启动shell环境

6.3 启动shell环境

init_post函数来自同一个文件的814行：

 

811/* This is a non __init function. Force it to be noinline otherwise gcc  812 * makes it inline to init() and it becomes part of init.text section  813 */  814static noinline int init_post(void)  815        __releases(kernel_lock)  816{  817        /* need to finish all async __init code before freeing the memory */  818        async_synchronize_full();  819        free_initmem();  820        unlock_kernel();  821        mark_rodata_ro();  822        system_state = SYSTEM_RUNNING;  823        numa_default_policy();  824  825  826        current->signal->flags |= SIGNAL_UNKILLABLE;  827  828        if (ramdisk_execute_command) {  829                run_init_process(ramdisk_execute_command);  830                printk(KERN_WARNING "Failed to execute %s/n",  831                                ramdisk_execute_command);  832        }  833  834        /*  835         * We try each of these until one succeeds.  836         *  837         * The Bourne shell can be used instead of init if we are  838         * trying to recover a really broken machine.  839         */  840        if (execute_command) {  841                run_init_process(execute_command);  842                printk(KERN_WARNING "Failed to execute %s.  Attempting "  843                                        "defaults.../n", execute_command);  844        }  845        run_init_process("/sbin/init");  846        run_init_process("/etc/init");  847        run_init_process("/bin/init");  848        run_init_process("/bin/sh");  849  850        panic("No init found.  Try passing init= option to kernel. "  851              "See Linux Documentation/init.txt for guidance.");  852}

 

 

819行，这就是上面说到的那个释放init代码的函数了，它显然不能是__init打头：

void free_initmem(void)

{

       free_init_pages("unused kernel memory",

                     (unsigned long)(&__init_begin),

                     (unsigned long)(&__init_end));

}

 

这个函数基本上就是执行init了，失败就panic了。顺便说一句，/dev/console最后被012描述符引用，也就是所有没有reopen的进程的标准输入输出和出错。

 

到此，内核启动过程就完成了，init根据根文件系统的配置在初始化用户态的进程，启动系统。我们的疯狂内核，也就到此告一段落了。