高通平台 reboot 分析

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reboot 分析

1 版本

平台：高通8009

busybox：1.24

linux kernel：3.18.48

2 流程

可以通过reboot、halt、poweroff等命令,对linux操作系统进行控制，具体的操作流程如下：

3 分析

在arm 板上，可知：

# ls /sbin/reboot -la

lrwxrwxrwx 1 1000 1000 14 Jun 21 2017 /sbin/reboot -> ../bin/busybox

常规reboot是以busybox为入口，然后进入halt_main函数。

reboot不带参数执行，会给init进程发送SIGTERM信号，init进程接收到信号后给其他进程发送终止信号，最后调用C库函数reboot，reboot通过系统调用sys_reboot进入内核，系统重启。

reboot -f 带参数执行，则通过halt_main直接调用C函数reboot，不经过init进程。

函数实现如下：

int halt_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;

int halt_main(int argc UNUSED_PARAM, char **argv)

{

static const int magic[] = {

RB_HALT_SYSTEM,

RB_POWER_OFF,

RB_AUTOBOOT

};

static const smallintsignals[] = { SIGUSR1, SIGUSR2, SIGTERM };

int delay = 0;

int which, flags, rc;

/* Figure out which appletwe're running */

for (which = 0;"hpr"[which] != applet_name[0]; which++)

continue;

/* Parse and handlearguments */

opt_complementary ="d+"; /* -d N */

/* We support -w even if!ENABLE_FEATURE_WTMP,

* in order to not break scripts.

* -i (shut down network interfaces) isignored.

flags = getopt32(argv,"d:nfwi", &delay);

sleep(delay);

write_wtmp();

if (flags & 8) /* -w */

return EXIT_SUCCESS;

if (!(flags & 2)) /* no-n */

sync();

/* Perform action. */

rc = 1;

if (!(flags & 4)) { /*no -f */

//TODO: I tend to think that signalling linuxrc is wrong

// pity original author didn't comment on it...

if (ENABLE_FEATURE_INITRD){

/* talk tolinuxrc */

/* bboxinit/linuxrc assumed */

pid_t *pidlist= find_pid_by_name("linuxrc");

if (pidlist[0]> 0)

rc =kill(pidlist[0], signals[which]);

if(ENABLE_FEATURE_CLEAN_UP)

free(pidlist);

}

if (rc) {

/* talk toinit */

if(!ENABLE_FEATURE_CALL_TELINIT) {

/* bboxinit assumed */

rc =kill(1, signals[which]);

} else {

/* SysVstyle init assumed */

/*runlevels:

* 0 == shutdown

* 6 == reboot */

execlp(CONFIG_TELINIT_PATH,

CONFIG_TELINIT_PATH,

which== 2 ? "6" : "0",

(char*)NULL

);

bb_perror_msg_and_die("can'texecute '%s'",

CONFIG_TELINIT_PATH);

}

} else {

rc =reboot(magic[which]);

}

if (rc)

bb_perror_nomsg_and_die();

return rc;

}

进入linux内核后，实现位于kernel/reboot.c，函数原型如下：

SYSCALL_DEFINE4(reboot,int, magic1, int, magic2, unsigned int, cmd,

void __user *, arg)

该函数的参数解释如下：

magic1、magic2：两个int类型的magic，用于防止误操作。

cmd： reboot方式。

arg：其它的额外参数。

magic1、magic2、cmd具体在 include/uapi/linux/reboot.h 中定义。

reboot 方式：

位于： include/uapi/linux/reboot.h

* Commands accepted by the _reboot() systemcall.

* RESTART Restart system using default command and mode.

* HALT Stop OS and give system control to ROM monitor, if any.

* CAD_ON Ctrl-Alt-Del sequence causes RESTART command.

* CAD_OFF Ctrl-Alt-Del sequence sends SIGINT to init task.

* POWER_OFF Stop OS and remove all power from system, if possible.

* RESTART2 Restart system using given command string.

* SW_SUSPEND Suspend system using software suspend if compiled in.

* KEXEC Restart system using a previously loaded Linux kernel

#define LINUX_REBOOT_CMD_RESTART 0x01234567

#define LINUX_REBOOT_CMD_HALT 0xCDEF0123

#define LINUX_REBOOT_CMD_CAD_ON 0x89ABCDEF

#define LINUX_REBOOT_CMD_CAD_OFF 0x00000000

#define LINUX_REBOOT_CMD_POWER_OFF 0x4321FEDC

#define LINUX_REBOOT_CMD_RESTART2 0xA1B2C3D4

#define LINUX_REBOOT_CMD_SW_SUSPEND 0xD000FCE2

#define LINUX_REBOOT_CMD_KEXEC 0x45584543

kernel_restart 函数实现

/**

* kernel_restart- reboot the system

* @cmd:pointer to buffer containing command to execute for restart

* or%NULL

* Shutdowneverything and perform a clean reboot.

* Thisis not safe to call in interrupt context.

voidkernel_restart(char *cmd)

{

kernel_restart_prepare(cmd);

migrate_to_reboot_cpu();

syscore_shutdown();

if (!cmd)

pr_emerg("Restartingsystem\n");

else

pr_emerg("Restarting system withcommand '%s'\n", cmd);

kmsg_dump(KMSG_DUMP_RESTART);

machine_restart(cmd);

}

说明：

Ø 调用kernel_restart_prepare，前期准备工作

Ø 调用migrate_to_reboot_cpu(); 将当前的进程（task）移到一个CPU上；对于多CPU的机器，无论哪个CPU触发了当前的系统调用，代码都可以运行在任意的CPU上。这个接口将代码分派到一个特定的CPU上，并禁止调度器分派代码到其它CPU上。也就是说，这个接口被执行后，只有一个CPU在运行，用于完成后续的reboot动作。

Ø 调用syscore_shutdown接口，将系统核心器件关闭（例如中断等）；

Ø 调用printk以及kmsg_dump，打印日志；

Ø 最后，machine_restart。

machine_restart是属于Architecture相关的处理函数，如ARM。ARM在“arch/arm/kernel/process.c”中实现，具体如下：

* Restart requires that the secondary CPUsstop performing any activity

* while the primary CPU resets the system.Systems with a single CPU can

* use soft_restart() as their machinedescriptor's .restart hook, since that

* will cause the only available CPU to reset.Systems with multiple CPUs must

* provide a HW restart implementation, toensure that all CPUs reset at once.

* This is required so that any code runningafter reset on the primary CPU

* doesn't have to co-ordinate with other CPUsto ensure they aren't still

* executing pre-reset code, and using RAM thatthe primary CPU's code wishes

* to use. Implementing such co-ordinationwould be essentially impossible.

voidmachine_restart(char *cmd)

{

local_irq_disable();

smp_send_stop();

/* Flush the console to make sure all therelevant messages make it

* outto the console drivers */

arm_machine_flush_console();

if (arm_pm_restart)

arm_pm_restart(reboot_mode, cmd);

else

do_kernel_restart(cmd);

/* Give a grace period for failure torestart of 1s */

mdelay(1000);

/* Whoops - the platform was unable toreboot. Tell the user! */

printk("Reboot failed -- Systemhalted\n");

local_irq_disable();

while (1);

}

接口注释，大意如下：

1）单CPU系统时，可以直接用soft_restart 实现reboot。

2）多CPU系统时，当主CPU重置系统时，重启要求辅助CPU停止执行任何活动。

系统的多个CPU必须提供一个硬件启动实施，确保所有的CPU复位一次。以保证所有CPU同步重启。

函数实现：

1）调用smp_send_stop接口，确保其它CPU处于非活动状态；

2）arm_pm_restart，实现真正的restart。在“arch/arm/kernel/process.c”声明。

void (*arm_pm_restart)(enum reboot_mode reboot_mode,const char *cmd);

3）等待1s；

4）如果没有返回，则restart成功，否则失败，打印错误信息。

arm_pm_restart 在arch/arm 中对应平台restart函数，执行复位动作。

高通平台arch/arm/mach-msm 目前代码无restart函数，

那么就执行do_kernel_restart(cmd);

其它平台例子：

arch/arm/mach-omap2/board-omap3logic.c

MACHINE_START(OMAP3_TORPEDO, "LogicOMAP3 Torpedo board")

.atag_offset = 0x100,

.reserve = omap_reserve,

.map_io = omap3_map_io,

.init_early = omap35xx_init_early,

.init_irq = omap3_init_irq,

.init_machine = omap3logic_init,

.init_late = omap35xx_init_late,

.init_time = omap3_sync32k_timer_init,

.restart = omap3xxx_restart,

MACHINE_END

omap3xxx_restart 开始触发硬件复位

/**

*omap3xxx_restart - trigger a software restart of the SoC

*@mode: the "reboot mode", see arch/arm/kernel/{setup,process}.c

*@cmd: passed from the userspace program rebooting the system (if provided)

*Resets the SoC. For @cmd, see the'reboot' syscall in

*kernel/sys.c. No return value.

void omap3xxx_restart(enum reboot_modemode, const char *cmd)

{

omap3_ctrl_write_boot_mode((cmd? (u8)*cmd : 0));

omap3xxx_prm_dpll3_reset();/* never returns */

while(1);

}

参数cmd,每个平台可以自已定义，比如bootloader，recovery。

例子，应用层到驱动的流程：

androidrecovery模式启动进入流程

http://blog.csdn.net/yzhang8703/article/details/7166593

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