构建Linux根文件系统一：内核init进程的启动分析

出处：http://hi.baidu.com/chris_zheng

 

内核启动的最后一步就是启动init进程，代码在init/main.c文件中：

/* This is a non __init function. Force it to be noinline otherwise gcc
* makes it inline to init() and it becomes part of init.text section
*/
static int noinline init_post(void)
{
...

if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
   printk(KERN_WARNING "Warning: unable to open an initial console./n");

(void) sys_dup(0);
(void) sys_dup(0);

if (ramdisk_execute_command) {
   run_init_process(ramdisk_execute_command);
   printk(KERN_WARNING "Failed to execute %s/n",
     ramdisk_execute_command);
}

/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
if (execute_command) {
   run_init_process(execute_command);
   printk(KERN_WARNING "Failed to execute %s. Attempting "
      "defaults.../n", execute_command);
}
run_init_process("/sbin/init");
run_init_process("/etc/init");
run_init_process("/bin/init");
run_init_process("/bin/sh");

panic("No init found. Try passing init= option to kernel.");
}

启动过程；

1.打开标准输入、标准输出、标准错误设备；

2.如果ramdisk_execute_command变量指定了要运行的程序，启动它；

3.如果execute_command变量指定了要运行的程序，启动它；

4.依次执行/sbin/init、/bin/init、/bin/sh。

 

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