前面我准备开始讲性能优化，讲到一半发现根本讲不下去。性能优化是基于对Framework深入理解的基础上的应用，如果对Framework没有深入的理解的话，又怎么能去很好的去做性能优化呢？所以，我调整了一下顺序。先讲清楚Framework这一块，然后再去补充性能优化专题。我们也是从开机到应用程序画面显示在我们面前这一流程开始。这一过程看似简单，其实细分一下有3个方面：
- 系统启动流程
- 应用进程启动流程
- Activity启动流程
我们就从系统启动流程开始吧。
init进程启动过程
- 启动电源以及系统启动：当电源按下时引导芯片代码从预定义的地方（固化在ROM）开始执行。加载引导程序BootLoader到RAM中，然后执行。ROM可以理解为硬盘，RAM可以理解为内存。
- 引导程序BootLoader：引导程序BootLoader是在Android操作系统开始运行前的一个小程序，它的主要作用是把系统OS拉起来并运行。
- Linux内核启动：当内核启动时，会有一系列系统设置。当内核完成系统设置后，它首先在系统文件中寻找init.rc文件，并启动init进程。
- init进程启动：init进程做的工作比较多，主要用来初始化和启动属性服务，也用来启动Zygote进程。
我们来看看init的入口函数：
路径：system/core/init/init.cpp
int main(int argc, char** argv) {
if (!strcmp(basename(argv[0]), "ueventd")) {
return ueventd_main(argc, argv);
}
if (!strcmp(basename(argv[0]), "watchdogd")) {
return watchdogd_main(argc, argv);
}
if (argc > 1 && !strcmp(argv[1], "subcontext")) {
InitKernelLogging(argv);
const BuiltinFunctionMap function_map;
return SubcontextMain(argc, argv, &function_map);
}
if (REBOOT_BOOTLOADER_ON_PANIC) {
InstallRebootSignalHandlers();
}
bool is_first_stage = (getenv("INIT_SECOND_STAGE") == nullptr);
if (is_first_stage) {
boot_clock::time_point start_time = boot_clock::now();
// Clear the umask.
umask(0);
clearenv();
setenv("PATH", _PATH_DEFPATH, 1);
// Get the basic filesystem setup we need put together in the initramdisk
// on / and then we'll let the rc file figure out the rest.
mount("tmpfs", "/dev", "tmpfs", MS_NOSUID, "mode=0755");
mkdir("/dev/pts", 0755);
mkdir("/dev/socket", 0755);
mount("devpts", "/dev/pts", "devpts", 0, NULL);
#define MAKE_STR(x) __STRING(x)
mount("proc", "/proc", "proc", 0, "hidepid=2,gid=" MAKE_STR(AID_READPROC));
// Don't expose the raw commandline to unprivileged processes.
chmod("/proc/cmdline", 0440);
gid_t groups[] = { AID_READPROC };
setgroups(arraysize(groups), groups);
mount("sysfs", "/sys", "sysfs", 0, NULL);
mount("selinuxfs", "/sys/fs/selinux", "selinuxfs", 0, NULL);
mknod("/dev/kmsg", S_IFCHR | 0600, makedev(1, 11));
if constexpr (WORLD_WRITABLE_KMSG) {
mknod("/dev/kmsg_debug", S_IFCHR | 0622, makedev(1, 11));
}
mknod("/dev/random", S_IFCHR | 0666, makedev(1, 8));
mknod("/dev/urandom", S_IFCHR | 0666, makedev(1, 9));
// Mount staging areas for devices managed by vold
// See storage config details at http://source.android.com/devices/storage/
mount("tmpfs", "/mnt", "tmpfs", MS_NOEXEC | MS_NOSUID | MS_NODEV,
"mode=0755,uid=0,gid=1000");
// /mnt/vendor is used to mount vendor-specific partitions that can not be
// part of the vendor partition, e.g. because they are mounted read-write.
mkdir("/mnt/vendor", 0755);
// Now that tmpfs is mounted on /dev and we have /dev/kmsg, we can actually
// talk to the outside world...
InitKernelLogging(argv);
LOG(INFO) << "init first stage started!";
if (!DoFirstStageMount()) {
LOG(FATAL) << "Failed to mount required partitions early ...";
}
SetInitAvbVersionInRecovery();
// Enable seccomp if global boot option was passed (otherwise it is enabled in zygote).
global_seccomp();
// Set up SELinux, loading the SELinux policy.
SelinuxSetupKernelLogging();
SelinuxInitialize();
// We're in the kernel domain, so re-exec init to transition to the init domain now
// that the SELinux policy has been loaded.
if (selinux_android_restorecon("/init", 0) == -1) {
PLOG(FATAL) << "restorecon failed of /init failed";
}
setenv("INIT_SECOND_STAGE", "true", 1);
static constexpr uint32_t kNanosecondsPerMillisecond = 1e6;
uint64_t start_ms = start_time.time_since_epoch().count() / kNanosecondsPerMillisecond;
setenv("INIT_STARTED_AT", std::to_string(start_ms).c_str(), 1);
char* path = argv[0];
char* args[] = { path, nullptr };
execv(path, args);
// execv() only returns if an error happened, in which case we
// panic and never fall through this conditional.
PLOG(FATAL) << "execv(\"" << path << "\") failed";
}
// At this point we're in the second stage of init.
InitKernelLogging(argv);
LOG(INFO) << "init second stage started!";
// Set up a session keyring that all processes will have access to. It
// will hold things like FBE encryption keys. No process should override
// its session keyring.
keyctl_get_keyring_ID(KEY_SPEC_SESSION_KEYRING, 1);
// Indicate that booting is in progress to background fw loaders, etc.
close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
property_init();//1 对属性进行初始化
// If arguments are passed both on the command line and in DT,
// properties set in DT always have priority over the command-line ones.
process_kernel_dt();
process_kernel_cmdline();
// Propagate the kernel variables to internal variables
// used by init as well as the current required properties.
export_kernel_boot_props();
// Make the time that init started available for bootstat to log.
property_set("ro.boottime.init", getenv("INIT_STARTED_AT"));
property_set("ro.boottime.init.selinux", getenv("INIT_SELINUX_TOOK"));
// Set libavb version for Framework-only OTA match in Treble build.
const char* avb_version = getenv("INIT_AVB_VERSION");
if (avb_version) property_set("ro.boot.avb_version", avb_version);
// Clean up our environment.
unsetenv("INIT_SECOND_STAGE");
unsetenv("INIT_STARTED_AT");
unsetenv("INIT_SELINUX_TOOK");
unsetenv("INIT_AVB_VERSION");
// Now set up SELinux for second stage.
SelinuxSetupKernelLogging();
SelabelInitialize();
SelinuxRestoreContext();
epoll_fd = epoll_create1(EPOLL_CLOEXEC);
if (epoll_fd == -1) {
PLOG(FATAL) << "epoll_create1 failed";
}
sigchld_handler_init();
if (!IsRebootCapable()) {
// If init does not have the CAP_SYS_BOOT capability, it is running in a container.
// In that case, receiving SIGTERM will cause the system to shut down.
InstallSigtermHandler();
}
property_load_boot_defaults();
export_oem_lock_status();
start_property_service();
set_usb_controller();
const BuiltinFunctionMap function_map;
Action::set_function_map(&function_map);
subcontexts = InitializeSubcontexts();
ActionManager& am = ActionManager::GetInstance();
ServiceList& sm = ServiceList::GetInstance();
LoadBootScripts(am, sm); //2
// Turning this on and letting the INFO logging be discarded adds 0.2s to
// Nexus 9 boot time, so it's disabled by default.
if (false) DumpState();
am.QueueEventTrigger("early-init");
// Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...
am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");
// ... so that we can start queuing up actions that require stuff from /dev.
am.QueueBuiltinAction(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");
am.QueueBuiltinAction(SetMmapRndBitsAction, "SetMmapRndBits");
am.QueueBuiltinAction(SetKptrRestrictAction, "SetKptrRestrict");
am.QueueBuiltinAction(keychord_init_action, "keychord_init");
am.QueueBuiltinAction(console_init_action, "console_init");
// Trigger all the boot actions to get us started.
am.QueueEventTrigger("init");
// Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
// wasn't ready immediately after wait_for_coldboot_done
am.QueueBuiltinAction(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");
// Don't mount filesystems or start core system services in charger mode.
std::string bootmode = GetProperty("ro.bootmode", "");
if (bootmode == "charger") {
am.QueueEventTrigger("charger");
} else {
am.QueueEventTrigger("late-init");
}
// Run all property triggers based on current state of the properties.
am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");
while (true) {
// By default, sleep until something happens.
int epoll_timeout_ms = -1;
if (do_shutdown && !shutting_down) {
do_shutdown = false;
if (HandlePowerctlMessage(shutdown_command)) {
shutting_down = true;
}
}
if (!(waiting_for_prop || Service::is_exec_service_running())) {
am.ExecuteOneCommand();
}
if (!(waiting_for_prop || Service::is_exec_service_running())) {
if (!shutting_down) {
auto next_process_restart_time = RestartProcesses();
// If there's a process that needs restarting, wake up in time for that.
if (next_process_restart_time) {
epoll_timeout_ms = std::chrono::ceil<std::chrono::milliseconds>(
*next_process_restart_time - boot_clock::now())
.count();
if (epoll_timeout_ms < 0) epoll_timeout_ms = 0;
}
}
// If there's more work to do, wake up again immediately.
if (am.HasMoreCommands()) epoll_timeout_ms = 0;
}
epoll_event ev;
int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));
if (nr == -1) {
PLOG(ERROR) << "epoll_wait failed";
} else if (nr == 1) {
((void (*)()) ev.data.ptr)();
}
}
return 0;
}
static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {
Parser parser = CreateParser(action_manager, service_list);
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
parser.ParseConfig("/init.rc");//3 解析init.rc
if (!parser.ParseConfig("/system/etc/init")) {
late_import_paths.emplace_back("/system/etc/init");
}
if (!parser.ParseConfig("/product/etc/init")) {
late_import_paths.emplace_back("/product/etc/init");
}
if (!parser.ParseConfig("/odm/etc/init")) {
late_import_paths.emplace_back("/odm/etc/init");
}
if (!parser.ParseConfig("/vendor/etc/init")) {
late_import_paths.emplace_back("/vendor/etc/init");
}
} else {
parser.ParseConfig(bootscript);
}
}
init的入口函数代码很长，但是我们只需要关注一个点：会去解析init.rc。
那么，init.rc又是什么呢？我们翻看源码发现有init.rc还有init.zygote64.rc，这两个文件之间又是什么关系呢？
init.rc是一个非常重要的配置文件，它是由安卓初始化语言编写的脚本，这种语言主要有5种类型的语句：Action,Command,Service,Option,Import。
on <trigger> //Action语句 设置触发器
<command> //动作触发后执行的命令
<command>
<command>
service <name> <pathname> [ <argument> ]* //Service类型语句 service名称/执行程序路径/传递参数
<option> //option是service修饰词，影响什么时候启动，如何启动service
<option>
我们来看看init.rc具体内容：
路径：system/core/rootdir/init.rc
# Copyright (C) 2012 The Android Open Source Project
#
# IMPORTANT: Do not create world writable files or directories.
# This is a common source of Android security bugs.
#
import /init.environ.rc
import /init.usb.rc
import /init.${ro.hardware}.rc
import /vendor/etc/init/hw/init.${ro.hardware}.rc
import /init.usb.configfs.rc
import /init.${ro.zygote}.rc //1
on early-init
# Set init and its forked children's oom_adj.
write /proc/1/oom_score_adj -1000
# Disable sysrq from keyboard
write /proc/sys/kernel/sysrq 0
# Set the security context of /adb_keys if present.
restorecon /adb_keys
# Set the security context of /postinstall if present.
restorecon /postinstall
# Mount cgroup mount point for cpu accounting
mount cgroup none /acct nodev noexec nosuid cpuacct
mkdir /acct/uid
# root memory control cgroup, used by lmkd
mkdir /dev/memcg 0700 root system
mount cgroup none /dev/memcg nodev noexec nosuid memory
# app mem cgroups, used by activity manager, lmkd and zygote
mkdir /dev/memcg/apps/ 0755 system system
# cgroup for system_server and surfaceflinger
mkdir /dev/memcg/system 0550 system system
start ueventd
on init
sysclktz 0
# Mix device-specific information into the entropy pool
copy /proc/cmdline /dev/urandom
copy /default.prop /dev/urandom
symlink /system/bin /bin
symlink /system/etc /etc
# Backward compatibility.
symlink /sys/kernel/debug /d
# Link /vendor to /system/vendor for devices without a vendor partition.
symlink /system/vendor /vendor
# Create energy-aware scheduler tuning nodes
mkdir /dev/stune
mount cgroup none /dev/stune nodev noexec nosuid schedtune
mkdir /dev/stune/foreground
mkdir /dev/stune/background
mkdir /dev/stune/top-app
mkdir /dev/stune/rt
chown system system /dev/stune
chown system system /dev/stune/foreground
chown system system /dev/stune/background
chown system system /dev/stune/top-app
chown system system /dev/stune/rt
chown system system /dev/stune/tasks
chown system system /dev/stune/foreground/tasks
chown system system /dev/stune/background/tasks
chown system system /dev/stune/top-app/tasks
chown system system /dev/stune/rt/tasks
chmod 0664 /dev/stune/tasks
chmod 0664 /dev/stune/foreground/tasks
chmod 0664 /dev/stune/background/tasks
chmod 0664 /dev/stune/top-app/tasks
chmod 0664 /dev/stune/rt/tasks
restorecon_recursive /mnt
mount configfs none /config nodev noexec nosuid
chmod 0770 /config/sdcardfs
chown system package_info /config/sdcardfs
mkdir /mnt/secure 0700 root root
mkdir /mnt/secure/asec 0700 root root
mkdir /mnt/asec 0755 root system
mkdir /mnt/obb 0755 root system
mkdir /mnt/media_rw 0750 root media_rw
mkdir /mnt/user 0755 root root
mkdir /mnt/user/0 0755 root root
mkdir /mnt/expand 0771 system system
mkdir /mnt/appfuse 0711 root root
# Storage views to support runtime permissions
mkdir /mnt/runtime 0700 root root
mkdir /mnt/runtime/default 0755 root root
mkdir /mnt/runtime/default/self 0755 root root
mkdir /mnt/runtime/read 0755 root root
mkdir /mnt/runtime/read/self 0755 root root
mkdir /mnt/runtime/write 0755 root root
mkdir /mnt/runtime/write/self 0755 root root
# Symlink to keep legacy apps working in multi-user world
symlink /storage/self/primary /sdcard
symlink /storage/self/primary /mnt/sdcard
symlink /mnt/user/0/primary /mnt/runtime/default/self/primary
write /proc/sys/kernel/panic_on_oops 1
write /proc/sys/kernel/hung_task_timeout_secs 0
write /proc/cpu/alignment 4
# scheduler tunables
# Disable auto-scaling of scheduler tunables with hotplug. The tunables
# will vary across devices in unpredictable ways if allowed to scale with
# cpu cores.
write /proc/sys/kernel/sched_tunable_scaling 0
write /proc/sys/kernel/sched_latency_ns 10000000
write /proc/sys/kernel/sched_wakeup_granularity_ns 2000000
write /proc/sys/kernel/sched_child_runs_first 0
write /proc/sys/kernel/randomize_va_space 2
write /proc/sys/vm/mmap_min_addr 32768
write /proc/sys/net/ipv4/ping_group_range "0 2147483647"
write /proc/sys/net/unix/max_dgram_qlen 600
write /proc/sys/kernel/sched_rt_runtime_us 950000
write /proc/sys/kernel/sched_rt_period_us 1000000
# Assign reasonable ceiling values for socket rcv/snd buffers.
# These should almost always be overridden by the target per the
# the corresponding technology maximums.
write /proc/sys/net/core/rmem_max 262144
write /proc/sys/net/core/wmem_max 262144
# reflect fwmark from incoming packets onto generated replies
write /proc/sys/net/ipv4/fwmark_reflect 1
write /proc/sys/net/ipv6/fwmark_reflect 1
# set fwmark on accepted sockets
write /proc/sys/net/ipv4/tcp_fwmark_accept 1
# disable icmp redirects
write /proc/sys/net/ipv4/conf/all/accept_redirects 0
write /proc/sys/net/ipv6/conf/all/accept_redirects 0
# /proc/net/fib_trie leaks interface IP addresses
chmod 0400 /proc/net/fib_trie
# Create cgroup mount points for process groups
mkdir /dev/cpuctl
mount cgroup none /dev/cpuctl nodev noexec nosuid cpu
chown system system /dev/cpuctl
chown system system /dev/cpuctl/tasks
chmod 0666 /dev/cpuctl/tasks
write /dev/cpuctl/cpu.rt_period_us 1000000
write /dev/cpuctl/cpu.rt_runtime_us 950000
# sets up initial cpusets for ActivityManager
mkdir /dev/cpuset
mount cpuset none /dev/cpuset nodev noexec nosuid
# this ensures that the cpusets are present and usable, but the device's
# init.rc must actually set the correct cpus
mkdir /dev/cpuset/foreground
copy /dev/cpuset/cpus /dev/cpuset/foreground/cpus
copy /dev/cpuset/mems /dev/cpuset/foreground/mems
mkdir /dev/cpuset/background
copy /dev/cpuset/cpus /dev/cpuset/background/cpus
copy /dev/cpuset/mems /dev/cpuset/background/mems
# system-background is for system tasks that should only run on
# little cores, not on bigs
# to be used only by init, so don't change system-bg permissions
mkdir /dev/cpuset/system-background
copy /dev/cpuset/cpus /dev/cpuset/system-background/cpus
copy /dev/cpuset/mems /dev/cpuset/system-background/mems
# restricted is for system tasks that are being throttled
# due to screen off.
mkdir /dev/cpuset/restricted
copy /dev/cpuset/cpus /dev/cpuset/restricted/cpus
copy /dev/cpuset/mems /dev/cpuset/restricted/mems
mkdir /dev/cpuset/top-app
copy /dev/cpuset/cpus /dev/cpuset/top-app/cpus
copy /dev/cpuset/mems /dev/cpuset/top-app/mems
# change permissions for all cpusets we'll touch at runtime
chown system system /dev/cpuset
chown system system /dev/cpuset/foreground
chown system system /dev/cpuset/background
chown system system /dev/cpuset/system-background
chown system system /dev/cpuset/top-app
chown system system /dev/cpuset/restricted
chown system system /dev/cpuset/tasks
chown system system /dev/cpuset/foreground/tasks
chown system system /dev/cpuset/background/tasks
chown system system /dev/cpuset/system-background/tasks
chown system system /dev/cpuset/top-app/tasks
chown system system /dev/cpuset/restricted/tasks
# set system-background to 0775 so SurfaceFlinger can touch it
chmod 0775 /dev/cpuset/system-background
chmod 0664 /dev/cpuset/foreground/tasks
chmod 0664 /dev/cpuset/background/tasks
chmod 0664 /dev/cpuset/system-background/tasks
chmod 0664 /dev/cpuset/top-app/tasks
chmod 0664 /dev/cpuset/restricted/tasks
chmod 0664 /dev/cpuset/tasks
# qtaguid will limit access to specific data based on group memberships.
# net_bw_acct grants impersonation of socket owners.
# net_bw_stats grants access to other apps' detailed tagged-socket stats.
chown root net_bw_acct /proc/net/xt_qtaguid/ctrl
chown root net_bw_stats /proc/net/xt_qtaguid/stats
# Allow everybody to read the xt_qtaguid resource tracking misc dev.
# This is needed by any process that uses socket tagging.
chmod 0644 /dev/xt_qtaguid
mkdir /dev/cg2_bpf
mount cgroup2 cg2_bpf /dev/cg2_bpf nodev noexec nosuid
chown root root /dev/cg2_bpf
chmod 0600 /dev/cg2_bpf
mount bpf bpf /sys/fs/bpf nodev noexec nosuid
# Create location for fs_mgr to store abbreviated output from filesystem
# checker programs.
mkdir /dev/fscklogs 0770 root system
# pstore/ramoops previous console log
mount pstore pstore /sys/fs/pstore nodev noexec nosuid
chown system log /sys/fs/pstore/console-ramoops
chmod 0440 /sys/fs/pstore/console-ramoops
chown system log /sys/fs/pstore/console-ramoops-0
chmod 0440 /sys/fs/pstore/console-ramoops-0
chown system log /sys/fs/pstore/pmsg-ramoops-0
chmod 0440 /sys/fs/pstore/pmsg-ramoops-0
# enable armv8_deprecated instruction hooks
write /proc/sys/abi/swp 1
# Linux's execveat() syscall may construct paths containing /dev/fd
# expecting it to point to /proc/self/fd
symlink /proc/self/fd /dev/fd
export DOWNLOAD_CACHE /data/cache
# set RLIMIT_NICE to allow priorities from 19 to -20
setrlimit nice 40 40
# Allow up to 32K FDs per process
setrlimit nofile 32768 32768
# This allows the ledtrig-transient properties to be created here so
# that they can be chown'd to system:system later on boot
write /sys/class/leds/vibrator/trigger "transient"
# Healthd can trigger a full boot from charger mode by signaling this
# property when the power button is held.
on property:sys.boot_from_charger_mode=1
class_stop charger
trigger late-init
on load_persist_props_action
load_persist_props
start logd
start logd-reinit
# Indicate to fw loaders that the relevant mounts are up.
on firmware_mounts_complete
rm /dev/.booting
# Mount filesystems and start core system services.
on late-init
trigger early-fs
# Mount fstab in init.{$device}.rc by mount_all command. Optional parameter
# '--early' can be specified to skip entries with 'latemount'.
# /system and /vendor must be mounted by the end of the fs stage,
# while /data is optional.
trigger fs
trigger post-fs
# Mount fstab in init.{$device}.rc by mount_all with '--late' parameter
# to only mount entries with 'latemount'. This is needed if '--early' is
# specified in the previous mount_all command on the fs stage.
# With /system mounted and properties form /system + /factory available,
# some services can be started.
trigger late-fs
# Now we can mount /data. File encryption requires keymaster to decrypt
# /data, which in turn can only be loaded when system properties are present.
trigger post-fs-data
# Now we can start zygote for devices with file based encryption
trigger zygote-start
# Load persist properties and override properties (if enabled) from /data.
trigger load_persist_props_action
# Remove a file to wake up anything waiting for firmware.
trigger firmware_mounts_complete
trigger early-boot
trigger boot
on post-fs
# Load properties from
# /system/build.prop,
# /odm/build.prop,
# /vendor/build.prop and
# /factory/factory.prop
load_system_props
# start essential services
start logd
start servicemanager
start hwservicemanager
start vndservicemanager
# Once everything is setup, no need to modify /.
# The bind+ro combination avoids modifying any other mount flags.
mount rootfs rootfs / remount bind ro
# Mount shared so changes propagate into child namespaces
mount rootfs rootfs / shared rec
# Mount default storage into root namespace
mount none /mnt/runtime/default /storage bind rec
mount none none /storage slave rec
# Make sure /sys/kernel/debug (if present) is labeled properly
# Note that tracefs may be mounted under debug, so we need to cross filesystems
restorecon --recursive --cross-filesystems /sys/kernel/debug
# We chown/chmod /cache again so because mount is run as root + defaults
chown system cache /cache
chmod 0770 /cache
# We restorecon /cache in case the cache partition has been reset.
restorecon_recursive /cache
# Create /cache/recovery in case it's not there. It'll also fix the odd
# permissions if created by the recovery system.
mkdir /cache/recovery 0770 system cache
# Backup/restore mechanism uses the cache partition
mkdir /cache/backup_stage 0700 system system
mkdir /cache/backup 0700 system system
#change permissions on vmallocinfo so we can grab it from bugreports
chown root log /proc/vmallocinfo
chmod 0440 /proc/vmallocinfo
chown root log /proc/slabinfo
chmod 0440 /proc/slabinfo
#change permissions on kmsg & sysrq-trigger so bugreports can grab kthread stacks
chown root system /proc/kmsg
chmod 0440 /proc/kmsg
chown root system /proc/sysrq-trigger
chmod 0220 /proc/sysrq-trigger
chown system log /proc/last_kmsg
chmod 0440 /proc/last_kmsg
# make the selinux kernel policy world-readable
chmod 0444 /sys/fs/selinux/policy
# create the lost+found directories, so as to enforce our permissions
mkdir /cache/lost+found 0770 root root
restorecon_recursive /metadata
mkdir /metadata/vold
chmod 0700 /metadata/vold
on late-fs
# Ensure that tracefs has the correct permissions.
# This does not work correctly if it is called in post-fs.
chmod 0755 /sys/kernel/debug/tracing
# HALs required before storage encryption can get unlocked (FBE/FDE)
class_start early_hal
on post-fs-data
# We chown/chmod /data again so because mount is run as root + defaults
chown system system /data
chmod 0771 /data
# We restorecon /data in case the userdata partition has been reset.
restorecon /data
# Make sure we have the device encryption key.
start vold
installkey /data
# Start bootcharting as soon as possible after the data partition is
# mounted to collect more data.
mkdir /data/bootchart 0755 shell shell
bootchart start
# Avoid predictable entropy pool. Carry over entropy from previous boot.
copy /data/system/entropy.dat /dev/urandom
# create basic filesystem structure
mkdir /data/misc 01771 system misc
mkdir /data/misc/recovery 0770 system log
copy /data/misc/recovery/ro.build.fingerprint /data/misc/recovery/ro.build.fingerprint.1
chmod 0440 /data/misc/recovery/ro.build.fingerprint.1
chown system log /data/misc/recovery/ro.build.fingerprint.1
write /data/misc/recovery/ro.build.fingerprint ${ro.build.fingerprint}
chmod 0440 /data/misc/recovery/ro.build.fingerprint
chown system log /data/misc/recovery/ro.build.fingerprint
mkdir /data/misc/recovery/proc 0770 system log
copy /data/misc/recovery/proc/version /data/misc/recovery/proc/version.1
chmod 0440 /data/misc/recovery/proc/version.1
chown system log /data/misc/recovery/proc/version.1
copy /proc/version /data/misc/recovery/proc/version
chmod 0440 /data/misc/recovery/proc/version
chown system log /data/misc/recovery/proc/version
mkdir /data/misc/bluedroid 02770 bluetooth bluetooth
# Fix the access permissions and group ownership for 'bt_config.conf'
chmod 0660 /data/misc/bluedroid/bt_config.conf
chown bluetooth bluetooth /data/misc/bluedroid/bt_config.conf
mkdir /data/misc/bluetooth 0770 bluetooth bluetooth
mkdir /data/misc/bluetooth/logs 0770 bluetooth bluetooth
mkdir /data/misc/keystore 0700 keystore keystore
mkdir /data/misc/gatekeeper 0700 system system
mkdir /data/misc/keychain 0771 system system
mkdir /data/misc/net 0750 root shell
mkdir /data/misc/radio 0770 system radio
mkdir /data/misc/sms 0770 system radio
mkdir /data/misc/carrierid 0770 system radio
mkdir /data/misc/apns 0770 system radio
mkdir /data/misc/zoneinfo 0775 system system
mkdir /data/misc/network_watchlist 0774 system system
mkdir /data/misc/textclassifier 0771 system system
mkdir /data/misc/vpn 0770 system vpn
mkdir /data/misc/shared_relro 0771 shared_relro shared_relro
mkdir /data/misc/systemkeys 0700 system system
mkdir /data/misc/wifi 0770 wifi wifi
mkdir /data/misc/wifi/sockets 0770 wifi wifi
mkdir /data/misc/wifi/wpa_supplicant 0770 wifi wifi
mkdir /data/misc/ethernet 0770 system system
mkdir /data/misc/dhcp 0770 dhcp dhcp
mkdir /data/misc/user 0771 root root
mkdir /data/misc/perfprofd 0775 root root
# give system access to wpa_supplicant.conf for backup and restore
chmod 0660 /data/misc/wifi/wpa_supplicant.conf
mkdir /data/local 0751 root root
mkdir /data/misc/media 0700 media media
mkdir /data/misc/audioserver 0700 audioserver audioserver
mkdir /data/misc/cameraserver 0700 cameraserver cameraserver
mkdir /data/misc/vold 0700 root root
mkdir /data/misc/boottrace 0771 system shell
mkdir /data/misc/update_engine 0700 root root
mkdir /data/misc/update_engine_log 02750 root log
mkdir /data/misc/trace 0700 root root
# create location to store surface and window trace files
mkdir /data/misc/wmtrace 0700 system system
# profile file layout
mkdir /data/misc/profiles 0771 system system
mkdir /data/misc/profiles/cur 0771 system system
mkdir /data/misc/profiles/ref 0771 system system
mkdir /data/misc/profman 0770 system shell
mkdir /data/misc/gcov 0770 root root
mkdir /data/vendor 0771 root root
mkdir /data/vendor_ce 0771 root root
mkdir /data/vendor_de 0771 root root
mkdir /data/vendor/hardware 0771 root root
# For security reasons, /data/local/tmp should always be empty.
# Do not place files or directories in /data/local/tmp
mkdir /data/local/tmp 0771 shell shell
mkdir /data/local/traces 0777 shell shell
mkdir /data/data 0771 system system
mkdir /data/app-private 0771 system system
mkdir /data/app-ephemeral 0771 system system
mkdir /data/app-asec 0700 root root
mkdir /data/app-lib 0771 system system
mkdir /data/app 0771 system system
mkdir /data/property 0700 root root
mkdir /data/tombstones 0771 system system
mkdir /data/vendor/tombstones 0771 root root
mkdir /data/vendor/tombstones/wifi 0771 wifi wifi
# create dalvik-cache, so as to enforce our permissions
mkdir /data/dalvik-cache 0771 root root
# create the A/B OTA directory, so as to enforce our permissions
mkdir /data/ota 0771 root root
# create the OTA package directory. It will be accessed by GmsCore (cache
# group), update_engine and update_verifier.
mkdir /data/ota_package 0770 system cache
# create resource-cache and double-check the perms
mkdir /data/resource-cache 0771 system system
chown system system /data/resource-cache
chmod 0771 /data/resource-cache
# create the lost+found directories, so as to enforce our permissions
mkdir /data/lost+found 0770 root root
# create directory for DRM plug-ins - give drm the read/write access to
# the following directory.
mkdir /data/drm 0770 drm drm
# create directory for MediaDrm plug-ins - give drm the read/write access to
# the following directory.
mkdir /data/mediadrm 0770 mediadrm mediadrm
mkdir /data/anr 0775 system system
# NFC: create data/nfc for nv storage
mkdir /data/nfc 0770 nfc nfc
mkdir /data/nfc/param 0770 nfc nfc
# Create all remaining /data root dirs so that they are made through init
# and get proper encryption policy installed
mkdir /data/backup 0700 system system
mkdir /data/ss 0700 system system
mkdir /data/system 0775 system system
mkdir /data/system/heapdump 0700 system system
mkdir /data/system/users 0775 system system
mkdir /data/system_de 0770 system system
mkdir /data/system_ce 0770 system system
mkdir /data/misc_de 01771 system misc
mkdir /data/misc_ce 01771 system misc
mkdir /data/user 0711 system system
mkdir /data/user_de 0711 system system
symlink /data/data /data/user/0
mkdir /data/media 0770 media_rw media_rw
mkdir /data/media/obb 0770 media_rw media_rw
mkdir /data/cache 0770 system cache
mkdir /data/cache/recovery 0770 system cache
mkdir /data/cache/backup_stage 0700 system system
mkdir /data/cache/backup 0700 system system
init_user0
# Set SELinux security contexts on upgrade or policy update.
restorecon --recursive --skip-ce /data
# Check any timezone data in /data is newer than the copy in /system, delete if not.
exec - system system -- /system/bin/tzdatacheck /system/usr/share/zoneinfo /data/misc/zoneinfo
# If there is no post-fs-data action in the init.<device>.rc file, you
# must uncomment this line, otherwise encrypted filesystems
# won't work.
# Set indication (checked by vold) that we have finished this action
#setprop vold.post_fs_data_done 1
# 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 //2
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on zygote-start && property:ro.crypto.state=unsupported
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on zygote-start && property:ro.crypto.state=encrypted && property:ro.crypto.type=file
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on boot
# basic network init
ifup lo
hostname localhost
domainname localdomain
# IPsec SA default expiration length
write /proc/sys/net/core/xfrm_acq_expires 3600
# Memory management. Basic kernel parameters, and allow the high
# level system server to be able to adjust the kernel OOM driver
# parameters to match how it is managing things.
write /proc/sys/vm/overcommit_memory 1
write /proc/sys/vm/min_free_order_shift 4
chown root system /sys/module/lowmemorykiller/parameters/adj
chmod 0664 /sys/module/lowmemorykiller/parameters/adj
chown root system /sys/module/lowmemorykiller/parameters/minfree
chmod 0664 /sys/module/lowmemorykiller/parameters/minfree
# Tweak background writeout
write /proc/sys/vm/dirty_expire_centisecs 200
write /proc/sys/vm/dirty_background_ratio 5
# Permissions for System Server and daemons.
chown radio system /sys/android_power/state
chown radio system /sys/android_power/request_state
chown radio system /sys/android_power/acquire_full_wake_lock
chown radio system /sys/android_power/acquire_partial_wake_lock
chown radio system /sys/android_power/release_wake_lock
chown system system /sys/power/autosleep
chown system system /sys/power/state
chown system system /sys/power/wakeup_count
chown radio wakelock /sys/power/wake_lock
chown radio wakelock /sys/power/wake_unlock
chmod 0660 /sys/power/state
chmod 0660 /sys/power/wake_lock
chmod 0660 /sys/power/wake_unlock
chown system system /sys/devices/system/cpu/cpufreq/interactive/timer_rate
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/timer_rate
chown system system /sys/devices/system/cpu/cpufreq/interactive/timer_slack
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/timer_slack
chown system system /sys/devices/system/cpu/cpufreq/interactive/min_sample_time
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/min_sample_time
chown system system /sys/devices/system/cpu/cpufreq/interactive/hispeed_freq
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/hispeed_freq
chown system system /sys/devices/system/cpu/cpufreq/interactive/target_loads
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/target_loads
chown system system /sys/devices/system/cpu/cpufreq/interactive/go_hispeed_load
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/go_hispeed_load
chown system system /sys/devices/system/cpu/cpufreq/interactive/above_hispeed_delay
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/above_hispeed_delay
chown system system /sys/devices/system/cpu/cpufreq/interactive/boost
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/boost
chown system system /sys/devices/system/cpu/cpufreq/interactive/boostpulse
chown system system /sys/devices/system/cpu/cpufreq/interactive/input_boost
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/input_boost
chown system system /sys/devices/system/cpu/cpufreq/interactive/boostpulse_duration
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/boostpulse_duration
chown system system /sys/devices/system/cpu/cpufreq/interactive/io_is_busy
chmod 0660 /sys/devices/system/cpu/cpufreq/interactive/io_is_busy
# Assume SMP uses shared cpufreq policy for all CPUs
chown system system /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
chmod 0660 /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
chown system system /sys/class/leds/vibrator/trigger
chown system system /sys/class/leds/vibrator/activate
chown system system /sys/class/leds/vibrator/brightness
chown system system /sys/class/leds/vibrator/duration
chown system system /sys/class/leds/vibrator/state
chown system system /sys/class/timed_output/vibrator/enable
chown system system /sys/class/leds/keyboard-backlight/brightness
chown system system /sys/class/leds/lcd-backlight/brightness
chown system system /sys/class/leds/button-backlight/brightness
chown system system /sys/class/leds/jogball-backlight/brightness
chown system system /sys/class/leds/red/brightness
chown system system /sys/class/leds/green/brightness
chown system system /sys/class/leds/blue/brightness
chown system system /sys/class/leds/red/device/grpfreq
chown system system /sys/class/leds/red/device/grppwm
chown system system /sys/class/leds/red/device/blink
chown system system /sys/module/sco/parameters/disable_esco
chown system system /sys/kernel/ipv4/tcp_wmem_min
chown system system /sys/kernel/ipv4/tcp_wmem_def
chown system system /sys/kernel/ipv4/tcp_wmem_max
chown system system /sys/kernel/ipv4/tcp_rmem_min
chown system system /sys/kernel/ipv4/tcp_rmem_def
chown system system /sys/kernel/ipv4/tcp_rmem_max
chown root radio /proc/cmdline
# Define default initial receive window size in segments.
setprop net.tcp.default_init_rwnd 60
# Start standard binderized HAL daemons
class_start hal
class_start core
on nonencrypted
class_start main
class_start late_start
on property:sys.init_log_level=*
loglevel ${sys.init_log_level}
on charger
class_start charger
on property:vold.decrypt=trigger_reset_main
class_reset main
on property:vold.decrypt=trigger_load_persist_props
load_persist_props
start logd
start logd-reinit
on property:vold.decrypt=trigger_post_fs_data
trigger post-fs-data
trigger zygote-start
on property:vold.decrypt=trigger_restart_min_framework
# A/B update verifier that marks a successful boot.
exec_start update_verifier
class_start main
on property:vold.decrypt=trigger_restart_framework
stop surfaceflinger
start surfaceflinger
# A/B update verifier that marks a successful boot.
exec_start update_verifier
class_start main
class_start late_start
on property:vold.decrypt=trigger_shutdown_framework
class_reset late_start
class_reset main
on property:sys.boot_completed=1
bootchart stop
# system server cannot write to /proc/sys files,
# and chown/chmod does not work for /proc/sys/ entries.
# So proxy writes through init.
on property:sys.sysctl.extra_free_kbytes=*
write /proc/sys/vm/extra_free_kbytes ${sys.sysctl.extra_free_kbytes}
# "tcp_default_init_rwnd" Is too long!
on property:sys.sysctl.tcp_def_init_rwnd=*
write /proc/sys/net/ipv4/tcp_default_init_rwnd ${sys.sysctl.tcp_def_init_rwnd}
on property:security.perf_harden=0
write /proc/sys/kernel/perf_event_paranoid 1
on property:security.perf_harden=1
write /proc/sys/kernel/perf_event_paranoid 3
# on shutdown
# In device's init.rc, this trigger can be used to do device-specific actions
# before shutdown. e.g disable watchdog and mask error handling
## Daemon processes to be run by init.
##
service ueventd /sbin/ueventd
class core
critical
seclabel u:r:ueventd:s0
shutdown critical
service console /system/bin/sh
class core
console
disabled
user shell
group shell log readproc
seclabel u:r:shell:s0
setenv HOSTNAME console
on property:ro.debuggable=1
# Give writes to anyone for the trace folder on debug builds.
# The folder is used to store method traces.
chmod 0773 /data/misc/trace
# Give reads to anyone for the window trace folder on debug builds.
chmod 0775 /data/misc/wmtrace
start console
service flash_recovery /system/bin/install-recovery.sh
class main
oneshot
内容很多，但是我们只需要关心两个注释的地方：
import /init.${ro.zygote}.rc //Import类型
init.rc中zygote相关的启动配置文件根据ro.zygote而定，ro.zygote的值可分为zygote32、zygote64、zygote32_64、zygote64_32四种，分别代表：
- init.zygote32.rc：32位的zygote进程，对应的执行程序是app_process
- init.zygote64.rc：64位的zygote进程，对应的执行程序是app_process64
- init.zygote32_64.rc：启动两个zygote进程 (zygote和 zygote_secondary)，32位的app_process32 为主、64位的app_process64为辅。
- init.zygote64_32.rc：启动两个zygote进程 (zygote和 zygote_secondary)，64位的app_process64为主、32位的app_process32为辅。
那么：ro.zygote是在什么地方定义的呢？
接着看：
路径：build/make/target/product/core_64_bit.mk
PRODUCT_COPY_FILES += system/core/rootdir/init.zygote64_32.rc:root/init.zygote64_32.rc
# Set the zygote property to select the 64-bit primary, 32-bit secondary script
# This line must be parsed before the one in core_minimal.mk
PRODUCT_DEFAULT_PROPERTY_OVERRIDES += ro.zygote=zygote64_32
TARGET_SUPPORTS_32_BIT_APPS := true
TARGET_SUPPORTS_64_BIT_APPS := true
很明显：init.rc里面引入了init.zygote64_32.rc这个文件：
路径：system/core/rootdir/init.zygote64_32.rc
service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server --socket-name=zygote
class main
priority -20
user root
group root readproc reserved_disk
socket zygote stream 660 root system
onrestart write /sys/android_power/request_state wake
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
service zygote_secondary /system/bin/app_process32 -Xzygote /system/bin --zygote --socket-name=zygote_secondary --enable-lazy-preload
class main
priority -20
user root
group root readproc reserved_disk
socket zygote_secondary stream 660 root system
onrestart restart zygote
writepid /dev/cpuset/foreground/tasks
我们再来看init.rc里面的语句：
on zygote-start && property:ro.crypto.state=unencrypted
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on zygote-start && property:ro.crypto.state=unsupported
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on zygote-start && property:ro.crypto.state=encrypted && property:ro.crypto.type=file
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
分别启动zygote和zygote_secondary服务。我们再来看：
路径：system/core/init/service.cpp
Result<Success> Service::Start() {
bool disabled = (flags_ & (SVC_DISABLED | SVC_RESET));
// Starting a service removes it from the disabled or reset state and
// immediately takes it out of the restarting state if it was in there.
flags_ &= (~(SVC_DISABLED|SVC_RESTARTING|SVC_RESET|SVC_RESTART|SVC_DISABLED_START));
// Running processes require no additional work --- if they're in the
// process of exiting, we've ensured that they will immediately restart
// on exit, unless they are ONESHOT. For ONESHOT service, if it's in
// stopping status, we just set SVC_RESTART flag so it will get restarted
// in Reap().
if (flags_ & SVC_RUNNING) {
if ((flags_ & SVC_ONESHOT) && disabled) {
flags_ |= SVC_RESTART;
}
// It is not an error to try to start a service that is already running.
return Success();
}
bool needs_console = (flags_ & SVC_CONSOLE);
if (needs_console) {
if (console_.empty()) {
console_ = default_console;
}
// Make sure that open call succeeds to ensure a console driver is
// properly registered for the device node
int console_fd = open(console_.c_str(), O_RDWR | O_CLOEXEC);
if (console_fd < 0) {
flags_ |= SVC_DISABLED;
return ErrnoError() << "Couldn't open console '" << console_ << "'";
}
close(console_fd);
}
struct stat sb;
if (stat(args_[0].c_str(), &sb) == -1) {
flags_ |= SVC_DISABLED;
return ErrnoError() << "Cannot find '" << args_[0] << "'";
}
std::string scon;
if (!seclabel_.empty()) {
scon = seclabel_;
} else {
auto result = ComputeContextFromExecutable(args_[0]);
if (!result) {
return result.error();
}
scon = *result;
}
LOG(INFO) << "starting service '" << name_ << "'...";
pid_t pid = -1;
if (namespace_flags_) {
pid = clone(nullptr, nullptr, namespace_flags_ | SIGCHLD, nullptr);
} else {
pid = fork();//1
}
if (pid == 0) {
umask(077);
if (auto result = EnterNamespaces(); !result) {
LOG(FATAL) << "Service '" << name_ << "' could not enter namespaces: " << result.error();
}
if (namespace_flags_ & CLONE_NEWNS) {
if (auto result = SetUpMountNamespace(); !result) {
LOG(FATAL) << "Service '" << name_
<< "' could not set up mount namespace: " << result.error();
}
}
if (namespace_flags_ & CLONE_NEWPID) {
// This will fork again to run an init process inside the PID
// namespace.
if (auto result = SetUpPidNamespace(); !result) {
LOG(FATAL) << "Service '" << name_
<< "' could not set up PID namespace: " << result.error();
}
}
for (const auto& [key, value] : environment_vars_) {
setenv(key.c_str(), value.c_str(), 1);
}
std::for_each(descriptors_.begin(), descriptors_.end(),
std::bind(&DescriptorInfo::CreateAndPublish, std::placeholders::_1, scon));
// See if there were "writepid" instructions to write to files under /dev/cpuset/.
auto cpuset_predicate = [](const std::string& path) {
return StartsWith(path, "/dev/cpuset/");
};
auto iter = std::find_if(writepid_files_.begin(), writepid_files_.end(), cpuset_predicate);
if (iter == writepid_files_.end()) {
// There were no "writepid" instructions for cpusets, check if the system default
// cpuset is specified to be used for the process.
std::string default_cpuset = GetProperty("ro.cpuset.default", "");
if (!default_cpuset.empty()) {
// Make sure the cpuset name starts and ends with '/'.
// A single '/' means the 'root' cpuset.
if (default_cpuset.front() != '/') {
default_cpuset.insert(0, 1, '/');
}
if (default_cpuset.back() != '/') {
default_cpuset.push_back('/');
}
writepid_files_.push_back(
StringPrintf("/dev/cpuset%stasks", default_cpuset.c_str()));
}
}
std::string pid_str = std::to_string(getpid());
for (const auto& file : writepid_files_) {
if (!WriteStringToFile(pid_str, file)) {
PLOG(ERROR) << "couldn't write " << pid_str << " to " << file;
}
}
if (ioprio_class_ != IoSchedClass_NONE) {
if (android_set_ioprio(getpid(), ioprio_class_, ioprio_pri_)) {
PLOG(ERROR) << "failed to set pid " << getpid()
<< " ioprio=" << ioprio_class_ << "," << ioprio_pri_;
}
}
if (needs_console) {
setsid();
OpenConsole();
} else {
ZapStdio();
}
// As requested, set our gid, supplemental gids, uid, context, and
// priority. Aborts on failure.
SetProcessAttributes();
if (!ExpandArgsAndExecv(args_)) {
PLOG(ERROR) << "cannot execve('" << args_[0] << "')";
}
_exit(127);
}
if (pid < 0) {
pid_ = 0;
return ErrnoError() << "Failed to fork";
}
if (oom_score_adjust_ != -1000) {
std::string oom_str = std::to_string(oom_score_adjust_);
std::string oom_file = StringPrintf("/proc/%d/oom_score_adj", pid);
if (!WriteStringToFile(oom_str, oom_file)) {
PLOG(ERROR) << "couldn't write oom_score_adj: " << strerror(errno);
}
}
time_started_ = boot_clock::now();
pid_ = pid;
flags_ |= SVC_RUNNING;
start_order_ = next_start_order_++;
process_cgroup_empty_ = false;
errno = -createProcessGroup(uid_, pid_);
if (errno != 0) {
PLOG(ERROR) << "createProcessGroup(" << uid_ << ", " << pid_ << ") failed for service '"
<< name_ << "'";
} else {
if (swappiness_ != -1) {
if (!setProcessGroupSwappiness(uid_, pid_, swappiness_)) {
PLOG(ERROR) << "setProcessGroupSwappiness failed";
}
}
if (soft_limit_in_bytes_ != -1) {
if (!setProcessGroupSoftLimit(uid_, pid_, soft_limit_in_bytes_)) {
PLOG(ERROR) << "setProcessGroupSoftLimit failed";
}
}
if (limit_in_bytes_ != -1) {
if (!setProcessGroupLimit(uid_, pid_, limit_in_bytes_)) {
PLOG(ERROR) << "setProcessGroupLimit failed";
}
}
}
NotifyStateChange("running");
return Success();
}
注释1出fork了一个新的进程，自此，zygote进程创建就完成了。
Zygote进程启动过程
我们先来关注一下zegote的执行路径：
service zygote /system/bin/app_process64
进这里面看一看代码逻辑：
路径：frameworks/base/cmds/app_process/app_main.cpp
int main(int argc, char* const argv[])
{
if (!LOG_NDEBUG) {
String8 argv_String;
for (int i = 0; i < argc; ++i) {
argv_String.append("\"");
argv_String.append(argv[i]);
argv_String.append("\" ");
}
ALOGV("app_process main with argv: %s", argv_String.string());
}
AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
// Process command line arguments
// ignore argv[0]
argc--;
argv++;
const char* spaced_commands[] = { "-cp", "-classpath" };
// Allow "spaced commands" to be succeeded by exactly 1 argument (regardless of -s).
bool known_command = false;
int i;
for (i = 0; i < argc; i++) {
if (known_command == true) {
runtime.addOption(strdup(argv[i]));
// The static analyzer gets upset that we don't ever free the above
// string. Since the allocation is from main, leaking it doesn't seem
// problematic. NOLINTNEXTLINE
ALOGV("app_process main add known option '%s'", argv[i]);
known_command = false;
continue;
}
for (int j = 0;
j < static_cast<int>(sizeof(spaced_commands) / sizeof(spaced_commands[0]));
++j) {
if (strcmp(argv[i], spaced_commands[j]) == 0) {
known_command = true;
ALOGV("app_process main found known command '%s'", argv[i]);
}
}
if (argv[i][0] != '-') {
break;
}
if (argv[i][1] == '-' && argv[i][2] == 0) {
++i; // Skip --.
break;
}
runtime.addOption(strdup(argv[i]));
// The static analyzer gets upset that we don't ever free the above
// string. Since the allocation is from main, leaking it doesn't seem
// problematic. NOLINTNEXTLINE
ALOGV("app_process main add option '%s'", argv[i]);
}
// Parse runtime arguments. Stop at first unrecognized option.
bool zygote = false;
bool startSystemServer = false;
bool application = false;
String8 niceName;
String8 className;
++i; // Skip unused "parent dir" argument.
while (i < argc) {
const char* arg = argv[i++];
if (strcmp(arg, "--zygote") == 0) {//1
//如果运行在zygote进程中，将zygote设置为true
zygote = true;
niceName = ZYGOTE_NICE_NAME;
} else if (strcmp(arg, "--start-system-server") == 0) {//2
//如果运行在systemserver进程中，则startSystemServer设置为true
startSystemServer = true;
} else if (strcmp(arg, "--application") == 0) {//3
//如果在应用进程中
application = true;
} else if (strncmp(arg, "--nice-name=", 12) == 0) {
niceName.setTo(arg + 12);
} else if (strncmp(arg, "--", 2) != 0) {
className.setTo(arg);
break;
} else {
--i;
break;
}
}
Vector<String8> args;
if (!className.isEmpty()) {
// We're not in zygote mode, the only argument we need to pass
// to RuntimeInit is the application argument.
//
// The Remainder of args get passed to startup class main(). Make
// copies of them before we overwrite them with the process name.
args.add(application ? String8("application") : String8("tool"));
runtime.setClassNameAndArgs(className, argc - i, argv + i);
if (!LOG_NDEBUG) {
String8 restOfArgs;
char* const* argv_new = argv + i;
int argc_new = argc - i;
for (int k = 0; k < argc_new; ++k) {
restOfArgs.append("\"");
restOfArgs.append(argv_new[k]);
restOfArgs.append("\" ");
}
ALOGV("Class name = %s, args = %s", className.string(), restOfArgs.string());
}
} else {
// We're in zygote mode.
maybeCreateDalvikCache();
if (startSystemServer) {
args.add(String8("start-system-server"));
}
char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
ABI_LIST_PROPERTY);
return 11;
}
String8 abiFlag("--abi-list=");
abiFlag.append(prop);
args.add(abiFlag);
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) {
args.add(String8(argv[i]));
}
}
if (!niceName.isEmpty()) {
runtime.setArgv0(niceName.string(), true /* setProcName */);
}
if (zygote) {//4
//如果在zygote进程中，调用AppRuntime的start函数
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
} else if (className) {
runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
} else {
fprintf(stderr, "Error: no class name or --zygote supplied.\n");
app_usage();
LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
}
}
我们再来看AppRuntime的start函数：
路径：frameworks/base/core/jni/AndroidRuntime.cpp
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
ALOGD(">>>>>> START %s uid %d <<<<<<\n",
className != NULL ? className : "(unknown)", getuid());
static const String8 startSystemServer("start-system-server");
/*
* 'startSystemServer == true' means runtime is obsolete and not run from
* init.rc anymore, so we print out the boot start event here.
*/
for (size_t i = 0; i < options.size(); ++i) {
if (options[i] == startSystemServer) {
/* track our progress through the boot sequence */
const int LOG_BOOT_PROGRESS_START = 3000;
LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START, ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
}
}
const char* rootDir = getenv("ANDROID_ROOT");
if (rootDir == NULL) {
rootDir = "/system";
if (!hasDir("/system")) {
LOG_FATAL("No root directory specified, and /android does not exist.");
return;
}
setenv("ANDROID_ROOT", rootDir, 1);
}
//const char* kernelHack = getenv("LD_ASSUME_KERNEL");
//ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
//启动java虚拟机
if (startVm(&mJavaVM, &env, zygote) != 0) {//1
return;
}
onVmCreated(env);
/*
* Register android functions.
*/
//为java虚拟机注册JNI方法
if (startReg(env) < 0) {//2
ALOGE("Unable to register all android natives\n");
return;
}
/*
* We want to call main() with a String array with arguments in it.
* At present we have two arguments, the class name and an option string.
* Create an array to hold them.
*/
jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
stringClass = env->FindClass("java/lang/String");
assert(stringClass != NULL);
strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);
assert(strArray != NULL);
//className为com.android.internal.os.ZygoteInit
classNameStr = env->NewStringUTF(className);//3
assert(classNameStr != NULL);
env->SetObjectArrayElement(strArray, 0, classNameStr);
for (size_t i = 0; i < options.size(); ++i) {
jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());
assert(optionsStr != NULL);
env->SetObjectArrayElement(strArray, i + 1, optionsStr);
}
/*
* Start VM. This thread becomes the main thread of the VM, and will
* not return until the VM exits.
*/
//将className的.替换为/
char* slashClassName = toSlashClassName(className != NULL ? className : "");//4
//找到zygoteInit
jclass startClass = env->FindClass(slashClassName);//5
if (startClass == NULL) {
ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
/* keep going */
} else {
//找到zygoteInit的main方法
jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
"([Ljava/lang/String;)V");//6
if (startMeth == NULL) {
ALOGE("JavaVM unable to find main() in '%s'\n", className);
/* keep going */
} else {
//通过JNI调用zygoteInit的main方法
env->CallStaticVoidMethod(startClass, startMeth, strArray);//7
#if 0
if (env->ExceptionCheck())
threadExitUncaughtException(env);
#endif
}
}
free(slashClassName);
ALOGD("Shutting down VM\n");
if (mJavaVM->DetachCurrentThread() != JNI_OK)
ALOGW("Warning: unable to detach main thread\n");
if (mJavaVM->DestroyJavaVM() != 0)
ALOGW("Warning: VM did not shut down cleanly\n");
}
自然而然我们就进入了ZygoteInit的main方法，自此也就进入了Java层。
路径：frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
public static void main(String argv[]) {
ZygoteServer zygoteServer = new ZygoteServer();//初始化一个server
// Mark zygote start. This ensures that thread creation will throw
// an error.
ZygoteHooks.startZygoteNoThreadCreation();
// Zygote goes into its own process group.
try {
Os.setpgid(0, 0);
} catch (ErrnoException ex) {
throw new RuntimeException("Failed to setpgid(0,0)", ex);
}
final Runnable caller;
try {
// Report Zygote start time to tron unless it is a runtime restart
if (!"1".equals(SystemProperties.get("sys.boot_completed"))) {
MetricsLogger.histogram(null, "boot_zygote_init",
(int) SystemClock.elapsedRealtime());
}
String bootTimeTag = Process.is64Bit() ? "Zygote64Timing" : "Zygote32Timing";
TimingsTraceLog bootTimingsTraceLog = new TimingsTraceLog(bootTimeTag,
Trace.TRACE_TAG_DALVIK);
bootTimingsTraceLog.traceBegin("ZygoteInit");
RuntimeInit.enableDdms();
boolean startSystemServer = false;
String socketName = "zygote";
String abiList = null;
boolean enableLazyPreload = false;
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {
startSystemServer = true;
} else if ("--enable-lazy-preload".equals(argv[i])) {
enableLazyPreload = true;
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList = argv[i].substring(ABI_LIST_ARG.length());
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
socketName = argv[i].substring(SOCKET_NAME_ARG.length());
} else {
throw new RuntimeException("Unknown command line argument: " + argv[i]);
}
}
if (abiList == null) {
throw new RuntimeException("No ABI list supplied.");
}
//创建一个server端的socket
zygoteServer.registerServerSocketFromEnv(socketName);//1
// In some configurations, we avoid preloading resources and classes eagerly.
// In such cases, we will preload things prior to our first fork.
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
} else {
Zygote.resetNicePriority();
}
// Do an initial gc to clean up after startup
bootTimingsTraceLog.traceBegin("PostZygoteInitGC");
gcAndFinalize();
bootTimingsTraceLog.traceEnd(); // PostZygoteInitGC
bootTimingsTraceLog.traceEnd(); // ZygoteInit
// Disable tracing so that forked processes do not inherit stale tracing tags from
// Zygote.
Trace.setTracingEnabled(false, 0);
Zygote.nativeSecurityInit();
// Zygote process unmounts root storage spaces.
Zygote.nativeUnmountStorageOnInit();
ZygoteHooks.stopZygoteNoThreadCreation();
//启动systemServer进程
if (startSystemServer) {
Runnable r = forkSystemServer(abiList, socketName, zygoteServer);
// {@code r == null} in the parent (zygote) process, and {@code r != null} in the
// child (system_server) process.
if (r != null) {
r.run();
return;
}
}
Log.i(TAG, "Accepting command socket connections");
// The select loop returns early in the child process after a fork and
// loops forever in the zygote.
//等待AMS请求
caller = zygoteServer.runSelectLoop(abiList);
} catch (Throwable ex) {
Log.e(TAG, "System zygote died with exception", ex);
throw ex;
} finally {
zygoteServer.closeServerSocket();
}
// We're in the child process and have exited the select loop. Proceed to execute the
// command.
if (caller != null) {
caller.run();
}
}
本文转载自: https://blog.csdn.net/qq_36428821/article/details/127234904
版权归原作者 AD钙奶-lalala 所有， 如有侵权，请联系我们删除。
版权归原作者 AD钙奶-lalala 所有， 如有侵权，请联系我们删除。