Android 9.0 Bluetooth源码分析（三）蓝牙配对流程

1 UI

蓝牙配对开始于settings设备列表 /packages/apps/Settings/src/com/android/settings/bluetooth/DeviceListPreferenceFragment.java中。
DeviceListPreferenceFragment是蓝牙扫描到的设备列表，点击其中一个蓝牙设备，调用onPreferenceTreeClick方法开始蓝牙的配对过程。
@Override
public boolean onPreferenceTreeClick(PreferenceScreen preferenceScreen,
Preference preference) {
if (KEY_BT_SCAN.equals(preference.getKey())) {
mLocalAdapter.startScanning(true);
return true;
}

    if (preference instanceof BluetoothDevicePreference) {
        BluetoothDevicePreference btPreference = (BluetoothDevicePreference) preference;
        CachedBluetoothDevice device = btPreference.getCachedDevice();
        mSelectedDevice = device.getDevice();
        //配对连接
        onDevicePreferenceClick(btPreference);
        return true;
    }

    return super.onPreferenceTreeClick(preferenceScreen, preference);
}

在本地onDevicePreferenceClick方法中调用/packages/apps/Settings/src/com/android/settings/bluetooth/BluetoothDevicePreference.java的onClicked方法：
void onClicked() {
Context context = getContext();
int bondState = mCachedDevice.getBondState();// 获取设备的绑定状态

      final MetricsFeatureProvider metricsFeatureProvider =
              FeatureFactory.getFactory(context).getMetricsFeatureProvider();
      if (mCachedDevice.isConnected()) {
          metricsFeatureProvider.action(context,
                  MetricsEvent.ACTION_SETTINGS_BLUETOOTH_DISCONNECT);
          askDisconnect(); // 已连接，询问是否断开连接
      } else if (bondState == BluetoothDevice.BOND_BONDED) {
          metricsFeatureProvider.action(context,
                  MetricsEvent.ACTION_SETTINGS_BLUETOOTH_CONNECT);
          mCachedDevice.connect(true);// 已绑定，则进行连接
      } else if (bondState == BluetoothDevice.BOND_NONE) {
          metricsFeatureProvider.action(context,
                  MetricsEvent.ACTION_SETTINGS_BLUETOOTH_PAIR);
          if (!mCachedDevice.hasHumanReadableName()) {
              metricsFeatureProvider.action(context,
                  MetricsEvent.ACTION_SETTINGS_BLUETOOTH_PAIR_DEVICES_WITHOUT_NAMES);
          }
          pair();// 如果未绑定，则进行配对
      }
  }

这里先获取mCachedDevice的绑定状态，如果已经连接，则询问是否断开；如果已经绑定未连接，则开始连接；如果未连接也未绑定，则开始配对。这里我们先看配对。配对调用的是本地的pair方法：
private void pair() {
if (!mCachedDevice.startPairing()) {
Utils.showError(getContext(), mCachedDevice.getName(),
R.string.bluetooth_pairing_error_message);
}
}

pair方法会调用/frameworks/base/packages/SettingsLib/src/com/android/settingslib/bluetooth/CachedBluetoothDevice.java中的startPairing，启动配对
2 framework
public boolean startPairing() {
// Pairing is unreliable while scanning, so cancel discovery
// 配对时，如果正在扫描，则取消扫描
if (mLocalAdapter.isDiscovering()) {
mLocalAdapter.cancelDiscovery();
}
// 开始配对
if (!mDevice.createBond()) {
return false;
}
// 标识位，配对完成后，自动连接
mConnectAfterPairing = true; // auto-connect after pairing
return true;
}

createBond调用/frameworks/base/core/java/android/bluetooth/BluetoothDevice.java
中的createBond方法：
public boolean createBond(int transport) {
final IBluetooth service = sService;
if (service == null) {
Log.e(TAG, “BT not enabled. Cannot create bond to Remote Device”);
return false;
}
if (TRANSPORT_AUTO > transport || transport > TRANSPORT_LE) {
throw new IllegalArgumentException(transport + " is not a valid Bluetooth transport");
}
try {
Log.i(TAG, "createBond() for device " + getAddress()
+ " called by pid: " + Process.myPid()
+ " tid: " + Process.myTid());
return service.createBond(this, transport);
} catch (RemoteException e) {
Log.e(TAG, “”, e);
}
return false;
}

createBond接着调用IBluetooth的createBond方法，通过aidl方式调用蓝牙远程服务。
3 Bluetooth app

和蓝牙扫描一样，实现IBluetooth接口的类是AdapterServiceBinder，AdapterServiceBinder实现IBluetooth.Stub接口，是/packages/apps/Bluetooth/src/com/android/bluetooth/btservice/AdapterService的私有内部类，AdapterServiceBinder收到的操作，都会转交AdapterService处理，所以会调用AdapterService的createBond方法。
boolean createBond(BluetoothDevice device, int transport) {
enforceCallingOrSelfPermission(BLUETOOTH_ADMIN_PERM,
“Need BLUETOOTH ADMIN permission”);
DeviceProperties deviceProp = mRemoteDevices.getDeviceProperties(device);
//属性检查
if (deviceProp != null && deviceProp.getBondState() != BluetoothDevice.BOND_NONE) {
return false;
}

    // Pairing is unreliable while scanning, so cancel discovery
    // Note, remove this when native stack improves
    cancelDiscoveryNative();// 配对过程，取消扫描
    // 给配对的状态机发消息，创建了BondStateMachine.CREATE_BOND
    Message msg = mBondStateMachine.obtainMessage(BondStateMachine.CREATE_BOND);
    msg.obj = device;
    msg.arg1 = transport;
    mBondStateMachine.sendMessage(msg);
    return true;
}

createBond 方法会检查一下远程设备属性信息，取消蓝牙扫描任务，将配对任务转交mBondStateMachine，由状态机处理该信息。
@Override
public boolean processMessage(Message msg) {

        BluetoothDevice dev = (BluetoothDevice)msg.obj;

        switch (msg.what) {
            case CREATE_BOND:
                OobData oobData = null;
                if (msg.getData() != null) {
                    oobData = msg.getData().getParcelable(OOBDATA);
                }

                result = createBond(dev, msg.arg1, oobData, false);
                break;
                ........................省略.................................
                }
        }

BondStateMachine处理服务发送过来的BondStateMachine.CREATE_BOND消息 ，在processMessage 中调用 BondStateMachine的createBond 方法:
private boolean createBond(BluetoothDevice dev, int transport, OobData oobData,
boolean transition) {
if (dev.getBondState() == BluetoothDevice.BOND_NONE) {
infoLog(“Bond address is:” + dev);
byte[] addr = Utils.getBytesFromAddress(dev.getAddress());
boolean result;
if (oobData != null) {// 判断是否借助其他硬件进行无绑定配对
result = mAdapterService.createBondOutOfBandNative(addr, transport, oobData);
} else {
result = mAdapterService.createBondNative(addr, transport);// 调用到JNI层，进行配对
}

          if (!result) {
              sendIntent(dev, BluetoothDevice.BOND_NONE, BluetoothDevice.UNBOND_REASON_REMOVED);
              return false;
          } else if (transition) {
              transitionTo(mPendingCommandState);
          }
          return true;
      }
      return false;
  }

createBondNative方法实现在/packages/apps/Bluetooth/jni/com_android_bluetooth_btservice_AdapterService.cpp中：
static jboolean createBondNative(JNIEnv* env, jobject obj, jbyteArray address,
jint transport) {
ALOGV("%s", func);

if (!sBluetoothInterface) return JNI_FALSE;

jbyte* addr = env->GetByteArrayElements(address, NULL);
if (addr == NULL) {
  jniThrowIOException(env, EINVAL);
  return JNI_FALSE;
}
// 调用到hal层的配对函数
int ret = sBluetoothInterface->create_bond((RawAddress*)addr, transport);
env->ReleaseByteArrayElements(address, addr, 0);
return (ret == BT_STATUS_SUCCESS) ? JNI_TRUE : JNI_FALSE;

}

这里通过create_bond这个方法调用到了蓝牙协议栈里面。
4 蓝牙协议栈

create_bond方法位于/system/bt/btif/src/bluetooth.cc：
static int create_bond(const RawAddress* bd_addr, int transport) {
/* sanity check */
if (!interface_ready()) return BT_STATUS_NOT_READY;

return btif_dm_create_bond(bd_addr, transport);

}

create_bond方法调用/system/bt/btif/src/btif_dm.cc的btif_dm_create_bond方法：
bt_status_t btif_dm_create_bond(const RawAddress* bd_addr, int transport) {
btif_dm_create_bond_cb_t create_bond_cb;
create_bond_cb.transport = transport;
create_bond_cb.bdaddr = *bd_addr;

BTIF_TRACE_EVENT("%s: bd_addr=%s, transport=%d", __func__,
                 bd_addr->ToString().c_str(), transport);
// 如果如果不是未配对状态，则取消配对
if (pairing_cb.state != BT_BOND_STATE_NONE) return BT_STATUS_BUSY;

btif_stats_add_bond_event(*bd_addr, BTIF_DM_FUNC_CREATE_BOND,
                          pairing_cb.state);// 添加了绑定事件

// 这里create_bond_cb在上面已经传入了要绑定的蓝牙地址，
// 会分别发送给底层两部分，最后会调用btif_dm_generic_evt
btif_transfer_context(btif_dm_generic_evt, BTIF_DM_CB_CREATE_BOND,
                      (char*)&create_bond_cb,
                      sizeof(btif_dm_create_bond_cb_t), NULL);

return BT_STATUS_SUCCESS;

}

btif_dm_create_bond方法最终调用了本地的btif_dm_generic_evt方法，传入BTIF_DM_CB_CREATE_BOND事件：
static void btif_dm_generic_evt(uint16_t event, char* p_param) {
BTIF_TRACE_EVENT("%s: event=%d", func, event);
switch (event) {
…省略…
case BTIF_DM_CB_CREATE_BOND: {// 根据传入的事件，走这里进行配对
pairing_cb.timeout_retries = NUM_TIMEOUT_RETRIES;
btif_dm_create_bond_cb_t* create_bond_cb =
(btif_dm_create_bond_cb_t*)p_param;
btif_dm_cb_create_bond(create_bond_cb->bdaddr, create_bond_cb->transport);
} break;
…省略…
}
}

这里又调用本地的btif_dm_cb_create_bond方法：
static void btif_dm_cb_create_bond(const RawAddress& bd_addr,
tBTA_TRANSPORT transport) {
bool is_hid = check_cod(&bd_addr, COD_HID_POINTING);
// 这里开始回调，将绑定状态变成绑定中
bond_state_changed(BT_STATUS_SUCCESS, bd_addr, BT_BOND_STATE_BONDING);
…省略…
if (is_hid && (device_type & BT_DEVICE_TYPE_BLE) == 0) {
bt_status_t status;
status = (bt_status_t)btif_hh_connect(&bd_addr);
if (status != BT_STATUS_SUCCESS)
bond_state_changed(status, bd_addr, BT_BOND_STATE_NONE);
} else {
BTA_DmBondByTransport(bd_addr, transport);// 第一次调用会走这里
}
/* Track originator of bond creation */
pairing_cb.is_local_initiated = true;
}

BTA_DmBondByTransport方法位于\system\bt\bta\dm\bta_dm_api.c：
void BTA_DmBondByTransport(BD_ADDR bd_addr, tBTA_TRANSPORT transport)
{
// 调用bta的bta_dm_bond方法
do_in_bta_thread(FROM_HERE, base::Bind(bta_dm_bond, bd_addr, transport));
}

这里通过do_in_bta_thread调用/system/bt/bta/dm/bta_dm_act.cc里面的bta_dm_bond方法，进入bta进程：
void bta_dm_bond (tBTA_DM_MSG *p_data)
{
tBTM_STATUS status;
tBTA_DM_SEC sec_event;
char *p_name;

if (p_data->bond.transport == BTA_TRANSPORT_UNKNOWN)
    status = BTM_SecBond ( p_data->bond.bd_addr, 0, NULL, 0 );
else
    status = BTM_SecBondByTransport ( p_data->bond.bd_addr, p_data->bond.transport, 0, NULL, 0 );


if (bta_dm_cb.p_sec_cback && (status != BTM_CMD_STARTED))
{

    memset(&sec_event, 0, sizeof(tBTA_DM_SEC));
    bdcpy(sec_event.auth_cmpl.bd_addr, p_data->bond.bd_addr);
    p_name = BTM_SecReadDevName(p_data->bond.bd_addr);
    if (p_name != NULL)
    {
        memcpy(sec_event.auth_cmpl.bd_name, p_name, (BD_NAME_LEN-1));
        sec_event.auth_cmpl.bd_name[BD_NAME_LEN-1] = 0;
    }

/* taken care of by memset [above]
sec_event.auth_cmpl.key_present = FALSE;
sec_event.auth_cmpl.success = FALSE;
/
sec_event.auth_cmpl.fail_reason = HCI_ERR_ILLEGAL_COMMAND;
if (status == BTM_SUCCESS)
{
sec_event.auth_cmpl.success = TRUE;
}
else
{
/ delete this device entry from Sec Dev DB */
bta_dm_remove_sec_dev_entry(p_data->bond.bd_addr);
}
bta_dm_cb.p_sec_cback(BTA_DM_AUTH_CMPL_EVT, &sec_event);// 配对事件回调
}
}

然后来到\system\bt\stack\btm\btm_sec.c的BTM_SecBondByTransport 方法：
tBTM_STATUS BTM_SecBondByTransport (BD_ADDR bd_addr, tBT_TRANSPORT transport,
UINT8 pin_len, UINT8 *p_pin, UINT32 trusted_mask[])
{
tBT_DEVICE_TYPE dev_type;
tBLE_ADDR_TYPE addr_type;

BTM_ReadDevInfo(bd_addr, &dev_type, &addr_type);
/* LE device, do SMP pairing */
if ((transport == BT_TRANSPORT_LE && (dev_type & BT_DEVICE_TYPE_BLE) == 0) ||
    (transport == BT_TRANSPORT_BR_EDR && (dev_type & BT_DEVICE_TYPE_BREDR) == 0))
{
    return BTM_ILLEGAL_ACTION;
}
return btm_sec_bond_by_transport(bd_addr, transport, pin_len, p_pin, trusted_mask);

}

调用本地btm_sec_bond_by_transport方法，这个方法内容很多，着重看这段代码：
if (!controller_get_interface()->supports_simple_pairing())//这里做一个判断，看是否支持简单配对方式
{
/* The special case when we authenticate keyboard. Set pin type to fixed /
/ It would be probably better to do it from the application, but it is /
/ complicated */
if (((p_dev_rec->dev_class[1] & BTM_COD_MAJOR_CLASS_MASK) == BTM_COD_MAJOR_PERIPHERAL)
&& (p_dev_rec->dev_class[2] & BTM_COD_MINOR_KEYBOARD)
&& (btm_cb.cfg.pin_type != HCI_PIN_TYPE_FIXED)) {
btm_cb.pin_type_changed = TRUE;
btsnd_hcic_write_pin_type (HCI_PIN_TYPE_FIXED);// 这里就在和hci层打交道
}
}

这里调用system/bt/stack/hcic/hcicmds.cc的btsnd_hcic_write_pin_type方法通过HCI向底层发送命令进行控制
void btsnd_hcic_write_pin_type (UINT8 type)
{
BT_HDR *p = (BT_HDR *)osi_malloc(HCI_CMD_BUF_SIZE);
UINT8 *pp = (UINT8 *)(p + 1);

p->len    = HCIC_PREAMBLE_SIZE + HCIC_PARAM_SIZE_WRITE_PARAM1;
p->offset = 0;

UINT16_TO_STREAM (pp, HCI_WRITE_PIN_TYPE);
UINT8_TO_STREAM  (pp, HCIC_PARAM_SIZE_WRITE_PARAM1);

UINT8_TO_STREAM (pp, type);

btu_hcif_send_cmd (LOCAL_BR_EDR_CONTROLLER_ID,  p);//这里是向hci层发命令，

}

可以看出，这里是通过和hci层的通信，host告诉controlor蓝牙地址、数据、命令等，从而控制其底层硬件发起配对操作。具体btu如何与hci通信，过程也是很繁琐，可以参考《Android BT STACK BTU 和 HCI之间的消息传递》这篇文章。
到此绑定的流程就结束了。有一个遗留问题就是绑定状态是如何返回给上层的呢？
5 配对状态改变的回传

上文我们在bta里面调用/system/bt/bta/dm/bta_dm_act.cc里面的bta_dm_bond方法，进行配对，这个方法里面有这样一段代码：
bta_dm_cb.p_sec_cback(BTA_DM_AUTH_CMPL_EVT, &sec_event);

这个就是bta的回调函数，回调事件是BTA_DM_AUTH_CMPL_EVT，根据这个事件标志，我们找到了 /system/bt/btif/src/btif_dm.cc里面的btif_dm_upstreams_evt方法，这个方法就是用于向上层回调消息的，相关代码是：
case BTA_DM_AUTH_CMPL_EVT:
btif_dm_auth_cmpl_evt(&p_data->auth_cmpl);
break;

可以看到是调用这个函数，返回配对完成的事件，这个函数代码很多这里就不引用了，无论配对成功还是失败，这里都会用 bond_state_changed这个方法进行处理：
static void bond_state_changed(bt_status_t status, const RawAddress& bd_addr,
bt_bond_state_t state) {
btif_stats_add_bond_event(bd_addr, BTIF_DM_FUNC_BOND_STATE_CHANGED, state);

// Send bonding state only once - based on outgoing/incoming we may receive
// duplicates
if ((pairing_cb.state == state) && (state == BT_BOND_STATE_BONDING)) {
  // Cross key pairing so send callback for static address
  if (!pairing_cb.static_bdaddr.IsEmpty()) {
    auto tmp = bd_addr;
    HAL_CBACK(bt_hal_cbacks, bond_state_changed_cb, status, &tmp, state);
  }
  return;
}

if (pairing_cb.bond_type == BOND_TYPE_TEMPORARY) state = BT_BOND_STATE_NONE;

BTIF_TRACE_DEBUG("%s: state=%d, prev_state=%d, sdp_attempts = %d", __func__,
                 state, pairing_cb.state, pairing_cb.sdp_attempts);

auto tmp = bd_addr;
HAL_CBACK(bt_hal_cbacks, bond_state_changed_cb, status, &tmp, state);

if (state == BT_BOND_STATE_BONDING) {
  pairing_cb.state = state;
  pairing_cb.bd_addr = bd_addr;
} else if ((state == BT_BOND_STATE_NONE) &&
    ((bd_addr == pairing_cb.bd_addr) ||
    (bd_addr == pairing_cb.static_bdaddr))) {
   memset(&pairing_cb, 0, sizeof(pairing_cb));
}else{
  if ((!pairing_cb.sdp_attempts)&&
        ((bd_addr == pairing_cb.bd_addr) ||
        (bd_addr == pairing_cb.static_bdaddr)))
    memset(&pairing_cb, 0, sizeof(pairing_cb));
  else
    BTIF_TRACE_DEBUG("%s: BR-EDR service discovery active", __func__);
}

}

可以发现也是通过HAL_CBACK(bt_hal_cbacks, bond_state_changed_cb, status, &tmp, state);这样的方法进行回调的，bond_state_changed_cb这个函数在bluetooth.h被定义对应的是com_android_bluetooth_btservice_AdapterService.cpp里的bond_state_changed_callback，关键代码如下：
sCallbackEnv->CallVoidMethod(sJniCallbacksObj, method_bondStateChangeCallback,
(jint)status, addr.get(), (jint)state);

这里将bondStateChangeCallback方法对应到jni的method_bondStateChangeCallback方法
jclass jniCallbackClass =
env->FindClass(“com/android/bluetooth/btservice/JniCallbacks”);
…省略…
method_bondStateChangeCallback =
env->GetMethodID(jniCallbackClass, “bondStateChangeCallback”, “(I[BI)V”);

就找到了JniCallbacks.java里面的bondStateChangeCallback方法
void bondStateChangeCallback(int status, byte[] address, int newState) {
mBondStateMachine.bondStateChangeCallback(status, address, newState);
}

接下来便进入了/packages/apps/Bluetooth/src/com/android/bluetooth/btservice/BondStateMachine.java状态机里面：
void bondStateChangeCallback(int status, byte[] address, int newState) {
BluetoothDevice device = mRemoteDevices.getDevice(address);

      if (device == null) {
          infoLog("No record of the device:" + device);
          // This device will be added as part of the BONDING_STATE_CHANGE intent processing
          // in sendIntent above
          device = mAdapter.getRemoteDevice(Utils.getAddressStringFromByte(address));
      }

      infoLog("bondStateChangeCallback: Status: " + status + " Address: " + device
              + " newState: " + newState);

      Message msg = obtainMessage(BONDING_STATE_CHANGE);
      msg.obj = device;

      if (newState == BOND_STATE_BONDED)
          msg.arg1 = BluetoothDevice.BOND_BONDED;
      else if (newState == BOND_STATE_BONDING)
          msg.arg1 = BluetoothDevice.BOND_BONDING;
      else
          msg.arg1 = BluetoothDevice.BOND_NONE;
      msg.arg2 = status;

      sendMessage(msg);
  }

状态机里面通过sendMessage进行配对状态的变更。
到此，配对流程就分析结束了。

作者：猫疏
链接：https://www.jianshu.com/p/0b748b11fa62
来源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。