FreeBSD kernel 笔记（2）——“preparing a device”和“preparing a device for I/O”

“preparing (or initializing) a device”通常发生在加载设备驱动模块时，举例如下：

static int hello_modevent(module_t mod __unused, int /* modeventtype_t */ event, void *arg __unused)
{
    ......
    switch (event) 
    {
        case MOD_LOAD:
        {
            make_dev_args_init(&args);
            args.mda_devsw = &hello_cdevsw;
            args.mda_uid = UID_ROOT;
            args.mda_gid = GID_WHEEL;
            args.mda_mode = 0600;
            uprintf("Hello is loaded:%d\n", make_dev_s(&args, &hello_dev, "hello"));
            break;
        }
        ......
    }
    return error;
}

“preparing a device for I/O”则是发生在open这个设备时，比如cdevsw结构体的d_open函数：

struct cdevsw {
    ......
    d_open_t        *d_open;  
    ......
}