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/*

 * Copyright (c) 2006 Ondrej Palkovsky

 * 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.

 */

/** @addtogroup genericipc

 * @{

 */

/** @file

 */

/* Lock ordering

 *

 * First the answerbox, then the phone.

 */

#include <synch/synch.h>

#include <synch/spinlock.h>

#include <synch/mutex.h>

#include <synch/waitq.h>

#include <synch/synch.h>

#include <ipc/ipc.h>

#include <errno.h>

#include <mm/slab.h>

#include <arch.h>

#include <proc/task.h>

#include <memstr.h>

#include <debug.h>

#include <print.h>

#include <console/console.h>

#include <proc/thread.h>

#include <arch/interrupt.h>

#include <ipc/irq.h>

/** Open channel that is assigned automatically to new tasks */

answerbox_t *ipc_phone_0 = NULL;

static slab_cache_t *ipc_call_slab;

/** Initialize a call structure.

 *

 * @param call      Call structure to be initialized.

 */

static void _ipc_call_init(call_t *call)

{

    memsetb(call, sizeof(*call), 0);

    call->callerbox = &TASK->answerbox;

    call->sender = TASK;

    call->buffer = NULL;

}

/** Allocate and initialize a call structure.

 *

 * The call is initialized, so that the reply will be directed to

 * TASK->answerbox.

 *

 * @param flags     Parameters for slab_alloc (e.g FRAME_ATOMIC).

 *

 * @return      If flags permit it, return NULL, or initialized kernel

 *          call structure.

 */

call_t *ipc_call_alloc(int flags)

{

    call_t *call;

    call = slab_alloc(ipc_call_slab, flags);

    _ipc_call_init(call);

    return call;

}

/** Initialize a statically allocated call structure.

 *

 * @param call      Statically allocated kernel call structure to be

 *          initialized.

 */

void ipc_call_static_init(call_t *call)

{

    _ipc_call_init(call);

    call->flags |= IPC_CALL_STATIC_ALLOC;

}

/** Deallocate a call structure.

 *

 * @param call      Call structure to be freed.

 */

void ipc_call_free(call_t *call)

{

    ASSERT(!(call->flags & IPC_CALL_STATIC_ALLOC));

    /* Check to see if we have data in the IPC_M_DATA_SEND buffer. */

    if (call->buffer)

        free(call->buffer);

    slab_free(ipc_call_slab, call);

}

/** Initialize an answerbox structure.

 *

 * @param box       Answerbox structure to be initialized.

 * @param task      Task to which the answerbox belongs.

 */

void ipc_answerbox_init(answerbox_t *box, task_t *task)

{

    spinlock_initialize(&box->lock, "ipc_box_lock");

    spinlock_initialize(&box->irq_lock, "ipc_box_irqlock");

    waitq_initialize(&box->wq);

    list_initialize(&box->connected_phones);

    list_initialize(&box->calls);

    list_initialize(&box->dispatched_calls);

    list_initialize(&box->answers);

    list_initialize(&box->irq_notifs);

    list_initialize(&box->irq_head);

    box->task = task;

}

/** Connect a phone to an answerbox.

 *

 * @param phone     Initialized phone structure.

 * @param box       Initialized answerbox structure.

 */

void ipc_phone_connect(phone_t *phone, answerbox_t *box)

{

    mutex_lock(&phone->lock);

    phone->state = IPC_PHONE_CONNECTED;

    phone->callee = box;

    spinlock_lock(&box->lock);

    list_append(&phone->link, &box->connected_phones);

    spinlock_unlock(&box->lock);

    mutex_unlock(&phone->lock);

}

/** Initialize a phone structure.

 *

 * @param phone     Phone structure to be initialized.

 */

void ipc_phone_init(phone_t *phone)

{

    mutex_initialize(&phone->lock);

    phone->callee = NULL;

    phone->state = IPC_PHONE_FREE;

    atomic_set(&phone->active_calls, 0);

}

/** Helper function to facilitate synchronous calls.

 *

 * @param phone     Destination kernel phone structure.

 * @param request   Call structure with request.

 */

void ipc_call_sync(phone_t *phone, call_t *request)

{

    answerbox_t sync_box;

    ipc_answerbox_init(&sync_box, TASK);

    /* We will receive data in a special box. */

    request->callerbox = &sync_box;

    ipc_call(phone, request);

    ipc_wait_for_call(&sync_box, SYNCH_NO_TIMEOUT, SYNCH_FLAGS_NONE);

}

/** Answer a message which was not dispatched and is not listed in any queue.

 *

 * @param call      Call structure to be answered.

 */

static void _ipc_answer_free_call(call_t *call)

{

    answerbox_t *callerbox = call->callerbox;

    call->flags |= IPC_CALL_ANSWERED;

    spinlock_lock(&callerbox->lock);

    list_append(&call->link, &callerbox->answers);

    spinlock_unlock(&callerbox->lock);

    waitq_wakeup(&callerbox->wq, WAKEUP_FIRST);

}

/** Answer a message which is in a callee queue.

 *

 * @param box       Answerbox that is answering the message.

 * @param call      Modified request that is being sent back.

 */

void ipc_answer(answerbox_t *box, call_t *call)

{

    /* Remove from active box */

    spinlock_lock(&box->lock);

    list_remove(&call->link);

    spinlock_unlock(&box->lock);

    /* Send back answer */

    _ipc_answer_free_call(call);

}

/** Simulate sending back a message.

 *

 * Most errors are better handled by forming a normal backward

 * message and sending it as a normal answer.

 *

 * @param phone     Phone structure the call should appear to come from.

 * @param call      Call structure to be answered.

 * @param err       Return value to be used for the answer.

 */

void ipc_backsend_err(phone_t *phone, call_t *call, unative_t err)

{

    call->data.phone = phone;

    atomic_inc(&phone->active_calls);

    IPC_SET_RETVAL(call->data, err);

    _ipc_answer_free_call(call);

}

/** Unsafe unchecking version of ipc_call.

 *

 * @param phone     Phone structure the call comes from.

 * @param box       Destination answerbox structure.

 * @param call      Call structure with request.

 */

static void _ipc_call(phone_t *phone, answerbox_t *box, call_t *call)

{

    if (!(call->flags & IPC_CALL_FORWARDED)) {

        atomic_inc(&phone->active_calls);

        call->data.phone = phone;

    }

    spinlock_lock(&box->lock);

    list_append(&call->link, &box->calls);

    spinlock_unlock(&box->lock);

    waitq_wakeup(&box->wq, WAKEUP_FIRST);

}

/** Send an asynchronous request using a phone to an answerbox.

 *

 * @param phone     Phone structure the call comes from and which is

 *          connected to the destination answerbox.

 * @param call      Call structure with request.

 *

 * @return      Return 0 on success, ENOENT on error.

 */

int ipc_call(phone_t *phone, call_t *call)

{

    answerbox_t *box;

    mutex_lock(&phone->lock);

    if (phone->state != IPC_PHONE_CONNECTED) {

        mutex_unlock(&phone->lock);

        if (call->flags & IPC_CALL_FORWARDED) {

            IPC_SET_RETVAL(call->data, EFORWARD);

            _ipc_answer_free_call(call);

        } else {

            if (phone->state == IPC_PHONE_HUNGUP)

                ipc_backsend_err(phone, call, EHANGUP);

            else

                ipc_backsend_err(phone, call, ENOENT);

        }

        return ENOENT;

    }

    box = phone->callee;

    _ipc_call(phone, box, call);

    mutex_unlock(&phone->lock);

    return 0;

}

/** Disconnect phone from answerbox.

 *

 * This call leaves the phone in the HUNGUP state. The change to 'free' is done

 * lazily later.

 *

 * @param phone     Phone structure to be hung up.

 *              

 * @return      Return 0 if the phone is disconnected.

 *          Return -1 if the phone was already disconnected.

 */

int ipc_phone_hangup(phone_t *phone)

{

    answerbox_t *box;

    call_t *call;

    mutex_lock(&phone->lock);

    if (phone->state == IPC_PHONE_FREE ||

        phone->state == IPC_PHONE_HUNGUP ||

        phone->state == IPC_PHONE_CONNECTING) {

        mutex_unlock(&phone->lock);

        return -1;

    }

    box = phone->callee;

    if (phone->state != IPC_PHONE_SLAMMED) {

        /* Remove myself from answerbox */

        spinlock_lock(&box->lock);

        list_remove(&phone->link);

        spinlock_unlock(&box->lock);

        if (phone->state != IPC_PHONE_SLAMMED) {

            call = ipc_call_alloc(0);

            IPC_SET_METHOD(call->data, IPC_M_PHONE_HUNGUP);

            call->flags |= IPC_CALL_DISCARD_ANSWER;

            _ipc_call(phone, box, call);

        }

    }

    phone->state = IPC_PHONE_HUNGUP;

    mutex_unlock(&phone->lock);

    return 0;

}

/** Forwards call from one answerbox to another one.

 *

 * @param call      Call structure to be redirected.

 * @param newphone  Phone structure to target answerbox.

 * @param oldbox    Old answerbox structure.

 * @param mode      Flags that specify mode of the forward operation.

 *

 * @return      Return 0 if forwarding succeeded or an error code if

 *          there was error.

 *

 * The return value serves only as an information for the forwarder,

 * the original caller is notified automatically with EFORWARD.

 */

int ipc_forward(call_t *call, phone_t *newphone, answerbox_t *oldbox, int mode)

{

    spinlock_lock(&oldbox->lock);

    list_remove(&call->link);

    spinlock_unlock(&oldbox->lock);

    if (mode & IPC_FF_ROUTE_FROM_ME)

        call->data.phone = newphone;

    return ipc_call(newphone, call);

}

/** Wait for a phone call.

 *

 * @param box       Answerbox expecting the call.

 * @param usec      Timeout in microseconds. See documentation for

 *          waitq_sleep_timeout() for decription of its special

 *          meaning.

 * @param flags     Select mode of sleep operation. See documentation for

 *          waitq_sleep_timeout() for description of its special

 *          meaning.

 * @return      Recived call structure or NULL.

 *

 * To distinguish between a call and an answer, have a look at call->flags.

 */

call_t *ipc_wait_for_call(answerbox_t *box, uint32_t usec, int flags)

{

    call_t *request;

    ipl_t ipl;

    int rc;

restart:

    rc = waitq_sleep_timeout(&box->wq, usec, flags);

    if (SYNCH_FAILED(rc))

        return NULL;

    spinlock_lock(&box->lock);

    if (!list_empty(&box->irq_notifs)) {

        ipl = interrupts_disable();

        spinlock_lock(&box->irq_lock);

        request = list_get_instance(box->irq_notifs.next, call_t, link);

        list_remove(&request->link);

        spinlock_unlock(&box->irq_lock);

        interrupts_restore(ipl);

    } else if (!list_empty(&box->answers)) {

        /* Handle asynchronous answers */

        request = list_get_instance(box->answers.next, call_t, link);

        list_remove(&request->link);

        atomic_dec(&request->data.phone->active_calls);

    } else if (!list_empty(&box->calls)) {

        /* Handle requests */

        request = list_get_instance(box->calls.next, call_t, link);

        list_remove(&request->link);

        /* Append request to dispatch queue */

        list_append(&request->link, &box->dispatched_calls);

    } else {

        /* This can happen regularly after ipc_cleanup */

        spinlock_unlock(&box->lock);

        goto restart;

    }

    spinlock_unlock(&box->lock);

    return request;

}

/** Answer all calls from list with EHANGUP answer.

 *

 * @param lst       Head of the list to be cleaned up.

 */

static void ipc_cleanup_call_list(link_t *lst)

{

    call_t *call;

    while (!list_empty(lst)) {

        call = list_get_instance(lst->next, call_t, link);

        if (call->buffer)

            free(call->buffer);

        list_remove(&call->link);

        IPC_SET_RETVAL(call->data, EHANGUP);

        _ipc_answer_free_call(call);

    }

}

/** Disconnects all phones connected to an answerbox.

 *

 * @param box       Answerbox to disconnect phones from.

 * @param notify_box    If true, the answerbox will get a hangup message for

 *          each disconnected phone.

 */

static void ipc_answerbox_slam_phones(answerbox_t *box, bool notify_box)

{

    phone_t *phone;

    DEADLOCK_PROBE_INIT(p_phonelck);

    ipl_t ipl;

    call_t *call;

    call = ipc_call_alloc(0);

    /* Disconnect all phones connected to our answerbox */

restart_phones:

    ipl = interrupts_disable();

    spinlock_lock(&box->lock);

    while (!list_empty(&box->connected_phones)) {

        phone = list_get_instance(box->connected_phones.next,

            phone_t, link);

        if (SYNCH_FAILED(mutex_trylock(&phone->lock))) {

            spinlock_unlock(&box->lock);

            interrupts_restore(ipl);

            DEADLOCK_PROBE(p_phonelck, DEADLOCK_THRESHOLD);

            goto restart_phones;

        }

        /* Disconnect phone */

        ASSERT(phone->state == IPC_PHONE_CONNECTED);

        list_remove(&phone->link);

        phone->state = IPC_PHONE_SLAMMED;

        if (notify_box) {

            mutex_unlock(&phone->lock);

            spinlock_unlock(&box->lock);

            interrupts_restore(ipl);

            /*

             * Send one message to the answerbox for each

             * phone. Used to make sure the kbox thread

             * wakes up after the last phone has been

             * disconnected.

             */

            IPC_SET_METHOD(call->data, IPC_M_PHONE_HUNGUP);

            call->flags |= IPC_CALL_DISCARD_ANSWER;

            _ipc_call(phone, box, call);

            /* Allocate another call in advance */

            call = ipc_call_alloc(0);

            /* Must start again */

            goto restart_phones;

        }

        mutex_unlock(&phone->lock);

    }

    spinlock_unlock(&box->lock);

    interrupts_restore(ipl);

    /* Free unused call */

    if (call) ipc_call_free(call);

}

static void ipc_kbox_cleanup()

{

    bool have_kb_thread;

    /* Only hold kb_cleanup_lock while setting kb_finished - this is enough */

    mutex_lock(&TASK->kb_cleanup_lock);

    TASK->kb_finished = true;

    mutex_unlock(&TASK->kb_cleanup_lock);

    have_kb_thread = (TASK->kb_thread != NULL);

    /* From now on nobody will try to connect phones or attach kbox threads */

    /*

     * Disconnect all phones connected to our kbox. Passing true for

     * notify_box causes a HANGUP message to be inserted for each

     * disconnected phone. This ensures the kbox thread is going to

     * wake up and terminate.

     */

    ipc_answerbox_slam_phones(&TASK->kernel_box, have_kb_thread);

    if (have_kb_thread) {

        printf("join kb_thread..\n");

        thread_join(TASK->kb_thread);

        thread_detach(TASK->kb_thread);

        printf("join done\n");

        TASK->kb_thread = NULL;

    }

    /* Answer all messages in 'calls' and 'dispatched_calls' queues */

    spinlock_lock(&TASK->kernel_box.lock);

    ipc_cleanup_call_list(&TASK->kernel_box.dispatched_calls);

    ipc_cleanup_call_list(&TASK->kernel_box.calls);

    spinlock_unlock(&TASK->kernel_box.lock);

}

/** Cleans up all IPC communication of the current task.

 *

 * Note: ipc_hangup sets returning answerbox to TASK->answerbox, you

 * have to change it as well if you want to cleanup other tasks than TASK.

 */

void ipc_cleanup(void)

{

    int i;

    call_t *call;

    /* Disconnect all our phones ('ipc_phone_hangup') */

    for (i = 0; i < IPC_MAX_PHONES; i++)

        ipc_phone_hangup(&TASK->phones[i]);

    /* Disconnect all connected irqs */

    ipc_irq_cleanup(&TASK->answerbox);

    /* Disconnect all phones connected to our regular answerbox */

    ipc_answerbox_slam_phones(&TASK->answerbox, false);

    /* Clean up kbox thread and communications */

    ipc_kbox_cleanup();

    /* Answer all messages in 'calls' and 'dispatched_calls' queues */

    spinlock_lock(&TASK->answerbox.lock);

    ipc_cleanup_call_list(&TASK->answerbox.dispatched_calls);

    ipc_cleanup_call_list(&TASK->answerbox.calls);

    spinlock_unlock(&TASK->answerbox.lock);

    /* Wait for all async answers to arrive */

    while (1) {

        /* Go through all phones, until all are FREE... */

        /* Locking not needed, no one else should modify

         * it, when we are in cleanup */

        for (i = 0; i < IPC_MAX_PHONES; i++) {

            if (TASK->phones[i].state == IPC_PHONE_HUNGUP &&

                atomic_get(&TASK->phones[i].active_calls) == 0)

                TASK->phones[i].state = IPC_PHONE_FREE;

            /* Just for sure, we might have had some

             * IPC_PHONE_CONNECTING phones */

            if (TASK->phones[i].state == IPC_PHONE_CONNECTED)

                ipc_phone_hangup(&TASK->phones[i]);

            /* If the hangup succeeded, it has sent a HANGUP

             * message, the IPC is now in HUNGUP state, we

             * wait for the reply to come */

            if (TASK->phones[i].state != IPC_PHONE_FREE)

                break;

        }

        /* Voila, got into cleanup */

        if (i == IPC_MAX_PHONES)

            break;

        call = ipc_wait_for_call(&TASK->answerbox, SYNCH_NO_TIMEOUT,

            SYNCH_FLAGS_NONE);

        ASSERT((call->flags & IPC_CALL_ANSWERED) ||

            (call->flags & IPC_CALL_NOTIF));

        ASSERT(!(call->flags & IPC_CALL_STATIC_ALLOC));

        atomic_dec(&TASK->active_calls);

        ipc_call_free(call);

    }

}

/** Initilize IPC subsystem */

void ipc_init(void)

{

    ipc_call_slab = slab_cache_create("ipc_call", sizeof(call_t), 0, NULL,

        NULL, 0);

}

/** List answerbox contents.

 *

 * @param taskid    Task ID.

 */

void ipc_print_task(task_id_t taskid)

{

    task_t *task;

    int i;

    call_t *call;

    link_t *tmp;

    spinlock_lock(&tasks_lock);

    task = task_find_by_id(taskid);

    if (task)

        spinlock_lock(&task->lock);

    spinlock_unlock(&tasks_lock);

    if (!task)

        return;

    /* Print opened phones & details */

    printf("PHONE:\n");

    for (i = 0; i < IPC_MAX_PHONES; i++) {

        if (SYNCH_FAILED(mutex_trylock(&task->phones[i].lock))) {

            printf("%d: mutex busy\n", i);

            continue;

        }

        if (task->phones[i].state != IPC_PHONE_FREE) {

            printf("%d: ", i);

            switch (task->phones[i].state) {

            case IPC_PHONE_CONNECTING:

                printf("connecting ");

                break;

            case IPC_PHONE_CONNECTED:

                printf("connected to: %p ",

                       task->phones[i].callee);

                break;

            case IPC_PHONE_SLAMMED:

                printf("slammed by: %p ",

                       task->phones[i].callee);

                break;

            case IPC_PHONE_HUNGUP:

                printf("hung up - was: %p ",

                       task->phones[i].callee);

                break;

            default:

                break;

            }

            printf("active: %ld\n",

                atomic_get(&task->phones[i].active_calls));

        }

        mutex_unlock(&task->phones[i].lock);

    }

    /* Print answerbox - calls */

    spinlock_lock(&task->answerbox.lock);

    printf("ABOX - CALLS:\n");

    for (tmp = task->answerbox.calls.next; tmp != &task->answerbox.calls;

        tmp = tmp->next) {

        call = list_get_instance(tmp, call_t, link);

        printf("Callid: %p Srctask:%" PRIu64 " M:%" PRIun

            " A1:%" PRIun " A2:%" PRIun " A3:%" PRIun

            " A4:%" PRIun " A5:%" PRIun " Flags:%x\n", call, call->sender->taskid,

            IPC_GET_METHOD(call->data), IPC_GET_ARG1(call->data),

            IPC_GET_ARG2(call->data), IPC_GET_ARG3(call->data),

            IPC_GET_ARG4(call->data), IPC_GET_ARG5(call->data),

            call->flags);

    }

    /* Print answerbox - calls */

    printf("ABOX - DISPATCHED CALLS:\n");

    for (tmp = task->answerbox.dispatched_calls.next;

        tmp != &task->answerbox.dispatched_calls;

        tmp = tmp->next) {

        call = list_get_instance(tmp, call_t, link);

        printf("Callid: %p Srctask:%" PRIu64 " M:%" PRIun

            " A1:%" PRIun " A2:%" PRIun " A3:%" PRIun

            " A4:%" PRIun " A5:%" PRIun " Flags:%x\n", call, call->sender->taskid,

            IPC_GET_METHOD(call->data), IPC_GET_ARG1(call->data),

            IPC_GET_ARG2(call->data), IPC_GET_ARG3(call->data),

            IPC_GET_ARG4(call->data), IPC_GET_ARG5(call->data),

            call->flags);

    }

    /* Print answerbox - calls */

    printf("ABOX - ANSWERS:\n");

    for (tmp = task->answerbox.answers.next; tmp != &task->answerbox.answers;

        tmp = tmp->next) {

        call = list_get_instance(tmp, call_t, link);

        printf("Callid:%p M:%" PRIun " A1:%" PRIun " A2:%" PRIun

            " A3:%" PRIun " A4:%" PRIun " A5:%" PRIun " Flags:%x\n",

            call, IPC_GET_METHOD(call->data), IPC_GET_ARG1(call->data),

            IPC_GET_ARG2(call->data), IPC_GET_ARG3(call->data),

            IPC_GET_ARG4(call->data), IPC_GET_ARG5(call->data),

            call->flags);

    }

    spinlock_unlock(&task->answerbox.lock);

    spinlock_unlock(&task->lock);

}

#include <ipc/ipcrsc.h>

#include <print.h>

#include <udebug/udebug_ipc.h>

static void kbox_thread_proc(void *arg)

{

    call_t *call;

    int method;

    bool done;

    ipl_t ipl;

    (void)arg;

    printf("kbox_thread_proc()\n");

    done = false;

    while (!done) {

        //printf("kbox: wait for call\n");

        call = ipc_wait_for_call(&TASK->kernel_box, SYNCH_NO_TIMEOUT,

            SYNCH_FLAGS_NONE);

        if (call != NULL) {

            method = IPC_GET_METHOD(call->data);

            if (method == IPC_M_DEBUG_ALL) {

                udebug_call_receive(call);

            }

            if (method == IPC_M_PHONE_HUNGUP) {

                printf("kbox: handle hangup message\n");

                /* Was it our debugger, who hung up? */

                if (call->sender == TASK->udebug.debugger) {

                    /* Terminate debugging session (if any) */

                    printf("kbox: terminate debug session\n");

                    ipl = interrupts_disable();

                    spinlock_lock(&TASK->lock);

                    udebug_task_cleanup(TASK);

                    spinlock_unlock(&TASK->lock);

                    interrupts_restore(ipl);

                } else {

                    printf("kbox: was not debugger\n");

                }

                printf("kbox: continue with hangup message\n");

                IPC_SET_RETVAL(call->data, 0);

                ipc_answer(&TASK->kernel_box, call);

                ipl = interrupts_disable();

                spinlock_lock(&TASK->lock);

                spinlock_lock(&TASK->answerbox.lock);

                if (list_empty(&TASK->answerbox.connected_phones)) {

                    /* Last phone has been disconnected */

                    TASK->kb_thread = NULL;

                    done = true;

                    printf("phone list is empty\n");

                }

                spinlock_unlock(&TASK->answerbox.lock);

                spinlock_unlock(&TASK->lock);

                interrupts_restore(ipl);

            }

        }

    }

    printf("kbox: finished\n");

}

/**

 * Connect phone to a task kernel-box specified by id.

 *