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在Android?7之前的版本中，系統(tǒng)Native服務(wù)，不管它們的可執(zhí)行文件位于系統(tǒng)什么位置都定義在根分區(qū)的init.*.rc文件中。這造成init＊.rc文件臃腫龐大，給維護(hù)帶來(lái)了一些不便，而且其中定義的一些服務(wù)的二進(jìn)制文件根本不存在。

但在Android 7.0中，對(duì)該機(jī)制做了一些改變 。

單一的init＊.rc，被拆分，服務(wù)根據(jù)其二進(jìn)制文件的位置（／system，／vendor，／odm）定義到對(duì)應(yīng)分區(qū)的etc／init目錄中，每個(gè)服務(wù)一個(gè)rc文件。與該服務(wù)相關(guān)的觸發(fā)器、操作等也定義在同一rc文件中。?

• ／system/etc/init，包含系統(tǒng)核心服務(wù)的定義，如SurfaceFlinger、MediaServer、Logcatd等。
• /vendor/etc/init， SOC廠商針對(duì)SOC核心功能定義的一些服務(wù)。比如高通、MTK某一款SOC的相關(guān)的服務(wù)。
• ／odm/etc/init，OEM/ODM廠商如小米、華為、OPP其產(chǎn)品所使用的外設(shè)以及差異化功能相關(guān)的服務(wù)。

這樣的目錄結(jié)構(gòu)拆分，也與Android產(chǎn)品的開發(fā)流程相吻合，減輕了維護(hù)的負(fù)擔(dān)。下圖為Android7.0 模擬器／system/etc/init中定義的服務(wù)。

david@daviddeMBP:~$ adb shell generic_x86:/ $ su generic_x86:/ # cd /system/etc/init generic_x86:/system/etc/init # ls atrace.rc gatekeeperd.rc mediacodec.rc rild.rc audioserver.rc init-debug.rc mediadrmserver.rc servicemanager.rc bootanim.rc installd.rc mediaextractor.rc surfaceflinger.rc bootstat.rc keystore.rc mediaserver.rc uncrypt.rc cameraserver.rc lmkd.rc mtpd.rc vdc.rc debuggerd.rc logcatd.rc netd.rc vold.rc drmserver.rc logd.rc perfprofd.rc dumpstate.rc mdnsd.rc racoon.rc generic_x86:/system/etc/init #

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2.提供一個(gè)編譯宏LOCAL_INIT_RC用于將服務(wù)相關(guān)的RC文件編譯到相應(yīng)位置。這能確保服務(wù)定義和服務(wù)的可執(zhí)行文件同時(shí)存在，避免了之前出現(xiàn)的服務(wù)對(duì)應(yīng)的可執(zhí)行程序不存在的問(wèn)題。?
例如logcatd的Android.mk中，通過(guò)LOCAL_INIT_RC將logcatd對(duì)應(yīng)的logcatd.rc編譯到/system/etc/init目錄中。

#system/core/logcat/Android.mk include $(CLEAR_VARS)LOCAL_MODULE := logpersist.start LOCAL_MODULE_TAGS := debug LOCAL_MODULE_CLASS := EXECUTABLES LOCAL_INIT_RC := logcatd.rc LOCAL_MODULE_PATH := $(bin_dir) LOCAL_SRC_FILES := logpersist ALL_TOOLS := logpersist.start logpersist.stop logpersist.cat LOCAL_POST_INSTALL_CMD := $(hide) $(foreach t,$(filter-out $(LOCAL_MODULE),$(ALL_TOOLS)),ln -sf $(LOCAL_MODULE) $(TARGET_OUT)/bin/$(t);) include $(BUILD_PREBUILT)

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3.在init執(zhí)行mount_all指令掛載分區(qū)時(shí)，會(huì)加載這些目錄中的rc文件，并在合適的時(shí)機(jī)運(yùn)行這些服務(wù)和操作。下面位Android7.0模擬器的log。

[ 0.912389] init: init first stage started! －－－－－－－－－加載根分區(qū)的rc文件 [ 0.996447] init: waitpid failed: No child processes [ 0.996558] init: (Loading properties from /default.prop took 0.00s.) [ 0.997274] init: (Parsing /init.environ.rc took 0.00s.) [ 0.997457] init: (Parsing /init.usb.rc took 0.00s.) [ 0.997561] init: (Parsing /init.ranchu.rc took 0.00s.) [ 0.997823] init: (Parsing /init.usb.configfs.rc took 0.00s.) [ 0.997876] init: (Parsing /init.zygote32.rc took 0.00s.) [ 0.997895] init: (Parsing /init.rc took 0.00s.) [ 1.121126] init: Starting service 'ueventd'... [ 1.121422] init: Waiting for /dev/.coldboot_done...-----------掛載分區(qū)，加載附加rc文件 [ 1.384113] EXT4-fs (vdc): Ignoring removed nomblk_io_submit option [ 1.386155] EXT4-fs (vdc): mounted filesystem with ordered data mode. Opts: nomblk_io_submit,errors=panic [ 1.386165] SELinux: initialized (dev vdc, type ext4), uses xattr [ 1.386179] fs_mgr: __mount(source=/dev/block/vdc,target=/data,type=ext4)=0 [ 1.387397] init: (Parsing /system/etc/init/atrace.rc took 0.00s.) [ 1.387762] init: (Parsing /system/etc/init/audioserver.rc took 0.00s.) [ 1.388078] init: (Parsing /system/etc/init/bootanim.rc took 0.00s.) [ 1.388424] init: (Parsing /system/etc/init/bootstat.rc took 0.00s.) [ 1.388805] init: (Parsing /system/etc/init/cameraserver.rc took 0.00s.) [ 1.389125] init: (Parsing /system/etc/init/debuggerd.rc took 0.00s.) [ 1.389443] init: (Parsing /system/etc/init/drmserver.rc took 0.00s.) [ 1.389781] init: (Parsing /system/etc/init/dumpstate.rc took 0.00s.) [ 1.392698] init: (Parsing /system/etc/init/gatekeeperd.rc took 0.00s.) [ 1.393060] init: (Parsing /system/etc/init/init-debug.rc took 0.00s.) [ 1.393361] init: (Parsing /system/etc/init/installd.rc took 0.00s.) [ 1.393674] init: (Parsing /system/etc/init/keystore.rc took 0.00s.) [ 1.393992] init: (Parsing /system/etc/init/lmkd.rc took 0.00s.)

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相關(guān)內(nèi)容可以參考android 7.0 system/etc/init/readme.txt.

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