

=over 4

=item *

If an initialization function was given with ossl_provider_new(), that
function will get called.

=item *

If no initialization function was given with ossl_provider_new(), a
loadable module with the I<name> that was given to ossl_provider_new()
will be located and loaded, then the symbol B<OSSL_provider_init> will
be located in that module, and called.

=back

ossl_provider_available() activates all fallbacks if no provider is
activated yet, then checks if given provider object I<prov> is
activated.

ossl_provider_ctx() returns a context created by the provider.
Outside of the provider, it's completely opaque, but it needs to be
passed back to some of the provider functions.

ossl_provider_forall_loaded() iterates over all the currently
"activated" providers, and calls I<cb> for each of them.
If no providers have been "activated" yet, it tries to activate all
available fallback providers and tries another iteration.

ossl_provider_name() returns the name that was given with
ossl_provider_new().

ossl_provider_dso() returns a reference to the module, for providers
that come in the form of loadable modules.

ossl_provider_module_name() returns the filename of the module, for
providers that come in the form of loadable modules.

ossl_provider_module_path() returns the full path of the module file,
for providers that come in the form of loadable modules.

ossl_provider_teardown() calls the provider's I<teardown> function, if
the provider has one.

ossl_provider_gettable_params() calls the provider's I<gettable_params>
function, if the provider has one.
It should return an array of I<OSSL_PARAM> to describe all the
parameters that the provider has for the provider object.

ossl_provider_get_params() calls the provider's parameter request
responder.
It should treat the given I<OSSL_PARAM> array as described in
L<OSSL_PARAM(3)>.

ossl_provider_query_operation() calls the provider's
I<query_operation> function, if the provider has one.
It should return an array of I<OSSL_ALGORITHM> for the given
I<operation_id>.

=head1 NOTES

Locating a provider module happens as follows:

=over 4

=item 1.

If a path was given with ossl_provider_set_module_path(), use that as
module path.
Otherwise, use the provider object's name as module path, with
platform specific standard extensions added.

=item 2.

If the environment variable B<OPENSSL_MODULES> is defined, assume its
value is a directory specification and merge it with the module path.
Otherwise, merge the value of the OpenSSL built in macro B<MODULESDIR>
with the module path.

=back

When this process is done, the result is used when trying to load the
provider module.

The command C<openssl version -m> can be used to find out the value
of the built in macro B<MODULESDIR>.

=head1 RETURN VALUES

ossl_provider_find() and ossl_provider_new() return a pointer to a
provider object (I<OSSL_PROVIDER>) on success, or NULL on error.

ossl_provider_up_ref() returns the value of the reference count after
it has been incremented.

ossl_provider_free() doesn't return any value.

ossl_provider_set_module_path(), ossl_provider_set_fallback() and
ossl_provider_activate() return 1 on success, or 0 on error.

ossl_provider_available() return 1 if the provider is available,
otherwise 0.

ossl_provider_name(), ossl_provider_dso(),
ossl_provider_module_name(), and ossl_provider_module_path() return a
pointer to their respective data if it's available, otherwise NULL
is returned.

ossl_provider_library_context() return a pointer to the library context.
This may be NULL, and is perfectly valid, as it denotes the default
global library context.

ossl_provider_teardown() doesn't return any value.

ossl_provider_gettable_params() returns a pointer to a constant
I<OSSL_PARAM> array if this function is available in the provider,
otherwise NULL.

ossl_provider_get_params() returns 1 on success, or 0 on error.
If this function isn't available in the provider, 0 is returned.

=head1 SEE ALSO

L<OSSL_PROVIDER(3)>, L<provider(7)>, L<openssl(1)>

=head1 HISTORY

The functions described here were all added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (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
