BusyBox制作的文件系统的启动过程

内核初始化过程中，挂载根文件系统后，怎么初始化的呢？以linux-2.6.35为例，先看看内核初始化时候，做了些什么？

相关阅读：BusyBox各版本下载 2011-08/40704.htm

1、内核初始化到文件系统初始化

init/main.c（内核C入口）

asmlinkage void __init start_kernel(void)
{
    ...
    rest_init();
}
static noinline void __init_refok rest_init(void)
    __releases(kernel_lock)
{
    ...
    /*
    * We need to spawn init first so that it obtains pid 1, however
    * the init task will end up wanting to create kthreads, which, if
    * we schedule it before we create kthreadd, will OOPS.
    */
    kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
    ...
}
static int __init kernel_init(void * unused)
{
    ...
    init_post();
    return 0;
}
static noinline int init_post(void)
    __releases(kernel_lock)
{
    ...
    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. "
          "See Linux Documentation/init.txt for guidance.");
}
static void run_init_process(char *init_filename)
{
    argv_init[0] = init_filename;
    kernel_execve(init_filename, argv_init, envp_init);
}
static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
int kernel_execve(const char *filename, char *const argv[], char *const envp[])
{
    struct pt_regs regs;
    int ret;

    memset(®s, 0, sizeof(struct pt_regs));
    ret = do_execve((char *)filename, (char __user * __user *)argv,
            (char __user * __user *)envp, ®s);
    ...

}

简单说就是：

start_kernel()--->rest_init()--开启内核线程-->kernel_init()--->init_post()--->run_init_process("/sbin/init")