Android Reboot briefing

1. shutdown flow

0: run command

# reboot -p tired
# /system/bin/reboot -p tired

1: set property

system/core/reboot/reboot.c
function:
property_set("sys.powerctl", "shutdown,tired")
log:
[  115.889033] init: Received sys.powerctl='shutdown,tired' from pid: 3200 (reboot)

2: init

init/reboot.cpp
function:
->HandlePowerctlMessage("shutdown,tired")
-->DoReboot(cmd=ANDROID_RB_POWEROFF, reason="shutdown,tired", reboot_target="")
log:
[  115.997095] init: Reboot start, reason: shutdown,tired, reboot_target:

3.4 init

init/reboot_utils.cpp
function:
RebootSystem(cmd=ANDROID_RB_POWEROFF, rebootTarget="")
->reboot(RB_POWER_OFF)
log:
[  120.301823] init: Reboot ending, jumping to kernel

5.6 bionic

bionic/libc/bionic/reboot.cpp
function:
reboot(mode=LINUX_REBOOT_CMD_POWER_OFF)
->__reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, mode, nullptr)
log:
无

7. kernel

[   83.079073] reboot: Power down

2. reboot flow

The main difference is reboot will invoke kernel syscall __NR_reboot directly.

reboot target

boot target	sys.powerctl	kernel	misc	note
normal	reboot,userrequested	kernel_restart(“userrequested”)
bootloader	reboot,bootoader	kernel_restart(“bootloader”)	(command=bootonce-bootloader)
fastbootd	reboot,fastboot	kernel_restart(“recovery”)	(command=boot-recovery, status=, recovery=recovery –fastboot)	w/ dynamic partition
bootloader	reboot,fastboot	kernel_restart(“bootloader”)	(command=bootonce-bootloader)	w/o dynamic partition
fastbootd	-	-	(command=boot-fastboot, status=, recovery=recovery )
recovery	reboot,recovery	kernel_restart(“recovery”)
rescue	-	-	(command=boot-rescue, status=, recovery=recovery)
sideload	reboot,sideload	kernel_restart(“recovery”)
sideload	reboot,sideload-auto-reboot	kernel_restart(“recovery”)	(command=boot-recovery, status=, recovery=recovery –sideload_auto_reboot )