module_device_table
kernel open source\drivers\USB\usb-skeleton.c 提供了一个最基础的USB驱动程序实例，即USB骨架程序。
USB 骨架程序的 usb_driver 结构体
static struct usb_driver skel_driver = {
.name = "skeleton",
.probe = skel_probe,
.disconnect = skel_disconnect,
.suspend = skel_suspend,
.resume = skel_resume,
.pre_reset = skel_pre_reset,
.post_reset = skel_post_reset,
.id_table = skel_table,
.supports_autosuspend = 1,
};上面代码中[ .id_table = skel_table, ]定义了该驱动程序支持的设备列表数组skel_table[]，代码如下：
/* table of devices that work with this driver */
static const struct usb_device_id skel_table[] = {
{ USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
{ } /* Terminating entry */
};
module_device_table(usb, skel_table);对上面 usb_driver 的注册与注销发生在USB骨架程序的模块加载与卸载函数内，分别调用了 usb_register()和usb_deregister()函数。这两个函数使用快捷宏 module_usb_driver 实现->快捷宏module_usb_driver
module_usb_driver(skel_driver);
usb_driver 的注册与注销发生在USB骨架程序的模块加载与卸载函数内，分别调用了 usb_register()和usb_deregister()函数。
这两个函数使用快捷宏 module_usb_driver 实现，该宏在 include/linux/usb.h 中：
#define usb_register(driver) \
usb_register_driver(driver, THIS_MODULE, Kbuild_MODNAME)
void usb_deregister(struct usb_driver *driver)
{
pr_info("%s: deregistering interface driver %s\n",
usbcore_name, driver->name);
usb_remove_newid_files(driver);
driver_unregister(&driver->drvwrap.driver);
usb_free_dynids(driver);
}
export_symbol_GPL(usb_deregister);
#define module_driver(__driver, __register, __unregister, ...) \
static int __init __driver##_init(void) \
{ \
return __register(&(__driver) , ##__VA_ARGS__); \
} \
module_init(__driver##_init); \
static void __exit __driver##_exit(void) \
{ \
__unregister(&(__driver) , ##__VA_ARGS__); \
} \
module_exit(__driver##_exit);
#define module_usb_driver(__usb_driver) \
module_driver(__usb_driver, usb_register, \
usb_deregister)在 usb_probe 成员函数中，根据 usb_interface 成员寻找第一个批量输入和批量输出端点，并将端点地址、缓冲区等信息存入为USB骨架程序定义的 usb_skel 结构体中，并将 usb_skel 实例指针传入 usb_set_intfdata() 中以作为usb接口的私有数据，最后注册USB设备，代码清单如下：
static int skel_probe(struct usb_interface *interface,
const struct usb_device_id *id)
{
……
/* allocate memory for our device state and initialize it */
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
……
dev->udev = usb_get_dev(interface_to_usbdev(interface));
dev->interface = interface;
/* set up the endpoint information */
/* use only the first bulk-in and bulk-out endpoints */
iface_desc = interface->cur_altsetting;
for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
endpoint = &iface_desc->endpoint[i].desc;
if (!dev->bulk_in_endpointAddr &&
usb_endpoint_is_bulk_in(endpoint)) {
/* we found a bulk in endpoint */
buffer_size = usb_endpoint_maxp(endpoint);
dev->bulk_in_size = buffer_size;
dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
dev->bulk_in_buffer = kmalloc(buffer_size, GFP_KERNEL);
if (!dev->bulk_in_buffer)
goto ERROR;
dev->bulk_in_urb = usb_alloc_urb(0, GFP_KERNEL);
if (!dev->bulk_in_urb)
goto error;
}
if (!dev->bulk_out_endpointAddr &&
usb_endpoint_is_bulk_out(endpoint)) {
/* we found a bulk out endpoint */
dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
}
}
if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
dev_err(&interface->dev,
"Could not find both bulk-in and bulk-out endpoints\n");
goto error;
}
/* save our data pointer in this interface device */
usb_set_intfdata(interface, dev);
/* we can register the device now, as it is ready */
retval = usb_register_dev(interface, &skel_class);
……
return 0;
……
}usb_skel 结构体可以被看作一个私有数据结构，定义如下：
/* Structure to hold all of our device specific stuff */
struct usb_skel {
struct usb_device *udev; /* the usb device for this device */
struct usb_interface *interface; /* the interface for this device */
struct semaphore limit_sem; /* limiting the number of writes in progress */
struct usb_anchor submitted; /* in case we need to retract our submissions */
struct urb *bulk_in_urb; /* the urb to read data with */
unsigned char *bulk_in_buffer; /* the buffer to receive data */
size_t bulk_in_size; /* the size of the receive buffer */
size_t bulk_in_filled; /* number of bytes in the buffer */
size_t bulk_in_copied; /* already copied to user space */
__u8 bulk_in_endpointAddr; /* the address of the bulk in endpoint */
__u8 bulk_out_endpointAddr; /* the address of the bulk out endpoint */
int errors; /* the last request tanked */
bool ongoing_read; /* a read is going on */
spinlock_t err_lock; /* lock for errors */
struct kref kref;
struct mutex io_mutex; /* synchronize I/O with disconnect */
wait_queue_head_t bulk_in_wait; /* to wait for an ongoing read */
};断开函数会完成与probe() 相反的工作，设置接口数据为NULL，注销USB设备，代码如下：
static void skel_disconnect(struct usb_interface *interface)
{
struct usb_skel *dev;
int minor = interface->minor;
dev = usb_get_intfdata(interface);
usb_set_intfdata(interface, NULL);
/* give back our minor */
usb_deregister_dev(interface, &skel_class);
/* prevent more I/O from starting */
mutex_lock(&dev->io_mutex);
dev->interface = NULL;
mutex_unlock(&dev->io_mutex);
usb_kill_anchored_urbs(&dev->submitted);
/* decrement our usage count */
kref_put(&dev->kref, skel_delete);
dev_info(&interface->dev, "USB Skeleton #%d now disconnected", minor);
}usb_probe()函数中的 usb_register_dev(interface, &skel_class)中的第二个参数包含字符设备的 file_operation 结构体指针，而这个结构体的成员也是USB字符设备的另一个组成部分。代码如下：
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,
};skel_open()函数实现的非常简单，根据 usb_driver 和次设备号通过 usb_find_interface() 获得USB接口，之后通过 usb_get_intfdata()获得接口的私有数据并赋予 file->private_data,代码如下：
static int skel_open(struct inode *inode, struct file *file)
{
struct usb_skel *dev;
struct usb_interface *interface;
int subminor;
int retval = 0;
subminor = iminor(inode);
interface = usb_find_interface(&skel_driver, subminor);
……
dev = usb_get_intfdata(interface);
……
retval = usb_autopm_get_interface(interface);
if (retval)
goto exit;
/* increment our usage count for the device */
kref_get(&dev->kref);
/* save our object in the file's private structure */
file->private_data = dev;
exit:
return retval;
}贯穿读写函数函数的时URB结构体，在 skel_write() 函数中进行了URB的分配（调用usb_alloc_urb()），初始化(调用usb_fill_bluk_urb())和提交（调用usb_submit_urb()），代码如下：
static ssize_t skel_write(struct file *file, const char *user_buffer,
size_t count, loff_t *ppos)
{
struct usb_skel *dev;
int retval = 0;
struct urb *urb = NULL;
char *buf = NULL;
size_t writesize = min(count, (size_t)MAX_TRANSFER);
dev = file->private_data;
……
spin_lock_irq(&dev->err_lock);
retval = dev->errors;
……
spin_unlock_irq(&dev->err_lock);
……
/* create a urb, and a buffer for it, and copy the data to the urb */
urb = usb_alloc_urb(0, GFP_KERNEL);
……
buf = usb_alloc_coherent(dev->udev, writesize, GFP_KERNEL,
&urb->transfer_dma);
……
if (copy_from_user(buf, user_buffer, writesize)) {
retval = -EFAULT;
goto error;
}
/* this lock makes sure we don't submit URBs to gone devices */
mutex_lock(&dev->io_mutex);
……
/* initialize the urb properly */
usb_fill_bulk_urb(urb, dev->udev,
usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
buf, writesize, skel_write_bulk_callback, dev);
urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
usb_anchor_urb(urb, &dev->submitted);
/* send the data out the bulk port */
retval = usb_submit_urb(urb, GFP_KERNEL);
mutex_unlock(&dev->io_mutex);
……
usb_free_urb(urb);
return writesize;
……
}在写函数中发起的URB结束后，在 usb_fill_bulk_urb() 函数中填入的完成函数 skel_write_bulk_callback() 将会被调用，进行urb->status的判断，代码如下：
static void skel_write_bulk_callback(struct urb *urb)
{
struct usb_skel *dev;
dev = urb->context;
/* sync/async unlink faults aren't errors */
if (urb->status) {
if (!(urb->status == -ENOENT ||
urb->status == -ECONNRESET ||
urb->status == -ESHUTDOWN))
dev_err(&dev->interface->dev,
"%s - nonzero write bulk status received: %d\n",
__func__, urb->status);
spin_lock(&dev->err_lock);
dev->errors = urb->status;
spin_unlock(&dev->err_lock);
}
/* free up our allocated buffer */
usb_free_coherent(urb->dev, urb->transfer_buffer_length,
urb->transfer_buffer, urb->transfer_dma);
up(&dev->limit_sem);
}
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