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Category: FreeBSD kernel 笔记 (Page 2 of 2)

FreeBSD kernel 笔记(3)——设备名字

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

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;  
    ......
}

FreeBSD kernel 笔记(1)——什么是KLD?

下面内容选自 FreeBSD Device Drivers

A device driver can be either statically compiled into the system or dynamically loaded using a loadable kernel module (KLD).

NOTE: Most operating systems call a loadable kernel module an LKM—FreeBSD just had to be different.

A KLD is a kernel subsystem that can be loaded, unloaded, started, and stopped after bootup. In other words, a KLD can add functionality to the kernel and later remove said functionality while the system is running. Needless to say, our “functionality” will be device drivers.

In general, two components are common to all KLDs:
 A module event handler
 A DECLARE_MODULE macro call

 

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