usb-skeleton例程

有了前面的设备驱动基础，以及usb方面的基础知识，则可以很轻松的就理解usb-skeleton例程，并轻松的就能写出自己的简易usb driver了。

下面是usb-skeleton例程的简易解析：

/*
 * USB Skeleton driver - 2.0
 *
 * Copyright (C) 2001-2004 Greg Kroah-Hartman ()
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, version 2.
 *
 * This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c 
 * but has been rewritten to be easy to read and use, as no locks are now
 * needed anymore.
 *
 */

#include
#include
#include
#include
#include
#include
#include
#include

/* Define these values to match your devices */
#define USB_SKEL_VENDOR_ID 0xfff0
#define USB_SKEL_PRODUCT_ID 0xfff0

/* table of devices that work with this driver */
static struct usb_device_id skel_table [] = {
 { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
 { }     /* Terminating entry */
};
MODULE_DEVICE_TABLE (usb, skel_table);

/* Get a minor range for your devices from the usb maintainer */
#define USB_SKEL_MINOR_BASE 192

/* our private defines. if this grows any larger, use your own .h file */
#define MAX_TRANSFER  ( PAGE_SIZE - 512 )
#define WRITES_IN_FLIGHT 8

/* 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 */
 unsigned char *  bulk_in_buffer;  /* the buffer to receive data */
 size_t   bulk_in_size;  /* the size of the receive buffer */
 __u8   bulk_in_endpointAddr; /* the address of the bulk in endpoint */
 __u8   bulk_out_endpointAddr; /* the address of the bulk out endpoint */
 struct kref  kref;
};
#define to_skel_dev(d) container_of(d, struct usb_skel, kref)

static struct usb_driver skel_driver;

static void skel_delete(struct kref *kref)
{ 
/*
1.获得设备
2.减少设备的引用次数
3.释放分配的数据空间
4.释放分配的驱动空间
*/
 struct usb_skel *dev = to_skel_dev(kref);

 usb_put_dev(dev->udev);
 kfree (dev->bulk_in_buffer);
 kfree (dev);
}

static int skel_open(struct inode *inode, struct file *file)
{
/*
1.通过驱动结构体和此设备号，获得设备接口
2.通过接口，获得设备结构体
3.增加设备的引用次数
4.把设备驱动跟文件句柄关联起来，便于后面使用
5.
6.
*/
 struct usb_skel *dev;
 struct usb_interface *interface;
 int subminor;
 int retval = 0;

 subminor = iminor(inode);

 interface = usb_find_interface(&skel_driver, subminor);
 if (!interface) {
  err ("%s - error, can't find device for minor %d",
       __FUNCTION__, subminor);
  retval = -ENODEV;
  goto exit;
 }

 dev = usb_get_intfdata(interface);
 if (!dev) {
  retval = -ENODEV;
  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;
}

static int skel_release(struct inode *inode, struct file *file)
{
/*
减少设备的引用次数
*/
 struct usb_skel *dev;

 dev = (struct usb_skel *)file->private_data;
 if (dev == NULL)
  return -ENODEV;

 /* decrement the count on our device */
 kref_put(&dev->kref, skel_delete);
 return 0;
}

static ssize_t skel_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
{
/*
读数据函数的功能，主要实现如下:
1.通过文件句柄，获得设备驱动数据
2.通过设备驱动数据的操作集，向设备发送获得数据的命令
3.获得从设备返回的数据
4.把数据从内核空间复制到用户空间
5.
*/
 struct usb_skel *dev;
 int retval = 0;
 int bytes_read;

 dev = (struct usb_skel *)file->private_data;
 
 /* do a blocking bulk read to get data from the device */
 retval = usb_bulk_msg(dev->udev,
         usb_rcvbulkpipe(dev->udev, dev->bulk_in_endpointAddr),
         dev->bulk_in_buffer,
         min(dev->bulk_in_size, count),
         &bytes_read, 10000);

 /* if the read was successful, copy the data to userspace */
 if (!retval) {
  if (copy_to_user(buffer, dev->bulk_in_buffer, bytes_read))
   retval = -EFAULT;
  else
   retval = bytes_read;
 }

 return retval;
}

static void skel_write_bulk_callback(struct urb *urb, struct pt_regs *regs)
{
/*
提交urb被主控制器处理后的调用函数，主要反映数据处理的情况。
*/
 struct usb_skel *dev;

 dev = (struct usb_skel *)urb->context;

 /* sync/async unlink faults aren't errors */
 if (urb->status && 
     !(urb->status == -ENOENT || 
       urb->status == -ECONNRESET ||
       urb->status == -ESHUTDOWN)) {
  dbg("%s - nonzero write bulk status received: %d",
      __FUNCTION__, urb->status);
 }

 /* free up our allocated buffer */
 usb_buffer_free(urb->dev, urb->transfer_buffer_length, 
   urb->transfer_buffer, urb->transfer_dma);
 up(&dev->limit_sem);
}

tatic ssize_t skel_write(struct file *file, const char *user_buffer, size_t count, loff_t *ppos)
{
/*
1.写数据到设备文件的函数，首先要通过文件句柄，得到句柄所指向的设备文件，即我们在probe函数中注册的设备文件。
2.通过文件句柄，可以获得设备的文件操作集，这个操作集一般放在private_data这个指针所指向的位置。
3.分配urb空间
4.分配用户数据空间大小的内核空间，用于接收用户数据
5.填充urb跟发送数据的关系
6.提交urb数据
7.根据提交的返回信息，判断是否正常发送
*/
 struct usb_skel *dev;
 int retval = 0;
 struct urb *urb = NULL;
 char *buf = NULL;
 size_t writesize = min(count, (size_t)MAX_TRANSFER);

 dev = (struct usb_skel *)file->private_data;

 /* verify that we actually have some data to write */
 if (count == 0)
  goto exit;

 /* limit the number of URBs in flight to stop a user from using up all RAM */
 if (down_interruptible(&dev->limit_sem)) {

  retval = -ERESTARTSYS;
  goto exit;
 }

 /* create a urb, and a buffer for it, and copy the data to the urb */
 urb = usb_alloc_urb(0, GFP_KERNEL);
 if (!urb) {
  retval = -ENOMEM;
  goto error;
 }

 buf = usb_buffer_alloc(dev->udev, writesize, GFP_KERNEL, &urb->transfer_dma);
 if (!buf) {
  retval = -ENOMEM;
  goto error;
 }

 if (copy_from_user(buf, user_buffer, writesize)) {
  retval = -EFAULT;
  goto error;
 }

 /* 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;

 /* send the data out the bulk port */
 retval = usb_submit_urb(urb, GFP_KERNEL);

 if (retval) {
  err("%s - failed submitting write urb, error %d", __FUNCTION__, retval);
  goto error;
 }

 /* release our reference to this urb, the USB core will eventually free it entirely */
 usb_free_urb(urb);

exit:
 return writesize;

error:
 usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
 usb_free_urb(urb);
 up(&dev->limit_sem);
 return retval;
}

static struct file_operations skel_fops = {
 .owner = THIS_MODULE,
 .read =  skel_read,
 .write = skel_write,
 .open =  skel_open,
 .release = skel_release,
};

/* 
 * 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,
};

static int skel_probe(struct usb_interface *interface, const struct usb_device_id *id)
{
/*
probe函数主要完成以下工作:
1.分配一个设备驱动空间，并对这个设备进行引用计数
2.设备空间中的usb device,interface两个成员，分别由真实成员来赋值，目的是把这些真实成员跟这个新的设备空间关联起来
3.判断接口所包含的端点特性，看跟硬件是否一致，如果不一致，则出错，即返回值不等于0
4.注册一个文件设备，这个文件设备是提供给应用程序用于操作设备的，包含打开，关闭，读，写等功能。
5.成功则返回0
*/
 struct usb_skel *dev = NULL;
 struct usb_host_interface *iface_desc;
 struct usb_endpoint_descriptor *endpoint;
 size_t buffer_size;
 int i;
 int retval = -ENOMEM;

 /* allocate memory for our device state and initialize it */
 dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 if (dev == NULL) {
  err("Out of memory");
  goto error;
 }
 kref_init(&dev->kref);
 sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);

 dev->udev = usb_get_dev(interface_to_usbdev(interface));/*通过设备的接口，获得这个接口所对应的设备，并增加设备的引用次数*/
 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 &&
      ((endpoint->bEndpointAddress & USB_ENDPOINT_DIR_MASK)
     == USB_DIR_IN) &&
      ((endpoint->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK)
     == USB_ENDPOINT_XFER_BULK)) {
   /* we found a bulk in endpoint */
   buffer_size = le16_to_cpu(endpoint->wMaxPacketSize);
   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) {
    err("Could not allocate bulk_in_buffer");
    goto error;
   }
  }

  if (!dev->bulk_out_endpointAddr &&
      ((endpoint->bEndpointAddress & USB_ENDPOINT_DIR_MASK)
     == USB_DIR_OUT) &&
      ((endpoint->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK)
     == USB_ENDPOINT_XFER_BULK)) {
   /* we found a bulk out endpoint */
   dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
  }
 }
 if (!(dev->bulk_in_endpointAddr && dev->bulk_out_endpointAddr)) {
  err("Could not find both bulk-in and bulk-out endpoints");
  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);
 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;
 }

 /* let the user know what node this device is now attached to */
 info("USB Skeleton device now attached to USBSkel-%d", interface->minor);
 return 0;

error:
 if (dev)
  kref_put(&dev->kref, skel_delete);
 return retval;
}

static void skel_disconnect(struct usb_interface *interface)
{
 struct usb_skel *dev;
 int minor = interface->minor;

 /* prevent skel_open() from racing skel_disconnect() */
 lock_kernel();

 dev = usb_get_intfdata(interface);
 usb_set_intfdata(interface, NULL);

 /* give back our minor */
 usb_deregister_dev(interface, &skel_class);

 unlock_kernel();

 /* decrement our usage count */
 kref_put(&dev->kref, skel_delete);

 info("USB Skeleton #%d now disconnected", minor);
}

static struct usb_driver skel_driver = {
 .name =  "skeleton",
 .probe = skel_probe,
 .disconnect = skel_disconnect,
 .id_table = skel_table,
};

static int __init usb_skel_init(void)
{
 int result;

 /* register this driver with the USB subsystem */
 result = usb_register(&skel_driver);

 if (result)
  err("usb_register failed. Error number %d", result);

 return result;
}

static void __exit usb_skel_exit(void)
{
 /* deregister this driver with the USB subsystem */
 usb_deregister(&skel_driver);
}

module_init (usb_skel_init);
module_exit (usb_skel_exit);

MODULE_LICENSE("GPL");