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/*
* Asterisk -- An open source telephony toolkit.
*
* Copyright (C) 2013, Digium, Inc.
*
* David M. Lee, II <dlee@digium.com>
*
* See http://www.asterisk.org for more information about
* the Asterisk project. Please do not directly contact
* any of the maintainers of this project for assistance;
* the project provides a web site, mailing lists and IRC
* channels for your use.
*
* This program is free software, distributed under the terms of
* the GNU General Public License Version 2. See the LICENSE file
* at the top of the source tree.
*/
#include "asterisk.h"
#include "asterisk/optional_api.h"
#include "asterisk/utils.h"
#include "asterisk/vector.h"
#if defined(OPTIONAL_API)
/*
* \file Optional API innards.
*
* The calls to ast_optional_api_*() happen implicitly from \c __constructor__
* calls which are defined in header files. This means that some number of them
* happen before main() is called. This makes calling most Asterisk APIs
* dangerous, since we could be called before they are initialized. This
* includes things like AO2, malloc debug, and static mutexes.
*
* Another limitation is that most functions are called from the midst of
* dlopen() or dlclose(), and there is no opportunity to return a failure code.
* The best we can do is log an error, and call ast_do_crash().
*
* Fortunately, there are some constraints that help us out. The \c
* ast_optional_api_*() are called during module loads, which happens either
* before main(), or during dlopen() calls. These are already serialized, so we
* don't have to lock ourselves.
*/
/*! \brief A user of an optional API */
struct optional_api_user {
/*! Pointer to function pointer to link */
ast_optional_fn *optional_ref;
/*! Stub to use when impl is unavailable */
ast_optional_fn stub;
/*! Name of the module using the API */
char module[];
};
/*! \brief An optional API */
struct optional_api {
/*! Pointer to the implementation function; could be null */
ast_optional_fn impl;
/*! Users of the API */
AST_VECTOR(, struct optional_api_user *) users;
/*! Name of the optional API function */
char symname[];
};
/*! Vector of \ref optional_api functions */
AST_VECTOR(, struct optional_api *) apis;
#define USER_OPTIONAL_REF_CMP(ele, value) (ele->optional_ref == value)
#define OPTIONAL_API_SYMNAME_CMP(ele, value) (!strcmp(ele->symname, value))
/*!
* \brief Free an \ref optional_api_user.
*
* \param user User struct to free.
*/
static void optional_api_user_destroy(struct optional_api_user *user)
{
*user->optional_ref = user->stub;
ast_free(user);
}
/*!
* \brief Create an \ref optional_api_user.
*
* \param optional_ref Pointer-to-function-pointer to link to impl/stub.
* \param stub Stub function to link to when impl is not available.
* \param module Name of the module requesting the API.
*
* \return New \ref optional_api_user.
* \return \c NULL on error.
*/
static struct optional_api_user *optional_api_user_create(
ast_optional_fn *optional_ref, ast_optional_fn stub, const char *module)
{
struct optional_api_user *user;
size_t size = sizeof(*user) + strlen(module) + 1;
user = ast_calloc(1, size);
if (!user) {
ast_do_crash();
return NULL;
}
user->optional_ref = optional_ref;
user->stub = stub;
strcpy(user->module, module); /* SAFE */
return user;
}
/*!
* \brief Free an \ref optional_api.
*
* \param api API struct to free.
*/
static void optional_api_destroy(struct optional_api *api)
{
AST_VECTOR_REMOVE_CMP_UNORDERED(&apis, api,
AST_VECTOR_ELEM_DEFAULT_CMP, AST_VECTOR_ELEM_CLEANUP_NOOP);
AST_VECTOR_CALLBACK_VOID(&api->users, optional_api_user_destroy);
AST_VECTOR_FREE(&api->users);
ast_free(api);
}
/*!
* \brief Create and link an \ref optional_api.
*
* \param symname Name of the optional function.
* \return New \ref optional_api.
* \return \c NULL on error.
*/
static struct optional_api *optional_api_create(const char *symname)
{
struct optional_api *api;
api = ast_calloc(1, sizeof(*api) + strlen(symname) + 1);
if (!api || AST_VECTOR_APPEND(&apis, api)) {
ast_free(api);
ast_do_crash();
return NULL;
}
strcpy(api->symname, symname); /* SAFE */
return api;
}
/*!
* \brief Gets (or creates) the \ref optional_api for the given function.
*
* \param sysname Name of the function to look up.
* \return Corresponding \ref optional_api.
* \return \c NULL on error.
*/
static struct optional_api *get_api(const char *symname)
{
struct optional_api **api;
/* Find one, if we already have it */
api = AST_VECTOR_GET_CMP(&apis, symname, OPTIONAL_API_SYMNAME_CMP);
if (api) {
return *api;
}
/* API not found. Build one */
return optional_api_create(symname);
}
/*!
* \brief Re-links a given \a user against its associated \a api.
*
* If the \a api has an implementation, the \a user is linked to that
* implementation. Otherwise, the \a user is linked to its \a stub.
*
* \param user \ref optional_api_user to link.
* \param api \ref optional_api to link.
*/
static void optional_api_user_relink(struct optional_api_user *user,
struct optional_api *api)
{
if (api->impl && *user->optional_ref != api->impl) {
*user->optional_ref = api->impl;
} else if (!api->impl && *user->optional_ref != user->stub) {
*user->optional_ref = user->stub;
}
}
/*!
* \brief Sets the implementation function pointer for an \a api.
*
* \param api API to implement/stub out.
* \param impl Pointer to implementation function. Can be 0 to remove
* implementation.
*/
static void optional_api_set_impl(struct optional_api *api,
ast_optional_fn impl)
{
api->impl = impl;
/* re-link all users */
if (AST_VECTOR_SIZE(&api->users)) {
AST_VECTOR_CALLBACK_VOID(&api->users, optional_api_user_relink, api);
} else if (!impl) {
/* No users or impl means we should delete this api. */
optional_api_destroy(api);
}
}
void ast_optional_api_provide(const char *symname, ast_optional_fn impl)
{
struct optional_api *api;
api = get_api(symname);
if (api) {
optional_api_set_impl(api, impl);
}
}
void ast_optional_api_unprovide(const char *symname, ast_optional_fn impl)
{
struct optional_api *api;
api = get_api(symname);
if (api) {
optional_api_set_impl(api, 0);
}
}
void ast_optional_api_use(const char *symname, ast_optional_fn *optional_ref,
ast_optional_fn stub, const char *module)
{
struct optional_api_user *user;
struct optional_api *api;
api = get_api(symname);
if (!api) {
return;
}
user = optional_api_user_create(optional_ref, stub, module);
if (!user) {
return;
}
/* Add user to the API */
if (!AST_VECTOR_APPEND(&api->users, user)) {
optional_api_user_relink(user, api);
} else {
optional_api_user_destroy(user);
ast_do_crash();
}
}
void ast_optional_api_unuse(const char *symname, ast_optional_fn *optional_ref,
const char *module)
{
struct optional_api *api;
api = get_api(symname);
if (api) {
AST_VECTOR_REMOVE_CMP_UNORDERED(&api->users, optional_ref, USER_OPTIONAL_REF_CMP, optional_api_user_destroy);
if (!api->impl && !AST_VECTOR_SIZE(&api->users)) {
optional_api_destroy(api);
}
}
}
#endif /* defined(OPTIONAL_API) */
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