android从应用到驱动之—camera(2)---cameraHAL的实现

本文是camera系列博客,上一篇是:

android从应用到驱动之—camera(1)---程序调用流程

本来想用这一篇博客把cameraHAL的实现和流程都给写完的.搞了半天,东西实在是太多了.这篇先写cameraHAL的基本实现框架,下一篇在具体写camerahal的流程吧.

cameraHAL的实现:

对于初学者来说,最大的疑问是系统是如何调用hardware的.

这里就以camera来举例说明.

调用hardware的程序是cameraservice,我们就去它里面看看它是如何找到hardware的

先把源码贴上来:

/*
**
** Copyright (C) 2008, The Android Open Source Project
**
** 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.
*/

#define LOG_TAG "CameraService"
//#define LOG_NDEBUG 0

#include <stdio.h>
#include <sys/types.h>
#include <pthread.h>

#include <binder/IPCThreadState.h>
#include <binder/IServiceManager.h>
#include <binder/MemoryBase.h>
#include <binder/MemoryHeapBase.h>
#include <cutils/atomic.h>
#include <cutils/properties.h>
#include <gui/SurfaceTextureClient.h>
#include <hardware/hardware.h>
#include <media/AudioSystem.h>
#include <media/mediaplayer.h>
#include <surfaceflinger/ISurface.h>
#include <utils/Errors.h>
#include <utils/Log.h>
#include <utils/String16.h>

#include "CameraService.h"
#include "CameraHardwareInterface.h"

namespace android {

// ----------------------------------------------------------------------------
// Logging support -- this is for debugging only
// Use "adb shell dumpsys media.camera -v 1" to change it.
static volatile int32_t gLogLevel = 0;

#define LOG1(...) LOGD_IF(gLogLevel >= 1, __VA_ARGS__);
#define LOG2(...) LOGD_IF(gLogLevel >= 2, __VA_ARGS__);

static void setLogLevel(int level) {
android_atomic_write(level, &gLogLevel);
}

// ----------------------------------------------------------------------------

static int getCallingPid() {
return IPCThreadState::self()->getCallingPid();
}

static int getCallingUid() {
return IPCThreadState::self()->getCallingUid();
}

// ----------------------------------------------------------------------------

// This is ugly and only safe if we never re-create the CameraService, but
// should be ok for now.
static CameraService *gCameraService;

CameraService::CameraService()
:mSoundRef(0), mModule(0)
{
LOGI("CameraService started (pid=%d)", getpid());
gCameraService = this;
}

void CameraService::onFirstRef()
{
BnCameraService::onFirstRef();

if (hw_get_module(CAMERA_HARDWARE_MODULE_ID,
(const hw_module_t **)&mModule) < 0) {
LOGE("Could not load camera HAL module");
mNumberOfCameras = 0;
}
else {
mNumberOfCameras = mModule->get_number_of_cameras();
if (mNumberOfCameras > MAX_CAMERAS) {
LOGE("Number of cameras(%d) > MAX_CAMERAS(%d).",
mNumberOfCameras, MAX_CAMERAS);
mNumberOfCameras = MAX_CAMERAS;
}
for (int i = 0; i < mNumberOfCameras; i++) {
setCameraFree(i);
}
}

// Read the system property to determine if we have to use the
// AUDIO_STREAM_ENFORCED_AUDIBLE type.
char value[PROPERTY_VALUE_MAX];
property_get("ro.camera.sound.forced", value, "0");
if (strcmp(value, "0") != 0) {
mAudioStreamType = AUDIO_STREAM_ENFORCED_AUDIBLE;
} else {
mAudioStreamType = AUDIO_STREAM_MUSIC;
}
}

CameraService::~CameraService() {
for (int i = 0; i < mNumberOfCameras; i++) {
if (mBusy[i]) {
LOGE("camera %d is still in use in destructor!", i);
}
}

gCameraService = NULL;
}

int32_t CameraService::getNumberOfCameras() {
return mNumberOfCameras;
}

status_t CameraService::getCameraInfo(int cameraId,
struct CameraInfo* cameraInfo) {
if (!mModule) {
return NO_INIT;
}

if (cameraId < 0 || cameraId >= mNumberOfCameras) {
return BAD_VALUE;
}

struct camera_info info;
status_t rc = mModule->get_camera_info(cameraId, &info);
cameraInfo->facing = info.facing;
cameraInfo->orientation = info.orientation;
return rc;
}

sp<ICamera> CameraService::connect(
const sp<ICameraClient>& cameraClient, int cameraId) {
int callingPid = getCallingPid();
sp<CameraHardwareInterface> hardware = NULL;

LOG1("CameraService::connect E (pid %d, id %d)", callingPid, cameraId);

if (!mModule) {
LOGE("Camera HAL module not loaded");
return NULL;
}

sp<Client> client;
if (cameraId < 0 || cameraId >= mNumberOfCameras) {
LOGE("CameraService::connect X (pid %d) rejected (invalid cameraId %d).",
callingPid, cameraId);
return NULL;
}

char value[PROPERTY_VALUE_MAX];
property_get("sys.secpolicy.camera.disabled", value, "0");
if (strcmp(value, "1") == 0) {
// Camera is disabled by DevicePolicyManager.
LOGI("Camera is disabled. connect X (pid %d) rejected", callingPid);
return NULL;
}

Mutex::Autolock lock(mServiceLock);
if (mClient[cameraId] != 0) {
client = mClient[cameraId].promote();
if (client != 0) {
if (cameraClient->asBinder() == client->getCameraClient()->asBinder()) {
LOG1("CameraService::connect X (pid %d) (the same client)",
callingPid);
return client;
} else {
LOGW("CameraService::connect X (pid %d) rejected (existing client).",
callingPid);
return NULL;
}
}
mClient[cameraId].clear();
}

if (mBusy[cameraId]) {
LOGW("CameraService::connect X (pid %d) rejected"
" (camera %d is still busy).", callingPid, cameraId);
return NULL;
}

struct camera_info info;
if (mModule->get_camera_info(cameraId, &info) != OK) {
LOGE("Invalid camera id %d", cameraId);
return NULL;
}

char camera_device_name[10];
snprintf(camera_device_name, sizeof(camera_device_name), "%d", cameraId);

hardware = new CameraHardwareInterface(camera_device_name);
if (hardware->initialize(&mModule->common) != OK) {
hardware.clear();
return NULL;
}

client = new Client(this, cameraClient, hardware, cameraId, info.facing, callingPid);
mClient[cameraId] = client;
LOG1("CameraService::connect X");
return client;
}

void CameraService::removeClient(const sp<ICameraClient>& cameraClient) {
int callingPid = getCallingPid();
LOG1("CameraService::removeClient E (pid %d)", callingPid);

for (int i = 0; i < mNumberOfCameras; i++) {
// Declare this before the lock to make absolutely sure the
// destructor won't be called with the lock held.
sp<Client> client;

Mutex::Autolock lock(mServiceLock);

// This happens when we have already disconnected (or this is
// just another unused camera).
if (mClient[i] == 0) continue;

// Promote mClient. It can fail if we are called from this path:
// Client::~Client() -> disconnect() -> removeClient().
client = mClient[i].promote();

if (client == 0) {
mClient[i].clear();
continue;
}

if (cameraClient->asBinder() == client->getCameraClient()->asBinder()) {
// Found our camera, clear and leave.
LOG1("removeClient: clear camera %d", i);
mClient[i].clear();
break;
}
}

LOG1("CameraService::removeClient X (pid %d)", callingPid);
}

sp<CameraService::Client> CameraService::getClientById(int cameraId) {
if (cameraId < 0 || cameraId >= mNumberOfCameras) return NULL;
return mClient[cameraId].promote();
}

status_t CameraService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) {
// Permission checks
switch (code) {
case BnCameraService::CONNECT:
const int pid = getCallingPid();
const int self_pid = getpid();
if (pid != self_pid) {
// we're called from a different process, do the real check
if (!checkCallingPermission(
String16("android.permission.CAMERA"))) {
const int uid = getCallingUid();
LOGE("Permission Denial: "
"can't use the camera pid=%d, uid=%d", pid, uid);
return PERMISSION_DENIED;
}
}
break;
}

return BnCameraService::onTransact(code, data, reply, flags);
}

// The reason we need this busy bit is a new CameraService::connect() request
// may come in while the previous Client's destructor has not been run or is
// still running. If the last strong reference of the previous Client is gone
// but the destructor has not been finished, we should not allow the new Client
// to be created because we need to wait for the previous Client to tear down
// the hardware first.
void CameraService::setCameraBusy(int cameraId) {
android_atomic_write(1, &mBusy[cameraId]);
}

void CameraService::setCameraFree(int cameraId) {
android_atomic_write(0, &mBusy[cameraId]);
}

// We share the media players for shutter and recording sound for all clients.
// A reference count is kept to determine when we will actually release the
// media players.

MediaPlayer* CameraService::newMediaPlayer(const char *file) {
MediaPlayer* mp = new MediaPlayer();
if (mp->setDataSource(file, NULL) == NO_ERROR) {
mp->setAudioStreamType(mAudioStreamType);
mp->prepare();
} else {
LOGE("Failed to load CameraService sounds: %s", file);
return NULL;
}
return mp;
}

void CameraService::loadSound() {
Mutex::Autolock lock(mSoundLock);
LOG1("CameraService::loadSound ref=%d", mSoundRef);
if (mSoundRef++) return;

mSoundPlayer[SOUND_SHUTTER] = newMediaPlayer("/system/media/audio/ui/camera_click.ogg");
mSoundPlayer[SOUND_RECORDING] = newMediaPlayer("/system/media/audio/ui/VideoRecord.ogg");
}

void CameraService::releaseSound() {
Mutex::Autolock lock(mSoundLock);
LOG1("CameraService::releaseSound ref=%d", mSoundRef);
if (--mSoundRef) return;

for (int i = 0; i < NUM_SOUNDS; i++) {
if (mSoundPlayer[i] != 0) {
mSoundPlayer[i]->disconnect();
mSoundPlayer[i].clear();
}
}
}

void CameraService::playSound(sound_kind kind) {
LOG1("playSound(%d)", kind);
Mutex::Autolock lock(mSoundLock);
sp<MediaPlayer> player = mSoundPlayer[kind];
if (player != 0) {
player->seekTo(0);
player->start();
}
}

// ----------------------------------------------------------------------------

CameraService::Client::Client(const sp<CameraService>& cameraService,
const sp<ICameraClient>& cameraClient,
const sp<CameraHardwareInterface>& hardware,
int cameraId, int cameraFacing, int clientPid) {
int callingPid = getCallingPid();
LOG1("Client::Client E (pid %d)", callingPid);

mCameraService = cameraService;
mCameraClient = cameraClient;
mHardware = hardware;
mCameraId = cameraId;
mCameraFacing = cameraFacing;
mClientPid = clientPid;
mMsgEnabled = 0;
mSurface = 0;
mPreviewWindow = 0;
mHardware->setCallbacks(notifyCallback,
dataCallback,
dataCallbackTimestamp,
(void *)cameraId);

// Enable zoom, error, focus, and metadata messages by default
enableMsgType(CAMERA_MSG_ERROR | CAMERA_MSG_ZOOM | CAMERA_MSG_FOCUS |
CAMERA_MSG_PREVIEW_METADATA);

// Callback is disabled by default
mPreviewCallbackFlag = CAMERA_FRAME_CALLBACK_FLAG_NOOP;
mOrientation = getOrientation(0, mCameraFacing == CAMERA_FACING_FRONT);
mPlayShutterSound = true;
cameraService->setCameraBusy(cameraId);
cameraService->loadSound();
LOG1("Client::Client X (pid %d)", callingPid);
}

// tear down the client
CameraService::Client::~Client() {
int callingPid = getCallingPid();
LOG1("Client::~Client E (pid %d, this %p)", callingPid, this);

// set mClientPid to let disconnet() tear down the hardware
mClientPid = callingPid;
disconnect();
mCameraService->releaseSound();
LOG1("Client::~Client X (pid %d, this %p)", callingPid, this);
}

// ----------------------------------------------------------------------------

status_t CameraService::Client::checkPid() const {
int callingPid = getCallingPid();
if (callingPid == mClientPid) return NO_ERROR;

LOGW("attempt to use a locked camera from a different process"
" (old pid %d, new pid %d)", mClientPid, callingPid);
return EBUSY;
}

status_t CameraService::Client::checkPidAndHardware() const {
status_t result = checkPid();
if (result != NO_ERROR) return result;
if (mHardware == 0) {
LOGE("attempt to use a camera after disconnect() (pid %d)", getCallingPid());
return INVALID_OPERATION;
}
return NO_ERROR;
}

status_t CameraService::Client::lock() {
int callingPid = getCallingPid();
LOG1("lock (pid %d)", callingPid);
Mutex::Autolock lock(mLock);

// lock camera to this client if the the camera is unlocked
if (mClientPid == 0) {
mClientPid = callingPid;
return NO_ERROR;
}

// returns NO_ERROR if the client already owns the camera, EBUSY otherwise
return checkPid();
}

status_t CameraService::Client::unlock() {
int callingPid = getCallingPid();
LOG1("unlock (pid %d)", callingPid);
Mutex::Autolock lock(mLock);

// allow anyone to use camera (after they lock the camera)
status_t result = checkPid();
if (result == NO_ERROR) {
if (mHardware->recordingEnabled()) {
LOGE("Not allowed to unlock camera during recording.");
return INVALID_OPERATION;
}
mClientPid = 0;
LOG1("clear mCameraClient (pid %d)", callingPid);
// we need to remove the reference to ICameraClient so that when the app
// goes away, the reference count goes to 0.
mCameraClient.clear();
}
return result;
}

// connect a new client to the camera
status_t CameraService::Client::connect(const sp<ICameraClient>& client) {
int callingPid = getCallingPid();
LOG1("connect E (pid %d)", callingPid);
Mutex::Autolock lock(mLock);

if (mClientPid != 0 && checkPid() != NO_ERROR) {
LOGW("Tried to connect to a locked camera (old pid %d, new pid %d)",
mClientPid, callingPid);
return EBUSY;
}

if (mCameraClient != 0 && (client->asBinder() == mCameraClient->asBinder())) {
LOG1("Connect to the same client");
return NO_ERROR;
}

mPreviewCallbackFlag = CAMERA_FRAME_CALLBACK_FLAG_NOOP;
mClientPid = callingPid;
mCameraClient = client;

LOG1("connect X (pid %d)", callingPid);
return NO_ERROR;
}

static void disconnectWindow(const sp<ANativeWindow>& window) {
if (window != 0) {
status_t result = native_window_api_disconnect(window.get(),
NATIVE_WINDOW_API_CAMERA);
if (result != NO_ERROR) {
LOGW("native_window_api_disconnect failed: %s (%d)", strerror(-result),
result);
}
}
}

void CameraService::Client::disconnect() {
int callingPid = getCallingPid();
LOG1("disconnect E (pid %d)", callingPid);
Mutex::Autolock lock(mLock);

if (checkPid() != NO_ERROR) {
LOGW("different client - don't disconnect");
return;
}

if (mClientPid <= 0) {
LOG1("camera is unlocked (mClientPid = %d), don't tear down hardware", mClientPid);
return;
}

// Make sure disconnect() is done once and once only, whether it is called
// from the user directly, or called by the destructor.
if (mHardware == 0) return;

LOG1("hardware teardown");
// Before destroying mHardware, we must make sure it's in the
// idle state.
// Turn off all messages.
disableMsgType(CAMERA_MSG_ALL_MSGS);
mHardware->stopPreview();
mHardware->cancelPicture();
// Release the hardware resources.
mHardware->release();

// Release the held ANativeWindow resources.
if (mPreviewWindow != 0) {
disconnectWindow(mPreviewWindow);
mPreviewWindow = 0;
mHardware->setPreviewWindow(mPreviewWindow);
}
mHardware.clear();

mCameraService->removeClient(mCameraClient);
mCameraService->setCameraFree(mCameraId);

LOG1("disconnect X (pid %d)", callingPid);
}

// ----------------------------------------------------------------------------

status_t CameraService::Client::setPreviewWindow(const sp<IBinder>& binder,
const sp<ANativeWindow>& window) {
Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

// return if no change in surface.
if (binder == mSurface) {
return NO_ERROR;
}

if (window != 0) {
result = native_window_api_connect(window.get(), NATIVE_WINDOW_API_CAMERA);
if (result != NO_ERROR) {
LOGE("native_window_api_connect failed: %s (%d)", strerror(-result),
result);
return result;
}
}

// If preview has been already started, register preview buffers now.
if (mHardware->previewEnabled()) {
if (window != 0) {
native_window_set_scaling_mode(window.get(),
NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
native_window_set_buffers_transform(window.get(), mOrientation);
result = mHardware->setPreviewWindow(window);
}
}

if (result == NO_ERROR) {
// Everything has succeeded.  Disconnect the old window and remember the
// new window.
disconnectWindow(mPreviewWindow);
mSurface = binder;
mPreviewWindow = window;
} else {
// Something went wrong after we connected to the new window, so
// disconnect here.
disconnectWindow(window);
}

return result;
}

// set the Surface that the preview will use
status_t CameraService::Client::setPreviewDisplay(const sp<Surface>& surface) {
LOG1("setPreviewDisplay(%p) (pid %d)", surface.get(), getCallingPid());

sp<IBinder> binder(surface != 0 ? surface->asBinder() : 0);
sp<ANativeWindow> window(surface);
return setPreviewWindow(binder, window);
}

// set the SurfaceTexture that the preview will use
status_t CameraService::Client::setPreviewTexture(
const sp<ISurfaceTexture>& surfaceTexture) {
LOG1("setPreviewTexture(%p) (pid %d)", surfaceTexture.get(),
getCallingPid());

sp<IBinder> binder;
sp<ANativeWindow> window;
if (surfaceTexture != 0) {
binder = surfaceTexture->asBinder();
window = new SurfaceTextureClient(surfaceTexture);
}
return setPreviewWindow(binder, window);
}

// set the preview callback flag to affect how the received frames from
// preview are handled.
void CameraService::Client::setPreviewCallbackFlag(int callback_flag) {
LOG1("setPreviewCallbackFlag(%d) (pid %d)", callback_flag, getCallingPid());
Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return;

mPreviewCallbackFlag = callback_flag;
if (mPreviewCallbackFlag & CAMERA_FRAME_CALLBACK_FLAG_ENABLE_MASK) {
enableMsgType(CAMERA_MSG_PREVIEW_FRAME);
} else {
disableMsgType(CAMERA_MSG_PREVIEW_FRAME);
}
}

// start preview mode
status_t CameraService::Client::startPreview() {
LOG1("startPreview (pid %d)", getCallingPid());
return startCameraMode(CAMERA_PREVIEW_MODE);
}

// start recording mode
status_t CameraService::Client::startRecording() {
LOG1("startRecording (pid %d)", getCallingPid());
return startCameraMode(CAMERA_RECORDING_MODE);
}

// start preview or recording
status_t CameraService::Client::startCameraMode(camera_mode mode) {
LOG1("startCameraMode(%d)", mode);
Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

switch(mode) {
case CAMERA_PREVIEW_MODE:
if (mSurface == 0 && mPreviewWindow == 0) {
LOG1("mSurface is not set yet.");
// still able to start preview in this case.
}
return startPreviewMode();
case CAMERA_RECORDING_MODE:
if (mSurface == 0 && mPreviewWindow == 0) {
LOGE("mSurface or mPreviewWindow must be set before startRecordingMode.");
return INVALID_OPERATION;
}
return startRecordingMode();
default:
return UNKNOWN_ERROR;
}
}

status_t CameraService::Client::startPreviewMode() {
LOG1("startPreviewMode");
status_t result = NO_ERROR;

// if preview has been enabled, nothing needs to be done
if (mHardware->previewEnabled()) {
return NO_ERROR;
}

if (mPreviewWindow != 0) {
native_window_set_scaling_mode(mPreviewWindow.get(),
NATIVE_WINDOW_SCALING_MODE_SCALE_TO_WINDOW);
native_window_set_buffers_transform(mPreviewWindow.get(),
mOrientation);
}
mHardware->setPreviewWindow(mPreviewWindow);
result = mHardware->startPreview();

return result;
}

status_t CameraService::Client::startRecordingMode() {
LOG1("startRecordingMode");
status_t result = NO_ERROR;

// if recording has been enabled, nothing needs to be done
if (mHardware->recordingEnabled()) {
return NO_ERROR;
}

// if preview has not been started, start preview first
if (!mHardware->previewEnabled()) {
result = startPreviewMode();
if (result != NO_ERROR) {
return result;
}
}

// start recording mode
enableMsgType(CAMERA_MSG_VIDEO_FRAME);
mCameraService->playSound(SOUND_RECORDING);
result = mHardware->startRecording();
if (result != NO_ERROR) {
LOGE("mHardware->startRecording() failed with status %d", result);
}
return result;
}

// stop preview mode
void CameraService::Client::stopPreview() {
LOG1("stopPreview (pid %d)", getCallingPid());
Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return;

disableMsgType(CAMERA_MSG_PREVIEW_FRAME);
mHardware->stopPreview();

mPreviewBuffer.clear();
}

// stop recording mode
void CameraService::Client::stopRecording() {
LOG1("stopRecording (pid %d)", getCallingPid());
Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return;

mCameraService->playSound(SOUND_RECORDING);
disableMsgType(CAMERA_MSG_VIDEO_FRAME);
mHardware->stopRecording();

mPreviewBuffer.clear();
}

// release a recording frame
void CameraService::Client::releaseRecordingFrame(const sp<IMemory>& mem) {
Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return;
mHardware->releaseRecordingFrame(mem);
}

status_t CameraService::Client::storeMetaDataInBuffers(bool enabled)
{
LOG1("storeMetaDataInBuffers: %s", enabled? "true": "false");
Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) {
return UNKNOWN_ERROR;
}
return mHardware->storeMetaDataInBuffers(enabled);
}

bool CameraService::Client::previewEnabled() {
LOG1("previewEnabled (pid %d)", getCallingPid());

Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return false;
return mHardware->previewEnabled();
}

bool CameraService::Client::recordingEnabled() {
LOG1("recordingEnabled (pid %d)", getCallingPid());

Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return false;
return mHardware->recordingEnabled();
}

status_t CameraService::Client::autoFocus() {
LOG1("autoFocus (pid %d)", getCallingPid());

Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

return mHardware->autoFocus();
}

status_t CameraService::Client::cancelAutoFocus() {
LOG1("cancelAutoFocus (pid %d)", getCallingPid());

Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

return mHardware->cancelAutoFocus();
}

// take a picture - image is returned in callback
status_t CameraService::Client::takePicture(int msgType) {
LOG1("takePicture (pid %d): 0x%x", getCallingPid(), msgType);

Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

if ((msgType & CAMERA_MSG_RAW_IMAGE) &&
(msgType & CAMERA_MSG_RAW_IMAGE_NOTIFY)) {
LOGE("CAMERA_MSG_RAW_IMAGE and CAMERA_MSG_RAW_IMAGE_NOTIFY"
" cannot be both enabled");
return BAD_VALUE;
}

// We only accept picture related message types
// and ignore other types of messages for takePicture().
int picMsgType = msgType
& (CAMERA_MSG_SHUTTER |
CAMERA_MSG_POSTVIEW_FRAME |
CAMERA_MSG_RAW_IMAGE |
CAMERA_MSG_RAW_IMAGE_NOTIFY |
CAMERA_MSG_COMPRESSED_IMAGE);

enableMsgType(picMsgType);

return mHardware->takePicture();
}

// set preview/capture parameters - key/value pairs
status_t CameraService::Client::setParameters(const String8& params) {
LOG1("setParameters (pid %d) (%s)", getCallingPid(), params.string());

Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

CameraParameters p(params);
return mHardware->setParameters(p);
}

// get preview/capture parameters - key/value pairs
String8 CameraService::Client::getParameters() const {
Mutex::Autolock lock(mLock);
if (checkPidAndHardware() != NO_ERROR) return String8();

String8 params(mHardware->getParameters().flatten());
LOG1("getParameters (pid %d) (%s)", getCallingPid(), params.string());
return params;
}

// enable shutter sound
status_t CameraService::Client::enableShutterSound(bool enable) {
LOG1("enableShutterSound (pid %d)", getCallingPid());

status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

if (enable) {
mPlayShutterSound = true;
return OK;
}

// Disabling shutter sound may not be allowed. In that case only
// allow the mediaserver process to disable the sound.
char value[PROPERTY_VALUE_MAX];
property_get("ro.camera.sound.forced", value, "0");
if (strcmp(value, "0") != 0) {
// Disabling shutter sound is not allowed. Deny if the current
// process is not mediaserver.
if (getCallingPid() != getpid()) {
LOGE("Failed to disable shutter sound. Permission denied (pid %d)", getCallingPid());
return PERMISSION_DENIED;
}
}

mPlayShutterSound = false;
return OK;
}

status_t CameraService::Client::sendCommand(int32_t cmd, int32_t arg1, int32_t arg2) {
LOG1("sendCommand (pid %d)", getCallingPid());
int orientation;
Mutex::Autolock lock(mLock);
status_t result = checkPidAndHardware();
if (result != NO_ERROR) return result;

if (cmd == CAMERA_CMD_SET_DISPLAY_ORIENTATION) {
// Mirror the preview if the camera is front-facing.
orientation = getOrientation(arg1, mCameraFacing == CAMERA_FACING_FRONT);
if (orientation == -1) return BAD_VALUE;

if (mOrientation != orientation) {
mOrientation = orientation;
if (mPreviewWindow != 0) {
native_window_set_buffers_transform(mPreviewWindow.get(),
mOrientation);
}
}
return OK;
} else if (cmd == CAMERA_CMD_ENABLE_SHUTTER_SOUND) {
switch (arg1) {
case 0:
enableShutterSound(false);
break;
case 1:
enableShutterSound(true);
break;
default:
return BAD_VALUE;
}
return OK;
} else if (cmd == CAMERA_CMD_PLAY_RECORDING_SOUND) {
mCameraService->playSound(SOUND_RECORDING);
}

return mHardware->sendCommand(cmd, arg1, arg2);
}

// ----------------------------------------------------------------------------

void CameraService::Client::enableMsgType(int32_t msgType) {
android_atomic_or(msgType, &mMsgEnabled);
mHardware->enableMsgType(msgType);
}

void CameraService::Client::disableMsgType(int32_t msgType) {
android_atomic_and(~msgType, &mMsgEnabled);
mHardware->disableMsgType(msgType);
}

#define CHECK_MESSAGE_INTERVAL 10 // 10ms
bool CameraService::Client::lockIfMessageWanted(int32_t msgType) {
int sleepCount = 0;
while (mMsgEnabled & msgType) {
if (mLock.tryLock() == NO_ERROR) {
if (sleepCount > 0) {
LOG1("lockIfMessageWanted(%d): waited for %d ms",
msgType, sleepCount * CHECK_MESSAGE_INTERVAL);
}
return true;
}
if (sleepCount++ == 0) {
LOG1("lockIfMessageWanted(%d): enter sleep", msgType);
}
usleep(CHECK_MESSAGE_INTERVAL * 1000);
}
LOGW("lockIfMessageWanted(%d): dropped unwanted message", msgType);
return false;
}

// ----------------------------------------------------------------------------

// Converts from a raw pointer to the client to a strong pointer during a
// hardware callback. This requires the callbacks only happen when the client
// is still alive.
sp<CameraService::Client> CameraService::Client::getClientFromCookie(void* user) {
sp<Client> client = gCameraService->getClientById((int) user);

// This could happen if the Client is in the process of shutting down (the
// last strong reference is gone, but the destructor hasn't finished
// stopping the hardware).
if (client == 0) return NULL;

// The checks below are not necessary and are for debugging only.
if (client->mCameraService.get() != gCameraService) {
LOGE("mismatch service!");
return NULL;
}

if (client->mHardware == 0) {
LOGE("mHardware == 0: callback after disconnect()?");
return NULL;
}

return client;
}

// Callback messages can be dispatched to internal handlers or pass to our
// client's callback functions, depending on the message type.
//
// notifyCallback:
//      CAMERA_MSG_SHUTTER              handleShutter
//      (others)                        c->notifyCallback
// dataCallback:
//      CAMERA_MSG_PREVIEW_FRAME        handlePreviewData
//      CAMERA_MSG_POSTVIEW_FRAME       handlePostview
//      CAMERA_MSG_RAW_IMAGE            handleRawPicture
//      CAMERA_MSG_COMPRESSED_IMAGE     handleCompressedPicture
//      (others)                        c->dataCallback
// dataCallbackTimestamp
//      (others)                        c->dataCallbackTimestamp
//
// NOTE: the *Callback functions grab mLock of the client before passing
// control to handle* functions. So the handle* functions must release the
// lock before calling the ICameraClient's callbacks, so those callbacks can
// invoke methods in the Client class again (For example, the preview frame
// callback may want to releaseRecordingFrame). The handle* functions must
// release the lock after all accesses to member variables, so it must be
// handled very carefully.

void CameraService::Client::notifyCallback(int32_t msgType, int32_t ext1,
int32_t ext2, void* user) {
LOG2("notifyCallback(%d)", msgType);

sp<Client> client = getClientFromCookie(user);
if (client == 0) return;
if (!client->lockIfMessageWanted(msgType)) return;

switch (msgType) {
case CAMERA_MSG_SHUTTER:
// ext1 is the dimension of the yuv picture.
client->handleShutter();
break;
default:
client->handleGenericNotify(msgType, ext1, ext2);
break;
}
}

void CameraService::Client::dataCallback(int32_t msgType,
const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata, void* user) {
LOG2("dataCallback(%d)", msgType);

sp<Client> client = getClientFromCookie(user);
if (client == 0) return;
if (!client->lockIfMessageWanted(msgType)) return;

if (dataPtr == 0 && metadata == NULL) {
LOGE("Null data returned in data callback");
client->handleGenericNotify(CAMERA_MSG_ERROR, UNKNOWN_ERROR, 0);
return;
}

switch (msgType & ~CAMERA_MSG_PREVIEW_METADATA) {
case CAMERA_MSG_PREVIEW_FRAME:
client->handlePreviewData(msgType, dataPtr, metadata);
break;
case CAMERA_MSG_POSTVIEW_FRAME:
client->handlePostview(dataPtr);
break;
case CAMERA_MSG_RAW_IMAGE:
client->handleRawPicture(dataPtr);
break;
case CAMERA_MSG_COMPRESSED_IMAGE:
client->handleCompressedPicture(dataPtr);
break;
default:
client->handleGenericData(msgType, dataPtr, metadata);
break;
}
}

void CameraService::Client::dataCallbackTimestamp(nsecs_t timestamp,
int32_t msgType, const sp<IMemory>& dataPtr, void* user) {
LOG2("dataCallbackTimestamp(%d)", msgType);

sp<Client> client = getClientFromCookie(user);
if (client == 0) return;
if (!client->lockIfMessageWanted(msgType)) return;

if (dataPtr == 0) {
LOGE("Null data returned in data with timestamp callback");
client->handleGenericNotify(CAMERA_MSG_ERROR, UNKNOWN_ERROR, 0);
return;
}

client->handleGenericDataTimestamp(timestamp, msgType, dataPtr);
}

// snapshot taken callback
void CameraService::Client::handleShutter(void) {
if (mPlayShutterSound) {
mCameraService->playSound(SOUND_SHUTTER);
}

sp<ICameraClient> c = mCameraClient;
if (c != 0) {
mLock.unlock();
c->notifyCallback(CAMERA_MSG_SHUTTER, 0, 0);
if (!lockIfMessageWanted(CAMERA_MSG_SHUTTER)) return;
}
disableMsgType(CAMERA_MSG_SHUTTER);

mLock.unlock();
}

// preview callback - frame buffer update
void CameraService::Client::handlePreviewData(int32_t msgType,
const sp<IMemory>& mem,
camera_frame_metadata_t *metadata) {
ssize_t offset;
size_t size;
sp<IMemoryHeap> heap = mem->getMemory(&offset, &size);

// local copy of the callback flags
int flags = mPreviewCallbackFlag;

// is callback enabled?
if (!(flags & CAMERA_FRAME_CALLBACK_FLAG_ENABLE_MASK)) {
// If the enable bit is off, the copy-out and one-shot bits are ignored
LOG2("frame callback is disabled");
mLock.unlock();
return;
}

// hold a strong pointer to the client
sp<ICameraClient> c = mCameraClient;

// clear callback flags if no client or one-shot mode
if (c == 0 || (mPreviewCallbackFlag & CAMERA_FRAME_CALLBACK_FLAG_ONE_SHOT_MASK)) {
LOG2("Disable preview callback");
mPreviewCallbackFlag &= ~(CAMERA_FRAME_CALLBACK_FLAG_ONE_SHOT_MASK |
CAMERA_FRAME_CALLBACK_FLAG_COPY_OUT_MASK |
CAMERA_FRAME_CALLBACK_FLAG_ENABLE_MASK);
disableMsgType(CAMERA_MSG_PREVIEW_FRAME);
}

if (c != 0) {
// Is the received frame copied out or not?
if (flags & CAMERA_FRAME_CALLBACK_FLAG_COPY_OUT_MASK) {
LOG2("frame is copied");
copyFrameAndPostCopiedFrame(msgType, c, heap, offset, size, metadata);
} else {
LOG2("frame is forwarded");
mLock.unlock();
c->dataCallback(msgType, mem, metadata);
}
} else {
mLock.unlock();
}
}

// picture callback - postview image ready
void CameraService::Client::handlePostview(const sp<IMemory>& mem) {
disableMsgType(CAMERA_MSG_POSTVIEW_FRAME);

sp<ICameraClient> c = mCameraClient;
mLock.unlock();
if (c != 0) {
c->dataCallback(CAMERA_MSG_POSTVIEW_FRAME, mem, NULL);
}
}

// picture callback - raw image ready
void CameraService::Client::handleRawPicture(const sp<IMemory>& mem) {
disableMsgType(CAMERA_MSG_RAW_IMAGE);

ssize_t offset;
size_t size;
sp<IMemoryHeap> heap = mem->getMemory(&offset, &size);

sp<ICameraClient> c = mCameraClient;
mLock.unlock();
if (c != 0) {
c->dataCallback(CAMERA_MSG_RAW_IMAGE, mem, NULL);
}
}

// picture callback - compressed picture ready
void CameraService::Client::handleCompressedPicture(const sp<IMemory>& mem) {
disableMsgType(CAMERA_MSG_COMPRESSED_IMAGE);

sp<ICameraClient> c = mCameraClient;
mLock.unlock();
if (c != 0) {
c->dataCallback(CAMERA_MSG_COMPRESSED_IMAGE, mem, NULL);
}
}

void CameraService::Client::handleGenericNotify(int32_t msgType,
int32_t ext1, int32_t ext2) {
sp<ICameraClient> c = mCameraClient;
mLock.unlock();
if (c != 0) {
c->notifyCallback(msgType, ext1, ext2);
}
}

void CameraService::Client::handleGenericData(int32_t msgType,
const sp<IMemory>& dataPtr, camera_frame_metadata_t *metadata) {
sp<ICameraClient> c = mCameraClient;
mLock.unlock();
if (c != 0) {
c->dataCallback(msgType, dataPtr, metadata);
}
}

void CameraService::Client::handleGenericDataTimestamp(nsecs_t timestamp,
int32_t msgType, const sp<IMemory>& dataPtr) {
sp<ICameraClient> c = mCameraClient;
mLock.unlock();
if (c != 0) {
c->dataCallbackTimestamp(timestamp, msgType, dataPtr);
}
}

void CameraService::Client::copyFrameAndPostCopiedFrame(
int32_t msgType, const sp<ICameraClient>& client,
const sp<IMemoryHeap>& heap, size_t offset, size_t size,
camera_frame_metadata_t *metadata) {
LOG2("copyFrameAndPostCopiedFrame");
// It is necessary to copy out of pmem before sending this to
// the callback. For efficiency, reuse the same MemoryHeapBase
// provided it's big enough. Don't allocate the memory or
// perform the copy if there's no callback.
// hold the preview lock while we grab a reference to the preview buffer
sp<MemoryHeapBase> previewBuffer;

if (mPreviewBuffer == 0) {
mPreviewBuffer = new MemoryHeapBase(size, 0, NULL);
} else if (size > mPreviewBuffer->virtualSize()) {
mPreviewBuffer.clear();
mPreviewBuffer = new MemoryHeapBase(size, 0, NULL);
}
if (mPreviewBuffer == 0) {
LOGE("failed to allocate space for preview buffer");
mLock.unlock();
return;
}
previewBuffer = mPreviewBuffer;

memcpy(previewBuffer->base(), (uint8_t *)heap->base() + offset, size);

sp<MemoryBase> frame = new MemoryBase(previewBuffer, 0, size);
if (frame == 0) {
LOGE("failed to allocate space for frame callback");
mLock.unlock();
return;
}

mLock.unlock();
client->dataCallback(msgType, frame, metadata);
}

int CameraService::Client::getOrientation(int degrees, bool mirror) {
if (!mirror) {
if (degrees == 0) return 0;
else if (degrees == 90) return HAL_TRANSFORM_ROT_90;
else if (degrees == 180) return HAL_TRANSFORM_ROT_180;
else if (degrees == 270) return HAL_TRANSFORM_ROT_270;
} else {  // Do mirror (horizontal flip)
if (degrees == 0) {           // FLIP_H and ROT_0
return HAL_TRANSFORM_FLIP_H;
} else if (degrees == 90) {   // FLIP_H and ROT_90
return HAL_TRANSFORM_FLIP_H | HAL_TRANSFORM_ROT_90;
} else if (degrees == 180) {  // FLIP_H and ROT_180
return HAL_TRANSFORM_FLIP_V;
} else if (degrees == 270) {  // FLIP_H and ROT_270
return HAL_TRANSFORM_FLIP_V | HAL_TRANSFORM_ROT_90;
}
}
LOGE("Invalid setDisplayOrientation degrees=%d", degrees);
return -1;
}

// ----------------------------------------------------------------------------

static const int kDumpLockRetries = 50;
static const int kDumpLockSleep = 60000;

static bool tryLock(Mutex& mutex)
{
bool locked = false;
for (int i = 0; i < kDumpLockRetries; ++i) {
if (mutex.tryLock() == NO_ERROR) {
locked = true;
break;
}
usleep(kDumpLockSleep);
}
return locked;
}

status_t CameraService::dump(int fd, const Vector<String16>& args) {
static const char* kDeadlockedString = "CameraService may be deadlocked\n";

const size_t SIZE = 256;
char buffer[SIZE];
String8 result;
if (checkCallingPermission(String16("android.permission.DUMP")) == false) {
snprintf(buffer, SIZE, "Permission Denial: "
"can't dump CameraService from pid=%d, uid=%d\n",
getCallingPid(),
getCallingUid());
result.append(buffer);
write(fd, result.string(), result.size());
} else {
bool locked = tryLock(mServiceLock);
// failed to lock - CameraService is probably deadlocked
if (!locked) {
String8 result(kDeadlockedString);
write(fd, result.string(), result.size());
}

bool hasClient = false;
for (int i = 0; i < mNumberOfCameras; i++) {
sp<Client> client = mClient[i].promote();
if (client == 0) continue;
hasClient = true;
sprintf(buffer, "Client[%d] (%p) PID: %d\n",
i,
client->getCameraClient()->asBinder().get(),
client->mClientPid);
result.append(buffer);
write(fd, result.string(), result.size());
client->mHardware->dump(fd, args);
}
if (!hasClient) {
result.append("No camera client yet.\n");
write(fd, result.string(), result.size());
}

if (locked) mServiceLock.unlock();

// change logging level
int n = args.size();
for (int i = 0; i + 1 < n; i++) {
if (args[i] == String16("-v")) {
String8 levelStr(args[i+1]);
int level = atoi(levelStr.string());
sprintf(buffer, "Set Log Level to %d", level);
result.append(buffer);
setLogLevel(level);
}
}
}
return NO_ERROR;
}

}; // namespace android

void CameraService::onFirstRef()看这个函数:

void CameraService::onFirstRef()
{
BnCameraService::onFirstRef();

if (hw_get_module(CAMERA_HARDWARE_MODULE_ID,
(const hw_module_t **)&mModule) < 0) {
LOGE("Could not load camera HAL module");
mNumberOfCameras = 0;
}
else {
mNumberOfCameras = mModule->get_number_of_cameras();			//获取camera设备的个数.对应下文中的获取camera个数函数.
if (mNumberOfCameras > MAX_CAMERAS) {
LOGE("Number of cameras(%d) > MAX_CAMERAS(%d).",
mNumberOfCameras, MAX_CAMERAS);
mNumberOfCameras = MAX_CAMERAS;
}
for (int i = 0; i < mNumberOfCameras; i++) {
setCameraFree(i);
}
}

// Read the system property to determine if we have to use the
// AUDIO_STREAM_ENFORCED_AUDIBLE type.
char value[PROPERTY_VALUE_MAX];
property_get("ro.camera.sound.forced", value, "0");
if (strcmp(value, "0") != 0) {
mAudioStreamType = AUDIO_STREAM_ENFORCED_AUDIBLE;
} else {
mAudioStreamType = AUDIO_STREAM_MUSIC;
}
}

找了半天也就是它这个函数里边有hw_get_module()这个函数,一看名字就知道是获取hardware的,不找它找谁啊。那么onFirstRef()函数又是何时调用的？

onFirstRef（）属于其父类RefBase，该函数在强引用sp新增引用计数时调用，什么意思？就是当 有sp包装的类初始化的时候调用。这里在frameworks/base/services/camera/libcameraservice/CameraService.h 中class CameraService :中有定义

// these are initialized in the constructor.
sp<CameraService>               mCameraService;  // immutable after constructor
sp<ICameraClient>               mCameraClient;
int                             mCameraId;       // immutable after constructor
int                             mCameraFacing;   // immutable after constructor
pid_t                           mClientPid;
sp<CameraHardwareInterface>     mHardware;       // cleared after disconnect()
int                             mPreviewCallbackFlag;
int                             mOrientation;     // Current display orientation
bool                            mPlayShutterSound;

很明显是这里来初始化的,当然这里不是重点,如果全部都写的话,那基本上就写不完了.

找到了hw_get_module()这个函数,让我们看它的具体实现.

hardware/libhardware/hardware.c

代码如下:

/*
* Copyright (C) 2008 The Android Open Source Project
*
* 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 <hardware/hardware.h>

#include <cutils/properties.h>

#include <dlfcn.h>
#include <string.h>
#include <pthread.h>
#include <errno.h>
#include <limits.h>

#define LOG_TAG "HAL"
#include <utils/Log.h>

/** Base path of the hal modules */
#define HAL_LIBRARY_PATH1 "/system/lib/hw"
#define HAL_LIBRARY_PATH2 "/vendor/lib/hw"

/**
* There are a set of variant filename for modules. The form of the filename
* is "<MODULE_ID>.variant.so" so for the led module the Dream variants
* of base "ro.product.board", "ro.board.platform" and "ro.arch" would be:
*
* led.trout.so
* led.msm7k.so
* led.ARMV6.so
* led.default.so
*/

static const char *variant_keys[] = {
"ro.hardware",  /* This goes first so that it can pick up a different
file on the emulator. */
"ro.product.board",
"ro.board.platform",
"ro.arch"
};

static const int HAL_VARIANT_KEYS_COUNT =
(sizeof(variant_keys)/sizeof(variant_keys[0]));

/**
* Load the file defined by the variant and if successful
* return the dlopen handle and the hmi.
* @return 0 = success, !0 = failure.
*/
static int load(const char *id,
const char *path,
const struct hw_module_t **pHmi)
{
int status;
void *handle;
struct hw_module_t *hmi;

/*
* load the symbols resolving undefined symbols before
* dlopen returns. Since RTLD_GLOBAL is not or'd in with
* RTLD_NOW the external symbols will not be global
*/
handle = dlopen(path, RTLD_NOW);
if (handle == NULL) {
char const *err_str = dlerror();
LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
status = -EINVAL;
goto done;
}

/* Get the address of the struct hal_module_info. */
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
hmi = (struct hw_module_t *)dlsym(handle, sym);
if (hmi == NULL) {
LOGE("load: couldn't find symbol %s", sym);
status = -EINVAL;
goto done;
}

/* Check that the id matches */
if (strcmp(id, hmi->id) != 0) {
LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
status = -EINVAL;
goto done;
}

hmi->dso = handle;

/* success */
status = 0;

done:
if (status != 0) {
hmi = NULL;
if (handle != NULL) {
dlclose(handle);
handle = NULL;
}
} else {
LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
id, path, *pHmi, handle);
}

*pHmi = hmi;

return status;
}

int hw_get_module_by_class(const char *class_id, const char *inst,
const struct hw_module_t **module)
{
int status;
int i;
const struct hw_module_t *hmi = NULL;
char prop[PATH_MAX];
char path[PATH_MAX];
char name[PATH_MAX];

if (inst)
snprintf(name, PATH_MAX, "%s.%s", class_id, inst);
else
strlcpy(name, class_id, PATH_MAX);

/*
* Here we rely on the fact that calling dlopen multiple times on
* the same .so will simply increment a refcount (and not load
* a new copy of the library).
* We also assume that dlopen() is thread-safe.
*/

/* Loop through the configuration variants looking for a module */
for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
if (i < HAL_VARIANT_KEYS_COUNT) {
if (property_get(variant_keys[i], prop, NULL) == 0) {
continue;
}
snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH2, name, prop);
if (access(path, R_OK) == 0) break;

snprintf(path, sizeof(path), "%s/%s.%s.so",
HAL_LIBRARY_PATH1, name, prop);
if (access(path, R_OK) == 0) break;
} else {
snprintf(path, sizeof(path), "%s/%s.default.so",
HAL_LIBRARY_PATH1, name);
if (access(path, R_OK) == 0) break;
}
}

status = -ENOENT;
if (i < HAL_VARIANT_KEYS_COUNT+1) {
/* load the module, if this fails, we're doomed, and we should not try
* to load a different variant. */
status = load(class_id, path, module);
}

return status;
}

int hw_get_module(const char *id, const struct hw_module_t **module)
{
return hw_get_module_by_class(id, NULL, module);
}

让我们看看它的流程:

int hw_get_module(const char *id, const struct hw_module_t **module)
int hw_get_module_by_class(const char *class_id, const char *inst,const struct hw_module_t **module)
static int load(const char *id,const char *path,const struct hw_module_t **pHmi)
/* Check that the id matches */
if (strcmp(id, hmi->id) != 0) {
LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
status = -EINVAL;
goto done;
}
...

可以知道,真正来寻找hardware的桥梁是这个ID,在if (strcmp(id, hmi->id) != 0)中,id是frameworks/base/services/camera/libcameraservice/CameraService.cpp中直接赋值的

如下:

if (hw_get_module(CAMERA_HARDWARE_MODULE_ID,
(const hw_module_t **)&mModule) < 0) {
LOGE("Could not load camera HAL module");
mNumberOfCameras = 0;
}

而hmi->id中的这个id很明显是hardware中应该定义的了.

我们看hmi是怎么得来的.

/* Get the address of the struct hal_module_info. */
const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
hmi = (struct hw_module_t *)dlsym(handle, sym);

不用跟踪这个函数就能看出来.hmi一定是从sym中来获取的.所以这里我们也就知道hardware中一定要有这个结构体.这也是实现一个hardware必须要做的事情,这里在hardware.h中也有说明:

/**
* Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
* and the fields of this data structure must begin with hw_module_t
* followed by module specific information.
*/

即hardware中一定要有这个叫HAL_MODULE_INFO_SYM的结构体.这也是实现一个hardware的第一步:Step-1:实现一个名字为HAL_MODULE_INFO_SYM的结构体,这个结构体必须以hw_module_t开头

好吧,来看一下camera的hardware中是怎么定义的.

看一下common是不是结构体hw_module_t

hardware/libhardware/include/hardware/camera.h

好了,既然hardware要有结构体,那么必须要给他初始化.自定义的函数也得给实现了.

上文注释已经写出来了.这里只是粘贴一下函数的实现.

所以也就自然而然的调用到了实现hardware的第二步,Step-2:

open函数的实现及作用.还是看cameraHAL中对其的实现.

层层包装啊,再看HAL_camera_device_open:

static int HAL_camera_device_open(const struct hw_module_t* module,
const char *id,
struct hw_device_t** device)
{
int cameraId = atoi(id);
if (cameraId < 0 || cameraId >= HAL_getNumberOfCameras()) {
return -EINVAL;
}
if (g_cam_device) {								//如果系统第二次打开摄像头,则此时g_cam_device已经填充完毕,可以不再填充了.
if (obj(g_cam_device)->getCameraId() == cameraId) {
goto done;
} else {
LOGE("Cannot open camera %d. camera %d is already running!",
cameraId, obj(g_cam_device)->getCameraId());
return -ENOSYS;
}
}
g_cam_device = (camera_device_t *)malloc(sizeof(camera_device_t));
if (!g_cam_device)
return -ENOMEM;
g_cam_device->common.tag     = HARDWARE_DEVICE_TAG;
g_cam_device->common.version = 1;
g_cam_device->common.module  = const_cast<hw_module_t *>(module);
g_cam_device->common.close   = HAL_camera_device_close;
g_cam_device->ops = &camera_device_ops;
LOGI("%s: open camera %s", __func__, id);
g_cam_device->priv = new CameraHardwareSec(cameraId, g_cam_device);
done:
*device = (hw_device_t *)g_cam_device;
LOGI("%s: opened camera %s (%p)", __func__, id, *device);
return 0;
}

这里我们知道.open的作用就是打开指定ID号的摄像头以及填充device结构体,供上层直接调用我们HAL的具体函数比如takePicture(),startPreview()等等.

但是应该怎么去填充这个结构体呢?

还是先看hardware/libhardware/include/hardware/hardware.h怎么说吧.

/**
* Every device data structure must begin with hw_device_t
* followed by module specific public methods and attributes.
*/

它说每一个设备都必须以hw_device_t开始,后面跟着methods和attributes.

那我们就在HAL中定义一个static的结构体,按着上边赋值完毕后返回这个指针就成了.看HAL

static camera_device_t *g_cam_device;			//定义设备的结构体具体如下.
typedef struct camera_device {
hw_device_t common;							//以hw_device_t开始
camera_device_ops_t *ops;					//紧跟着methods
void *priv;                             	//私有数据.
} camera_device_t;

看看是怎么填充的:

g_cam_device->common.tag     = HARDWARE_DEVICE_TAG;		//hardware.h中定义的.具体设备tag必须这样定义.
g_cam_device->common.module  = const_cast<hw_module_t *>(module);	//和module模块建立联系
g_cam_device->common.close   = HAL_camera_device_close;		//设备关闭的函数
g_cam_device->ops = &camera_device_ops;						// 这个里边包含的就是那些操作摄像头所需要的具体实现.讲HAL的运行流程时细讲.
g_cam_device->priv = new CameraHardwareSec(cameraId, g_cam_device);	//真正实现hardware初始化摄像头的函数,讲HAL的运行流程时细讲.

这里先看看camera_device_ops的具体实现,也牵扯到了HAL实现的第三步,Step-3:具体设备的函数实现.

#define SET_METHOD(m) m : HAL_camera_device_##m		//相当于m : HAL_camera_device_m
static camera_device_ops_t camera_device_ops = {
SET_METHOD(set_preview_window),				//展开后相当于set_preview_window : HAL_camera_device_set_preview_window,即HAL_camera_device_set_preview_window是set_preview_window的具体实现
SET_METHOD(set_callbacks),					//展开后相当于set_callbacks : HAL_camera_device_set_callbacks
SET_METHOD(enable_msg_type),				//同上
SET_METHOD(disable_msg_type),
SET_METHOD(msg_type_enabled),
SET_METHOD(start_preview),
SET_METHOD(stop_preview),
SET_METHOD(preview_enabled),
SET_METHOD(store_meta_data_in_buffers),
SET_METHOD(start_recording),
SET_METHOD(stop_recording),
SET_METHOD(recording_enabled),
SET_METHOD(release_recording_frame),
SET_METHOD(auto_focus),
SET_METHOD(cancel_auto_focus),
SET_METHOD(take_picture),
SET_METHOD(cancel_picture),
SET_METHOD(set_parameters),
SET_METHOD(get_parameters),
SET_METHOD(put_parameters),
SET_METHOD(send_command),
SET_METHOD(release),
SET_METHOD(dump),
};

先不说HAL中调用函数的具体实现,看看是service怎么调用的.

以start_preview为例.

camera.start_preview()	//应用程序
public native final void startPreview();       											//此处调用JNI frameworks/base/core/java/android/hardware/Camera.java
static void android_hardware_Camera_startPreview(JNIEnv *env, jobject thiz)			//JNI frameworks/base/core/jni/android_hardware_Camera.cpp
sp<Camera> camera = get_native_camera(env, thiz, NULL);						//获取cameraClient	frameworks/base/core/jni/android_hardware_Camera.cpp
camera->startPreview();														//执行cameraClient的函数	frameworks/base/libs/camera/Camera.cpp.
status_t CameraService::Client::startPreview();							//service中函数的实现	frameworks/base/services/camera/libcameraservice/CameraService.cpp
status_t CameraService::Client::startCameraMode(camera_mode mode) 	//service中的调用	frameworks/base/services/camera/libcameraservice/CameraService.cpp
status_t CameraService::Client::startPreviewMode()				//service最终调用	frameworks/base/services/camera/libcameraservice/CameraService.cpp
status_t startPreview()									//调用到hardware的接口	frameworks/base/services/camera/libcameraservice/CameraHardwareInterface.h
mDevice->ops->start_preview(mDevice);					//调用到HAL层的start_preview具体实现HAL_camera_device_start_preview.   device/magiclab/common/libcamera/SecCameraHWInterface_zoom.cpp

OK,函数调用到这里也就完成了应用程序调用hardware内具体设备函数的流程.HAL的实现其实也就是实现上面每个函数.使它们协同合作而已.

作者：joseph_lee

出处：joseh_lee2633的博客--http://www.cnblogs.com/joseph-linux

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