开源鸿蒙北向框架开发:系统服务理论详解
系统服务的启动
基本可以认为：OpenHarmony 的系统服务进程都是“由 init 直接或间接拉起”的。
- 直接方式：
- init 按 /system/etc/init/.cfg 启动可执行（如 /system/bin/sa_main、/system/bin/samgr 等），这些进程的 PPid=1。
- 间接方式:
- 应用进程由 appspawn 拉起，但 appspawn 自身也是 init 启动的；系统能力（SA）一般不走 appspawn，而是走 sa_main 宿主进程。
- 特殊/例外
- 开发测试可手动启动进程（不通过 init）；但系统正式启动路径都以 init 为根。
- 同一宿主可承载多个 SA，这些 SA 并非独立进程，但宿主仍由 init 启动。
通过OpenHarmony系统进程pid可证明如上的观点:
输入如下命令:
ps -o pid,ppid,comm,args -A | grep -E 'samgr|sa_main'
输出如下:
# ps -o pid,ppid,comm,args -A | grep -E 'samgr|sa_main'275 1 sa_main storage_manager277 1 sa_main khstabilitymgr278 1 samgr samgr279 1 sa_main resource_metrics280 1 sa_main param_watcher284 1 sa_main khmonitorservice286 1 sa_main khdeviceauth_service287 1 sa_main khcontainermanager_service290 1 sa_main cadaemon460 1 sa_main accessibility461 1 sa_main audio_server462 1 sa_main bluetooth_service468 1 sa_main concurrent_task_service506 1 sa_main huks_service510 1 sa_main kh_dids_agent_service521 1 sa_main khlink_service523 1 sa_main kh_sle_service542 1 sa_main memmgrservice546 1 sa_main multimodalinput578 1 sa_main resource_schedule_executor579 1 sa_main resource_schedule_service620 1 sa_main netmanager637 1 sa_main telephony638 1 sa_main wallpaper_service735 1 sa_main bgtaskmgr_service748 1 sa_main msdp770 1 sa_main time_service771 1 sa_main uart_service803 1 sa_main device_manager843 1 sa_main useriam853 1 sa_main ui_service854 1 sa_main thingmodel_service856 1 sa_main thing_accessmanager_service859 1 sa_main superdevice_thm860 1 sa_main superdevice_cfg862 1 sa_main superdevice_acs863 1 sa_main streaming_service874 1 sa_main softbus_server875 1 sa_main sensors876 1 sa_main security_guard878 1 sa_main khremoteops879 1 sa_main privacy_service880 1 sa_main powermgr882 1 sa_main pki_manager_service885 1 sa_main netsysnative887 1 sa_main miracast_service888 1 sa_main media_service889 1 sa_main media_monitor890 1 sa_main kloudaccount891 1 sa_main kh_update_sa892 1 sa_main khthingaccessmanager_peripherals894 1 sa_main khability_service895 1 sa_main khsharing_service896 1 sa_main khrule_engine_service897 1 sa_main khqrdetector_service898 1 sa_main license_sa899 1 sa_main khdlp_permission_service901 1 sa_main khcontainercomm_service911 1 sa_main kh_update913 1 sa_main kh_dids_manager_service916 1 sa_main inputmethod_service931 1 sa_main foundation932 1 sa_main drm_service934 1 sa_main distributeddata935 1 sa_main kh_dscreen936 1 sa_main deviceinfoservice938 1 sa_main camera_service940 1 sa_main av_session941 1 sa_main av_codec_service953 1 sa_main audio_magic_service956 1 sa_main accountmgr962 1 sa_main accesstoken_service1013 1 sa_main superdevice_khcomm1470 1 sa_main usb_service1471 1 sa_main hdf_ext_devmgr1788 1 sa_main kloudauth1789 1 sa_main otpauth1791 1 sa_main pinauth1886 1 sa_main wifi_manager_service2065 1 sa_main khwms_service2114 1 sa_main asset_service2207 1 sa_main download_server2245 1 sa_main cert_manager_service2879 1 sa_main deviceprofile6567 4997 toybox grep -E samgr|sa_main
可以看到很多sa_main,和一个samgr ,为什么呢?
分析命令:ps -o pid,ppid,comm,args -A | grep -E 'samgr|sa_main'
这里是使用ps查看当前的全部进程信息,且查看的信息是指定的4个字段
- pid 当前的进程号
- ppid 父进程号
- comm 可执行文件的文件名(原始文件名)
- args 完整的启动参数
通过上面的信息可知,所有的sa_main和samgr都是由init进程拉起的,因为init进程的进程号是1,且有很多个sa_main
查看init的进程号:
# ps -elf | grep init
root 1 0 0 07:59:59 ? 00:01:02 init --second-stage 2101515
root 7662 4997 1 01:42:09 pts/0 00:00:00 grep init
查看init的配置:
grep -Rni 'sa_main\|samgr' /system/etc/init
/system/etc/init/access_token.cfg:17: "path" : ["/system/bin/sa_main", "/system/profile/accesstoken_service.json"],
/system/etc/init/accessibility.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/accessibility.json"],
/system/etc/init/accountmgr.cfg:18: "path" : ["/system/bin/sa_main", "/system/profile/accountmgr.json"],
/system/etc/init/app_domain_verify_agent.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/app_domain_verify_agent.json"],
/system/etc/init/app_fwk_update_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/app_fwk_update_service.json"],
/system/etc/init/asset_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/asset_service.json"],
/system/etc/init/audio_magic_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/audio_magic_service.json"],
/system/etc/init/audio_server.cfg:44: "path" : ["/system/bin/sa_main", "/system/profile/audio_server.json"],
/system/etc/init/av_codec_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/av_codec_service.json"],
/system/etc/init/avsession_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/av_session.json"],
/system/etc/init/backup.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/backup_sa.json"],
/system/etc/init/bgtaskmgr_service.cfg:15: "path" : ["/system/bin/sa_main", "/system/profile/bgtaskmgr_service.json"],
/system/etc/init/bluetooth_service.cfg:16: "path" : ["/system/bin/sa_main", "/system/profile/bluetooth_service.json"],
/system/etc/init/cadaemon.cfg:16: "path" : ["/system/bin/sa_main", "/system/profile/cadaemon.json"],
/system/etc/init/camera_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/camera_service.json"],
/system/etc/init/cert_manager_service.cfg:20: "path" : ["/system/bin/sa_main", "/system/profile/cert_manager_service.json"],
/system/etc/init/compiler_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/compiler_service.json"],
/system/etc/init/concurrent_task_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/concurrent_task_service.json"],
/system/etc/init/daudio.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/daudio.json"],
/system/etc/init/dcamera.cfg:4: "path" : ["/system/bin/sa_main","/system/profile/dcamera.json"],
/system/etc/init/devattest_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/devattest_service.json"],
/system/etc/init/device_manager.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/device_manager.json"],
/system/etc/init/deviceinfoservice.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/deviceinfoservice.json"],
/system/etc/init/deviceprofile.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/deviceprofile.json"],
/system/etc/init/dhardware.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/dhardware.json"],
/system/etc/init/dhardwarecommon_service.cfg:10: "path" : ["/system/bin/sa_main", "/system/profile/kh_dscreen.json"],
/system/etc/init/dinput.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/dinput.json"],
/system/etc/init/distributed_data.cfg:18: "path" : ["/system/bin/sa_main","/system/profile/distributeddata.json"],
/system/etc/init/distributedbms.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/d-bms.json"],
/system/etc/init/distributedfile.cfg:11: "path": ["/system/bin/sa_main", "/system/profile/distributedfiledaemon.json"],
/system/etc/init/distributedfile.cfg:29: "path": ["/system/bin/sa_main", "/system/profile/cloudfiledaemon.json"],
/system/etc/init/distributedfile.cfg:46: "path": ["/system/bin/sa_main", "/system/profile/cloudfileservice.json"],
/system/etc/init/distributedsched.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/distributedsched.json"],
/system/etc/init/dlp_permission_service.cfg:17: "path" : ["/system/bin/sa_main", "/system/profile/dlp_permission_service.json"],
/system/etc/init/downloadservice.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/download_server.json"],
/system/etc/init/drm_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/drm_service.json"],
/system/etc/init/dscreen.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/dscreen.json"],
/system/etc/init/dslm_service.cfg:7: "/system/bin/sa_main",
/system/etc/init/edm.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/edm.json"],
/system/etc/init/el5_filekey_manager.cfg:15: "/system/bin/sa_main",
/system/etc/init/file_access_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/file_access_service.json"],
/system/etc/init/foundation.cfg:43: "path" : ["/system/bin/sa_main", "/system/profile/foundation.json"],
/system/etc/init/hdf_ext_devmgr.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/hdf_ext_devmgr.json"],
/system/etc/init/hidumper_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/hidumper_service.json"],
/system/etc/init/huks_service.cfg:17: "path" : ["/system/bin/sa_main", "/system/profile/huks_service.json"],
/system/etc/init/i18n_service.cfg:17: "path": ["/system/bin/sa_main", "/system/profile/i18n_service.json"],
/system/etc/init/inputmethodservice.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/inputmethod_service.json"],
/system/etc/init/installs.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/installs.json"],
/system/etc/init/intell_voice_service.cfg:16: "path" : ["/system/bin/sa_main", "/system/profile/intell_voice_service.json"],
/system/etc/init/kh_dids_agent_service.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/kh_dids_agent_service.json"],
/system/etc/init/kh_dids_manager_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/kh_dids_manager_service.json"],
/system/etc/init/kh_dinput.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/kh_dinput.json"],
/system/etc/init/kh_update.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/kh_update.json"],
/system/etc/init/khcontainercomm_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/khcontainercomm_service.json"],
/system/etc/init/khcontainermanager_service.cfg:26: "path" : ["/system/bin/sa_main", "/system/profile/khcontainermanager_service.json"]
/system/etc/init/khdeviceauthservice.cfg:13: "path": [ "/system/bin/sa_main", "/system/profile/khdeviceauth_service.json" ],
/system/etc/init/khdlp_permission_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/khdlp_permission_service.json"],
/system/etc/init/khlicense_sa.cfg:5: "path" : ["/system/bin/sa_main", "/system/profile/license_sa.json"],
/system/etc/init/khlink.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/khlink_service.json"],
/system/etc/init/khmonitor.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/khmonitorservice.json"],
/system/etc/init/khqrdetector_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/khqrdetector_service.json"],
/system/etc/init/khrule_engine_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/khrule_engine_service.json"],
/system/etc/init/khsharing_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/khsharing_service.json"],
/system/etc/init/khsle.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/kh_sle_service.json"],
/system/etc/init/khsysabilityservice_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/khability_service.json"],
/system/etc/init/khthingaccessmanager_peripherals.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/khthingaccessmanager_peripherals.json"],
/system/etc/init/khupdate_sa.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/kh_update_sa.json"],
/system/etc/init/khwms_service.cfg:14: "path" : ["/system/bin/sa_main", "/system/profile/khwms_service.json"],
/system/etc/init/kloud_account.cfg:10: "path" : ["/system/bin/sa_main", "/system/profile/kloudaccount.json"],
/system/etc/init/kloud_auth.cfg:17: "path" : ["/system/bin/sa_main", "/system/profile/kloudauth.json"],
/system/etc/init/local_code_sign.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/local_code_sign.json"],
/system/etc/init/locationsa.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/locationhub.json"],
/system/etc/init/mdnsmanager.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/mdnsmanager.json"],
/system/etc/init/media_monitor.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/media_monitor.json"],
/system/etc/init/media_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/media_service.json"],
/system/etc/init/memmgrservice.cfg:29: "path" : ["/system/bin/sa_main", "/system/profile/memmgrservice.json"],
/system/etc/init/miracast_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/miracast_service.json"],
/system/etc/init/module_update_sa.cfg:15: "path" : ["/system/bin/sa_main", "/system/profile/module_update_sa.json"],
/system/etc/init/msdp_musl.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/msdp.json"],
/system/etc/init/multimodalinput.cfg:26: "path" : ["/system/bin/sa_main", "/system/profile/multimodalinput.json"],
/system/etc/init/netmanager_base.cfg:23: "path" : ["/system/bin/sa_main", "/system/profile/netmanager.json"],
/system/etc/init/netsysnative.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/netsysnative.json"],
/system/etc/init/oaidservice.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/oaid_service.json"],
/system/etc/init/otp_auth.cfg:17: "path" : ["/system/bin/sa_main", "/system/profile/otpauth.json"],
/system/etc/init/param_watcher.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/param_watcher.json"],
/system/etc/init/pasteboardservice.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/pasteboard_service.json"],
/system/etc/init/pinauth_sa_profile.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/pinauth.json"],
/system/etc/init/pki_manager_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/pki_manager_service.json"],
/system/etc/init/powermgr.cfg:20: "path" : ["/system/bin/sa_main", "/system/profile/powermgr.json"],
/system/etc/init/printservice.cfg:30: "path" : ["/system/bin/sa_main", "/system/profile/print_service.json"],
/system/etc/init/privacy.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/privacy_service.json"],
/system/etc/init/quick_fix.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/quick_fix.json"],
/system/etc/init/remote_ops.cfg:18: "path" : ["/system/bin/sa_main", "/system/profile/khremoteops.json"],
/system/etc/init/resource_metrics_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/resource_metrics.json"],
/system/etc/init/resource_schedule_executor.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/resource_schedule_executor.json"],
/system/etc/init/resource_schedule_service.cfg:119: "path" : ["/system/bin/sa_main", "/system/profile/resource_schedule_service.json"],
/system/etc/init/samgr_standard.cfg:5: "mkdir /data/samgr 0740 samgr samgr"
/system/etc/init/samgr_standard.cfg:10: "name" : "samgr",
/system/etc/init/samgr_standard.cfg:11: "path" : ["/system/bin/samgr"],
/system/etc/init/samgr_standard.cfg:13: "uid" : "samgr",
/system/etc/init/samgr_standard.cfg:14: "gid" : ["samgr", "system", "readproc", "data_reserve"],
/system/etc/init/samgr_standard.cfg:16: "bootevents":"bootevent.samgr.ready",
/system/etc/init/samgr_standard.cfg:41: "secon" : "u:r:samgr:s0",
/system/etc/init/sandbox_manager_service.cfg:10: "path" : ["/system/bin/sa_main", "/system/profile/sandbox_manager_service.json"],
/system/etc/init/scanservice.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/scan_service.json"],
/system/etc/init/scanservice.rc:16:service scan_service /system/bin/sa_main /system/profile/scan_service.json
/system/etc/init/security_collector.cfg:6: "/system/bin/sa_main",
/system/etc/init/security_component_service.cfg:11: "path" : ["/system/bin/sa_main", "/system/profile/security_component_service.json"],
/system/etc/init/security_guard.cfg:15: "path" : ["/system/bin/sa_main", "/system/profile/security_guard.json"],
/system/etc/init/sensors_musl.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/sensors.json"],
/system/etc/init/softbus_server_musl.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/softbus_server.json"],
/system/etc/init/srms.cfg:5: "path" : ["/system/bin/sa_main", "/system/profile/service_router.json"],
/system/etc/init/stability_mgr_service.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/khstabilitymgr.json"],
/system/etc/init/storage_manager.cfg:4: "path": ["/system/bin/sa_main", "/system/profile/storage_manager.json"],
/system/etc/init/streaming_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/streaming_service.json"],
/system/etc/init/superdevice_acs.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/superdevice_acs.json"],
/system/etc/init/superdevice_cfg.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/superdevice_cfg.json"],
/system/etc/init/superdevice_khcloudcomm.cfg:19: "path" : ["/system/bin/sa_main", "/system/profile/superdevice_khcomm.json"],
/system/etc/init/superdevice_thm.cfg:15: "path" : ["/system/bin/sa_main", "/system/profile/superdevice_thm.json"],
/system/etc/init/sys_installer_sa.cfg:25: "path" : ["/system/bin/sa_main", "/system/profile/sys_installer_sa.json"],
/system/etc/init/telephony.cfg:13: "path" : ["/system/bin/sa_main", "/system/profile/telephony.json"],
/system/etc/init/testserver.cfg:6: "/system/bin/sa_main",
/system/etc/init/thing_accessmanager.cfg:16: "path" : ["/system/bin/sa_main", "/system/profile/thing_accessmanager_service.json"],
/system/etc/init/thingmodel_service.cfg:14: "path" : ["/system/bin/sa_main", "/system/profile/thingmodel_service.json"],
/system/etc/init/timeservice.cfg:14: "path" : ["/system/bin/sa_main", "/system/profile/time_service.json"],
/system/etc/init/token_sync.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/token_sync_service.json"],
/system/etc/init/uart.cfg:15: "path" : ["/system/bin/sa_main", "/system/profile/uart_service.json"],
/system/etc/init/ui_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/ui_service.json"],
/system/etc/init/updater_sa.cfg:24: "path" : ["/system/bin/sa_main", "/system/profile/updater_sa.json"],
/system/etc/init/usb_service.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/usb_service.json"],
/system/etc/init/useriam.cfg:4: "path" : ["/system/bin/sa_main", "/system/profile/useriam.json"],
/system/etc/init/wallpaperservice.cfg:12: "path" : ["/system/bin/sa_main", "/system/profile/wallpaper_service.json"],
/system/etc/init/wifi_standard.cfg:23: "path" : ["/system/bin/sa_main", "/system/profile/wifi_manager_service.json"],
可以看到形如:"path": ["/system/bin/sa_main", "/system/profile/xxx.json"] 等配置行
这表示init拉起的程序是sa_main,给sa_main的启动参数是/system/profile/xxx.json文件
至此可以得出如下结论:OpenHarmony 的系统服务进程都是“由 init 直接或间接拉起”的
那么我们自己创建的服务也应该由init进程去拉起,此时就需要配置init的拉起配置文件
系统服务启动的疑点
上面的命令行查出来的都是sa_main,但是实际上查看进程信息的时候压根就没有看到sa_main,比如如下命令:
ps -elf | grep storage_manager
# ps -elf | grep storage_manager
storage_manager 275 1 0 08:00:06 ? 00:00:02 storage_manager
root 8686 4997 0 01:56:53 pts/0 00:00:00 grep storage_manager
如上是我们最常用的查看进程信息的方法,但是查看storage_manager进程的时候没有发现sa_main字段,这是怎么回事呢?上面明明出现了
# ps -o pid,ppid,comm,args -A | grep -E 'samgr|sa_main'275 1 sa_main storage_manager
这个表示storage_manager只是启动的命令,为什么会变成进程名呢?
现在根据以上的信息我们可知:sa服务是由init拉起,且init拉起的可执行程序是sa_main,只是在sa_main的执行逻辑中把进程名改成了启动参数(storage_manager)
那么现在是不是还需要考虑下sa_main的启动配置文件
由上面两个章节可知:
一个系统服务至少需要两个配置文件:
- init启动配置文件
- sa_main的载入配置文件
什么是sa_main
sa_main 是 OpenHarmony 的“系统能力（SA）通用宿主可执行程序”，路径通常为 /system/bin/sa_main。
# pwd
/system/bin
# find ./ -name "*main*"
./dnsdomainname
./sa_main
职责：
启动后解析传入的SA Profile（如/system/profile/xxx.json）。
按libpath/depend/run-on-create 在同一进程内dlopen各 SA 动态库，创建实例并调用 OnStart。
将SA注册到系统能力管理器（SAMgr），用于跨进程发现与调用。
启动链路：init 通过 init 配置（.cfg）拉起 /system/bin/sa_main /system/profile/xxx.json → sa_main 装载和启动多个 SA → SA 对外经 SAMgr 提供 IPC。
特点：
- 一个 sa_main 进程可承载多个 SA（共驻进程，省进程/内存）。
- sa_main 不负责“创建进程”（这是 init 的事），负责“进程内加载 SA 并管理其生命周期”。
为什么OpenHarmony需要把系统服务做成sa形式而不是像linux那样使用systemd+守护进程
- 定位与约束不同
- OpenHarmony面向端侧/嵌入式/多内核（Linux/LiteOS），不依赖systemd生态；需要更轻量、可裁剪、统一于大小系统的机制。
- 资源敏感与启动确定性要求高，偏好“多服务共驻”与精细依赖编排。
- SA（System Ability）带来的架构收益
- 统一宿主与装载：sa_main+profile 在同一进程内 dlopen 多个 SA，减少进程数与内存占用，提升冷启速度。
- 依赖与生命周期：profile 的 depend/run-on-create/depend-time-out + OnStart/OnStop/OnAddSystemAbility，内置依赖等待与“后补初始化”回调。
- 统一发现与调用：SAMgr 以 SA_ID 做注册/发现，客户端经 iface_cast 获取 Proxy，天然走统一 IPC（Binder/LiteIPC）模型，类型安全、带死亡通知。
- 跨版本与多形态一致：同一套 SA/IPC 模型覆盖 AOSP 风格设备与轻量设备（LiteIPC），开发者心智统一。
- 安全一体化：与 AccessToken 权限、SELinux 域、init 能力位（caps）等打通，易做最小权限与进程级管控。
- 为什么不走“systemd+守护进程”常规做法
- systemd 体量与依赖链对端侧并不总适配；OHOS 自带 init 与参数服务、事件/权限体系，更易裁剪和跨内核迁移。
- 守护进程各自为政：依赖/发现/IPC/权限需自行约定；SA 模型把“发现（SAMgr）+ 调用（Proxy/Stub）+ 生命周期”做了平台级统一，降低系统集成与维护成本。
- 分布式场景友好：SA_ID 语义、跨设备能力扩展更顺滑（与分布式总线/能力发现结合）。
- 能否用套接字/自定义守护
- 可以，但会失去 SAMgr 统一发现、类型化 IPC、依赖编排与权限治理带来的平台收益。通常建议：对内用 SA；对外协议（MQTT/HTTP/TCP）由 SA 内部服务化暴露。
一句话：SA 是 OHOS 为端侧/多形态场景量身设计的“统一系统服务模型”，在资源、依赖、IPC、安全、分布式等维度提供平台级一体化能力，这是它相对“systemd+daemon”更契合 OHOS 目标的原因。
- 可以，但会失去 SAMgr 统一发现、类型化 IPC、依赖编排与权限治理带来的平台收益。通常建议：对内用 SA；对外协议（MQTT/HTTP/TCP）由 SA 内部服务化暴露。