esp-idf/components/bt/host/bluedroid/hci/hci_layer.c

/******************************************************************************
 *
 *  Copyright (C) 2014 Google, Inc.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at:
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 ******************************************************************************/
#include <string.h>
#include "sdkconfig.h"
#include "esp_bt.h"

#include "common/bt_defs.h"
#include "common/bt_trace.h"
#include "stack/hcidefs.h"
#include "stack/hcimsgs.h"
#include "stack/btu.h"
#include "common/bt_vendor_lib.h"
#include "hci/hci_internals.h"
#include "hci/hci_hal.h"
#include "hci/hci_layer.h"
#include "osi/allocator.h"
#include "hci/packet_fragmenter.h"
#include "osi/list.h"
#include "osi/alarm.h"
#include "osi/thread.h"
#include "osi/mutex.h"
#include "osi/fixed_queue.h"
#include "osi/fixed_pkt_queue.h"

#define HCI_HOST_TASK_PINNED_TO_CORE    (TASK_PINNED_TO_CORE)
#define HCI_HOST_TASK_STACK_SIZE        (2048 + BT_TASK_EXTRA_STACK_SIZE)
#define HCI_HOST_TASK_PRIO              (BT_TASK_MAX_PRIORITIES - 3)
#define HCI_HOST_TASK_NAME              "hciT"
#define HCI_HOST_TASK_WORKQUEUE_NUM     (2)
#define HCI_HOST_TASK_WORKQUEUE0_LEN    (1) // for downstream datapath
#define HCI_HOST_TASK_WORKQUEUE1_LEN    (1) // for upstream datapath

#define HCI_DOWNSTREAM_DATA_QUEUE_IDX   (0)

typedef struct {
    bool timer_is_set;
    osi_alarm_t *command_response_timer;
    list_t *commands_pending_response;
    osi_mutex_t commands_pending_response_lock;
} command_waiting_response_t;

typedef struct {
    int command_credits;
    fixed_pkt_queue_t *command_queue;
    fixed_queue_t *packet_queue;
    struct osi_event *downstream_data_ready;
    command_waiting_response_t cmd_waiting_q;

    /*
      non_repeating_timer_t *command_response_timer;
      list_t *commands_pending_response;
      osi_mutex_t commands_pending_response_lock;
    */
} hci_host_env_t;

// Using a define here, because it can be stringified for the property lookup
static const uint32_t COMMAND_PENDING_TIMEOUT = 8000;

// Our interface
static bool interface_created;
static hci_t interface;
static hci_host_env_t hci_host_env;
static osi_thread_t *hci_host_thread;
static bool hci_host_startup_flag;

// Modules we import and callbacks we export
static const hci_hal_t *hal;
static const hci_hal_callbacks_t hal_callbacks;
static const packet_fragmenter_t *packet_fragmenter;
static const packet_fragmenter_callbacks_t packet_fragmenter_callbacks;

static int hci_layer_init_env(void);
static void hci_layer_deinit_env(void);
static void hci_downstream_data_handler(void *arg);
static void event_command_ready(fixed_pkt_queue_t *queue);
static void event_packet_ready(fixed_queue_t *queue);
static void restart_command_waiting_response_timer(command_waiting_response_t *cmd_wait_q);
static void command_timed_out(void *context);
static void hal_says_packet_ready(BT_HDR *packet);
static bool filter_incoming_event(BT_HDR *packet);
static serial_data_type_t event_to_data_type(uint16_t event);
static pkt_linked_item_t *get_waiting_command(command_opcode_t opcode);
static void dispatch_reassembled(BT_HDR *packet);
static void dispatch_adv_report(pkt_linked_item_t *linked_pkt);

// Module lifecycle functions
int hci_start_up(void)
{
    if (hci_layer_init_env()) {
        goto error;
    }

    const size_t workqueue_len[] = {HCI_HOST_TASK_WORKQUEUE0_LEN, HCI_HOST_TASK_WORKQUEUE1_LEN};
    hci_host_thread = osi_thread_create(HCI_HOST_TASK_NAME, HCI_HOST_TASK_STACK_SIZE, HCI_HOST_TASK_PRIO, HCI_HOST_TASK_PINNED_TO_CORE,
                                        HCI_HOST_TASK_WORKQUEUE_NUM, workqueue_len);
    if (hci_host_thread == NULL) {
        return -2;
    }

    osi_event_bind(hci_host_env.downstream_data_ready, hci_host_thread, HCI_DOWNSTREAM_DATA_QUEUE_IDX);

    packet_fragmenter->init(&packet_fragmenter_callbacks);
    hal->open(&hal_callbacks, hci_host_thread);

    hci_host_startup_flag = true;
    return 0;
error:
    hci_shut_down();
    return -1;
}

void hci_shut_down(void)
{
    hci_host_startup_flag  = false;
    hci_layer_deinit_env();

    packet_fragmenter->cleanup();

    //low_power_manager->cleanup();
    hal->close();

    osi_thread_free(hci_host_thread);
    hci_host_thread = NULL;
}

bool hci_downstream_data_post(uint32_t timeout)
{
    if (hci_host_env.downstream_data_ready == NULL) {
        HCI_TRACE_WARNING("%s downstream_data_ready event not created", __func__);
        return false;
    }
    return osi_thread_post_event(hci_host_env.downstream_data_ready, timeout);
}

static int hci_layer_init_env(void)
{
    command_waiting_response_t *cmd_wait_q;

    // The host is only allowed to send at most one command initially,
    // as per the Bluetooth spec, Volume 2, Part E, 4.4 (Command Flow Control)
    // This value can change when you get a command complete or command status event.
    hci_host_env.command_credits = 1;
    hci_host_env.command_queue = fixed_pkt_queue_new(QUEUE_SIZE_MAX);
    if (hci_host_env.command_queue) {
        fixed_pkt_queue_register_dequeue(hci_host_env.command_queue, event_command_ready);
    } else {
        HCI_TRACE_ERROR("%s unable to create pending command queue.", __func__);
        return -1;
    }

    struct osi_event *event = osi_event_create(hci_downstream_data_handler, NULL);
    assert(event != NULL);
    hci_host_env.downstream_data_ready = event;

    hci_host_env.packet_queue = fixed_queue_new(QUEUE_SIZE_MAX);
    if (hci_host_env.packet_queue) {
        fixed_queue_register_dequeue(hci_host_env.packet_queue, event_packet_ready);
    } else {
        HCI_TRACE_ERROR("%s unable to create pending packet queue.", __func__);
        return -1;
    }

    // Init Commands waiting response list and timer
    cmd_wait_q = &hci_host_env.cmd_waiting_q;
    cmd_wait_q->timer_is_set = false;
    cmd_wait_q->commands_pending_response = list_new(NULL);
    if (!cmd_wait_q->commands_pending_response) {
        HCI_TRACE_ERROR("%s unable to create list for commands pending response.", __func__);
        return -1;
    }
    osi_mutex_new(&cmd_wait_q->commands_pending_response_lock);
    cmd_wait_q->command_response_timer = osi_alarm_new("cmd_rsp_to", command_timed_out, cmd_wait_q, COMMAND_PENDING_TIMEOUT);
    if (!cmd_wait_q->command_response_timer) {
        HCI_TRACE_ERROR("%s unable to create command response timer.", __func__);
        return -1;
    }
#if (BLE_50_FEATURE_SUPPORT == TRUE)
    btsnd_hcic_ble_sync_sem_init();
#endif // #if (BLE_50_FEATURE_SUPPORT == TRUE)

    return 0;
}

static void hci_layer_deinit_env(void)
{
    command_waiting_response_t *cmd_wait_q;

    osi_event_delete(hci_host_env.downstream_data_ready);
    hci_host_env.downstream_data_ready = NULL;

    if (hci_host_env.command_queue) {
        fixed_pkt_queue_free(hci_host_env.command_queue, (fixed_pkt_queue_free_cb)osi_free_func);
    }
    if (hci_host_env.packet_queue) {
        fixed_queue_free(hci_host_env.packet_queue, osi_free_func);
    }

    cmd_wait_q = &hci_host_env.cmd_waiting_q;
    list_free(cmd_wait_q->commands_pending_response);
    osi_mutex_free(&cmd_wait_q->commands_pending_response_lock);
    osi_alarm_free(cmd_wait_q->command_response_timer);
    cmd_wait_q->command_response_timer = NULL;
#if (BLE_50_FEATURE_SUPPORT == TRUE)
    btsnd_hcic_ble_sync_sem_deinit();
#endif // #if (BLE_50_FEATURE_SUPPORT == TRUE)
}

static void hci_downstream_data_handler(void *arg)
{
    /*
     * Previous task handles RX queue and two TX Queues, Since there is
     * a RX Thread Task in H4 layer which receives packet from driver layer.
     * Now HCI Host Task has been optimized to only process TX Queue
     * including command and data queue. And command queue has high priority,
     * All packets will be directly copied to single queue in driver layer with
     * H4 type header added (1 byte).
     */
    while (esp_vhci_host_check_send_available()) {
        /*Now Target only allowed one packet per TX*/
        BT_HDR *pkt = packet_fragmenter->fragment_current_packet();
        if (pkt != NULL) {
            packet_fragmenter->fragment_and_dispatch(pkt);
        } else if (!fixed_pkt_queue_is_empty(hci_host_env.command_queue) &&
                    hci_host_env.command_credits > 0) {
            fixed_pkt_queue_process(hci_host_env.command_queue);
        } else if (!fixed_queue_is_empty(hci_host_env.packet_queue)) {
            fixed_queue_process(hci_host_env.packet_queue);
        } else {
            // No downstream packet to send, stop processing
            break;
        }
    }
}

static void transmit_command(
    BT_HDR *command,
    command_complete_cb complete_callback,
    command_status_cb status_callback,
    void *context)
{
    hci_cmd_metadata_t *metadata = HCI_GET_CMD_METAMSG(command);
    pkt_linked_item_t *linked_pkt = HCI_GET_CMD_LINKED_STRUCT(metadata);

    assert(command->layer_specific == HCI_CMD_BUF_TYPE_METADATA);
    metadata->flags_vnd |= HCI_CMD_MSG_F_VND_QUEUED;

    // Store the command message type in the event field
    // in case the upper layer didn't already
    command->event = MSG_STACK_TO_HC_HCI_CMD;

    HCI_TRACE_DEBUG("HCI Enqueue Command opcode=0x%x\n", metadata->opcode);
    BTTRC_DUMP_BUFFER(NULL, command->data + command->offset, command->len);

    fixed_pkt_queue_enqueue(hci_host_env.command_queue, linked_pkt, FIXED_PKT_QUEUE_MAX_TIMEOUT);
    hci_downstream_data_post(OSI_THREAD_MAX_TIMEOUT);

}

static future_t *transmit_command_futured(BT_HDR *command)
{
    hci_cmd_metadata_t *metadata = HCI_GET_CMD_METAMSG(command);
    pkt_linked_item_t *linked_pkt = HCI_GET_CMD_LINKED_STRUCT(metadata);

    assert(command->layer_specific == HCI_CMD_BUF_TYPE_METADATA);
    metadata->flags_vnd |= (HCI_CMD_MSG_F_VND_QUEUED | HCI_CMD_MSG_F_VND_FUTURE);

    future_t *future = future_new();

    metadata->complete_future = future;

    // Store the command message type in the event field
    // in case the upper layer didn't already
    command->event = MSG_STACK_TO_HC_HCI_CMD;

    fixed_pkt_queue_enqueue(hci_host_env.command_queue, linked_pkt, FIXED_PKT_QUEUE_MAX_TIMEOUT);
    hci_downstream_data_post(OSI_THREAD_MAX_TIMEOUT);
    return future;
}

static void transmit_downward(uint16_t type, void *data)
{
    if (type == MSG_STACK_TO_HC_HCI_CMD) {
        HCI_TRACE_ERROR("%s legacy transmit of command. Use transmit_command instead.\n", __func__);
        assert(0);
    } else {
        fixed_queue_enqueue(hci_host_env.packet_queue, data, FIXED_QUEUE_MAX_TIMEOUT);
    }

    hci_downstream_data_post(OSI_THREAD_MAX_TIMEOUT);
}


// Command/packet transmitting functions
static void event_command_ready(fixed_pkt_queue_t *queue)
{
    pkt_linked_item_t *wait_entry = NULL;
    command_waiting_response_t *cmd_wait_q = &hci_host_env.cmd_waiting_q;

    wait_entry = fixed_pkt_queue_dequeue(queue, FIXED_QUEUE_MAX_TIMEOUT);
    hci_cmd_metadata_t *metadata = (hci_cmd_metadata_t *)(wait_entry->data);
    metadata->flags_vnd |= HCI_CMD_MSG_F_VND_SENT;
    metadata->flags_vnd &= ~HCI_CMD_MSG_F_VND_QUEUED;

    if (metadata->flags_src & HCI_CMD_MSG_F_SRC_NOACK) {
        packet_fragmenter->fragment_and_dispatch(&metadata->command);
        hci_cmd_free_cb free_func = metadata->command_free_cb ? metadata->command_free_cb : (hci_cmd_free_cb) osi_free_func;
        free_func(wait_entry);
        return;
    }
    hci_host_env.command_credits--;
    // Move it to the list of commands awaiting response
    osi_mutex_lock(&cmd_wait_q->commands_pending_response_lock, OSI_MUTEX_MAX_TIMEOUT);
    list_append(cmd_wait_q->commands_pending_response, wait_entry);
    osi_mutex_unlock(&cmd_wait_q->commands_pending_response_lock);

    // Send it off
    packet_fragmenter->fragment_and_dispatch(&metadata->command);

    restart_command_waiting_response_timer(cmd_wait_q);
}

static void event_packet_ready(fixed_queue_t *queue)
{
    BT_HDR *packet = (BT_HDR *)fixed_queue_dequeue(queue, FIXED_QUEUE_MAX_TIMEOUT);
    // The queue may be the command queue or the packet queue, we don't care

    packet_fragmenter->fragment_and_dispatch(packet);
}

// Callback for the fragmenter to send a fragment
static void transmit_fragment(BT_HDR *packet, bool send_transmit_finished)
{
    uint16_t event = packet->event & MSG_EVT_MASK;
    serial_data_type_t type = event_to_data_type(event);

    hal->transmit_data(type, packet->data + packet->offset, packet->len);

    if (event != MSG_STACK_TO_HC_HCI_CMD && send_transmit_finished) {
        osi_free(packet);
    }
}

static void fragmenter_transmit_finished(BT_HDR *packet, bool all_fragments_sent)
{
    if (all_fragments_sent) {
        osi_free(packet);
    } else {
        // This is kind of a weird case, since we're dispatching a partially sent packet
        // up to a higher layer.
        // TODO(zachoverflow): rework upper layer so this isn't necessary.
        //osi_free(packet);

        /* dispatch_reassembled(packet) will send the packet back to the higher layer
           when controller buffer is not enough. hci will send the remain packet back
           to the l2cap layer and saved in the Link Queue (p_lcb->link_xmit_data_q).
           The l2cap layer will resend the packet to lower layer when controller buffer
           can be used.
        */

        dispatch_reassembled(packet);
        //data_dispatcher_dispatch(interface.event_dispatcher, packet->event & MSG_EVT_MASK, packet);
    }
}

static void restart_command_waiting_response_timer(command_waiting_response_t *cmd_wait_q)
{
    osi_mutex_lock(&cmd_wait_q->commands_pending_response_lock, OSI_MUTEX_MAX_TIMEOUT);
    if (cmd_wait_q->timer_is_set) {
        osi_alarm_cancel(cmd_wait_q->command_response_timer);
        cmd_wait_q->timer_is_set = false;
    }
    if (!list_is_empty(cmd_wait_q->commands_pending_response)) {
        osi_alarm_set(cmd_wait_q->command_response_timer, COMMAND_PENDING_TIMEOUT);
        cmd_wait_q->timer_is_set = true;
    }
    osi_mutex_unlock(&cmd_wait_q->commands_pending_response_lock);
}

static void command_timed_out(void *context)
{
    command_waiting_response_t *cmd_wait_q = (command_waiting_response_t *)context;
    pkt_linked_item_t *wait_entry;

    osi_mutex_lock(&cmd_wait_q->commands_pending_response_lock, OSI_MUTEX_MAX_TIMEOUT);
    wait_entry = (list_is_empty(cmd_wait_q->commands_pending_response) ?
                  NULL : list_front(cmd_wait_q->commands_pending_response));
    osi_mutex_unlock(&cmd_wait_q->commands_pending_response_lock);

    if (wait_entry == NULL) {
        HCI_TRACE_ERROR("%s with no commands pending response", __func__);
    } else
        // We shouldn't try to recover the stack from this command timeout.
        // If it's caused by a software bug, fix it. If it's a hardware bug, fix it.
    {
        hci_cmd_metadata_t *metadata = (hci_cmd_metadata_t *)(wait_entry->data);
        HCI_TRACE_ERROR("%s hci layer timeout waiting for response to a command. opcode: 0x%x", __func__, metadata->opcode);
        UNUSED(metadata);
    }
}

// Event/packet receiving functions
static void hal_says_packet_ready(BT_HDR *packet)
{
    if (packet->event != MSG_HC_TO_STACK_HCI_EVT) {
        packet_fragmenter->reassemble_and_dispatch(packet);
    } else if (!filter_incoming_event(packet)) {
        dispatch_reassembled(packet);
    }
}

static void hal_says_adv_rpt_ready(pkt_linked_item_t *linked_pkt)
{
    dispatch_adv_report(linked_pkt);
}

// Returns true if the event was intercepted and should not proceed to
// higher layers. Also inspects an incoming event for interesting
// information, like how many commands are now able to be sent.
static bool filter_incoming_event(BT_HDR *packet)
{
    pkt_linked_item_t *wait_entry = NULL;
    hci_cmd_metadata_t *metadata = NULL;
    uint8_t *stream = packet->data + packet->offset;
    uint8_t event_code;
    command_opcode_t opcode;

    STREAM_TO_UINT8(event_code, stream);
    STREAM_SKIP_UINT8(stream); // Skip the parameter total length field

    HCI_TRACE_DEBUG("Receive packet event_code=0x%x\n", event_code);

    if (event_code == HCI_COMMAND_COMPLETE_EVT) {
        STREAM_TO_UINT8(hci_host_env.command_credits, stream);
        STREAM_TO_UINT16(opcode, stream);
        wait_entry = get_waiting_command(opcode);
        metadata = (hci_cmd_metadata_t *)(wait_entry->data);
        if (!wait_entry) {
            HCI_TRACE_WARNING("%s command complete event with no matching command. opcode: 0x%x.", __func__, opcode);
        } else if (metadata->command_complete_cb) {
            metadata->command_complete_cb(packet, metadata->context);
#if (BLE_50_FEATURE_SUPPORT == TRUE)
            BlE_SYNC *sync_info =  btsnd_hcic_ble_get_sync_info();
            if(!sync_info) {
                HCI_TRACE_WARNING("%s sync_info is NULL. opcode = 0x%x", __func__, opcode);
            } else {
                if (sync_info->sync_sem && sync_info->opcode == opcode) {
                    osi_sem_give(&sync_info->sync_sem);
                    sync_info->opcode = 0;
                }
            }
#endif // #if (BLE_50_FEATURE_SUPPORT == TRUE)
        } else if (metadata->flags_vnd & HCI_CMD_MSG_F_VND_FUTURE) {
            future_ready((future_t *)(metadata->complete_future), packet);
        }

        goto intercepted;
    } else if (event_code == HCI_COMMAND_STATUS_EVT) {
        uint8_t status;
        STREAM_TO_UINT8(status, stream);
        STREAM_TO_UINT8(hci_host_env.command_credits, stream);
        STREAM_TO_UINT16(opcode, stream);

        // If a command generates a command status event, it won't be getting a command complete event

        wait_entry = get_waiting_command(opcode);
        metadata = (hci_cmd_metadata_t *)(wait_entry->data);
        if (!wait_entry) {
            HCI_TRACE_WARNING("%s command status event with no matching command. opcode: 0x%x", __func__, opcode);
        } else if (metadata->command_status_cb) {
            metadata->command_status_cb(status, &metadata->command, metadata->context);
        }

        goto intercepted;
    }

    return false;
intercepted:
    restart_command_waiting_response_timer(&hci_host_env.cmd_waiting_q);

    /*Tell HCI Host Task to continue TX Pending commands*/
    if (hci_host_env.command_credits &&
            !fixed_pkt_queue_is_empty(hci_host_env.command_queue)) {
        hci_downstream_data_post(OSI_THREAD_MAX_TIMEOUT);
    }

    if (wait_entry) {
        // If it has a callback, it's responsible for freeing the packet
        if (event_code == HCI_COMMAND_STATUS_EVT ||
                (!metadata->command_complete_cb && !metadata->complete_future)) {
            osi_free(packet);
        }

        // If it has a callback, it's responsible for freeing the command
        if (event_code == HCI_COMMAND_COMPLETE_EVT || !metadata->command_status_cb) {
            hci_cmd_free_cb free_func = metadata->command_free_cb ? metadata->command_free_cb : (hci_cmd_free_cb) osi_free_func;
            free_func(wait_entry);
        }
    } else {
        osi_free(packet);
    }

    return true;
}

// Callback for the fragmenter to dispatch up a completely reassembled packet
static void dispatch_reassembled(BT_HDR *packet)
{
    // Events should already have been dispatched before this point
    //Tell Up-layer received packet.
    if (btu_task_post(SIG_BTU_HCI_MSG, packet, OSI_THREAD_MAX_TIMEOUT) == false) {
        osi_free(packet);
    }
}

static void dispatch_adv_report(pkt_linked_item_t *linked_pkt)
{
    // Events should already have been dispatched before this point
    //Tell Up-layer received packet.
    if (btu_task_post(SIG_BTU_HCI_ADV_RPT_MSG, linked_pkt, OSI_THREAD_MAX_TIMEOUT) == false) {
        osi_free(linked_pkt);
#if (BLE_ADV_REPORT_FLOW_CONTROL == TRUE)
        hci_adv_credits_try_release(1);
#endif
    }
}
// Misc internal functions

// TODO(zachoverflow): we seem to do this a couple places, like the HCI inject module. #centralize
static serial_data_type_t event_to_data_type(uint16_t event)
{
    if (event == MSG_STACK_TO_HC_HCI_ACL) {
        return DATA_TYPE_ACL;
    } else if (event == MSG_STACK_TO_HC_HCI_SCO) {
        return DATA_TYPE_SCO;
    } else if (event == MSG_STACK_TO_HC_HCI_CMD) {
        return DATA_TYPE_COMMAND;
    } else {
        HCI_TRACE_ERROR("%s invalid event type, could not translate 0x%x\n", __func__, event);
    }

    return 0;
}

static pkt_linked_item_t *get_waiting_command(command_opcode_t opcode)
{
    command_waiting_response_t *cmd_wait_q = &hci_host_env.cmd_waiting_q;
    osi_mutex_lock(&cmd_wait_q->commands_pending_response_lock, OSI_MUTEX_MAX_TIMEOUT);

    for (const list_node_t *node = list_begin(cmd_wait_q->commands_pending_response);
            node != list_end(cmd_wait_q->commands_pending_response);
            node = list_next(node)) {
        pkt_linked_item_t *wait_entry = list_node(node);
        if (wait_entry) {
            hci_cmd_metadata_t *metadata = (hci_cmd_metadata_t *)(wait_entry->data);
            if (metadata->opcode == opcode) {
                list_remove(cmd_wait_q->commands_pending_response, wait_entry);
                osi_mutex_unlock(&cmd_wait_q->commands_pending_response_lock);
                return wait_entry;
            }
        }
    }

    osi_mutex_unlock(&cmd_wait_q->commands_pending_response_lock);
    return NULL;
}

static void init_layer_interface(void)
{
    if (!interface_created) {
        interface.transmit_command = transmit_command;
        interface.transmit_command_futured = transmit_command_futured;
        interface.transmit_downward = transmit_downward;
        interface_created = true;
    }
}

static const hci_hal_callbacks_t hal_callbacks = {
    hal_says_packet_ready,
    hal_says_adv_rpt_ready,
};

static const packet_fragmenter_callbacks_t packet_fragmenter_callbacks = {
    transmit_fragment,
    dispatch_reassembled,
    fragmenter_transmit_finished
};

const hci_t *hci_layer_get_interface(void)
{
    hal = hci_hal_h4_get_interface();
    packet_fragmenter = packet_fragmenter_get_interface();

    init_layer_interface();
    return &interface;
}