Linux关机重启停机(shutdown reboot halt)流程分析

由于本人水平相当有限，不当之处还望大家多多指教。

涉及的内核源码，基于linux-3.10.102。

首先，对于用户态发起的这类操作请求，最终都是通过sys_reboot系统调用（源码在kernel/sys.c）实现的。

其代码如下。如其注释所言，他除了可以重启关机停机，还可以修改ctrl-alt-del组合键的含义。

另外，注释还说到此系统调用不会做sync。即sync需要用户在调用此系统调用之前自己完成。

/*
 * Reboot system call: for obvious reasons only root may call it,
 * and even root needs to set up some magic numbers in the registers
 * so that some mistake won't make this reboot the whole machine.
 * You can also set the meaning of the ctrl-alt-del-key here.
 *
 * reboot doesn't sync: do that yourself before calling this.
 */
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 rebootin