libusb编程记录, 在WR703N自测成功

/install/lib/pkgconfig/libusb.pc, 内容如下:

prefix=/home/xxg/libusb-0.1.12/install

exec_prefix=${prefix}

libdir=${exec_prefix}/lib

includedir=${prefix}/include

Name: libusb

Description: USB access library

Version: 0.1.12

Libs: -L${libdir} -lusb

Cflags: -I${includedir}

一 libusb 介绍 

   libusb 设计了一系列的外部API 为应用程序所调用，通过这些API应用程序可以操作硬件，从libusb的源代码可以看出，这些API 调用了内核的底层接口，和kernel driver中所用到的函数所实现的功能差不多，只是libusb更加接近USB 规范。使得libusb的使用也比开发内核驱动相对容易的多。 

一些重要的数据结构:

struct usb_dev_handle {
    int fd;
    struct usb_bus *bus;
    struct usb_device *device;
    int config;
    int interface;
    int altsetting;
    void *impl_info;
};

struct usb_device {
    struct usb_device *next, *prev;
    char filename[PATH_MAX + 1];
    struct usb_bus *bus;
    struct usb_device_descriptor descriptor;
    struct usb_config_descriptor *config;
    void *dev; /* Darwin support */
};

struct usb_bus {
    struct usb_bus *next, *prev;
    char dirname[PATH_MAX + 1];
    struct usb_device *devices;
};

二  libusb 的外部接口 

2.1 初始化设备接口 

这些接口也可以称为核心函数，它们主要用来初始化并寻找相关设备。 

usb_init

函数定义： void usb_init(void);

从函数名称可以看出这个函数是用来初始化相关数据的，这个函数大家只要记住必须调用就行了，而且是一开始就要调用的.

 

usb_find_busses

函数定义： int usb_find_busses(void);

寻找系统上的usb总线，任何usb设备都通过usb总线和计算机总线通信。进而和其他设备通信。此函数返回总线数。

 

usb_find_devices

函数定义： int usb_find_devices(void);

寻找总线上的usb设备，这个函数必要在调用usb_find_busses()后使用。以上的三个函数都是一开始就要用到的，此函数返回设备数量。

 

usb_get_busses

函数定义： struct usb_bus *usb_get_busses(void);

这个函数返回总线的列表，在高一些的版本中已经用不到了，这在下面的实例中会有讲解

  

2.2 操作设备接口

     usb_open

函数定义： usb_dev_handle *usb_open(struct *usb_device dev);

  打开要使用的设备，在对硬件进行操作前必须要调用usb_open 来打开设备，这里大家看到有两个结构体 usb_dev_handle 和 usb_device 是我们在开发中经常碰到的，有必要把它们的结构看一看。在libusb 中的usb.h和usbi.h中有定义。

  这里我们不妨理解为返回的 usb_dev_handle 指针是指向设备的句柄，而行参里输入就是需要打开的设备。

 

   usb_close

   函数定义： int usb_close(usb_dev_handle *dev);

   与usb_open相对应，关闭设备，是必须调用的, 返回0成功，<0 失败。

 

   usb_set_configuration

   函数定义： int usb_set_configuration(usb_dev_handle *dev, int configuration);

   设置当前设备使用的configuration，参数configuration 是你要使用的configurtation descriptoes中的bConfigurationValue, 返回0成功，<0失败( 一个设备可能包含多个configuration,比如同时支持高速和低速的设备就有对应的两个configuration,详细可查看usb标准)

 

   usb_set_altinterface

   函数定义： int usb_set_altinterface(usb_dev_handle *dev, int alternate);

   和名字的意思一样，此函数设置当前设备配置的interface descriptor，参数alternate是指interface descriptor中的bAlternateSetting。返回0成功，<0失败

 

   usb_resetep

   函数定义： int usb_resetep(usb_dev_handle *dev, unsigned int ep);

   复位指定的endpoint，参数ep 是指bEndpointAddress,。这个函数不经常用，被下面介绍的usb_clear_halt函数所替代。

 

   usb_clear_halt

   函数定义： int usb_clear_halt (usb_dev_handle *dev, unsigned int ep);

   复位指定的endpoint，参数ep 是指bEndpointAddress。这个函数用来替代usb_resetep

 

   usb_reset

   函数定义： int usb_reset(usb_dev_handle *dev);

   这个函数现在基本不怎么用，不过这里我也讲一下，和名字所起的意思一样，这个函数reset设备，因为重启设备后还是要重新打开设备，所以用usb_close就已经可以满足要求了。

 

   usb_claim_interface

   函数定义： int usb_claim_interface(usb_dev_handle *dev, int interface);

   注册与操作系统通信的接口，这个函数必须被调用，因为只有注册接口，才能做相应的操作。

Interface 指 bInterfaceNumber. (下面介绍的usb_release_interface 与之相对应，也是必须调用的函数)

 

   usb_release_interface

   函数定义： int usb_release_interface(usb_dev_handle *dev, int interface);

   注销被usb_claim_interface函数调用后的接口，释放资源，和usb_claim_interface对应使用。

 

   2.3 控制传输接口 

   usb_control_msg

   函数定义：int usb_control_msg(usb_dev_handle *dev, int requesttype, int request, int value, int index, char *bytes, int size, int timeout);

   从默认的管道发送和接受控制数据

 

   usb_get_string

   函数定义： int usb_get_string(usb_dev_handle *dev, int index, int langid, char *buf, size_t buflen);

 

   usb_get_string_simple

函数定义：  int usb_get_string_simple(usb_dev_handle *dev, int index, char *buf, size_t buflen);

  

   usb_get_descriptor

   函数定义： int usb_get_descriptor(usb_dev_handle *dev, unsigned char type, unsigned char index, void *buf, int size);

 

   usb_get_descriptor_by_endpoint

   函数定义： int usb_get_descriptor_by_endpoint(usb_dev_handle *dev, int ep, unsigned char type, unsigned char index, void *buf, int size);

  

   2.4 批传输接口 

   usb_bulk_write

   函数定义： int usb_bulk_write(usb_dev_handle *dev, int ep, char *bytes, int size, int timeout);

 

    usb_interrupt_read

函数定义： int usb_interrupt_read(usb_dev_handle *dev, int ep, char *bytes, int size, int timeout);

  

2.5 中断传输接口

usb_bulk_write

函数定义： int usb_bulk_write(usb_dev_handle *dev, int ep, char *bytes, int size, int timeout);

 

usb_interrupt_read

函数定义： int usb_interrupt_read(usb_dev_handle *dev, int ep, char *bytes, int size, int timeout);

---

C代码:

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "usb.h"

#define IDVENDOR  0x0483
#define IDPRODUCT 0xD0D0	//ST公司的CR95HF

#define DEBUGP printf

//------------------------------------------------------------------
// handles to USB ports
#define MAX_PORTNUM 16
struct usb_dev_handle* usbhnd[MAX_PORTNUM];
struct usb_device *usb_dev_list[MAX_PORTNUM];
int usb_num_devices = -1;
int g_portnum = 0;

// Initialize the USB system
static char USBInit(void)
{
	struct usb_bus *bus;
	struct usb_device *dev;

  static int USBInitDone = 0;
  int i, iret = 0;

  if (USBInitDone != 0) return 0;

	// initialize USB subsystem
	usb_init();
	usb_set_debug(0);
	usb_find_busses();
	usb_find_devices();

	for (i=0; inext) {
		for (dev = bus->devices; dev; dev = dev->next) {
			DEBUGP("%s/%s     %04X/%04X\n", bus->dirname, dev->filename,
						dev->descriptor.idVendor, dev->descriptor.idProduct);
			if (dev->descriptor.idVendor == IDVENDOR && dev->descriptor.idProduct == IDPRODUCT) {
				DEBUGP("Find device \n");

				usbhnd[g_portnum] = usb_open(dev);
				iret = 1;
				if (usbhnd[g_portnum] == NULL) {
					iret = 0;
				}
				break;
			}
		}
	}

	DEBUGP("USBInit ret = %d\n", iret);
	USBInitDone = 1 ;
	return iret;
}

void USBClose(int portnum)
{
	usb_release_interface(usbhnd[portnum], 0);
	usb_close(usbhnd[portnum]);
	usbhnd[portnum] = NULL;
}

int main(void)
{
	int iret;

	iret = USBInit();
	if (iret) {
		USBClose(g_portnum);
	}

	return 1;
}

WR703N上运行结果:

root@OpenWrt:/xutest# ./libusbtest
001/005     04FA/2490
001/002     1A40/0101
001/001     1D6B/0002
root@OpenWrt:/xutest# ./libusbtest
libusb demo begin, qiushui_007 test ok
001/005     04FA/2490
001/002     1A40/0101
001/001     1D6B/0002
USBInit ret = 0
root@OpenWrt:/xutest# ./libusbtest
libusb demo begin, qiushui_007 test ok
001/006     0483/D0D0
Find device 
USBInit ret = 1
root@OpenWrt:/xutest# ./libusbtest
Segmentation fault
root@OpenWrt:/xutest# ./libusbtest
libusb demo begin, qiushui_007 test ok
001/006     0483/D0D0
Find device 
USBInit ret = 1

另: 封装了lua的运行结果

root@OpenWrt:/xutest# lua testow.lua

 a bc d , len = 9       a bc d, len = 6
1B 4C 75 61 51 00 01 02 03 04 07 08     12
1B 4C 75 61 51 00 00 04 04 04 08 04     false   12
13      27      Lua     81      0       0       4       4       4       8       4
A1 B0 B9 12 12 B9 B0 A1 12 B9 B0 A1 
13      314159265       314159265       314159265
313233343536, crc8_hex = 0xEC
array = F1 F2 F3 F4 F5 F6 
crc8 = 0x45
owAcquireEx_DS9490: USB
001/013     04FA/2490
Find DS2490, usb_num_devices = 0
owAcquireEx_DS9490: begin --- 
owAcquireEx_DS9490: portnum = 0
read_rom = 0001804400000002
direct read rom: 0001804400000002
read_1991 = E1 E2 E3 E4 E5 E6 E7 E8 E9 EA EB EC ED EE EF 
read_1991_hex = E1E2E3E4E5E6E7E8E9EAEBECEDEEEF

root@OpenWrt:/xutest# ./luatest
--> Hello LUA, this is my first lua program for yingying!
--> 2
lua: crc8 = EC, 07
owAcquireEx_DS9490: USB
001/013     04FA/2490
Find DS2490, usb_num_devices = 0
owAcquireEx_DS9490: begin --- 
owAcquireEx_DS9490: portnum = 0
ROM 1 = 02178145000000C3
ROM 2 = 01C1C64E1400000A

---

1. 源码参考: libusb-0.1.12的源码中参考 linux.c, 

/*
 * Linux USB support
 *
 * Copyright (c) 2000-2003 Johannes Erdfelt <[e-mail]>
 *
 * This library is covered by the LGPL, read LICENSE for details.
 */

#include <stdlib.h>    /* getenv, etc */
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/time.h>
#include <dirent.h>

#include "linux.h"
#include "usbi.h"

static char usb_path[PATH_MAX + 1] = "";

static int device_open(struct usb_device *dev)
{
  char filename[PATH_MAX + 1];
  int fd;

  snprintf(filename, sizeof(filename) - 1, "%s/%s/%s",
    usb_path, dev->bus->dirname, dev->filename);

  fd = open(filename, O_RDWR);
  if (fd < 0) {
    fd = open(filename, O_RDONLY);
    if (fd < 0)
      USB_ERROR_STR(-errno, "failed to open %s: %s",
    filename, strerror(errno));
  }

  return fd;
}

int usb_os_open(usb_dev_handle *dev)
{
  dev->fd = device_open(dev->device);

  return 0;
}

int usb_os_close(usb_dev_handle *dev)
{
  if (dev->fd < 0)
    return 0;

  if (close(dev->fd) == -1)
    /* Failing trying to close a file really isn't an error, so return 0 */
    USB_ERROR_STR(0, "tried to close device fd %d: %s", dev->fd,
    strerror(errno));

  return 0;
}

int usb_set_configuration(usb_dev_handle *dev, int configuration)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_SETCONFIG, &configuration);
  if (ret < 0)
    USB_ERROR_STR(-errno, "could not set config %d: %s", configuration,
    strerror(errno));

  dev->config = configuration;

  return 0;
}

int usb_claim_interface(usb_dev_handle *dev, int interface)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_CLAIMINTF, &interface);
  if (ret < 0) {
    if (errno == EBUSY && usb_debug > 0)
      fprintf(stderr, "Check that you have permissions to write to %s/%s and, if you don't, that you set up hotplug () correctly.\n", dev->bus->dirname, dev->device->filename);

    USB_ERROR_STR(-errno, "could not claim interface %d: %s", interface,
    strerror(errno));
  }

  dev->interface = interface;

  return 0;
}

int usb_release_interface(usb_dev_handle *dev, int interface)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_RELEASEINTF, &interface);
  if (ret < 0)
    USB_ERROR_STR(-errno, "could not release intf %d: %s", interface,
        strerror(errno));

  dev->interface = -1;

  return 0;
}

int usb_set_altinterface(usb_dev_handle *dev, int alternate)
{
  int ret;
  struct usb_setinterface setintf;

  if (dev->interface < 0)
    USB_ERROR(-EINVAL);

  setintf.interface = dev->interface;
  setintf.altsetting = alternate;

  ret = ioctl(dev->fd, IOCTL_USB_SETINTF, &setintf);
  if (ret < 0)
    USB_ERROR_STR(-errno, "could not set alt intf %d/%d: %s",
    dev->interface, alternate, strerror(errno));

  dev->altsetting = alternate;

  return 0;
}

/*
 * Linux usbfs has a limit of one page size for synchronous bulk read/write.
 * 4096 is the most portable maximum we can do for now.
 * Linux usbfs has a limit of 16KB for the URB interface. We use this now
 * to get better performance for USB 2.0 devices.
 */
#define MAX_READ_WRITE    (16 * 1024)

int usb_control_msg(usb_dev_handle *dev, int requesttype, int request,
    int value, int index, char *bytes, int size, int timeout)
{
  struct usb_ctrltransfer ctrl;
  int ret;

  ctrl.bRequestType = requesttype;
  ctrl.bRequest = request;
  ctrl.wValue = value;
  ctrl.wIndex = index;
  ctrl.wLength = size;

  ctrl.data = bytes;
  ctrl.timeout = timeout;

  ret = ioctl(dev->fd, IOCTL_USB_CONTROL, &ctrl);
  if (ret < 0)
    USB_ERROR_STR(-errno, "error sending control message: %s", strerror(errno));

  return ret;
}

#define URB_USERCONTEXT_COOKIE        ((void *)0x1)

/* Reading and writing are the same except for the endpoint */
static int usb_urb_transfer(usb_dev_handle *dev, int ep, int urbtype,
    char *bytes, int size, int timeout)
{
  struct usb_urb urb;
  int bytesdone = 0, requested;
  struct timeval tv, tv_ref, tv_now;
  struct usb_urb *context;
  int ret, waiting;

  /*
   * HACK: The use of urb.usercontext is a hack to get threaded applications
   * sort of working again. Threaded support is still not recommended, but
   * this should allow applications to work in the common cases. Basically,
   * if we get the completion for an URB we're not waiting for, then we update
   * the usercontext pointer to 1 for the other threads URB and it will see
   * the change after it wakes up from the the timeout. Ugly, but it works.
   */

  /*
   * Get actual time, and add the timeout value. The result is the absolute
   * time where we have to quit waiting for an message.
   */
  gettimeofday(&tv_ref, NULL);
  tv_ref.tv_sec = tv_ref.tv_sec + timeout / 1000;
  tv_ref.tv_usec = tv_ref.tv_usec + (timeout % 1000) * 1000;

  if (tv_ref.tv_usec > 1000000) {
    tv_ref.tv_usec -= 1000000;
    tv_ref.tv_sec++;
  }

  do {
    fd_set writefds;

    requested = size - bytesdone;
    if (requested > MAX_READ_WRITE)
      requested = MAX_READ_WRITE;

    urb.type = urbtype;
    urb.endpoint = ep;
    urb.flags = 0;
    urb.buffer = bytes + bytesdone;
    urb.buffer_length = requested;
    urb.signr = 0;
    urb.actual_length = 0;
    urb.number_of_packets = 0;    /* don't do isochronous yet */
    urb.usercontext = NULL;

    ret = ioctl(dev->fd, IOCTL_USB_SUBMITURB, &urb);
    if (ret < 0) {
      USB_ERROR_STR(-errno, "error submitting URB: %s", strerror(errno));
      return ret;
    }

    FD_ZERO(&writefds);
    FD_SET(dev->fd, &writefds);

restart:
    waiting = 1;
    context = NULL;
    while (!urb.usercontext && ((ret = ioctl(dev->fd, IOCTL_USB_REAPURBNDELAY, &context)) == -1) && waiting) {
      tv.tv_sec = 0;
      tv.tv_usec = 1000; // 1 msec
      select(dev->fd + 1, NULL, &writefds, NULL, &tv); //sub second wait

      if (timeout) {
        /* compare with actual time, as the select timeout is not that precise */
        gettimeofday(&tv_now, NULL);

        if ((tv_now.tv_sec > tv_ref.tv_sec) ||
            ((tv_now.tv_sec == tv_ref.tv_sec) && (tv_now.tv_usec >= tv_ref.tv_usec)))
          waiting = 0;
      }
    }

    if (context && context != &urb) {
      context->usercontext = URB_USERCONTEXT_COOKIE;
      /* We need to restart since we got a successful URB, but not ours */
      goto restart;
    }

    /*
     * If there was an error, that wasn't EAGAIN (no completion), then
     * something happened during the reaping and we should return that
     * error now
     */
    if (ret < 0 && !urb.usercontext && errno != EAGAIN)
      USB_ERROR_STR(-errno, "error reaping URB: %s", strerror(errno));

    bytesdone += urb.actual_length;
  } while ((ret == 0 || urb.usercontext) && bytesdone < size && urb.actual_length == requested);

  /* If the URB didn't complete in success or error, then let's unlink it */
  if (ret < 0 && !urb.usercontext) {
    int rc;

    if (!waiting)
      rc = -ETIMEDOUT;
    else
      rc = urb.status;

    ret = ioctl(dev->fd, IOCTL_USB_DISCARDURB, &urb);
    if (ret < 0 && errno != EINVAL && usb_debug >= 1)
      fprintf(stderr, "error discarding URB: %s", strerror(errno));

    /*
     * When the URB is unlinked, it gets moved to the completed list and
     * then we need to reap it or else the next time we call this function,
     * we'll get the previous completion and exit early
     */
    ioctl(dev->fd, IOCTL_USB_REAPURB, &context);

    return rc;
  }

  return bytesdone;
}

int usb_bulk_write(usb_dev_handle *dev, int ep, char *bytes, int size,
    int timeout)
{
  /* Ensure the endpoint address is correct */
  return usb_urb_transfer(dev, ep, USB_URB_TYPE_BULK, bytes, size,
        timeout);
}

int usb_bulk_read(usb_dev_handle *dev, int ep, char *bytes, int size,
    int timeout)
{
  /* Ensure the endpoint address is correct */
  ep |= USB_ENDPOINT_IN;
  return usb_urb_transfer(dev, ep, USB_URB_TYPE_BULK, bytes, size,
        timeout);
}

/*
 * FIXME: Packetize large buffers here. 2.4 HCDs (atleast, haven't checked
 * 2.5 HCDs yet) don't handle multi-packet Interrupt transfers. So we need
 * to lookup the endpoint packet size and packetize appropriately here.
 */
int usb_interrupt_write(usb_dev_handle *dev, int ep, char *bytes, int size,
    int timeout)
{
  /* Ensure the endpoint address is correct */
  return usb_urb_transfer(dev, ep, USB_URB_TYPE_INTERRUPT, bytes, size,
        timeout);
}

int usb_interrupt_read(usb_dev_handle *dev, int ep, char *bytes, int size,
    int timeout)
{
  /* Ensure the endpoint address is correct */
  ep |= USB_ENDPOINT_IN;
  return usb_urb_transfer(dev, ep, USB_URB_TYPE_INTERRUPT, bytes, size,
        timeout);
}

int usb_os_find_busses(struct usb_bus **busses)
{
  struct usb_bus *fbus = NULL;
  DIR *dir;
  struct dirent *entry;

  dir = opendir(usb_path);
  if (!dir)
    USB_ERROR_STR(-errno, "couldn't opendir(%s): %s", usb_path,
    strerror(errno));

  while ((entry = readdir(dir)) != NULL) {
    struct usb_bus *bus;

    /* Skip anything starting with a . */
    if (entry->d_name[0] == '.')
      continue;

    if (!strchr("0123456789", entry->d_name[strlen(entry->d_name) - 1])) {
      if (usb_debug >= 2)
        fprintf(stderr, "usb_os_find_busses: Skipping non bus directory %s\n",
        entry->d_name);
      continue;
    }

    bus = malloc(sizeof(*bus));
    if (!bus)
      USB_ERROR(-ENOMEM);

    memset((void *)bus, 0, sizeof(*bus));

    strncpy(bus->dirname, entry->d_name, sizeof(bus->dirname) - 1);
    bus->dirname[sizeof(bus->dirname) - 1] = 0;

    LIST_ADD(fbus, bus);

    if (usb_debug >= 2)
       fprintf(stderr, "usb_os_find_busses: Found %s\n", bus->dirname);
  }

  closedir(dir);

  *busses = fbus;

  return 0;
}

int usb_os_find_devices(struct usb_bus *bus, struct usb_device **devices)
{
  struct usb_device *fdev = NULL;
  DIR *dir;
  struct dirent *entry;
  char dirpath[PATH_MAX + 1];

  snprintf(dirpath, PATH_MAX, "%s/%s", usb_path, bus->dirname);

  dir = opendir(dirpath);
  if (!dir)
    USB_ERROR_STR(-errno, "couldn't opendir(%s): %s", dirpath,
    strerror(errno));

  while ((entry = readdir(dir)) != NULL) {
    unsigned char device_desc[DEVICE_DESC_LENGTH];
    char filename[PATH_MAX + 1];
    struct usb_device *dev;
    struct usb_connectinfo connectinfo;
    int i, fd, ret;

    /* Skip anything starting with a . */
    if (entry->d_name[0] == '.')
      continue;

    dev = malloc(sizeof(*dev));
    if (!dev)
      USB_ERROR(-ENOMEM);

    memset((void *)dev, 0, sizeof(*dev));

    dev->bus = bus;

    strncpy(dev->filename, entry->d_name, sizeof(dev->filename) - 1);
    dev->filename[sizeof(dev->filename) - 1] = 0;

    snprintf(filename, sizeof(filename) - 1, "%s/%s", dirpath, entry->d_name);
    fd = open(filename, O_RDWR);
    if (fd < 0) {
      fd = open(filename, O_RDONLY);
      if (fd < 0) {
        if (usb_debug >= 2)
          fprintf(stderr, "usb_os_find_devices: Couldn't open %s\n",
                  filename);

        free(dev);
        continue;
      }
    }

    /* Get the device number */
    ret = ioctl(fd, IOCTL_USB_CONNECTINFO, &connectinfo);
    if (ret < 0) {
      if (usb_debug)
        fprintf(stderr, "usb_os_find_devices: couldn't get connect info\n");
    } else
      dev->devnum = connectinfo.devnum;

    ret = read(fd, (void *)device_desc, DEVICE_DESC_LENGTH);
    if (ret < 0) {
      if (usb_debug)
        fprintf(stderr, "usb_os_find_devices: Couldn't read descriptor\n");

      free(dev);

      goto err;
    }

    /*
     * Linux kernel converts the words in this descriptor to CPU endian, so
     * we use the undocumented W character for usb_parse_descriptor() that
     * doesn't convert endianess when parsing the descriptor
     */
    usb_parse_descriptor(device_desc, "bbWbbbbWWWbbbb", &dev->descriptor);

    LIST_ADD(fdev, dev);

    if (usb_debug >= 2)
      fprintf(stderr, "usb_os_find_devices: Found %s on %s\n",
        dev->filename, bus->dirname);

    /* Now try to fetch the rest of the descriptors */
    if (dev->descriptor.bNumConfigurations > USB_MAXCONFIG)
      /* Silent since we'll try again later */
      goto err;

    if (dev->descriptor.bNumConfigurations < 1)
      /* Silent since we'll try again later */
      goto err;

    dev->config = (struct usb_config_descriptor *)malloc(dev->descriptor.bNumConfigurations * sizeof(struct usb_config_descriptor));
    if (!dev->config)
      /* Silent since we'll try again later */
      goto err;

    memset(dev->config, 0, dev->descriptor.bNumConfigurations *
          sizeof(struct usb_config_descriptor));

    for (i = 0; i < dev->descriptor.bNumConfigurations; i++) {
      unsigned char buffer[8], *bigbuffer;
      struct usb_config_descriptor config;

      /* Get the first 8 bytes so we can figure out what the total length is */
      ret = read(fd, (void *)buffer, 8);
      if (ret < 8) {
        if (usb_debug >= 1) {
          if (ret < 0)
            fprintf(stderr, "Unable to get descriptor (%d)\n", ret);
          else
            fprintf(stderr, "Config descriptor too short (expected %d, got %d)\n", 8, ret);
        }

        goto err;
      }

      usb_parse_descriptor(buffer, "bbw", &config);

      bigbuffer = malloc(config.wTotalLength);
      if (!bigbuffer) {
        if (usb_debug >= 1)
          fprintf(stderr, "Unable to allocate memory for descriptors\n");
        goto err;
      }

      /* Read the rest of the config descriptor */
      memcpy(bigbuffer, buffer, 8);

      ret = read(fd, (void *)(bigbuffer + 8), config.wTotalLength - 8);
      if (ret < config.wTotalLength - 8) {
        if (usb_debug >= 1) {
          if (ret < 0)
            fprintf(stderr, "Unable to get descriptor (%d)\n", ret);
          else
            fprintf(stderr, "Config descriptor too short (expected %d, got %d)\n", config.wTotalLength, ret);
        }

        free(bigbuffer);
        goto err;
      }

      ret = usb_parse_configuration(&dev->config[i], bigbuffer);
      if (usb_debug >= 2) {
        if (ret > 0)
          fprintf(stderr, "Descriptor data still left\n");
        else if (ret < 0)
          fprintf(stderr, "Unable to parse descriptors\n");
      }

      free(bigbuffer);
    }

err:
    close(fd);
  }

  closedir(dir);

  *devices = fdev;

  return 0;
}

int usb_os_determine_children(struct usb_bus *bus)
{
  struct usb_device *dev, *devices[256];
  struct usb_ioctl command;
  int ret, i, i1;

  /* Create a list of devices first */
  memset(devices, 0, sizeof(devices));
  for (dev = bus->devices; dev; dev = dev->next)
    if (dev->devnum)
      devices[dev->devnum] = dev;

  /* Now fetch the children for each device */
  for (dev = bus->devices; dev; dev = dev->next) {
    struct usb_hub_portinfo portinfo;
    int fd;

    fd = device_open(dev);
    if (fd < 0)
      continue;

    /* Query the hub driver for the children of this device */
    if (dev->config && dev->config->interface && dev->config->interface->altsetting)
      command.ifno = dev->config->interface->altsetting->bInterfaceNumber;
    else
      command.ifno = 0;
    command.ioctl_code = IOCTL_USB_HUB_PORTINFO;
    command.data = &portinfo;
    ret = ioctl(fd, IOCTL_USB_IOCTL, &command);
    if (ret < 0) {
      /* errno == ENOSYS means the device probably wasn't a hub */
      if (errno != ENOSYS && usb_debug > 1)
        fprintf(stderr, "error obtaining child information: %s\n",
        strerror(errno));

      close(fd);
      continue;
    }

    dev->num_children = 0;
    for (i = 0; i < portinfo.numports; i++)
      if (portinfo.port[i])
        dev->num_children++;

    /* Free any old children first */
    free(dev->children);

    dev->children = malloc(sizeof(struct usb_device *) * dev->num_children);
    if (!dev->children) {
      if (usb_debug > 1)
        fprintf(stderr, "error allocating %zu bytes memory for dev->children\n",
                sizeof(struct usb_device *) * dev->num_children);

      dev->num_children = 0;
      close(fd);
      continue;
    }

    for (i = 0, i1 = 0; i < portinfo.numports; i++) {
      if (!portinfo.port[i])
        continue;

      dev->children[i1++] = devices[portinfo.port[i]];

      devices[portinfo.port[i]] = NULL;
    }

    close(fd);
  }

  /*
   * There should be one device left in the devices list and that should be
   * the root device
   */
  for (i = 0; i < sizeof(devices) / sizeof(devices[0]); i++) {
    if (devices[i])
      bus->root_dev = devices[i];
  }

  return 0;
}

static int check_usb_vfs(const char *dirname)
{
  DIR *dir;
  struct dirent *entry;
  int found = 0;

  dir = opendir(dirname);
  if (!dir)
    return 0;

  while ((entry = readdir(dir)) != NULL) {
    /* Skip anything starting with a . */
    if (entry->d_name[0] == '.')
      continue;

    /* We assume if we find any files that it must be the right place */
    found = 1;
    break;
  }

  closedir(dir);

  return found;
}

void usb_os_init(void)
{
  /* Find the path to the virtual filesystem */
  if (getenv("USB_DEVFS_PATH")) {
    if (check_usb_vfs(getenv("USB_DEVFS_PATH"))) {
      strncpy(usb_path, getenv("USB_DEVFS_PATH"), sizeof(usb_path) - 1);
      usb_path[sizeof(usb_path) - 1] = 0;
    } else if (usb_debug)
      fprintf(stderr, "usb_os_init: couldn't find USB VFS in USB_DEVFS_PATH\n");
  }

  if (!usb_path[0]) {
    if (check_usb_vfs("/dev/bus/usb")) {
      strncpy(usb_path, "/dev/bus/usb", sizeof(usb_path) - 1);
      usb_path[sizeof(usb_path) - 1] = 0;
    } else if (check_usb_vfs("/proc/bus/usb")) {
      strncpy(usb_path, "/proc/bus/usb", sizeof(usb_path) - 1);
      usb_path[sizeof(usb_path) - 1] = 0;
    } else
      usb_path[0] = 0;    /* No path, no USB support */
  }

  if (usb_debug) {
    if (usb_path[0])
      fprintf(stderr, "usb_os_init: Found USB VFS at %s\n", usb_path);
    else
      fprintf(stderr, "usb_os_init: No USB VFS found, is it mounted?\n");
  }
}

int usb_resetep(usb_dev_handle *dev, unsigned int ep)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_RESETEP, &ep);
  if (ret)
    USB_ERROR_STR(-errno, "could not reset ep %d: %s", ep,
        strerror(errno));

  return 0;
}

int usb_clear_halt(usb_dev_handle *dev, unsigned int ep)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_CLEAR_HALT, &ep);
  if (ret)
    USB_ERROR_STR(-errno, "could not clear/halt ep %d: %s", ep,
        strerror(errno));

  return 0;
}

int usb_reset(usb_dev_handle *dev)
{
  int ret;

  ret = ioctl(dev->fd, IOCTL_USB_RESET, NULL);
  if (ret)
     USB_ERROR_STR(-errno, "could not reset: %s", strerror(errno));

  return 0;
}

int usb_get_driver_np(usb_dev_handle *dev, int interface, char *name,
    unsigned int namelen)
{
  struct usb_getdriver getdrv;
  int ret;

  getdrv.interface = interface;
  ret = ioctl(dev->fd, IOCTL_USB_GETDRIVER, &getdrv);
  if (ret)
    USB_ERROR_STR(-errno, "could not get bound driver: %s", strerror(errno));

  strncpy(name, getdrv.driver, namelen - 1);
  name[namelen - 1] = 0;

  return 0;
}

int usb_detach_kernel_driver_np(usb_dev_handle *dev, int interface)
{
  struct usb_ioctl command;
  int ret;

  command.ifno = interface;
  command.ioctl_code = IOCTL_USB_DISCONNECT;
  command.data = NULL;

  ret = ioctl(dev->fd, IOCTL_USB_IOCTL, &command);
  if (ret)
    USB_ERROR_STR(-errno, "could not detach kernel driver from interface %d: %s",
        interface, strerror(errno));

  return 0;
}

2.