<Android Framework 之路> N版本 Framework Camera的一些改动
前言
Android N版本最近发布，Nougat是否好吃，不得而知，慢慢看下~
感谢AndroidXref这个网站，给开发者提供了大量的便捷~以后学习Android就靠它了。
N版本上Framework关于Camera的一些改动
CameraServer
N版本之前，CameraService是运行在MediaServer下的，这样存在一定的问题，因为MediaServer下同时还运行这其他的多媒体内容
M版本
/frameworks/av/media/mediaserver/main_mediaserver.cpp
int main(int argc __unused, char** argv)
{
signal(SIGPIPE, SIG_IGN);
char value[PROPERTY_VALUE_MAX];
bool doLog = (property_get("ro.test_harness", value, "0") > 0) && (atoi(value) == 1);
pid_t childPid;
// FIXME The advantage of making the process containing media.log service the parent process of
// the process that contains all the other real services, is that it allows us to collect more
// detailed information such as signal numbers, stop and continue, resource usage, etc.
// But it is also more complex. Consider replacing this by independent processes, and using
// binder on death notification instead.
if (doLog && (childPid = fork()) != 0) {
// media.log service
//prctl(PR_SET_NAME, (unsigned long) "media.log", 0, 0, 0);
// unfortunately ps ignores PR_SET_NAME for the main thread, so use this ugly hack
strcpy(argv[0], "media.log");
sp<ProcessState> proc(ProcessState::self());
MediaLogService::instantiate();
ProcessState::self()->startThreadPool();
for (;;) {
siginfo_t info;
int ret = waitid(P_PID, childPid, &info, WEXITED | WSTOPPED | WCONTINUED);
if (ret == EINTR) {
continue;
}
if (ret < 0) {
break;
}
char buffer[32];
const char *code;
switch (info.si_code) {
case CLD_EXITED:
code = "CLD_EXITED";
break;
case CLD_KILLED:
code = "CLD_KILLED";
break;
case CLD_DUMPED:
code = "CLD_DUMPED";
break;
case CLD_STOPPED:
code = "CLD_STOPPED";
break;
case CLD_TRAPPED:
code = "CLD_TRAPPED";
break;
case CLD_CONTINUED:
code = "CLD_CONTINUED";
break;
default:
snprintf(buffer, sizeof(buffer), "unknown (%d)", info.si_code);
code = buffer;
break;
}
struct rusage usage;
getrusage(RUSAGE_CHILDREN, &usage);
ALOG(LOG_ERROR, "media.log", "pid %d status %d code %s user %ld.%03lds sys %ld.%03lds",
info.si_pid, info.si_status, code,
usage.ru_utime.tv_sec, usage.ru_utime.tv_usec / 1000,
usage.ru_stime.tv_sec, usage.ru_stime.tv_usec / 1000);
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder = sm->getService(String16("media.log"));
if (binder != 0) {
Vector<String16> args;
binder->dump(-1, args);
}
switch (info.si_code) {
case CLD_EXITED:
case CLD_KILLED:
case CLD_DUMPED: {
ALOG(LOG_INFO, "media.log", "exiting");
_exit(0);
// not reached
}
default:
break;
}
}
} else {
// all other services
if (doLog) {
prctl(PR_SET_PDEATHSIG, SIGKILL); // if parent media.log dies before me, kill me also
setpgid(0, 0); // but if I die first, don't kill my parent
}
InitializeIcuOrDie();
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
AudioFlinger::instantiate();
MediaPlayerService::instantiate();
ResourceManagerService::instantiate();
CameraService::instantiate();
AudioPolicyService::instantiate();
SoundTriggerHwService::instantiate();
RadioService::instantiate();
registerExtensions();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
}可以看到AudioFlinger，MediaPlayerService, ResourceManagerService,CameraService,AudioPolicyService,SoundTriggerHwService,RadioService等都是运行在这个进程下面的，这样就存在一个问题，假如说其他任何一个服务因为某些原因挂掉了，整个MediaServer将会重启，而这个重启的过程中，倘若相机正在操作，就会出现相机突然挂掉的问题。
N版本
/frameworks/av/media/mediaserver/main_mediaserver.cpp
int main(int argc __unused, char **argv __unused)
{
signal(SIGPIPE, SIG_IGN);
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm(defaultServiceManager());
ALOGI("ServiceManager: %p", sm.get());
InitializeIcuOrDie();
MediaPlayerService::instantiate();
ResourceManagerService::instantiate();
registerExtensions();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}有没有觉得少了很多，不仅CameraService被抽离出去了，还有一些内容好像也被抽离出去了。
在N版本的工程中多出来一个文件夹
/frameworks/av/camera/cameraserver/
说明CameraServer是独立于MediaServer的单独的进程，执行PS操作你讲看到独立的Camera进程。
#define LOG_TAG "cameraserver"
//#define LOG_NDEBUG 0
// from LOCAL_C_INCLUDES
#include "CameraService.h"
using namespace android;
int main(int argc __unused, char** argv __unused)
{
signal(SIGPIPE, SIG_IGN);
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
CameraService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}初始化的过程并没有变化，只是单纯的将它独立出来而已。
那么问题来了，CameraService何时启动？
看到cameraserver.rc文件，
service cameraserver /system/bin/cameraserver
class main
user cameraserver
group audio camera drmrpc inet media mediadrm net_bt net_bt_admin net_bw_acct
ioprio rt 4
writepid /dev/cpuset/foreground/tasks也就是说只要加载了cameraserver.rc文件，服务就开始启动了，就会往main_cameraserer.cpp的入口函数中执行，因为mk文件中定义了这个模块为cameraserver
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES:= \
main_cameraserver.cpp//源文件
LOCAL_SHARED_LIBRARIES := \//依赖库
libcameraservice \
libcutils \
libutils \
libbinder \
libcamera_client
LOCAL_MODULE:= cameraserver//模块名
LOCAL_32_BIT_ONLY := true//只支持32位
LOCAL_CFLAGS += -Wall -Wextra -Werror -Wno-unused-parameter//一些编译条件，N版本在编译这一块也作出了很大的改动，有机会再研究下
LOCAL_INIT_RC := cameraserver.rc
include $(BUILD_EXECUTABLE)//执行文件寻找，谁调用的camearserver.rc ????????????????
首先我们要看这个文件编译出来之后放在手机的什么位置
/build/core/base_rules.mk
# Rule to install the module's companion init.rc.
my_init_rc := $(LOCAL_INIT_RC_$(my_32_64_bit_suffix))
my_init_rc_src :=
my_init_rc_installed :=
ifndef my_init_rc
my_init_rc := $(LOCAL_INIT_RC)
# Make sure we don't define the rule twice in multilib module.
LOCAL_INIT_RC :=
endif
ifdef my_init_rc
my_init_rc_src := $(LOCAL_PATH)/$(my_init_rc)
my_init_rc_installed := $(TARGET_OUT$(partition_tag)_ETC)/init/$(notdir $(my_init_rc_src))
$(my_init_rc_installed) : $(my_init_rc_src) | $(ACP)
@echo "Install: $@"
$(copy-file-to-new-target)
$(my_register_name) : $(my_init_rc_installed)大致可以看出一些端倪，应该是放在xxx/etc/init目录下，这个xxx根据什么看判断，partition_tag变量
ifdef LOCAL_IS_HOST_MODULE
partition_tag :=
else
ifeq (true,$(LOCAL_PROPRIETARY_MODULE))
partition_tag := _VENDOR
else ifeq (true,$(LOCAL_OEM_MODULE))
partition_tag := _OEM
else ifeq (true,$(LOCAL_ODM_MODULE))
partition_tag := _ODM
else
# The definition of should-install-to-system will be different depending
# on which goal (e.g., sdk or just droid) is being built.
partition_tag := $(if $(call should-install-to-system,$(my_module_tags)),,_DATA)
endifcameraserver应该是系统所有的，不是oem或者odm特有，存放在system/etc/init目录下。
接下面看看这个文件
/system/core/init/readme.txt
One may specify paths in the mount_all command line to have it import
.rc files at the specified paths instead of the default ones listed above.
This is primarily for supporting factory mode and other non-standard boot
modes. The three default paths should be used for the normal boot process.
The intention of these directories is as follows
1) /system/etc/init/ is for core system items such as
SurfaceFlinger, MediaService, and logcatd.
2) /vendor/etc/init/ is for SoC vendor items such as actions or
daemons needed for core SoC functionality.
3) /odm/etc/init/ is for device manufacturer items such as
actions or daemons needed for motion sensor or other peripheral
functionality.显然是在执行“mount_all“的时候，CameraServer启动 ~ ，找到启动的位置，这一点和之前的版本是有很大差别的。
Aidl
N版本上对于Camera的一些接口采用了Aidl的文件格式
frameworks/av/camera/aidl/android/hardware/
其他模块想要访问这些接口，需要include libcamera_client模块才行
mk文件中有说明。
