Android 9.0 Bluetooth原始碼分析（三）藍芽配對流程
摘要：
1 UI
藍芽配對開始於settings裝置列表 /packages/apps/Settings/src/com/android/settings/bluetooth/DeviceListPreferenceFragment.java中。
DeviceListPr...
1 UI
藍芽配對開始於settings裝置列表 /packages/apps/Settings/src/com/android/settings/bluetooth/DeviceListPreferenceFragment.java中。
DeviceListPreferenceFragment是藍芽掃描到的裝置列表，點選其中一個藍芽裝置，呼叫onPreferenceTreeClick方法開始藍芽的配對過程。
@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();
//配對連線
onDevicePreferenceClick(btPreference);
return true;
}
return super.onPreferenceTreeClick(preferenceScreen, preference);
}
在本地onDevicePreferenceClick方法中呼叫/packages/apps/Settings/src/com/android/settings/bluetooth/BluetoothDevicePreference.java的onClicked方法：
void onClicked() {
Context context = getContext();
int bondState = mCachedDevice.getBondState();// 獲取裝置的繫結狀態
final MetricsFeatureProvider metricsFeatureProvider =
FeatureFactory.getFactory(context).getMetricsFeatureProvider();
if (mCachedDevice.isConnected()) {
metricsFeatureProvider.action(context,
MetricsEvent.ACTION_SETTINGS_BLUETOOTH_DISCONNECT);
askDisconnect(); // 已連線，詢問是否斷開連線
} else if (bondState == BluetoothDevice.BOND_BONDED) {
metricsFeatureProvider.action(context,
MetricsEvent.ACTION_SETTINGS_BLUETOOTH_CONNECT);
mCachedDevice.connect(true);// 已繫結，則進行連線
} 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();// 如果未繫結，則進行配對
}
}
這裡先獲取mCachedDevice的繫結狀態，如果已經連線，則詢問是否斷開；如果已經繫結未連線，則開始連線；如果未連線也未繫結，則開始配對。這裡我們先看配對。配對呼叫的是本地的pair方法：
private void pair() {
if (!mCachedDevice.startPairing()) {
Utils.showError(getContext(), mCachedDevice.getName(),
R.string.bluetooth_pairing_error_message);
}
}
pair方法會呼叫/frameworks/base/packages/SettingsLib/src/com/android/settingslib/bluetooth/CachedBluetoothDevice.java中的startPairing，啟動配對
2 framework
public boolean startPairing() {
// Pairing is unreliable while scanning, so cancel discovery
// 配對時，如果正在掃描，則取消掃描
if (mLocalAdapter.isDiscovering()) {
mLocalAdapter.cancelDiscovery();
}
// 開始配對
if (!mDevice.createBond()) {
return false;
}
// 標識位，配對完成後，自動連線
mConnectAfterPairing = true;// auto-connect after pairing
return true;
}
createBond呼叫/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接著呼叫IBluetooth的createBond方法，通過aidl方式呼叫藍芽遠端服務。
3 Bluetooth app
和藍芽掃描一樣，實現IBluetooth介面的類是AdapterServiceBinder，AdapterServiceBinder實現IBluetooth.Stub介面，是/packages/apps/Bluetooth/src/com/android/bluetooth/btservice/AdapterService的私有內部類，AdapterServiceBinder收到的操作，都會轉交AdapterService處理，所以會呼叫AdapterService的createBond方法。
boolean createBond(BluetoothDevice device, int transport) {
enforceCallingOrSelfPermission(BLUETOOTH_ADMIN_PERM,
"Need BLUETOOTH ADMIN permission");
DeviceProperties deviceProp = mRemoteDevices.getDeviceProperties(device);
//屬性檢查
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();// 配對過程，取消掃描
// 給配對的狀態機發訊息，建立了BondStateMachine.CREATE_BOND
Message msg = mBondStateMachine.obtainMessage(BondStateMachine.CREATE_BOND);
msg.obj = device;
msg.arg1 = transport;
mBondStateMachine.sendMessage(msg);
return true;
}
createBond 方法會檢查一下遠端裝置屬性資訊，取消藍芽掃描任務，將配對任務轉交mBondStateMachine，由狀態機處理該資訊。
@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處理服務傳送過來的BondStateMachine.CREATE_BOND訊息 ，在processMessage 中呼叫 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) {// 判斷是否藉助其他硬體進行無繫結配對
result = mAdapterService.createBondOutOfBandNative(addr, transport, oobData);
} else {
result = mAdapterService.createBondNative(addr, transport);// 呼叫到JNI層，進行配對
}
if (!result) {
sendIntent(dev, BluetoothDevice.BOND_NONE, BluetoothDevice.UNBOND_REASON_REMOVED);
return false;
} else if (transition) {
transitionTo(mPendingCommandState);
}
return true;
}
return false;
}
createBondNative方法實現在/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;
}
// 呼叫到hal層的配對函式
int ret = sBluetoothInterface->create_bond((RawAddress*)addr, transport);
env->ReleaseByteArrayElements(address, addr, 0);
return (ret == BT_STATUS_SUCCESS) ? JNI_TRUE : JNI_FALSE;
}
這裡通過create_bond這個方法呼叫到了藍芽協議棧裡面。
4 藍芽協議棧
create_bond方法位於/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方法呼叫/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);
// 如果如果不是未配對狀態，則取消配對
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);// 添加了繫結事件
// 這裡create_bond_cb在上面已經傳入了要繫結的藍芽地址，
// 會分別傳送給底層兩部分，最後會呼叫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方法最終呼叫了本地的btif_dm_generic_evt方法，傳入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: {// 根據傳入的事件，走這裡進行配對
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......................................
}
}
這裡又呼叫本地的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);
// 這裡開始回撥，將繫結狀態變成繫結中
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);// 第一次呼叫會走這裡
}
/*Trackoriginator of bond creation*/
pairing_cb.is_local_initiated = true;
}
BTA_DmBondByTransport方法位於\system\bt\bta\dm\bta_dm_api.c：
void BTA_DmBondByTransport(BD_ADDR bd_addr, tBTA_TRANSPORT transport)
{
// 呼叫bta的bta_dm_bond方法
do_in_bta_thread(FROM_HERE, base::Bind(bta_dm_bond, bd_addr, transport));
}
這裡通過do_in_bta_thread呼叫/system/bt/bta/dm/bta_dm_act.cc裡面的bta_dm_bond方法，進入bta程序：
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);// 配對事件回撥
}
}
然後來到\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_TYPEdev_type;
tBLE_ADDR_TYPEaddr_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);
}
呼叫本地btm_sec_bond_by_transport方法，這個方法內容很多，著重看這段程式碼：
if (!controller_get_interface()->supports_simple_pairing())//這裡做一個判斷，看是否支援簡單配對方式
{
/* 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);// 這裡就在和hci層打交道
}
}
這裡呼叫system/bt/stack/hcic/hcicmds.cc的btsnd_hcic_write_pin_type方法通過HCI向底層傳送命令進行控制
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);//這裡是向hci層發命令，
}
可以看出，這裡是通過和hci層的通訊，host告訴controlor藍芽地址、資料、命令等，從而控制其底層硬體發起配對操作。具體btu如何與hci通訊，過程也是很繁瑣，可以參考《Android BT STACK BTU 和 HCI之間的訊息傳遞》 這篇文章。
到此繫結的流程就結束了。有一個遺留問題就是繫結狀態是如何返回給上層的呢？
5 配對狀態改變的回傳
上文我們在bta裡面呼叫/system/bt/bta/dm/bta_dm_act.cc裡面的bta_dm_bond方法，進行配對，這個方法裡面有這樣一段程式碼：
bta_dm_cb.p_sec_cback(BTA_DM_AUTH_CMPL_EVT, &sec_event);
這個就是bta的回撥函式，回撥事件是BTA_DM_AUTH_CMPL_EVT，根據這個事件標誌，我們找到了 /system/bt/btif/src/btif_dm.cc裡面的btif_dm_upstreams_evt方法，這個方法就是用於向上層回撥訊息的，相關程式碼是：
case BTA_DM_AUTH_CMPL_EVT: btif_dm_auth_cmpl_evt(&p_data->auth_cmpl); break;
可以看到是呼叫這個函式，返回配對完成的事件，這個函式程式碼很多這裡就不引用了，無論配對成功還是失敗，這裡都會用 bond_state_changed這個方法進行處理：
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__);
}
}
可以發現也是通過HAL_CBACK(bt_hal_cbacks, bond_state_changed_cb, status, &tmp, state);這樣的方法進行回撥的，bond_state_changed_cb這個函式在bluetooth.h被定義對應的是com_android_bluetooth_btservice_AdapterService.cpp裡的bond_state_changed_callback，關鍵程式碼如下：
sCallbackEnv->CallVoidMethod(sJniCallbacksObj, method_bondStateChangeCallback, (jint)status, addr.get(), (jint)state);
這裡將bondStateChangeCallback方法對應到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裡面的bondStateChangeCallback方法
void bondStateChangeCallback(int status, byte[] address, int newState) {
mBondStateMachine.bondStateChangeCallback(status, address, newState);
}
接下來便進入了/packages/apps/Bluetooth/src/com/android/bluetooth/btservice/BondStateMachine.java狀態機裡面：
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);
}
狀態機裡面通過sendMessage進行配對狀態的變更。
到此，配對流程就分析結束了。