Add functions to see if a provider is available for use.

Public function OSSL_PROVIDER_available() takes a library context and
a provider name, and returns 1 if it's available for use, i.e. if it's
possible to fetch implementations from it, otherwise 0.

Internal function ossl_provider_activated() returns 1 if the given
OSSL_PROVIDER is activated, otherwise 0.

To make this possible, the activation of fallbacks got refactored out
to a separate function, which ended up simplifying the code.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9398)

2 files changed, 24 insertions, 4 deletions

diff --git a/doc/internal/man3/ossl_provider_new.pod b/doc/internal/man3/ossl_provider_new.pod
index 426d95393d..255f194e03 100644
--- a/doc/internal/man3/ossl_provider_new.pod
+++ b/doc/internal/man3/ossl_provider_new.pod
@@ -6,7 +6,7 @@ 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_activate, ossl_provider_available,
 ossl_provider_ctx,
 ossl_provider_forall_loaded,
 ossl_provider_name, ossl_provider_dso,
@@ -33,6 +33,8 @@ ossl_provider_get_params, ossl_provider_query_operation
 
  /* 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);
@@ -148,6 +150,10 @@ 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.
@@ -228,6 +234,9 @@ 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
diff --git a/doc/man3/OSSL_PROVIDER.pod b/doc/man3/OSSL_PROVIDER.pod
index 1453fcc50a..5608bf394c 100644
--- a/doc/man3/OSSL_PROVIDER.pod
+++ b/doc/man3/OSSL_PROVIDER.pod
@@ -3,6 +3,7 @@
 =head1 NAME
 
 OSSL_PROVIDER, OSSL_PROVIDER_load, OSSL_PROVIDER_unload,
+OSSL_PROVIDER_available,
 OSSL_PROVIDER_get_param_types, OSSL_PROVIDER_get_params,
 OSSL_PROVIDER_add_builtin, OSSL_PROVIDER_name - provider routines
 
@@ -12,13 +13,14 @@ OSSL_PROVIDER_add_builtin, OSSL_PROVIDER_name - provider routines
 
  typedef struct ossl_provider_st OSSL_PROVIDER;
 
- OSSL_PROVIDER *OSSL_PROVIDER_load(OPENSSL_CTX *, const char *name);
+ OSSL_PROVIDER *OSSL_PROVIDER_load(OPENSSL_CTX *libctx, const char *name);
  int OSSL_PROVIDER_unload(OSSL_PROVIDER *prov);
+ int OSSL_PROVIDER_available(OPENSSL_CTX *libctx, const char *name);
 
  const OSSL_PARAM *OSSL_PROVIDER_get_param_types(OSSL_PROVIDER *prov);
  int OSSL_PROVIDER_get_params(OSSL_PROVIDER *prov, OSSL_PARAM params[]);
 
- int OSSL_PROVIDER_add_builtin(OPENSSL_CTX *, const char *name,
+ int OSSL_PROVIDER_add_builtin(OPENSSL_CTX *libctx, const char *name,
                                ossl_provider_init_fn *init_fn);
 
  const char *OSSL_PROVIDER_name(const OSSL_PROVIDER *prov);
@@ -32,6 +34,9 @@ A provider can be built in to the application or the OpenSSL
 libraries, or can be a loadable module.
 The functions described here handle both forms.
 
+Some of these functions operate within a library context, please see
+L<OPENSSL_CTX(3)> for further details.
+
 =head2 Functions
 
 OSSL_PROVIDER_add_builtin() is used to add a built in provider to
@@ -49,6 +54,9 @@ OSSL_PROVIDER_unload() unloads the given provider.
 For a provider added with OSSL_PROVIDER_add_builtin(), this simply
 runs its teardown function.
 
+OSSL_PROVIDER_available() checks if a named provider is available
+for use.
+
 OSSL_PROVIDER_get_param_types() is used to get a provider parameter
 descriptor set as a constant B<OSSL_PARAM> array.
 See L<OSSL_PARAM(3)> for more information.
@@ -69,6 +77,9 @@ success, or B<NULL> on error.
 
 OSSL_PROVIDER_unload() returns 1 on success, or 0 on error.
 
+OSSL_PROVIDER_available() returns 1 if the named provider is available,
+otherwise 0.
+
 OSSL_PROVIDER_get_param_types() returns a pointer to an array
 of constant B<OSSL_PARAM>, or NULL if none is provided.
 
@@ -95,7 +106,7 @@ its build number.
 
 =head1 SEE ALSO
 
-L<openssl-core.h(7)>, L<provider(7)>
+L<openssl-core.h(7)>, L<OPENSSL_CTX(3)>, L<provider(7)>
 
 =head1 HISTORY