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本帖最后由 mxgsgtc 于 2017-03-17 16:23 编辑
static struct usb_class_driver skel_class = { .name = "skel%d",
.fops = &skel_fops,
.minor_base = USB_SKEL_MINOR_BASE,
};
在skel_probe 函数中
{
----
----
retval = usb_register_dev(interface, &skel_class);
if (retval) {
/* something prevented us from registering this driver */
err("Not able to get a minor for this device.");
usb_set_intfdata(interface, NULL);
goto error;
}
------
-----
}
我想问下关于:usb_register_dev这个函数的问题,这个函数会创建一个usb子设备A,并在/dev/生成节点
问题1: 这个子设备A是字符设备还是块设备,如何判断的呢?
根据我的分析
usb_register_dev-->device_add-->devtmpfs_create_node
devtmpfs_create_node函数中
{
----
nodename = device_get_devnode(dev, &mode, &tmp);
if (!nodename)
return -ENOMEM;
if (mode == 0)
mode = 0600;
if (is_blockdev(dev))
mode |= S_IFBLK;
else
mode |= S_IFCHR;//这里有个字符设备的赋值
-----
}
所以我大致判断, usb_register_dev生成出来的是字符设备,不知道对不对
问题2:假设通过usb_register_dev生成出来的是字符设备, 但是在此函数中我并没有找到cdev结构的分配(字符设备都需要分配这个结构吧),那cdev是从哪里分配的呢?
问题3:skel_class中的.fops在VFS的角度上讲是如何被调用的呢?
static const struct file_operations skel_fops = {
.owner = THIS_MODULE,
.read = skel_read,
.write = skel_write,
.open = skel_open,
.release = skel_release,
.flush = skel_flush,
.llseek = noop_llseek,
};
/*
* usb class driver info in order to get a minor number from the usb core,
* and to have the device registered with the driver core
*/
static struct usb_class_driver skel_class = {
.name = "skel%d",
.fops = &skel_fops,
.minor_base = USB_SKEL_MINOR_BASE,
};
usb_register_dev(interface, &skel_class);调用后, 新生成子设备A, 但是cdev结构并没有被分配,既然没有分配,就没有在内核全局变量cdev_map中注册
那么open("/dev/A"); 是如何调用的skel_open呢?
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