Linux内核USB驱动

Posted 2020-08-26 请给我倒杯茶

本文转载自：http://www.360doc.com/content/12/0321/14/8363527_196286673.shtml

注意,该文件是2.4的内核的驱动源文件,并不保证在2.6内核中可用.文件路径为kernel/driver/usb/usb_skelton.c

该文件是usb驱动的一个框架,很多usb的驱动都可以在这个文件的基础上进行修改得到.

下面就是该源文件,中文部分是我的注释,如有错误的地方,欢迎指出.

  1 /*
  2 * USB Skeleton driver - 0.6
  3 *
  4 * Copyright (c) 2001 Greg Kroah-Hartman ([email protected])
  5 *
  6 * This program is free software; you can redistribute it and/or
  7 * modify it under the terms of the GNU General Public License as
  8 * published by the Free Software Foundation; either version 2 of
  9 * the License, or (at your option) any later version.
 10 *
 11 *
 12 * This driver is to be used as a skeleton driver to be able to create a
 13 * USB driver quickly. The design of it is based on the usb-serial and
 14 * dc2xx drivers.
 15 *
 16 * Thanks to Oliver Neukum and David Brownell for their help in debugging
 17 * this driver.
 18 *
 19 * TODO:
 20 * - fix urb->status race condition in write sequence
 21 * - move minor_table to a dynamic list.
 22 *
 23 * History:
 24 *
 25 * 2001_11_05 - 0.6 - fix minor locking problem in skel_disconnect.
 26 *    Thanks to Pete Zaitcev for the fix.
 27 * 2001_09_04 - 0.5 - fix devfs bug in skel_disconnect. Thanks to wim delvaux
 28 * 2001_08_21 - 0.4 - more small bug fixes.
 29 * 2001_05_29 - 0.3 - more bug fixes based on review from linux-usb-devel
 30 * 2001_05_24 - 0.2 - bug fixes based on review from linux-usb-devel people
 31 * 2001_05_01 - 0.1 - first version
 32 * 
 33 */
 34 #include <linux/config.h>
 35 #include <linux/kernel.h>
 36 #include <linux/sched.h>
 37 #include <linux/signal.h>
 38 #include <linux/errno.h>
 39 #include <linux/poll.h>
 40 #include <linux/init.h>
 41 #include <linux/slab.h>
 42 #include <linux/fcntl.h>
 43 #include <linux/module.h>
 44 #include <linux/spinlock.h>
 45 #include <linux/list.h>
 46 #include <linux/smp_lock.h>
 47 #include <linux/devfs_fs_kernel.h>
 48 #include <linux/usb.h>
 49 #ifdef CONFIG_USB_DEBUG
 50 static int debug = 1;
 51 #else
 52 static int debug;
 53 #endif
 54 //一个宏，用来调试时使用
 55 /* Use our own dbg macro */
 56 #undef dbg
 57 #define dbg(format, arg...) do { if (debug) printk(KERN_DEBUG __FILE__ ": " format "\n" , ## arg); } while (0)
 58 
 59 /* Version Information */
 60 #define DRIVER_VERSION "v0.4"
 61 #define DRIVER_AUTHOR "Greg Kroah-Hartman, [email protected]"
 62 #define DRIVER_DESC "USB Skeleton Driver"
 63 //参量，可以在lsmod中更改
 64 /* Module paramaters */
 65 MODULE_PARM(debug, "i");
 66 MODULE_PARM_DESC(debug, "Debug enabled or not");
 67 //分别是厂商id和产品id
 68 /* Define these values to match your device */
 69 #define USB_SKEL_VENDOR_ID 0xfff0
 70 #define USB_SKEL_PRODUCT_ID 0xfff0
 71 //根据厂商和芯片id创建usb_device_id结构体
 72 /* table of devices that work with this driver */
 73 static struct usb_device_id skel_table [] = {
 74 { USB_DEVICE(USB_SKEL_VENDOR_ID, USB_SKEL_PRODUCT_ID) },
 75 { }      /* Terminating entry */
 76 };
 77 //将此结构体注册，提供给用户区空间的工具使用
 78 MODULE_DEVICE_TABLE (usb, skel_table);
 79 
 80 //主设备号的起始值
 81 /* Get a minor range for your devices from the usb maintainer */
 82 #define USB_SKEL_MINOR_BASE 200 
 83 //设备数目
 84 /* we can have up to this number of device plugged in at once */
 85 #define MAX_DEVICES   16
 86 //一个自定义的结构体，用来存储驱动的相关信息
 87 //分别是设备，接口，设备句柄，主设备号的起始值，设备个数，中断端点数，批量输入端点数，批量输出端点数，
 88 //输入缓冲区首指针，大小，usb的端点地址
 89 //输出缓冲区首指针，大小，urb数组，usb的端点地址
 90 //工作队列，设备使用计数，信号量
 91 /* Structure to hold all of our device specific stuff */
 92 struct usb_skel {
 93 struct usb_device * udev;    /* save off the usb device pointer */
 94 struct usb_interface * interface;   /* the interface for this device */
 95 devfs_handle_t   devfs;    /* devfs device node */
 96 unsigned char   minor;    /* the starting minor number for this device */
 97 unsigned char   num_ports;   /* the number of ports this device has */
 98 char    num_interrupt_in; /* number of interrupt in endpoints we have */
 99 char    num_bulk_in;   /* number of bulk in endpoints we have */
100 char    num_bulk_out;   /* number of bulk out endpoints we have */
101 unsigned char *   bulk_in_buffer;   /* the buffer to receive data */
102 int    bulk_in_size;   /* the size of the receive buffer */
103 __u8    bulk_in_endpointAddr; /* the address of the bulk in endpoint */
104 unsigned char *   bulk_out_buffer; /* the buffer to send data */
105 int    bulk_out_size;   /* the size of the send buffer */
106 struct urb *   write_urb;   /* the urb used to send data */
107 __u8    bulk_out_endpointAddr; /* the address of the bulk out endpoint */
108 struct tq_struct tqueue;    /* task queue for line discipline waking up */
109 int    open_count;   /* number of times this port has been opened */
110 struct semaphore sem;    /* locks this structure */
111 };
112 //设备句柄
113 /* the global usb devfs handle */
114 extern devfs_handle_t usb_devfs_handle;
115 //用来注册file_operations结构体的一些函数
116 /* local function prototypes */
117 static ssize_t skel_read (struct file *file, char *buffer, size_t count, loff_t *ppos);
118 static ssize_t skel_write (struct file *file, const char *buffer, size_t count, loff_t *ppos);
119 static int skel_ioctl   (struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg);
120 static int skel_open   (struct inode *inode, struct file *file);
121 static int skel_release   (struct inode *inode, struct file *file);
122 
123 static void * skel_probe (struct usb_device *dev, unsigned int ifnum, const struct usb_device_id *id);
124 static void skel_disconnect (struct usb_device *dev, void *ptr);
125 static void skel_write_bulk_callback (struct urb *urb);
126 //保存usb设备信息的结构体
127 /* array of pointers to our devices that are currently connected */
128 static struct usb_skel   *minor_table[MAX_DEVICES];
129 //初始化信号量
130 /* lock to protect the minor_table structure */
131 static DECLARE_MUTEX (minor_table_mutex);
132 /*
133 * File operations needed when we register this driver.
134 * This assumes that this driver NEEDS file operations,
135 * of course, which means that the driver is expected
136 * to have a node in the /dev directory. If the USB
137 * device were for a network interface then the driver
138 * would use "struct net_driver" instead, and a serial
139 * device would use "struct tty_driver". 
140 */
141 //字符串型设备所必须的结构体
142 //依次为所有者，读函数，写函数，控制函数，打开函数，关闭函数
143 static struct file_operations skel_fops = {
144 /*
145 * The owner field is part of the module-locking
146 * mechanism. The idea is that the kernel knows
147 * which module to increment the use-counter of
148 * BEFORE it calls the device‘s open() function.
149 * This also means that the kernel can decrement
150 * the use-counter again before calling release()
151 * or should the open() function fail.
152 *
153 * Not all device structures have an "owner" field
154 * yet. "struct file_operations" and "struct net_device"
155 * do, while "struct tty_driver" does not. If the struct
156 * has an "owner" field, then initialize it to the value
157 * THIS_MODULE and the kernel will handle all module
158 * locking for you automatically. Otherwise, you must
159 * increment the use-counter in the open() function
160 * and decrement it again in the release() function
161 * yourself.
162 */
163 owner:   THIS_MODULE,
164 read:   skel_read,
165 write:   skel_write,
166 ioctl:   skel_ioctl,
167 open:   skel_open,
168 release: skel_release,
169 };     
170 //usb设备注册所必需的一个结构体，但只有name, probe, disconnect, idtable, owner五个是必须的
171 /* usb specific object needed to register this driver with the usb subsystem */
172 static struct usb_driver skel_driver = {
173 owner:   THIS_MODULE,
174 name:   "skeleton",
175 probe:   skel_probe,
176 disconnect: skel_disconnect,
177 fops:   &skel_fops,
178 minor:   USB_SKEL_MINOR_BASE,
179 id_table: skel_table,
180 };
181 /**
182 * usb_skel_debug_data
183 */
184 //用来debug的函数
185 static inline void usb_skel_debug_data (const char *function, int size, const unsigned char *data)
186 {
187 int i;
188 if (!debug)
189    return;
190 
191 printk (KERN_DEBUG __FILE__": %s - length = %d, data = ", 
192    function, size);
193 for (i = 0; i < size; ++i) {
194    printk ("%.2x ", data[i]);
195 }
196 printk ("\n");
197 }
198 
199 /**
200 * skel_delete
201 */
202 //usb驱动程序卸载时将调用的函数
203 static inline void skel_delete (struct usb_skel *dev)
204 {
205 minor_table[dev->minor] = NULL;
206 //回收输入缓冲区内存
207 if (dev->bulk_in_buffer != NULL)
208    kfree (dev->bulk_in_buffer);
209 //回收输出缓冲区内存
210 if (dev->bulk_out_buffer != NULL)
211    kfree (dev->bulk_out_buffer);
212 //释放写入urb内存
213 if (dev->write_urb != NULL)
214    usb_free_urb (dev->write_urb);
215 //释放整个结构体
216 kfree (dev);
217 }
218 
219 /**
220 * skel_open
221 */
222 //打开设备函数，主要是用来初始化usb_skel结构体
223 static int skel_open (struct inode *inode, struct file *file)
224 {
225 struct usb_skel *dev = NULL;
226 int subminor;
227 int retval = 0;
228 
229 dbg(__FUNCTION__);
230 //检测从设备号是否有问题
231 subminor = MINOR (inode->i_rdev) - USB_SKEL_MINOR_BASE;
232 if ((subminor < 0) ||
233      (subminor >= MAX_DEVICES)) {
234    return -ENODEV;
235 }
236 /* Increment our usage count for the module.
237 * This is redundant here, because "struct file_operations"
238 * has an "owner" field. This line is included here soley as
239 * a reference for drivers using lesser structures... ;-)
240 */
241 MOD_INC_USE_COUNT;
242 //占有全局信号量，进入临界区域
243 /* lock our minor table and get our local data for this minor */
244 down (&minor_table_mutex);
245 //得到当前设备的第subminor个usb_skel结构体
246 dev = minor_table[subminor];
247 if (dev == NULL) {
248 //该设备不可用
249    up (&minor_table_mutex);
250    MOD_DEC_USE_COUNT;
251    return -ENODEV;
252 }
253 //占有当前设备的信号量
254 /* lock this device */
255 down (&dev->sem);
256 //释放全局信号量
257 /* unlock the minor table */
258 up (&minor_table_mutex);
259 //打开设备计数加一
260 /* increment our usage count for the driver */
261 ++dev->open_count;
262 //把当前设备的信心保存到设备驱动的结构体中
263 /* save our object in the file‘s private structure */
264 file->private_data = dev;
265 //释放信号量
266 /* unlock this device */
267 up (&dev->sem);
268 return retval;
269 }
270 
271 /**
272 * skel_release
273 */
274 //关闭函数
275 static int skel_release (struct inode *inode, struct file *file)
276 {
277 struct usb_skel *dev;
278 int retval = 0;
279 dev = (struct usb_skel *)file->private_data;
280 if (dev == NULL) {
281    dbg (__FUNCTION__ " - object is NULL");
282    return -ENODEV;
283 }
284 dbg(__FUNCTION__ " - minor %d", dev->minor);
285 //占有全局信号量
286 /* lock our minor table */
287 down (&minor_table_mutex);
288 //占有局部信号量
289 /* lock our device */
290 down (&dev->sem);
291 //设备引用计数小于0，说明目前没有打开设备
292 if (dev->open_count <= 0) {
293    dbg (__FUNCTION__ " - device not opened");
294    retval = -ENODEV;
295    goto exit_not_opened;
296 }
297 //检测到设备已经拔出
298 if (dev->udev == NULL) {
299    /* the device was unplugged before the file was released */
300    up (&dev->sem);
301    skel_delete (dev);
302    up (&minor_table_mutex);
303    MOD_DEC_USE_COUNT;
304    return 0;
305 }
306 //设备打开计数减一
307 /* decrement our usage count for the device */
308 --dev->open_count;
309 if (dev->open_count <= 0) {
310 //没有任何人在使用该设备，则取消目前所有的数据传输
311    /* shutdown any bulk writes that might be going on */
312    usb_unlink_urb (dev->write_urb);
313    dev->open_count = 0;
314 }
315 //bookmark
316 /* decrement our usage count for the module */
317 MOD_DEC_USE_COUNT;
318 //没有执行open就执行close
319 exit_not_opened:
320 up (&dev->sem);
321 up (&minor_table_mutex);
322 return retval;
323 }
324 
325 /**
326 * skel_read
327 */
328 //注意这里的数据传输并没有利用urb，而是用了一种简单的方式
329 static ssize_t skel_read (struct file *file, char *buffer, size_t count, loff_t *ppos)
330 {
331 struct usb_skel *dev;
332 int retval = 0;
333 dev = (struct usb_skel *)file->private_data;
334 
335 dbg(__FUNCTION__ " - minor %d, count = %d", dev->minor, count);
336 //锁定信号量
337 /* lock this object */
338 down (&dev->sem);
339 //该设备是否可用
340 /* verify that the device wasn‘t unplugged */
341 if (dev->udev == NULL) {
342    up (&dev->sem);
343    return -ENODEV;
344 }
345 //接收批量数据，同时指定了设备信息，批量输入的端点（通过usb_rcvbulkpipe构造），缓冲区地址和大小，所需要数据的大小，超时时间 
346 /* do an immediate bulk read to get data from the device */
347 retval = usb_bulk_msg (dev->udev,
348           usb_rcvbulkpipe (dev->udev, 
349        dev->bulk_in_endpointAddr),
350           dev->bulk_in_buffer, dev->bulk_in_size,
351           &count, HZ*10);
352 //数据正常接收
353 //则把数据复制供给用户
354 /* if the read was successful, copy the data to userspace */
355 if (!retval) {
356    if (copy_to_user (buffer, dev->bulk_in_buffer, count))
357     retval = -EFAULT;
358    else
359     retval = count;
360 }
361 
362 /* unlock the device */
363 up (&dev->sem);
364 return retval;
365 }
366 
367 /**
368 * skel_write
369 */
370 static ssize_t skel_write (struct file *file, const char *buffer, size_t count, loff_t *ppos)
371 {
372 struct usb_skel *dev;
373 ssize_t bytes_written = 0;
374 int retval = 0;
375 dev = (struct usb_skel *)file->private_data;
376 dbg(__FUNCTION__ " - minor %d, count = %d", dev->minor, count);
377 /* lock this object */
378 down (&dev->sem);
379 /* verify that the device wasn‘t unplugged */
380 if (dev->udev == NULL) {
381    retval = -ENODEV;
382    goto exit;
383 }
384 //无效操作
385 /* verify that we actually have some data to write */
386 if (count == 0) {
387    dbg(__FUNCTION__ " - write request of 0 bytes");
388    goto exit;
389 }
390 //设备正在忙碌
391 /* see if we are already in the middle of a write */
392 if (dev->write_urb->status == -EINPROGRESS) {
393    dbg (__FUNCTION__ " - already writing");
394    goto exit;
395 }
396 //计算写入的数据大小
397 /* we can only write as much as 1 urb will hold */
398 bytes_written = (count > dev->bulk_out_size) ? 
399      dev->bulk_out_size : count;
400 /* copy the data from userspace into our urb */
401 if (copy_from_user(dev->write_urb->transfer_buffer, buffer, 
402       bytes_written)) {
403    retval = -EFAULT;
404    goto exit;
405 }
406 usb_skel_debug_data (__FUNCTION__, bytes_written, 
407         dev->write_urb->transfer_buffer);
408 //填充批量urb
409 //目标urb，usb设备，目标端点（通过usb_sndbulkpipe创建），数据首地址，已写入数据的返回值，回调函数，提供给回调函数的数据
410 /* set up our urb */
411 FILL_BULK_URB(dev->write_urb, dev->udev, 
412         usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
413         dev->write_urb->transfer_buffer, bytes_written,
414         skel_write_bulk_callback, dev);
415 //正是发送urb
416 /* send the data out the bulk port */
417 retval = usb_submit_urb(dev->write_urb);
418 if (retval) {
419    err(__FUNCTION__ " - failed submitting write urb, error %d",
420       retval);
421 } else {
422    retval = bytes_written;
423 }
424 //释放信号量
425 exit:
426 /* unlock the device */
427 up (&dev->sem);
428 return retval;
429 }
430 
431 /**
432 * skel_ioctl
433 */
434 //控制函数，并没有实质的功能
435 static int skel_ioctl (struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
436 {
437 struct usb_skel *dev;
438 dev = (struct usb_skel *)file->private_data;
439 /* lock this object */
440 down (&dev->sem);
441 /* verify that the device wasn‘t unplugged */
442 if (dev->udev == NULL) {
443    up (&dev->sem);
444    return -ENODEV;
445 }
446 dbg(__FUNCTION__ " - minor %d, cmd 0x%.4x, arg %ld", 
447      dev->minor, cmd, arg);
448 
449 /* fill in your device specific stuff here */
450 
451 /* unlock the device */
452 up (&dev->sem);
453 
454 /* return that we did not understand this ioctl call */
455 return -ENOTTY;
456 }
457 
458 /**
459 * skel_write_bulk_callback
460 */
461 //skel_write的回调函数
462 static void skel_write_bulk_callback (struct urb *urb)
463 {
464 //用来获取skel_write失败时的设备信息
465 struct usb_skel *dev = (struct usb_skel *)urb->context;
466 //提供给debug函数的信息
467 dbg(__FUNCTION__ " - minor %d", dev->minor);
468 if ((urb->status != -ENOENT) && 
469      (urb->status != -ECONNRESET)) {
470    dbg(__FUNCTION__ " - nonzero write bulk status received: %d",
471       urb->status);
472    return;
473 }
474 return;
475 }
476 
477 /**
478 * skel_probe
479 *
480 * Called by the usb core when a new device is connected that it thinks
481 * this driver might be interested in.
482 */
483 //设备的试探函数
484 static void * skel_probe(struct usb_device *udev, unsigned int ifnum, const struct usb_device_id *id)
485 {
486 //设备信息
487 struct usb_skel *dev = NULL;
488 //接口函数
489 struct usb_interface *interface;
490 //接口描述符
491 struct usb_interface_descriptor *iface_desc;
492 //端点结构体
493 struct usb_endpoint_descriptor *endpoint;
494 //从设备号
495 int minor;
496 //缓冲区大小
497 int buffer_size;
498 int i;
499 char name[10];
500 //验证厂商和芯片id
501 /* See if the device offered us matches what we can accept */
502 if ((udev->descriptor.idVendor != USB_SKEL_VENDOR_ID) ||
503      (udev->descriptor.idProduct != USB_SKEL_PRODUCT_ID)) {
504    return NULL;
505 }
506 //临界区
507 /* select a "subminor" number (part of a minor number) */
508 down (&minor_table_mutex);
509 //取得一个合适的从设备号
510 for (minor = 0; minor < MAX_DEVICES; ++minor) {
511    if (minor_table[minor] == NULL)
512     break;
513 }
514 //该从设备号不可用
515 if (minor >= MAX_DEVICES) {
516    info ("Too many devices plugged in, can not handle this device.");
517    goto exit;
518 }
519 //申请内存
520 /* allocate memory for our device state and intialize it */
521 dev = kmalloc (sizeof(struct usb_skel), GFP_KERNEL);
522 if (dev == NULL) {
523    err ("Out of memory");
524    goto exit;
525 }
526 minor_table[minor] = dev;
527 //特定设备特定配置的特定接口
528 interface = &udev->actconfig->interface[ifnum];
529 //初始化从设备的信号量
530 init_MUTEX (&dev->sem);
531 //保存设备，配置以及接口方面的信息
532 dev->udev = udev;
533 dev->interface = interface;
534 dev->minor = minor;
535 /* set up the endpoint information */
536 /* check out the endpoints */
537 //搜索设备中可用的端点
538 iface_desc = &interface->altsetting[0];
539 for (i = 0; i < iface_desc->bNumEndpoints; ++i) {
540    endpoint = &iface_desc->endpoint[i];
541 //找到一个批量入端点，并配置相关信息：缓冲区大小，端点地址，缓冲区地址
542 //由于采用简单方式，因此不需要在接收区使用urb
543    if ((endpoint->bEndpointAddress & 0x80) &&
544       ((endpoint->bmAttributes & 3) == 0x02)) {
545     /* we found a bulk in endpoint */
546     buffer_size = endpoint->wMaxPacketSize;
547     dev->bulk_in_size = buffer_size;
548     dev->bulk_in_endpointAddr = endpoint->bEndpointAddress;
549     dev->bulk_in_buffer = kmalloc (buffer_size, GFP_KERNEL);
550     if (!dev->bulk_in_buffer) {
551      err("Couldn‘t allocate bulk_in_buffer");
552      goto error;
553     }
554    }
555 //找到一个批量出端点，除前面的信息外还需要一个urb，并初始化该urb
556    if (((endpoint->bEndpointAddress & 0x80) == 0x00) &&
557       ((endpoint->bmAttributes & 3) == 0x02)) {
558     /* we found a bulk out endpoint */
559     dev->write_urb = usb_alloc_urb(0);
560     if (!dev->write_urb) {
561      err("No free urbs available");
562      goto error;
563     }
564     buffer_size = endpoint->wMaxPacketSize;
565     dev->bulk_out_size = buffer_size;
566     dev->bulk_out_endpointAddr = endpoint->bEndpointAddress;
567     dev->bulk_out_buffer = kmalloc (buffer_size, GFP_KERNEL);
568     if (!dev->bulk_out_buffer) {
569      err("Couldn‘t allocate bulk_out_buffer");
570      goto error;
571     }
572 //初始化该urbbookmark
573     FILL_BULK_URB(dev->write_urb, udev, 
574           usb_sndbulkpipe(udev, 
575             endpoint->bEndpointAddress),
576           dev->bulk_out_buffer, buffer_size,
577           skel_write_bulk_callback, dev);
578    }
579 }
580 /* initialize the devfs node for this device and register it */
581 sprintf(name, "skel%d", dev->minor);
582 //初始化该设备文件，参数依次是：
583 //设备句柄，驱动名称，名称长度（采用了默认值），主设备号，从设备号，权限（mode，gid，uid），file_operations结构体，额外的信息
584 dev->devfs = devfs_register (usb_devfs_handle, name,
585          DEVFS_FL_DEFAULT, USB_MAJOR,
586          USB_SKEL_MINOR_BASE + dev->minor,
587          S_IFCHR | S_IRUSR | S_IWUSR | 
588          S_IRGRP | S_IWGRP | S_IROTH, 
589          &skel_fops, NULL);
590 //提供给用户访问该文件系统时的信息
591 /* let the user know what node this device is now attached to */
592 info ("USB Skeleton device now attached to USBSkel%d", dev->minor);
593 goto exit;
594 //出错处理 
595 error:
596 skel_delete (dev);
597 dev = NULL;
598 exit:
599 up (&minor_table_mutex);
600 return dev;
601 }
602 
603 /**
604 * skel_disconnect
605 *
606 * Called by the usb core when the device is removed from the system.
607 */
608 //设备移除时调用的函数
609 static void skel_disconnect(struct usb_device *udev, void *ptr)
610 {
611 struct usb_skel *dev;
612 int minor;
613 //获取从设备信息
614 dev = (struct usb_skel *)ptr;
615 
616 down (&minor_table_mutex);
617 down (&dev->sem);
618   
619 minor = dev->minor;
620 //设备文件注销
621 /* remove our devfs node */
622 devfs_unregister(dev->devfs);
623 //当前设备没有被使用
624 /* if the device is not opened, then we clean up right now */
625 if (!dev->open_count) {
626    up (&dev->sem);
627    skel_delete (dev);
628 } else {
629    dev->udev = NULL;
630    up (&dev->sem);
631 }
632 info("USB Skeleton #%d now disconnected", minor);
633 up (&minor_table_mutex);
634 }
635 /**
636 * usb_skel_init
637 */
638 //设备的初始化
639 static int __init usb_skel_init(void)
640 {
641 int result;
642 //设备注册
643 /* register this driver with the USB subsystem */
644 result = usb_register(&skel_driver);
645 if (result < 0) {
646    err("usb_register failed for the "__FILE__" driver. Error number %d",
647       result);
648    return -1;
649 }
650 info(DRIVER_DESC " " DRIVER_VERSION);
651 return 0;
652 }
653 
654 /**
655 * usb_skel_exit
656 */
657 //设备的注销，注意用的是usb_deregister而不是usb_unregister
658 static void __exit usb_skel_exit(void)
659 {
660 /* deregister this driver with the USB subsystem */
661 usb_deregister(&skel_driver);
662 }
663 //采用默认的函数进行驱动模块的初始化和注销
664 module_init (usb_skel_init);
665 module_exit (usb_skel_exit);
666 MODULE_AUTHOR(DRIVER_AUTHOR);
667 MODULE_DESCRIPTION(DRIVER_DESC);
668 MODULE_LICENSE("GPL");