分类：FreeBSD kernel 笔记

在使用下列函数

int makedevs(struct makedevargs *args, struct cdev **cdev, const char *fmt, …);

struct cdev * make_dev(struct cdevsw *cdevsw, int unit, uidt uid, gidt gid, int perms, const char *fmt, …);

为设备创建cdev结构体时，fmt用来指定设备的名字：

The name is the expansion of fmt and following arguments as printf(9) would print it. The name determines its path under /dev or other devfs(5) mount point and may contain slash `/’ char- acters to denote subdirectories.

也就是/dev下面节点的名字。

cdevsw结构体中的d_name指定的是driver的名字：

struct cdevsw {
    ......
    const char      *d_name;
    ......
}

一个driver可以用来操作多个设备。

参考资料：
MAKE_DEV。

“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;  
    ......
}