source: mainline/uspace/lib/c/generic/loc.c@ 14b5c30f

/*
 * Copyright (c) 2007 Josef Cejka
 * Copyright (c) 2011 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <str.h>
#include <ipc/services.h>
#include <ns.h>
#include <ipc/loc.h>
#include <loc.h>
#include <fibril_synch.h>
#include <async.h>
#include <errno.h>
#include <stdlib.h>
#include <stdbool.h>

static FIBRIL_MUTEX_INITIALIZE(loc_supp_block_mutex);
static FIBRIL_MUTEX_INITIALIZE(loc_cons_block_mutex);

static FIBRIL_MUTEX_INITIALIZE(loc_supplier_mutex);
static FIBRIL_MUTEX_INITIALIZE(loc_consumer_mutex);

static FIBRIL_MUTEX_INITIALIZE(loc_callback_mutex);
static bool loc_callback_created = false;
static loc_cat_change_cb_t cat_change_cb = NULL;
static void *cat_change_arg = NULL;

static async_sess_t *loc_supp_block_sess = NULL;
static async_sess_t *loc_cons_block_sess = NULL;

static async_sess_t *loc_supplier_sess = NULL;
static async_sess_t *loc_consumer_sess = NULL;

static void loc_cb_conn(ipc_call_t *icall, void *arg)
{
        while (true) {
                ipc_call_t call;
                async_get_call(&call);

                if (!ipc_get_imethod(&call)) {
                        async_answer_0(&call, EOK);
                        return;
                }

                switch (ipc_get_imethod(&call)) {
                case LOC_EVENT_CAT_CHANGE:
                        fibril_mutex_lock(&loc_callback_mutex);
                        loc_cat_change_cb_t cb_fun = cat_change_cb;
                        void *cb_arg = cat_change_arg;
                        fibril_mutex_unlock(&loc_callback_mutex);

                        async_answer_0(&call, EOK);

                        if (cb_fun != NULL)
                                (*cb_fun)(cb_arg);

                        break;
                default:
                        async_answer_0(&call, ENOTSUP);
                }
        }
}

static void clone_session(fibril_mutex_t *mtx, async_sess_t *src,
    async_sess_t **dst)
{
        fibril_mutex_lock(mtx);

        if ((*dst == NULL) && (src != NULL))
                *dst = src;

        fibril_mutex_unlock(mtx);
}

/** Create callback
 *
 * Must be called with loc_callback_mutex locked.
 *
 * @return EOK on success.
 *
 */
static errno_t loc_callback_create(void)
{
        if (!loc_callback_created) {
                async_exch_t *exch =
                    loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);

                ipc_call_t answer;
                aid_t req = async_send_0(exch, LOC_CALLBACK_CREATE, &answer);

                port_id_t port;
                errno_t rc = async_create_callback_port(exch, INTERFACE_LOC_CB, 0, 0,
                    loc_cb_conn, NULL, &port);

                loc_exchange_end(exch);

                if (rc != EOK)
                        return rc;

                errno_t retval;
                async_wait_for(req, &retval);
                if (retval != EOK)
                        return retval;

                loc_callback_created = true;
        }

        return EOK;
}

/** Start an async exchange on the loc session (blocking).
 *
 * @param iface Location service interface to choose
 *
 * @return New exchange.
 *
 */
async_exch_t *loc_exchange_begin_blocking(iface_t iface)
{
        switch (iface) {
        case INTERFACE_LOC_SUPPLIER:
                fibril_mutex_lock(&loc_supp_block_mutex);

                while (loc_supp_block_sess == NULL) {
                        clone_session(&loc_supplier_mutex, loc_supplier_sess,
                            &loc_supp_block_sess);

                        if (loc_supp_block_sess == NULL)
                                loc_supp_block_sess =
                                    service_connect_blocking(SERVICE_LOC,
                                    INTERFACE_LOC_SUPPLIER, 0, NULL);
                }

                fibril_mutex_unlock(&loc_supp_block_mutex);

                clone_session(&loc_supplier_mutex, loc_supp_block_sess,
                    &loc_supplier_sess);

                return async_exchange_begin(loc_supp_block_sess);
        case INTERFACE_LOC_CONSUMER:
                fibril_mutex_lock(&loc_cons_block_mutex);

                while (loc_cons_block_sess == NULL) {
                        clone_session(&loc_consumer_mutex, loc_consumer_sess,
                            &loc_cons_block_sess);

                        if (loc_cons_block_sess == NULL)
                                loc_cons_block_sess =
                                    service_connect_blocking(SERVICE_LOC,
                                    INTERFACE_LOC_CONSUMER, 0, NULL);
                }

                fibril_mutex_unlock(&loc_cons_block_mutex);

                clone_session(&loc_consumer_mutex, loc_cons_block_sess,
                    &loc_consumer_sess);

                return async_exchange_begin(loc_cons_block_sess);
        default:
                return NULL;
        }
}

/** Start an async exchange on the loc session.
 *
 * @param iface Location service interface to choose
 *
 * @return New exchange.
 *
 */
async_exch_t *loc_exchange_begin(iface_t iface)
{
        switch (iface) {
        case INTERFACE_LOC_SUPPLIER:
                fibril_mutex_lock(&loc_supplier_mutex);

                if (loc_supplier_sess == NULL)
                        loc_supplier_sess =
                            service_connect(SERVICE_LOC,
                            INTERFACE_LOC_SUPPLIER, 0, NULL);

                fibril_mutex_unlock(&loc_supplier_mutex);

                if (loc_supplier_sess == NULL)
                        return NULL;

                return async_exchange_begin(loc_supplier_sess);
        case INTERFACE_LOC_CONSUMER:
                fibril_mutex_lock(&loc_consumer_mutex);

                if (loc_consumer_sess == NULL)
                        loc_consumer_sess =
                            service_connect(SERVICE_LOC,
                            INTERFACE_LOC_CONSUMER, 0, NULL);

                fibril_mutex_unlock(&loc_consumer_mutex);

                if (loc_consumer_sess == NULL)
                        return NULL;

                return async_exchange_begin(loc_consumer_sess);
        default:
                return NULL;
        }
}

/** Finish an async exchange on the loc session.
 *
 * @param exch Exchange to be finished.
 *
 */
void loc_exchange_end(async_exch_t *exch)
{
        async_exchange_end(exch);
}

/** Register new server with loc. */
errno_t loc_server_register(const char *name)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_SUPPLIER);

        ipc_call_t answer;
        aid_t req = async_send_2(exch, LOC_SERVER_REGISTER, 0, 0, &answer);
        errno_t retval = async_data_write_start(exch, name, str_size(name));

        if (retval != EOK) {
                async_forget(req);
                loc_exchange_end(exch);
                return retval;
        }

        async_connect_to_me(exch, INTERFACE_ANY, 0, 0);

        /*
         * First wait for the answer and then end the exchange. The opposite
         * order is generally wrong because it may lead to a deadlock under
         * certain circumstances.
         */
        async_wait_for(req, &retval);
        loc_exchange_end(exch);

        return retval;
}

/** Register new service.
 *
 * @param      fqsn  Fully qualified service name
 * @param[out] sid   Service ID of new service
 *
 */
errno_t loc_service_register(const char *fqsn, service_id_t *sid)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_SUPPLIER);

        ipc_call_t answer;
        aid_t req = async_send_0(exch, LOC_SERVICE_REGISTER, &answer);
        errno_t retval = async_data_write_start(exch, fqsn, str_size(fqsn));

        if (retval != EOK) {
                async_forget(req);
                loc_exchange_end(exch);
                return retval;
        }

        /*
         * First wait for the answer and then end the exchange. The opposite
         * order is generally wrong because it may lead to a deadlock under
         * certain circumstances.
         */
        async_wait_for(req, &retval);
        loc_exchange_end(exch);

        if (retval != EOK) {
                if (sid != NULL)
                        *sid = -1;

                return retval;
        }

        if (sid != NULL)
                *sid = (service_id_t) ipc_get_arg1(&answer);

        return retval;
}

/** Unregister service.
 *
 * @param sid   Service ID
 */
errno_t loc_service_unregister(service_id_t sid)
{
        async_exch_t *exch;
        errno_t retval;

        exch = loc_exchange_begin_blocking(INTERFACE_LOC_SUPPLIER);
        retval = async_req_1_0(exch, LOC_SERVICE_UNREGISTER, sid);
        loc_exchange_end(exch);

        return (errno_t)retval;
}

errno_t loc_service_get_id(const char *fqdn, service_id_t *handle,
    unsigned int flags)
{
        async_exch_t *exch;

        if (flags & IPC_FLAG_BLOCKING)
                exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
        else {
                exch = loc_exchange_begin(INTERFACE_LOC_CONSUMER);
                if (exch == NULL)
                        return errno;
        }

        ipc_call_t answer;
        aid_t req = async_send_2(exch, LOC_SERVICE_GET_ID, flags, 0,
            &answer);
        errno_t retval = async_data_write_start(exch, fqdn, str_size(fqdn));

        loc_exchange_end(exch);

        if (retval != EOK) {
                async_forget(req);
                return retval;
        }

        async_wait_for(req, &retval);

        if (retval != EOK) {
                if (handle != NULL)
                        *handle = (service_id_t) -1;

                return retval;
        }

        if (handle != NULL)
                *handle = (service_id_t) ipc_get_arg1(&answer);

        return retval;
}

/** Get object name.
 *
 * Provided ID of an object, return its name.
 *
 * @param method        IPC method
 * @param id            Object ID
 * @param name          Place to store pointer to new string. Caller should
 *                      free it using free().
 * @return              EOK on success or an error code
 */
static errno_t loc_get_name_internal(sysarg_t method, sysarg_t id, char **name)
{
        async_exch_t *exch;
        char name_buf[LOC_NAME_MAXLEN + 1];
        ipc_call_t dreply;
        size_t act_size;
        errno_t dretval;

        *name = NULL;
        exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);

        ipc_call_t answer;
        aid_t req = async_send_1(exch, method, id, &answer);
        aid_t dreq = async_data_read(exch, name_buf, LOC_NAME_MAXLEN,
            &dreply);
        async_wait_for(dreq, &dretval);

        loc_exchange_end(exch);

        if (dretval != EOK) {
                async_forget(req);
                return dretval;
        }

        errno_t retval;
        async_wait_for(req, &retval);

        if (retval != EOK)
                return retval;

        act_size = ipc_get_arg2(&dreply);
        assert(act_size <= LOC_NAME_MAXLEN);
        name_buf[act_size] = '\0';

        *name = str_dup(name_buf);
        if (*name == NULL)
                return ENOMEM;

        return EOK;
}

/** Get category name.
 *
 * Provided ID of a service, return its name.
 *
 * @param cat_id        Category ID
 * @param name          Place to store pointer to new string. Caller should
 *                      free it using free().
 * @return              EOK on success or an error code
 */
errno_t loc_category_get_name(category_id_t cat_id, char **name)
{
        return loc_get_name_internal(LOC_CATEGORY_GET_NAME, cat_id, name);
}

/** Get service name.
 *
 * Provided ID of a service, return its name.
 *
 * @param svc_id        Service ID
 * @param name          Place to store pointer to new string. Caller should
 *                      free it using free().
 * @return              EOK on success or an error code
 */
errno_t loc_service_get_name(service_id_t svc_id, char **name)
{
        return loc_get_name_internal(LOC_SERVICE_GET_NAME, svc_id, name);
}

/** Get service server name.
 *
 * Provided ID of a service, return the name of its server.
 *
 * @param svc_id        Service ID
 * @param name          Place to store pointer to new string. Caller should
 *                      free it using free().
 * @return              EOK on success or an error code
 */
errno_t loc_service_get_server_name(service_id_t svc_id, char **name)
{
        return loc_get_name_internal(LOC_SERVICE_GET_SERVER_NAME, svc_id, name);
}

errno_t loc_namespace_get_id(const char *name, service_id_t *handle,
    unsigned int flags)
{
        async_exch_t *exch;

        if (flags & IPC_FLAG_BLOCKING)
                exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
        else {
                exch = loc_exchange_begin(INTERFACE_LOC_CONSUMER);
                if (exch == NULL)
                        return errno;
        }

        ipc_call_t answer;
        aid_t req = async_send_2(exch, LOC_NAMESPACE_GET_ID, flags, 0,
            &answer);
        errno_t retval = async_data_write_start(exch, name, str_size(name));

        loc_exchange_end(exch);

        if (retval != EOK) {
                async_forget(req);
                return retval;
        }

        async_wait_for(req, &retval);

        if (retval != EOK) {
                if (handle != NULL)
                        *handle = (service_id_t) -1;

                return retval;
        }

        if (handle != NULL)
                *handle = (service_id_t) ipc_get_arg1(&answer);

        return retval;
}

/** Get category ID.
 *
 * Provided name of a category, return its ID.
 *
 * @param name          Category name
 * @param cat_id        Place to store ID
 * @param flags         IPC_FLAG_BLOCKING to wait for location service to start
 * @return              EOK on success or an error code
 */
errno_t loc_category_get_id(const char *name, category_id_t *cat_id,
    unsigned int flags)
{
        async_exch_t *exch;

        if (flags & IPC_FLAG_BLOCKING)
                exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
        else {
                exch = loc_exchange_begin(INTERFACE_LOC_CONSUMER);
                if (exch == NULL)
                        return errno;
        }

        ipc_call_t answer;
        aid_t req = async_send_0(exch, LOC_CATEGORY_GET_ID,
            &answer);
        errno_t retval = async_data_write_start(exch, name, str_size(name));

        loc_exchange_end(exch);

        if (retval != EOK) {
                async_forget(req);
                return retval;
        }

        async_wait_for(req, &retval);

        if (retval != EOK) {
                if (cat_id != NULL)
                        *cat_id = (category_id_t) -1;

                return retval;
        }

        if (cat_id != NULL)
                *cat_id = (category_id_t) ipc_get_arg1(&answer);

        return retval;
}

loc_object_type_t loc_id_probe(service_id_t handle)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);

        sysarg_t type;
        errno_t retval = async_req_1_1(exch, LOC_ID_PROBE, handle, &type);

        loc_exchange_end(exch);

        if (retval != EOK)
                return LOC_OBJECT_NONE;

        return (loc_object_type_t) type;
}

async_sess_t *loc_service_connect(service_id_t handle, iface_t iface,
    unsigned int flags)
{
        async_sess_t *sess;

        if (flags & IPC_FLAG_BLOCKING)
                sess = service_connect_blocking(SERVICE_LOC, iface, handle, NULL);
        else
                sess = service_connect(SERVICE_LOC, iface, handle, NULL);

        return sess;
}

/**
 * @return ID of a new NULL device, or -1 if failed.
 */
int loc_null_create(void)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);

        sysarg_t null_id;
        errno_t retval = async_req_0_1(exch, LOC_NULL_CREATE, &null_id);

        loc_exchange_end(exch);

        if (retval != EOK)
                return -1;

        return (int) null_id;
}

void loc_null_destroy(int null_id)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
        async_req_1_0(exch, LOC_NULL_DESTROY, (sysarg_t) null_id);
        loc_exchange_end(exch);
}

static size_t loc_count_namespaces_internal(async_exch_t *exch)
{
        sysarg_t count;
        errno_t retval = async_req_0_1(exch, LOC_GET_NAMESPACE_COUNT, &count);
        if (retval != EOK)
                return 0;

        return count;
}

/** Add service to category.
 *
 * @param svc_id        Service ID
 * @param cat_id        Category ID
 * @return              EOK on success or an error code
 */
errno_t loc_service_add_to_cat(service_id_t svc_id, service_id_t cat_id)
{
        async_exch_t *exch;
        errno_t retval;

        exch = loc_exchange_begin_blocking(INTERFACE_LOC_SUPPLIER);
        retval = async_req_2_0(exch, LOC_SERVICE_ADD_TO_CAT, svc_id, cat_id);
        loc_exchange_end(exch);

        return retval;
}

static size_t loc_count_services_internal(async_exch_t *exch,
    service_id_t ns_handle)
{
        sysarg_t count;
        errno_t retval = async_req_1_1(exch, LOC_GET_SERVICE_COUNT, ns_handle,
            &count);
        if (retval != EOK)
                return 0;

        return count;
}

size_t loc_count_namespaces(void)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
        size_t size = loc_count_namespaces_internal(exch);
        loc_exchange_end(exch);

        return size;
}

size_t loc_count_services(service_id_t ns_handle)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
        size_t size = loc_count_services_internal(exch, ns_handle);
        loc_exchange_end(exch);

        return size;
}

size_t loc_get_namespaces(loc_sdesc_t **data)
{
        /* Loop until read is succesful */
        while (true) {
                async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
                size_t count = loc_count_namespaces_internal(exch);
                loc_exchange_end(exch);

                if (count == 0)
                        return 0;

                loc_sdesc_t *devs = (loc_sdesc_t *) calloc(count, sizeof(loc_sdesc_t));
                if (devs == NULL)
                        return 0;

                exch = loc_exchange_begin(INTERFACE_LOC_CONSUMER);

                ipc_call_t answer;
                aid_t req = async_send_0(exch, LOC_GET_NAMESPACES, &answer);
                errno_t rc = async_data_read_start(exch, devs, count * sizeof(loc_sdesc_t));

                loc_exchange_end(exch);

                if (rc == EOVERFLOW) {
                        /*
                         * Number of namespaces has changed since
                         * the last call of LOC_GET_NAMESPACE_COUNT
                         */
                        free(devs);
                        continue;
                }

                if (rc != EOK) {
                        async_forget(req);
                        free(devs);
                        return 0;
                }

                errno_t retval;
                async_wait_for(req, &retval);

                if (retval != EOK)
                        return 0;

                *data = devs;
                return count;
        }
}

size_t loc_get_services(service_id_t ns_handle, loc_sdesc_t **data)
{
        /* Loop until read is succesful */
        while (true) {
                async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);
                size_t count = loc_count_services_internal(exch, ns_handle);
                loc_exchange_end(exch);

                if (count == 0)
                        return 0;

                loc_sdesc_t *devs = (loc_sdesc_t *) calloc(count, sizeof(loc_sdesc_t));
                if (devs == NULL)
                        return 0;

                exch = loc_exchange_begin(INTERFACE_LOC_CONSUMER);

                ipc_call_t answer;
                aid_t req = async_send_1(exch, LOC_GET_SERVICES, ns_handle, &answer);
                errno_t rc = async_data_read_start(exch, devs, count * sizeof(loc_sdesc_t));

                loc_exchange_end(exch);

                if (rc == EOVERFLOW) {
                        /*
                         * Number of services has changed since
                         * the last call of LOC_GET_SERVICE_COUNT
                         */
                        free(devs);
                        continue;
                }

                if (rc != EOK) {
                        async_forget(req);
                        free(devs);
                        return 0;
                }

                errno_t retval;
                async_wait_for(req, &retval);

                if (retval != EOK)
                        return 0;

                *data = devs;
                return count;
        }
}

static errno_t loc_category_get_ids_once(sysarg_t method, sysarg_t arg1,
    sysarg_t *id_buf, size_t buf_size, size_t *act_size)
{
        async_exch_t *exch = loc_exchange_begin_blocking(INTERFACE_LOC_CONSUMER);

        ipc_call_t answer;
        aid_t req = async_send_1(exch, method, arg1, &answer);
        errno_t rc = async_data_read_start(exch, id_buf, buf_size);

        loc_exchange_end(exch);

        if (rc != EOK) {
                async_forget(req);
                return rc;
        }

        errno_t retval;
        async_wait_for(req, &retval);

        if (retval != EOK) {
                return retval;
        }

        *act_size = ipc_get_arg1(&answer);
        return EOK;
}

/** Get list of IDs.
 *
 * Returns an allocated array of service IDs.
 *
 * @param method        IPC method
 * @param arg1          IPC argument 1
 * @param data          Place to store pointer to array of IDs
 * @param count         Place to store number of IDs
 * @return              EOK on success or an error code
 */
static errno_t loc_get_ids_internal(sysarg_t method, sysarg_t arg1,
    sysarg_t **data, size_t *count)
{
        *data = NULL;
        *count = 0;

        size_t act_size = 0;
        errno_t rc = loc_category_get_ids_once(method, arg1, NULL, 0,
            &act_size);
        if (rc != EOK)
                return rc;

        size_t alloc_size = act_size;
        service_id_t *ids = malloc(alloc_size);
        if (ids == NULL)
                return ENOMEM;

        while (true) {
                rc = loc_category_get_ids_once(method, arg1, ids, alloc_size,
                    &act_size);
                if (rc != EOK)
                        return rc;

                if (act_size <= alloc_size)
                        break;

                alloc_size = act_size;
                ids = realloc(ids, alloc_size);
                if (ids == NULL)
                        return ENOMEM;
        }

        *count = act_size / sizeof(category_id_t);
        *data = ids;
        return EOK;
}

/** Get list of services in category.
 *
 * Returns an allocated array of service IDs.
 *
 * @param cat_id        Category ID
 * @param data          Place to store pointer to array of IDs
 * @param count         Place to store number of IDs
 * @return              EOK on success or an error code
 */
errno_t loc_category_get_svcs(category_id_t cat_id, service_id_t **data,
    size_t *count)
{
        return loc_get_ids_internal(LOC_CATEGORY_GET_SVCS, cat_id,
            data, count);
}

/** Get list of categories.
 *
 * Returns an allocated array of category IDs.
 *
 * @param data          Place to store pointer to array of IDs
 * @param count         Place to store number of IDs
 * @return              EOK on success or an error code
 */
errno_t loc_get_categories(category_id_t **data, size_t *count)
{
        return loc_get_ids_internal(LOC_GET_CATEGORIES, 0,
            data, count);
}

errno_t loc_register_cat_change_cb(loc_cat_change_cb_t cb_fun, void *cb_arg)
{
        fibril_mutex_lock(&loc_callback_mutex);
        if (cat_change_cb != NULL) {
                fibril_mutex_unlock(&loc_callback_mutex);
                return EEXIST;
        }

        if (loc_callback_create() != EOK) {
                fibril_mutex_unlock(&loc_callback_mutex);
                return EIO;
        }

        cat_change_cb = cb_fun;
        cat_change_arg = cb_arg;
        fibril_mutex_unlock(&loc_callback_mutex);

        return EOK;
}