[點(diǎn)晴永久免費(fèi)OA]Android 開機(jī)流程介紹
一、目的 從2014年Android4.0開始接觸機(jī)器人,開發(fā)過App應(yīng)用軟件,研究過Framework層框架結(jié)構(gòu)、也梳理過Native層的系統(tǒng)流程,但是對于Hal層,以及底下的kernel方向,知之甚少。 二、環(huán)境
三、相關(guān)概念3.1 Android平臺架構(gòu)如下是Google官網(wǎng)提供的平臺架構(gòu)圖,很直觀地攘括了Android的層級,關(guān)于各個(gè)層級的結(jié)構(gòu),有想了解可以參考:https://developer.android.google.cn/guide/platform?hl=zh-cn ![]() ps: Android系統(tǒng)為什么要有Hal層? 3.2 Android啟動(dòng)架構(gòu)如下是從某大佬的文章里摘取的圖片,很詳細(xì)地描述了Android系統(tǒng)啟動(dòng)過程:Boot Loader引導(dǎo)開機(jī) -> Kernel -> Native -> Framework -> App ![]() 3.3 zImagezImage是一般情況下默認(rèn)的壓縮內(nèi)核映像文件,壓縮vmlinux,加上一段解壓啟動(dòng)代碼得到,只能從0X0地址運(yùn)行。 3.4 RAMDISK RAMDISK(initrd) 是一個(gè)小的分區(qū)像,在引導(dǎo)時(shí)內(nèi)核以只讀方式掛載它。它只保護(hù)/int和一些置文件,它用于初始化和掛載其它的文件系統(tǒng)鏡像。 3.5 RC文件rc文件,是用Android Init Language編寫的特殊文件。用這種語法編寫的文件,統(tǒng)一用".rc"后綴。所有rc文件,不會(huì)被編譯/鏈接。它是配置文件,不是程序,是一種用于android init的配置文件。真正加載rc文件,并進(jìn)行解析,做事情的是 Init進(jìn)程。 四、詳細(xì)設(shè)計(jì)![]() 4.1 Boot Rom當(dāng)長按電源開機(jī)的時(shí)候,引導(dǎo)芯片開始從固化在ROM的預(yù)設(shè)代碼開始執(zhí)行,然后將加載引導(dǎo)程序到RAM中。 4.2 BootLoaderBootLoader又稱為引導(dǎo)程序,它在運(yùn)行操作系統(tǒng)之前運(yùn)行的一段程序,是運(yùn)行的第一個(gè)程序。主要的功能有檢查RAM、初始化一些硬件外設(shè)等功能,它最終的目的是啟動(dòng)操作系統(tǒng)。 4.3 KernelKernel初始化可以分成三部分:zImage解壓縮、kernel的匯編啟動(dòng)階段、Kernel的C啟動(dòng)階段 4.3.1 zImage解壓縮階段
4.3.2 kernel的匯編啟動(dòng)階段idle進(jìn)程的啟動(dòng)是用匯編語言編寫(感興趣可以去研究下),對應(yīng)的啟動(dòng)如下: s @bsp\kernel\kernel5.4\arch\arm\kernel\head-common.S
ldmia r4, {r0, r1, r2, r3}
str r9, [r0] @ Save processor ID
str r7, [r1] @ Save machine type
str r8, [r2] @ Save atags pointer
cmp r3, #0
strne r10, [r3] @ Save control register values
mov lr, #0
b start_kernel //啟動(dòng)start_kernel函數(shù)其中,語句b start_kernel,b 是跳轉(zhuǎn)的意思,即跳轉(zhuǎn)到start_kernel函數(shù),對應(yīng)的實(shí)現(xiàn)在bsp/kernel/kernel5.4/init/main.c,至此idle進(jìn)程被啟動(dòng)。 4.3.3 Kernel的C啟動(dòng)階段start_kernel()函數(shù)是內(nèi)核初始化C語言部分的主體。這個(gè)函數(shù)完成系統(tǒng)底層基本機(jī)制,包括處理器、存儲管理系統(tǒng)、進(jìn)程管理系統(tǒng)、中斷機(jī)制、定時(shí)機(jī)制等的初始化工作。 c @bsp\kernel\kernel5.4\init\main.c
asmlinkage __visible void __init start_kernel(void){
char *command_line;
char *after_dashes;
set_task_stack_end_magic(&init_task);
smp_setup_processor_id();//打印了驅(qū)動(dòng)加載的第一行l(wèi)og
... //初始化一系列系統(tǒng)底層機(jī)制
pr_notice("%s", linux_banner);//打印內(nèi)核版本信息
...
pr_notice("Kernel command line: %s\n", saved_command_line);//打印從uboot傳遞過來的command_line字符串
...
/* Do the rest non-__init'ed, we're now alive */
arch_call_rest_init();//創(chuàng)建init進(jìn)程、kthread進(jìn)程、idle進(jìn)程
prevent_tail_call_optimization();}4.3.3.1 kernel啟動(dòng)log(1)kernel內(nèi)核啟動(dòng)階段,smp_setup_processor_id()函數(shù)會(huì)打印的第一條log(文中l(wèi)og可以在 [目錄5.1開機(jī)log] 下載查看),如下: none [ 0.000000] c0 Booting Linux on physical CPU 0x0 (2)接著會(huì)打印內(nèi)核的一些信息,版本,作者,編譯器版本,日期等,如下: none [ 0.000000]c0 Linux version 5.4.147+ (lzq@cz-PowerEdge-R730) (Android (7284624, based on r416183b) clang version 12.0.5 (https://android.googlesource.com/toolchain/llvm-project c935d99d7cf2016289302412d708641d52d2f7ee), LLD 12.0.5 (/buildbot/src/android/llvm-toolchain/out/llvm-project/lld c935d99d7cf2016289302412d708641d52d2f7ee)) #5 SMP PREEMPT Thu Sep 28 15:17:40 CST 2023 (3)打印出從uboot傳遞過來的command_line字符串,在setup_arch函數(shù)中獲得的(proc/cmdline) none [ 0.000000]c0 Kernel command line: earlycon=sprd_serial_ex,0x508d0000,115200n8 console=ttySE0,921600n8 loglevel=7 init=/init root=/dev/ram0 rw vmalloc=360M printk.devkmsg=on androidboot.boot_devices=soc/soc:ap-ahb/20600000.sdio initcall_debug=1 swiotlb=1 androidboot.selinux=permissive androidboot.hardware=sl8541e_1h10_32b androidboot.dtbo_idx=0 lcd_id=ID40396 lcd_name=lcd_st7123_truly_mipi_hd lcd_base=9e000000 lcd_size=1440x720 logo_bpix=24 androidboot.ddrsize=1024M androidboot.ddrsize.range=[1024,2048) sysdump_magic=80001000 sysdump_re_flag=1 androidboot.wdten=0 androidboot.dswdten=disable modem=shutdown ltemode=lcsfb rfboard.id=-1 rfhw.id=0 crystal=2 32k.less=1 androidboot.pmic.chipid=2721 modemboot.method=emmcboot cpcmdline=end androidboot.verifiedbootstate=orange androidboot.flash.locked=0 androidboot.serialno=LE210210001326000028 buildvariant=userdebug androidboot.vbmeta.device=PARTUUID=1.0 androidboot.vbmeta.avb_version=1.1 androidboot.vbmeta.device_state=unlocked androidboot. 4.3.3.2 init進(jìn)程&kthreadd進(jìn)程創(chuàng)建了Linux系統(tǒng)中兩個(gè)重要的進(jìn)程init和kthreadd,并且將當(dāng)前進(jìn)程設(shè)置為idle進(jìn)程: c @bsp\kernel\kernel5.4\init\main.cvoid __init __weak arch_call_rest_init(void){
rest_init();}noinline void __ref rest_init(void){
...
pid = kernel_thread(kernel_init, NULL, CLONE_FS);//創(chuàng)建init進(jìn)程
...
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);//創(chuàng)建kthreadd進(jìn)程
...
/* Call into cpu_idle with preempt disabled */
cpu_startup_entry(CPUHP_ONLINE);//設(shè)置當(dāng)前進(jìn)程為idle進(jìn)程} Linux下有三個(gè)特殊的進(jìn)程,idle(swapper)進(jìn)程(PID = 0),init進(jìn)程(PID = 1)和看threadd(PID = 2): (1)idle(swapper)進(jìn)程由系統(tǒng)自動(dòng)創(chuàng)建,運(yùn)行在內(nèi)核態(tài)。idle進(jìn)程其pid=0,其前身是系統(tǒng)創(chuàng)建的第一個(gè)進(jìn)程,也是唯一一個(gè)沒有通過fork或者kernel_thread產(chǎn)生的進(jìn)程。完成加載系統(tǒng)后,演變?yōu)檫M(jìn)程調(diào)度、交換,常常被稱為交換進(jìn)程。 4.3.3.3 idle進(jìn)程啟動(dòng)這個(gè)函數(shù)是Linux內(nèi)核為非引導(dǎo)CPU初始化和進(jìn)入空閑循環(huán)的入口函數(shù),負(fù)責(zé)在系統(tǒng)沒有任務(wù)需要執(zhí)行時(shí),讓CPU進(jìn)入空閑狀態(tài)。 c @bsp\kernel\kernel5.4\kernel\sched\idle.cvoid cpu_startup_entry(enum cpuhp_state state){
arch_cpu_idle_prepare();
cpuhp_online_idle(state);
while (1)
do_idle();}4.4 Init進(jìn)程由上一節(jié)可知,Init進(jìn)程由0號idle進(jìn)程啟動(dòng),kernel_init()為其入口函數(shù),該函數(shù)主要通過三種方式啟動(dòng)init程序。 c static int __ref kernel_init(void *unused){
...
if (ramdisk_execute_command) {
ret = run_init_process(ramdisk_execute_command);//Step 1. 根據(jù)ramdisk_execute_command的值來啟動(dòng)init程序
if (!ret)
return 0;
pr_err("Failed to execute %s (error %d)\n",
ramdisk_execute_command, ret);
}
if (execute_command) {
ret = run_init_process(execute_command);//Step 2. 根據(jù)execute_command的值來啟動(dòng)init程序
if (!ret)
return 0;
panic("Requested init %s failed (error %d).",
execute_command, ret);
}
if (!try_to_run_init_process("/sbin/init") ||
!try_to_run_init_process("/etc/init") ||
!try_to_run_init_process("/bin/init") ||
!try_to_run_init_process("/bin/sh")) //Step 3.根據(jù)系統(tǒng)默認(rèn)位置來啟動(dòng)init程序
return 0;
panic("No working init found. Try passing init= option to kernel. "
"See Linux Documentation/admin-guide/init.rst for guidance.");//Step 4.異常重啟}(1)ramdisk_execute_command是一個(gè)全局的char指針變量,值為“/init”,也就是根目錄下的init程序。該值通過uboot傳遞過來,具體可參考上一節(jié)的command_line。(如未配置該值,即會(huì)將該值默認(rèn)設(shè)置為"/init",該項(xiàng)目是從該處啟動(dòng)init進(jìn)程) log [ 1.000614]c1 Run /init as init process 4.4.1 init程序編譯 我們知道init程序是引用的根目錄下的init,即/init,但是其對應(yīng)的軟鏈接指向:system/bin/init,相關(guān)信息如下: 編譯makefile文件如下: none @system\core\init\Android.bp
phony {
name: "init",
required: [
"init_second_stage",
],
}
cc_binary {
name: "init_second_stage",
recovery_available: true,
stem: "init",//最終生成的二進(jìn)制文件名
defaults: ["init_defaults"],
static_libs: ["libinit"],
...
srcs: ["main.cpp"],
...
}4.4.2 init程序入口函數(shù)init程序的入口函數(shù),根據(jù)不同的入?yún)?,響?yīng)init不同階段、處理不同業(yè)務(wù)邏輯。 c @system\core\init\main.cppint main(int argc, char** argv) {
...
if (!strcmp(basename(argv[0]), "ueventd")) {
return ueventd_main(argc, argv);//初始化uevent事件
}
if (argc > 1) {
...
if (!strcmp(argv[1], "selinux_setup")) {
android::mboot::mdb("SELinux Setup ...");
return SetupSelinux(argv);//selinux權(quán)限
}
if (!strcmp(argv[1], "second_stage")) {
return SecondStageMain(argc, argv);//第二階段
}
}
return FirstStageMain(argc, argv);//第一階段}由于在kernel階段啟動(dòng)init程序時(shí),未配置參數(shù),故首先會(huì)引用FirstStageMain函數(shù)。另外,根據(jù)log可以看到,其引用順序如下: none [ 1.004958]c1 init: init first stage started! [ 2.547025]c0 init: Opening SELinux policy [ 3.226672]c0 init: init second stage started! [ 3.715657]c1 ueventd: ueventd started!
4.4.3 FirstStageMain第一階段,該階段所掛載的文件系統(tǒng)都屬于ramdisk,運(yùn)行在虛擬內(nèi)存上。 c @system\core\init\first_stage_mount.cppint FirstStageMain(int argc, char** argv) {
...
//Step 1. 創(chuàng)建&掛載最基本的文件系統(tǒng)
CHECKCALL(mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755"));//將/dev設(shè)置為tmpfs并掛載,設(shè)置0755權(quán)限,tmpfs是在內(nèi)存上建立的文件系統(tǒng)(Filesystem)
CHECKCALL(mkdir("/dev/pts", 0755));
CHECKCALL(mkdir("/dev/socket", 0755));
CHECKCALL(mkdir("/dev/dm-user", 0755));
...
//Step 2. 初始化log系統(tǒng)并打印
SetStdioToDevNull(argv);
InitKernelLogging(argv);
...
LOG(INFO) << "init first stage started!";
...
//Step 3. 加載內(nèi)核驅(qū)動(dòng)模塊
if (!LoadKernelModules(IsRecoveryMode() && !ForceNormalBoot(cmdline, bootconfig), want_console,
module_count)) {
...
}
...
//Step 4.掛載分區(qū)(system、vendor、product等分區(qū))
if (!DoFirstStageMount(!created_devices)) {
LOG(FATAL) << "Failed to mount required partitions early ...";
}
...
//Step 5.初始化Android的安全框架Android Verified Boot
SetInitAvbVersionInRecovery();
...
//Step 6.執(zhí)行下一個(gè)階段
const char* path = "/system/bin/init";
const char* args[] = {path, "selinux_setup", nullptr};
...
execv(path, const_cast<char**>(args));//exec系列函數(shù)可以把當(dāng)前進(jìn)程替換為一個(gè)新進(jìn)程,且新進(jìn)程與原進(jìn)程有相同的PID,即重新回到main.cpp
...}Step 1. 創(chuàng)建&掛載最基本的文件系統(tǒng),創(chuàng)建了如下五類文件系統(tǒng):
相關(guān)掛載情況如下: Step 2. 結(jié)合dev/kmsg節(jié)點(diǎn),初始化log系統(tǒng),并在第一階段開始時(shí),打印第一條log none [ 1.004958]c1 init: init first stage started! Step 3. 加載內(nèi)核驅(qū)動(dòng)模塊,第一階段加載的內(nèi)核模塊如下: none [ 1.012653]c1 init: Loaded kernel module /lib/modules/sprd_wdt.ko [ 1.020197]c0 init: Loaded kernel module /lib/modules/sc2721-regulator.ko [ 1.022427]c0 init: Loaded kernel module /lib/modules/nvmem-sc27xx-efuse.ko [ 1.026126]c0 init: Loaded kernel module /lib/modules/spool.ko [ 1.033668]c0 init: Loaded kernel module /lib/modules/sipx.ko [ 1.047553]c0 init: Loaded kernel module /lib/modules/seth.ko [ 1.048526]c0 init: Loaded kernel module /lib/modules/usb_f_vser.ko ... Step 4. 掛載分區(qū)。創(chuàng)建/first_stage_ramdisk并掛載,然后將根目錄切換到/first_stage_ramdisk,并掛載system、vendor 、product等系統(tǒng)分區(qū),掛載信息如上。 4.4.4 SetupSelinux該階段主要是初始化Selinux權(quán)限相關(guān)業(yè)務(wù),同時(shí)在業(yè)務(wù)流程最后一步時(shí),重新執(zhí)行system/bin/init程序,再次啟動(dòng)下一個(gè)階段SecondStageMain。 c @system\core\init\selinux.cppint SetupSelinux(char** argv) {
...
LOG(INFO) << "Opening SELinux policy";
...
const char* path = "/system/bin/init";
const char* args[] = {path, "second_stage", nullptr};
execv(path, const_cast<char**>(args));
...
return 1;}該階段log打印如下: none [ 2.547025]c0 init: Opening SELinux policy 4.4.5 SecondStageMain第二階段,涉及到文件系統(tǒng)掛載、屬性服務(wù)等系統(tǒng)相關(guān)業(yè)務(wù),其中最主要的一點(diǎn)去解析rc文件(創(chuàng)建目錄,修改權(quán)限,掛載分區(qū),啟動(dòng)服務(wù)進(jìn)程等),以期讓開機(jī)流程進(jìn)入下一階段。 c @system\core\init\init.cppint SecondStageMain(int argc, char** argv) {
//Step 1.初始化log
SetStdioToDevNull(argv);
InitKernelLogging(argv);
LOG(INFO) << "init second stage started!";
...
//Step 2.屬性服務(wù)初始化,讀取默認(rèn)屬性配置
PropertyInit();
...
//Step 3.掛載其他文件系統(tǒng),如/apex
MountExtraFilesystems();
...
//Step 4.啟動(dòng)屬性服務(wù)
StartPropertyService(&property_fd);
...
//Step 5.加載開機(jī)rc文件
ActionManager& am = ActionManager::GetInstance();
ServiceList& sm = ServiceList::GetInstance();
LoadBootScripts(am, sm);
...
//Step 6.設(shè)置進(jìn)程優(yōu)先級,主進(jìn)程不能退出
setpriority(PRIO_PROCESS, 0, 0);
while (true) {
...
}
return 0;}Step 1. 初始化log,該階段log打印如下: none [ 3.226672]c0 init: init second stage started! Step 2. 屬性服務(wù)初始化,讀取默認(rèn)屬性配置。獲取system/build.prop、vendor/build.prop、/odm/build.prop、/product/build.prop等其他build.prop屬性,并加載到properties map結(jié)構(gòu)中,然后通過MMAP映射到全局內(nèi)存中,供所有進(jìn)程調(diào)用; none [ 3.481952]c0 init: Parsing file /system/etc/init/hw/init.rc... [ 3.489693]c0 init: Parsing file /init.environ.rc... [ 3.490110]c0 init: Parsing file /system/etc/init/hw/init.usb.rc... [ 3.491867]c0 init: Parsing file /init.sl8541e_1h10_32b.rc... [ 3.493283]c0 init: Parsing file /vendor/etc/init/hw/init.sl8541e_1h10_32b.rc... [ 3.494372]c0 init: Parsing file /vendor/etc/init/hw/init.sl8541e_1h10_32b.usb.rc... [ 3.509664]c0 init: Parsing file /vendor/etc/init/hw/init.ram.rc... ... 解析init.rc會(huì)把一條條命令映射到內(nèi)存中,然后依次啟動(dòng),啟動(dòng)順序如下: none on on early-init:在初始化早期階段觸發(fā) on init:在初始化階段觸發(fā) on late-init:在初始化晚期階段觸發(fā) on boot/charger:當(dāng)系統(tǒng)啟動(dòng)/充電時(shí)觸發(fā) on property:當(dāng)屬性值滿足條件時(shí)觸發(fā) Step 6. 設(shè)置進(jìn)程優(yōu)先級,主進(jìn)程不能銷毀和退出。 4.5 Zygote進(jìn)程4.5.1 Zygote進(jìn)程啟動(dòng)腳本(1)rc文件編譯 c @system\core\rootdir\Android.bp
prebuilt_etc {
name: "init.rc",
src: "init.rc",
sub_dir: "init/hw",
required: [
"fsverity_init",
"platform-bootclasspath",
],}(2)init.rc c @system\core\rootdir\init.rc...import /system/etc/init/hw/init.${ro.zygote}.rc//導(dǎo)入zygote的rc文件,ro.zygote屬性可根據(jù)系統(tǒng)讀取...# Mount filesystems and start core system services.on late-init ...
# Now we can start zygote for devices with file based encryption
trigger zygote-start //在開機(jī)初始化晚期階段,觸發(fā)zygote啟動(dòng)
...# It is recommended to put unnecessary data/ initialization from post-fs-data# to start-zygote in device's init.rc to unblock zygote start.on zygote-start && property:ro.crypto.state=unencrypted
wait_for_prop odsign.verification.done 1
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start statsd
start netd
start zygote
start zygote_secondary(3)init.zygote32.rc r @system\core\rootdir\init.zygote32.rc
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
class main
priority -20
user root
group root readproc reserved_disk
socket zygote stream 660 root system
socket usap_pool_primary stream 660 root system
onrestart exec_background - system system -- /system/bin/vdc volume abort_fuse
onrestart write /sys/power/state on
onrestart restart audioserver
onrestart restart cameraserver
onrestart restart media
onrestart restart netd
onrestart restart wificond
writepid /dev/cpuset/foreground/tasks
critical window=${zygote.critical_window.minute:-off} target=zygote-fatal(4)zygote啟動(dòng)log none [ 7.916749]c3 init: starting service 'zygote'... 4.5.2 Zygote進(jìn)程(1)zygote編譯文件 none @frameworks\base\cmds\app_process\Android.bp
cc_binary {
name: "app_process",
srcs: ["app_main.cpp"],
...
}(2)app_process啟動(dòng) c int main(int argc, char* const argv[]){
...
while (i < argc) {//讀取rc文件傳進(jìn)來的參數(shù)
const char* arg = argv[i++];
if (strcmp(arg, "--zygote") == 0) {
zygote = true;
niceName = ZYGOTE_NICE_NAME;
} else if (strcmp(arg, "--start-system-server") == 0) {
startSystemServer = true;
}
...
}
...
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);//啟動(dòng)ZygoteInit
}
...}(3)AndroidRuntime c void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote){
ALOGD(">>>>>> START %s uid %d <<<<<<\n",
className != NULL ? className : "(unknown)", getuid());
...
//通過反射啟動(dòng)函數(shù)
char* slashClassName = toSlashClassName(className != NULL ? className : "");
jclass startClass = env->FindClass(slashClassName);
if (startClass == NULL) {
ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
/* keep going */
} else {
jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
"([Ljava/lang/String;)V");
if (startMeth == NULL) {
ALOGE("JavaVM unable to find main() in '%s'\n", className);
/* keep going */
} else {
env->CallStaticVoidMethod(startClass, startMeth, strArray);#if 0
if (env->ExceptionCheck())
threadExitUncaughtException(env);#endif
}
}
...}當(dāng)前流程會(huì)打印如下log: none 01-01 08:00:08.538 387 387 D AndroidRuntime: >>>>>> START com.android.internal.os.ZygoteInit uid 0 <<<<<< 4.5.3 Zygote進(jìn)程(java)(1)ZygoteInit java @frameworks\base\core\java\com\android\internal\os\ZygoteInit.javapublic static void main(String[] argv) {
...
try {
//Step 1. 預(yù)加載資源文件
if (!enableLazyPreload) {
bootTimingsTraceLog.traceBegin("ZygotePreload");
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload(bootTimingsTraceLog);
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());
bootTimingsTraceLog.traceEnd(); // ZygotePreload
}
...
//Step 2.注冊Zygote的socket監(jiān)聽接口
zygoteServer = new ZygoteServer(isPrimaryZygote);
//Step 3.創(chuàng)建system_server進(jìn)程
if (startSystemServer) {
Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);
if (r != null) {
r.run();
return;
}
}
//Step 4.主線程loop消息循環(huán)
caller = zygoteServer.runSelectLoop(abiList);
}
...}Step 1. 提前加載類,加載系統(tǒng)資源(如一些公共的庫、SDK等),這樣當(dāng)程序被fork處理后,應(yīng)用的進(jìn)程內(nèi)已經(jīng)包含了這些系統(tǒng)資源,大大節(jié)省了應(yīng)用的啟動(dòng)時(shí)間。 (2)forkSystemServer java @frameworks\base\core\java\com\android\internal\os\ZygoteInit.javaprivate static Runnable forkSystemServer(String abiList, String socketName,
ZygoteServer zygoteServer) {
...
/* Hardcoded command line to start the system server */
String[] args = {
"--setuid=1000",
"--setgid=1000",
"--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,1018,1021,1023,"
+ "1024,1032,1065,3001,3002,3003,3006,3007,3009,3010,3011",
"--capabilities=" + capabilities + "," + capabilities,
"--nice-name=system_server",
"--runtime-args",
"--target-sdk-version=" + VMRuntime.SDK_VERSION_CUR_DEVELOPMENT,
"com.android.server.SystemServer",
};//啟動(dòng)SystemServer相關(guān)參數(shù)
...
try {
...
/* Request to fork the system server process */
pid = Zygote.forkSystemServer(
parsedArgs.mUid, parsedArgs.mGid,
parsedArgs.mGids,
parsedArgs.mRuntimeFlags,
null,
parsedArgs.mPermittedCapabilities,
parsedArgs.mEffectiveCapabilities);//fork出SystemServer進(jìn)程
} catch (IllegalArgumentException ex) {
throw new RuntimeException(ex);
}
/* For child process */
if (pid == 0) {
...
return handleSystemServerProcess(parsedArgs);//通過反射調(diào)用SystemServer進(jìn)程的main函數(shù)
}
return null;}(3)handleSystemServerProcess java @frameworks\base\core\java\com\android\internal\os\RuntimeInit.javaprotected static Runnable findStaticMain(String className, String[] argv,
ClassLoader classLoader) {
Class<?> cl;
try {
cl = Class.forName(className, true, classLoader);//反射調(diào)用類:com.android.server.SystemServer
}
...
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });//反射調(diào)用方法:main
}
...
return new MethodAndArgsCaller(m, argv);}4.6 SystemServer進(jìn)程Android系統(tǒng)在啟動(dòng)的時(shí)候,在啟動(dòng)兩個(gè)重要的進(jìn)程,一個(gè)是Zygote進(jìn)程,另一個(gè)是由zygote進(jìn)程fork出來的system_server進(jìn)程。SystemSever負(fù)責(zé)啟動(dòng)系統(tǒng)的各項(xiàng)服務(wù),Android系統(tǒng)中Java世界的核心Service都在這里啟動(dòng)。 4.6.1 main函數(shù)由上一章節(jié)我們知道,SystemServer的入口函數(shù)是main方法,如下: java @frameworks\base\services\java\com\android\server\SystemServer.javapublic static void main(String[] args) {
new SystemServer().run();}private void run() {
...
Slog.i(TAG, "Entered the Android system server!");
...
// Start services.
try {
t.traceBegin("StartServices");
startBootstrapServices(t);//引導(dǎo)服務(wù)
startCoreServices(t);//核心服務(wù)
startOtherServices(t);//其他服務(wù)
}
...
// Loop forever.
Looper.loop();//主線程循環(huán)隊(duì)列
throw new RuntimeException("Main thread loop unexpectedly exited");}SystemServer進(jìn)程成功啟動(dòng),會(huì)打印如下log: none 01-01 08:00:21.430 1001 1001 I SystemServer: Entered the Android system server! 4.6.2 SystemServer中啟動(dòng)服務(wù)在一系列的java服務(wù)中,可以分為三類:系統(tǒng)boot級別服務(wù)、核心服務(wù)、其他服務(wù),其對應(yīng)如下:
4.7 Home進(jìn)程一般情況下,Android原生的軟體會(huì)包含兩個(gè)home進(jìn)程,一個(gè)是Settings進(jìn)程的Fallbackhome,一個(gè)是Launcher進(jìn)程。 4.7.1 Home進(jìn)程的編譯(1)FallbackHome編譯 none @packages\apps\Settings\Android.bp
android_app {
name: "Settings",
defaults: ["platform_app_defaults"],
platform_apis: true,
certificate: "platform",
system_ext_specific: true,
privileged: true,
...
}(2)Launcher進(jìn)程編譯 none @packages\apps\Launcher3\Android.mk include $(CLEAR_VARS) ... LOCAL_PACKAGE_NAME := Launcher3QuickStepGo LOCAL_PRIVILEGED_MODULE := true LOCAL_SYSTEM_EXT_MODULE := true LOCAL_OVERRIDES_PACKAGES := Home Launcher2 Launcher3 Launcher3QuickStep ... 4.7.2 Launcher進(jìn)程啟動(dòng)FallbackHome是系統(tǒng)由未解密到解密過程的一個(gè)過度界面,只要用戶把系統(tǒng)解鎖過一次后,F(xiàn)allbackHome收到解鎖廣播就會(huì)退出,而WMS檢測到當(dāng)前Acitivity棧是空的,進(jìn)而啟動(dòng)真正的Launcher。由于FallbackHome沒有界面,所以可能會(huì)出現(xiàn)一個(gè)問題,home進(jìn)程切換時(shí)會(huì)出現(xiàn)空白界面,接下來才是顯示Launcher的一個(gè)圖標(biāo)界面。 java @packages\apps\Settings\src\com\android\settings\FallbackHome.javaprotected void onCreate(Bundle savedInstanceState) {
...
registerReceiver(mReceiver, new IntentFilter(Intent.ACTION_USER_UNLOCKED));//注冊ACTION_USER_UNLOCKED廣播
maybeFinish();}private BroadcastReceiver mReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
maybeFinish();//接收ACTION_USER_UNLOCKED廣播
}};private void maybeFinish() {
if (getSystemService(UserManager.class).isUserUnlocked()) {
final Intent homeIntent = new Intent(Intent.ACTION_MAIN)
.addCategory(Intent.CATEGORY_HOME);
final ResolveInfo homeInfo = getPackageManager().resolveActivity(homeIntent, 0);//查詢home包名信息,此處一般是返回Launcher的信息
if (Objects.equals(getPackageName(), homeInfo.activityInfo.packageName)) {
Log.d(TAG, "User unlocked but no home; let's hope someone enables one soon?");
mHandler.sendEmptyMessageDelayed(0, 500);//間隔500ms輪詢
} else {
Log.d(TAG, "User unlocked and real home found; let's go!");
getSystemService(PowerManager.class).userActivity(
SystemClock.uptimeMillis(), false);
finish();//結(jié)束當(dāng)前Activity,啟動(dòng)Launcher應(yīng)用
}
}}4.7.3 FallbackHome進(jìn)程啟動(dòng)(1) 啟動(dòng)home進(jìn)程 java @frameworks\base\services\core\java\com\android\server\wm\RootWindowContainer.javavoid startHomeOnEmptyDisplays(String reason) {
forAllTaskDisplayAreas(taskDisplayArea -> {
if (taskDisplayArea.topRunningActivity() == null) {
startHomeOnTaskDisplayArea(mCurrentUser, reason, taskDisplayArea,
false /* allowInstrumenting */, false /* fromHomeKey */);
}
});}(2) ACTION_USER_UNLOCKED廣播發(fā)送 java @frameworks\base\services\core\java\com\android\server\am\UserController.javavoid finishUserUnlocked(final UserState uss) {
...
if (!mInjector.getUserManager().isPreCreated(userId)) {
// Dispatch unlocked to external apps
final Intent unlockedIntent = new Intent(Intent.ACTION_USER_UNLOCKED);
unlockedIntent.putExtra(Intent.EXTRA_USER_HANDLE, userId);
unlockedIntent.addFlags(
Intent.FLAG_RECEIVER_REGISTERED_ONLY | Intent.FLAG_RECEIVER_FOREGROUND);
mInjector.broadcastIntent(unlockedIntent, null, null, 0, null,
null, null, AppOpsManager.OP_NONE, null, false, false, MY_PID, SYSTEM_UID,
Binder.getCallingUid(), Binder.getCallingPid(), userId);
}
...}五、相關(guān)資源5.1 開機(jī)log串口+logcat:https://download.csdn.net/download/u013320490/88800008 六、小結(jié) 本文章涉獵Android多個(gè)層級,旨在梳理整體流程,對Android設(shè)備的啟動(dòng)有一個(gè)感性的認(rèn)識,能夠達(dá)到一定邏輯自洽。 七、參考資料
作者:林奮斗同學(xué),轉(zhuǎn)自博客園 https://www.cnblogs.com/zhiqinlin/p/18001113 該文章在 2024/2/1 16:39:13 編輯過 |
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