Linux kernel 关机的底层操作

最新推荐文章于 2025-05-21 11:01:14 发布

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最新推荐文章于 2025-05-21 11:01:14 发布

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本文链接：https://blog.youkuaiyun.com/qq_29729577/article/details/51852014

本文深入探讨了Linux系统的关机命令实现原理，包括halt、shutdown、poweroff等命令如何通过调用内核中的reboot syscall来实现不同类型的关机操作。

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Linux关机相关命令如：halt，shutdown，poweroff和reboot

其实它们底层都是调用名为reboot的system call，其具体实现是在内核目录的kernel/sys.c中的

SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd, void __user *, arg)这个函数里，函数原型如下：

SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
		void __user *, arg)
{
	struct pid_namespace *pid_ns = task_active_pid_ns(current);
	char buffer[256];
	int ret = 0;

	/* We only trust the superuser with rebooting the system. */
	if (!ns_capable(pid_ns->user_ns, CAP_SYS_BOOT))
		return -EPERM;

	/* For safety, we require "magic" arguments. */
	if (magic1 != LINUX_REBOOT_MAGIC1 ||
	    (magic2 != LINUX_REBOOT_MAGIC2 &&
	                magic2 != LINUX_REBOOT_MAGIC2A &&
			magic2 != LINUX_REBOOT_MAGIC2B &&
	                magic2 != LINUX_REBOOT_MAGIC2C))
		return -EINVAL;

	/*
	 * If pid namespaces are enabled and the current task is in a child
	 * pid_namespace, the command is handled by reboot_pid_ns() which will
	 * call do_exit().
	 */
	ret = reboot_pid_ns(pid_ns, cmd);
	if (ret)
		return ret;

	/* Instead of trying to make the power_off code look like
	 * halt when pm_power_off is not set do it the easy way.
	 */
	if ((cmd == LINUX_REBOOT_CMD_POWER_OFF) && !pm_power_off)
		cmd = LINUX_REBOOT_CMD_HALT;

	mutex_lock(&reboot_mutex);
	switch (cmd) {
	case LINUX_REBOOT_CMD_RESTART:
		kernel_restart(NULL);
		break;

	case LINUX_REBOOT_CMD_CAD_ON:
		C_A_D = 1;
		break;

	case LINUX_REBOOT_CMD_CAD_OFF:
		C_A_D = 0;
		break;

	case LINUX_REBOOT_CMD_HALT:
		kernel_halt();
		do_exit(0);
		panic("cannot halt");

	case LINUX_REBOOT_CMD_POWER_OFF:
		kernel_power_off();
		do_exit(0);
		break;

	case LINUX_REBOOT_CMD_RESTART2:
		if (strncpy_from_user(&buffer[0], arg, sizeof(buffer) - 1) < 0) {
			ret = -EFAULT;
			break;
		}
		buffer[sizeof(buffer) - 1] = '\0';

		kernel_restart(buffer);
		break;

#ifdef CONFIG_KEXEC
	case LINUX_REBOOT_CMD_KEXEC:
		ret = kernel_kexec();
		break;
#endif

#ifdef CONFIG_HIBERNATION
	case LINUX_REBOOT_CMD_SW_SUSPEND:
		ret = hibernate();
		break;
#endif

	default:
		ret = -EINVAL;
		break;
	}
	mutex_unlock(&reboot_mutex);
	return ret;
}

其中针对cmd有多个case，经过我在imx6平台上测试发现：

poweroff，halt和shutdown都是调用的 case LINUX_REBOOT_CMD_POWER_OFF

而reboot则是调用case LINUX_REBOOT_CMD_RESTART

这里以poweroff为例，会依次进行如下调用：

-->kernel_power_off() //kernel/sys.c

-->kernel_shutdown_prepare

-->migrate_to_reboot_cpu

-->syscore_shutdown

-->machine_power_off // 该函数根据具体平台而定，arm平台在arch/arm/kernel/process.c文件中

详细可以参考这篇文章http://www.wowotech.net/linux_kenrel/reboot.html