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authorBenjamin Dobell <benjamin.dobell+github@glassechidna.com.au>2010-12-04 14:25:04 +0100
committerBenjamin Dobell <benjamin.dobell+github@glassechidna.com.au>2010-12-04 14:25:04 +0100
commit46f2c1134d276944fb74584a61d90cc363aee7eb (patch)
tree6fa14b7ef509a3fb84305dec013dd24bcae6c17d /libusb-1.0/libusb/descriptor.c
parentAddresses: (diff)
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Diffstat (limited to 'libusb-1.0/libusb/descriptor.c')
-rw-r--r--libusb-1.0/libusb/descriptor.c721
1 files changed, 721 insertions, 0 deletions
diff --git a/libusb-1.0/libusb/descriptor.c b/libusb-1.0/libusb/descriptor.c
new file mode 100644
index 0000000..54a47b4
--- /dev/null
+++ b/libusb-1.0/libusb/descriptor.c
@@ -0,0 +1,721 @@
+/*
+ * USB descriptor handling functions for libusb
+ * Copyright (C) 2007 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <errno.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "libusbi.h"
+
+#define DESC_HEADER_LENGTH 2
+#define DEVICE_DESC_LENGTH 18
+#define CONFIG_DESC_LENGTH 9
+#define INTERFACE_DESC_LENGTH 9
+#define ENDPOINT_DESC_LENGTH 7
+#define ENDPOINT_AUDIO_DESC_LENGTH 9
+
+/** @defgroup desc USB descriptors
+ * This page details how to examine the various standard USB descriptors
+ * for detected devices
+ */
+
+/* set host_endian if the w values are already in host endian format,
+ * as opposed to bus endian. */
+int usbi_parse_descriptor(unsigned char *source, char *descriptor, void *dest,
+ int host_endian)
+{
+ unsigned char *sp = source, *dp = dest;
+ uint16_t w;
+ char *cp;
+
+ for (cp = descriptor; *cp; cp++) {
+ switch (*cp) {
+ case 'b': /* 8-bit byte */
+ *dp++ = *sp++;
+ break;
+ case 'w': /* 16-bit word, convert from little endian to CPU */
+ dp += ((uintptr_t)dp & 1); /* Align to word boundary */
+
+ if (host_endian) {
+ memcpy(dp, sp, 2);
+ } else {
+ w = (sp[1] << 8) | sp[0];
+ *((uint16_t *)dp) = w;
+ }
+ sp += 2;
+ dp += 2;
+ break;
+ }
+ }
+
+ return (int) (sp - source);
+}
+
+static void clear_endpoint(struct libusb_endpoint_descriptor *endpoint)
+{
+ if (endpoint->extra)
+ free((unsigned char *) endpoint->extra);
+}
+
+static int parse_endpoint(struct libusb_context *ctx,
+ struct libusb_endpoint_descriptor *endpoint, unsigned char *buffer,
+ int size, int host_endian)
+{
+ struct usb_descriptor_header header;
+ unsigned char *extra;
+ unsigned char *begin;
+ int parsed = 0;
+ int len;
+
+ usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+ /* Everything should be fine being passed into here, but we sanity */
+ /* check JIC */
+ if (header.bLength > size) {
+ usbi_err(ctx, "ran out of descriptors parsing");
+ return -1;
+ }
+
+ if (header.bDescriptorType != LIBUSB_DT_ENDPOINT) {
+ usbi_err(ctx, "unexpected descriptor %x (expected %x)",
+ header.bDescriptorType, LIBUSB_DT_ENDPOINT);
+ return parsed;
+ }
+
+ if (header.bLength >= ENDPOINT_AUDIO_DESC_LENGTH)
+ usbi_parse_descriptor(buffer, "bbbbwbbb", endpoint, host_endian);
+ else if (header.bLength >= ENDPOINT_DESC_LENGTH)
+ usbi_parse_descriptor(buffer, "bbbbwb", endpoint, host_endian);
+
+ buffer += header.bLength;
+ size -= header.bLength;
+ parsed += header.bLength;
+
+ /* Skip over the rest of the Class Specific or Vendor Specific */
+ /* descriptors */
+ begin = buffer;
+ while (size >= DESC_HEADER_LENGTH) {
+ usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+ if (header.bLength < 2) {
+ usbi_err(ctx, "invalid descriptor length %d", header.bLength);
+ return -1;
+ }
+
+ /* If we find another "proper" descriptor then we're done */
+ if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+ (header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
+ (header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+ (header.bDescriptorType == LIBUSB_DT_DEVICE))
+ break;
+
+ usbi_dbg("skipping descriptor %x", header.bDescriptorType);
+ buffer += header.bLength;
+ size -= header.bLength;
+ parsed += header.bLength;
+ }
+
+ /* Copy any unknown descriptors into a storage area for drivers */
+ /* to later parse */
+ len = (int)(buffer - begin);
+ if (!len) {
+ endpoint->extra = NULL;
+ endpoint->extra_length = 0;
+ return parsed;
+ }
+
+ extra = malloc(len);
+ endpoint->extra = extra;
+ if (!extra) {
+ endpoint->extra_length = 0;
+ return LIBUSB_ERROR_NO_MEM;
+ }
+
+ memcpy(extra, begin, len);
+ endpoint->extra_length = len;
+
+ return parsed;
+}
+
+static void clear_interface(struct libusb_interface *usb_interface)
+{
+ int i;
+ int j;
+
+ if (usb_interface->altsetting) {
+ for (i = 0; i < usb_interface->num_altsetting; i++) {
+ struct libusb_interface_descriptor *ifp =
+ (struct libusb_interface_descriptor *)
+ usb_interface->altsetting + i;
+ if (ifp->extra)
+ free((void *) ifp->extra);
+ if (ifp->endpoint) {
+ for (j = 0; j < ifp->bNumEndpoints; j++)
+ clear_endpoint((struct libusb_endpoint_descriptor *)
+ ifp->endpoint + j);
+ free((void *) ifp->endpoint);
+ }
+ }
+ free((void *) usb_interface->altsetting);
+ usb_interface->altsetting = NULL;
+ }
+
+}
+
+static int parse_interface(libusb_context *ctx,
+ struct libusb_interface *usb_interface, unsigned char *buffer, int size,
+ int host_endian)
+{
+ int i;
+ int len;
+ int r;
+ int parsed = 0;
+ int tmp;
+ struct usb_descriptor_header header;
+ struct libusb_interface_descriptor *ifp;
+ unsigned char *begin;
+
+ usb_interface->num_altsetting = 0;
+
+ while (size >= INTERFACE_DESC_LENGTH) {
+ struct libusb_interface_descriptor *altsetting =
+ (struct libusb_interface_descriptor *) usb_interface->altsetting;
+ altsetting = realloc(altsetting,
+ sizeof(struct libusb_interface_descriptor) *
+ (usb_interface->num_altsetting + 1));
+ if (!altsetting) {
+ r = LIBUSB_ERROR_NO_MEM;
+ goto err;
+ }
+ usb_interface->altsetting = altsetting;
+
+ ifp = altsetting + usb_interface->num_altsetting;
+ usb_interface->num_altsetting++;
+ usbi_parse_descriptor(buffer, "bbbbbbbbb", ifp, 0);
+ ifp->extra = NULL;
+ ifp->extra_length = 0;
+ ifp->endpoint = NULL;
+
+ /* Skip over the interface */
+ buffer += ifp->bLength;
+ parsed += ifp->bLength;
+ size -= ifp->bLength;
+
+ begin = buffer;
+
+ /* Skip over any interface, class or vendor descriptors */
+ while (size >= DESC_HEADER_LENGTH) {
+ usbi_parse_descriptor(buffer, "bb", &header, 0);
+ if (header.bLength < 2) {
+ usbi_err(ctx, "invalid descriptor of length %d",
+ header.bLength);
+ r = LIBUSB_ERROR_IO;
+ goto err;
+ }
+
+ /* If we find another "proper" descriptor then we're done */
+ if ((header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
+ (header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+ (header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+ (header.bDescriptorType == LIBUSB_DT_DEVICE))
+ break;
+
+ buffer += header.bLength;
+ parsed += header.bLength;
+ size -= header.bLength;
+ }
+
+ /* Copy any unknown descriptors into a storage area for */
+ /* drivers to later parse */
+ len = (int)(buffer - begin);
+ if (len) {
+ ifp->extra = malloc(len);
+ if (!ifp->extra) {
+ r = LIBUSB_ERROR_NO_MEM;
+ goto err;
+ }
+ memcpy((unsigned char *) ifp->extra, begin, len);
+ ifp->extra_length = len;
+ }
+
+ /* Did we hit an unexpected descriptor? */
+ usbi_parse_descriptor(buffer, "bb", &header, 0);
+ if ((size >= DESC_HEADER_LENGTH) &&
+ ((header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+ (header.bDescriptorType == LIBUSB_DT_DEVICE)))
+ return parsed;
+
+ if (ifp->bNumEndpoints > USB_MAXENDPOINTS) {
+ usbi_err(ctx, "too many endpoints (%d)", ifp->bNumEndpoints);
+ r = LIBUSB_ERROR_IO;
+ goto err;
+ }
+
+ if (ifp->bNumEndpoints > 0) {
+ struct libusb_endpoint_descriptor *endpoint;
+ tmp = ifp->bNumEndpoints * sizeof(struct libusb_endpoint_descriptor);
+ endpoint = malloc(tmp);
+ ifp->endpoint = endpoint;
+ if (!endpoint) {
+ r = LIBUSB_ERROR_NO_MEM;
+ goto err;
+ }
+
+ memset(endpoint, 0, tmp);
+ for (i = 0; i < ifp->bNumEndpoints; i++) {
+ usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+ if (header.bLength > size) {
+ usbi_err(ctx, "ran out of descriptors parsing");
+ r = LIBUSB_ERROR_IO;
+ goto err;
+ }
+
+ r = parse_endpoint(ctx, endpoint + i, buffer, size,
+ host_endian);
+ if (r < 0)
+ goto err;
+
+ buffer += r;
+ parsed += r;
+ size -= r;
+ }
+ }
+
+ /* We check to see if it's an alternate to this one */
+ ifp = (struct libusb_interface_descriptor *) buffer;
+ if (size < LIBUSB_DT_INTERFACE_SIZE ||
+ ifp->bDescriptorType != LIBUSB_DT_INTERFACE ||
+ !ifp->bAlternateSetting)
+ return parsed;
+ }
+
+ return parsed;
+err:
+ clear_interface(usb_interface);
+ return r;
+}
+
+static void clear_configuration(struct libusb_config_descriptor *config)
+{
+ if (config->interface) {
+ int i;
+ for (i = 0; i < config->bNumInterfaces; i++)
+ clear_interface((struct libusb_interface *)
+ config->interface + i);
+ free((void *) config->interface);
+ }
+ if (config->extra)
+ free((void *) config->extra);
+}
+
+static int parse_configuration(struct libusb_context *ctx,
+ struct libusb_config_descriptor *config, unsigned char *buffer,
+ int host_endian)
+{
+ int i;
+ int r;
+ int size;
+ int tmp;
+ struct usb_descriptor_header header;
+ struct libusb_interface *usb_interface;
+
+ usbi_parse_descriptor(buffer, "bbwbbbbb", config, host_endian);
+ size = config->wTotalLength;
+
+ if (config->bNumInterfaces > USB_MAXINTERFACES) {
+ usbi_err(ctx, "too many interfaces (%d)", config->bNumInterfaces);
+ return LIBUSB_ERROR_IO;
+ }
+
+ tmp = config->bNumInterfaces * sizeof(struct libusb_interface);
+ usb_interface = malloc(tmp);
+ config->interface = usb_interface;
+ if (!config->interface)
+ return LIBUSB_ERROR_NO_MEM;
+
+ memset(usb_interface, 0, tmp);
+ buffer += config->bLength;
+ size -= config->bLength;
+
+ config->extra = NULL;
+ config->extra_length = 0;
+
+ for (i = 0; i < config->bNumInterfaces; i++) {
+ int len;
+ unsigned char *begin;
+
+ /* Skip over the rest of the Class Specific or Vendor */
+ /* Specific descriptors */
+ begin = buffer;
+ while (size >= DESC_HEADER_LENGTH) {
+ usbi_parse_descriptor(buffer, "bb", &header, 0);
+
+ if ((header.bLength > size) ||
+ (header.bLength < DESC_HEADER_LENGTH)) {
+ usbi_err(ctx, "invalid descriptor length of %d",
+ header.bLength);
+ r = LIBUSB_ERROR_IO;
+ goto err;
+ }
+
+ /* If we find another "proper" descriptor then we're done */
+ if ((header.bDescriptorType == LIBUSB_DT_ENDPOINT) ||
+ (header.bDescriptorType == LIBUSB_DT_INTERFACE) ||
+ (header.bDescriptorType == LIBUSB_DT_CONFIG) ||
+ (header.bDescriptorType == LIBUSB_DT_DEVICE))
+ break;
+
+ usbi_dbg("skipping descriptor 0x%x\n", header.bDescriptorType);
+ buffer += header.bLength;
+ size -= header.bLength;
+ }
+
+ /* Copy any unknown descriptors into a storage area for */
+ /* drivers to later parse */
+ len = (int)(buffer - begin);
+ if (len) {
+ /* FIXME: We should realloc and append here */
+ if (!config->extra_length) {
+ config->extra = malloc(len);
+ if (!config->extra) {
+ r = LIBUSB_ERROR_NO_MEM;
+ goto err;
+ }
+
+ memcpy((unsigned char *) config->extra, begin, len);
+ config->extra_length = len;
+ }
+ }
+
+ r = parse_interface(ctx, usb_interface + i, buffer, size, host_endian);
+ if (r < 0)
+ goto err;
+
+ buffer += r;
+ size -= r;
+ }
+
+ return size;
+
+err:
+ clear_configuration(config);
+ return r;
+}
+
+/** \ingroup desc
+ * Get the USB device descriptor for a given device.
+ *
+ * This is a non-blocking function; the device descriptor is cached in memory.
+ *
+ * \param dev the device
+ * \param desc output location for the descriptor data
+ * \returns 0 on success or a LIBUSB_ERROR code on failure
+ */
+int API_EXPORTED libusb_get_device_descriptor(libusb_device *dev,
+ struct libusb_device_descriptor *desc)
+{
+ unsigned char raw_desc[DEVICE_DESC_LENGTH];
+ int host_endian = 0;
+ int r;
+
+ usbi_dbg("");
+ r = usbi_backend->get_device_descriptor(dev, raw_desc, &host_endian);
+ if (r < 0)
+ return r;
+
+ memcpy((unsigned char *) desc, raw_desc, sizeof(raw_desc));
+ if (!host_endian) {
+ desc->bcdUSB = libusb_le16_to_cpu(desc->bcdUSB);
+ desc->idVendor = libusb_le16_to_cpu(desc->idVendor);
+ desc->idProduct = libusb_le16_to_cpu(desc->idProduct);
+ desc->bcdDevice = libusb_le16_to_cpu(desc->bcdDevice);
+ }
+ return 0;
+}
+
+/** \ingroup desc
+ * Get the USB configuration descriptor for the currently active configuration.
+ * This is a non-blocking function which does not involve any requests being
+ * sent to the device.
+ *
+ * \param dev a device
+ * \param config output location for the USB configuration descriptor. Only
+ * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
+ * after use.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state
+ * \returns another LIBUSB_ERROR code on error
+ * \see libusb_get_config_descriptor
+ */
+int API_EXPORTED libusb_get_active_config_descriptor(libusb_device *dev,
+ struct libusb_config_descriptor **config)
+{
+ struct libusb_config_descriptor *_config = malloc(sizeof(*_config));
+ unsigned char tmp[8];
+ unsigned char *buf = NULL;
+ int host_endian = 0;
+ int r;
+
+ usbi_dbg("");
+ if (!_config)
+ return LIBUSB_ERROR_NO_MEM;
+
+ r = usbi_backend->get_active_config_descriptor(dev, tmp, sizeof(tmp),
+ &host_endian);
+ if (r < 0)
+ goto err;
+
+ usbi_parse_descriptor(tmp, "bbw", _config, host_endian);
+ buf = malloc(_config->wTotalLength);
+ if (!buf) {
+ r = LIBUSB_ERROR_NO_MEM;
+ goto err;
+ }
+
+ r = usbi_backend->get_active_config_descriptor(dev, buf,
+ _config->wTotalLength, &host_endian);
+ if (r < 0)
+ goto err;
+
+ r = parse_configuration(dev->ctx, _config, buf, host_endian);
+ if (r < 0) {
+ usbi_err(dev->ctx, "parse_configuration failed with error %d", r);
+ goto err;
+ } else if (r > 0) {
+ usbi_warn(dev->ctx, "descriptor data still left");
+ }
+
+ free(buf);
+ *config = _config;
+ return 0;
+
+err:
+ free(_config);
+ if (buf)
+ free(buf);
+ return r;
+}
+
+/** \ingroup desc
+ * Get a USB configuration descriptor based on its index.
+ * This is a non-blocking function which does not involve any requests being
+ * sent to the device.
+ *
+ * \param dev a device
+ * \param config_index the index of the configuration you wish to retrieve
+ * \param config output location for the USB configuration descriptor. Only
+ * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
+ * after use.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
+ * \returns another LIBUSB_ERROR code on error
+ * \see libusb_get_active_config_descriptor()
+ * \see libusb_get_config_descriptor_by_value()
+ */
+int API_EXPORTED libusb_get_config_descriptor(libusb_device *dev,
+ uint8_t config_index, struct libusb_config_descriptor **config)
+{
+ struct libusb_config_descriptor *_config;
+ unsigned char tmp[8];
+ unsigned char *buf = NULL;
+ int host_endian = 0;
+ int r;
+
+ usbi_dbg("index %d", config_index);
+ if (config_index >= dev->num_configurations)
+ return LIBUSB_ERROR_NOT_FOUND;
+
+ _config = malloc(sizeof(*_config));
+ if (!_config)
+ return LIBUSB_ERROR_NO_MEM;
+
+ r = usbi_backend->get_config_descriptor(dev, config_index, tmp,
+ sizeof(tmp), &host_endian);
+ if (r < 0)
+ goto err;
+
+ usbi_parse_descriptor(tmp, "bbw", _config, host_endian);
+ buf = malloc(_config->wTotalLength);
+ if (!buf) {
+ r = LIBUSB_ERROR_NO_MEM;
+ goto err;
+ }
+
+ host_endian = 0;
+ r = usbi_backend->get_config_descriptor(dev, config_index, buf,
+ _config->wTotalLength, &host_endian);
+ if (r < 0)
+ goto err;
+
+ r = parse_configuration(dev->ctx, _config, buf, host_endian);
+ if (r < 0) {
+ usbi_err(dev->ctx, "parse_configuration failed with error %d", r);
+ goto err;
+ } else if (r > 0) {
+ usbi_warn(dev->ctx, "descriptor data still left");
+ }
+
+ free(buf);
+ *config = _config;
+ return 0;
+
+err:
+ free(_config);
+ if (buf)
+ free(buf);
+ return r;
+}
+
+/* iterate through all configurations, returning the index of the configuration
+ * matching a specific bConfigurationValue in the idx output parameter, or -1
+ * if the config was not found.
+ * returns 0 or a LIBUSB_ERROR code
+ */
+int usbi_get_config_index_by_value(struct libusb_device *dev,
+ uint8_t bConfigurationValue, int *idx)
+{
+ uint8_t i;
+
+ usbi_dbg("value %d", bConfigurationValue);
+ for (i = 0; i < dev->num_configurations; i++) {
+ unsigned char tmp[6];
+ int host_endian;
+ int r = usbi_backend->get_config_descriptor(dev, i, tmp, sizeof(tmp),
+ &host_endian);
+ if (r < 0)
+ return r;
+ if (tmp[5] == bConfigurationValue) {
+ *idx = i;
+ return 0;
+ }
+ }
+
+ *idx = -1;
+ return 0;
+}
+
+/** \ingroup desc
+ * Get a USB configuration descriptor with a specific bConfigurationValue.
+ * This is a non-blocking function which does not involve any requests being
+ * sent to the device.
+ *
+ * \param dev a device
+ * \param bConfigurationValue the bConfigurationValue of the configuration you
+ * wish to retrieve
+ * \param config output location for the USB configuration descriptor. Only
+ * valid if 0 was returned. Must be freed with libusb_free_config_descriptor()
+ * after use.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
+ * \returns another LIBUSB_ERROR code on error
+ * \see libusb_get_active_config_descriptor()
+ * \see libusb_get_config_descriptor()
+ */
+int API_EXPORTED libusb_get_config_descriptor_by_value(libusb_device *dev,
+ uint8_t bConfigurationValue, struct libusb_config_descriptor **config)
+{
+ int idx;
+ int r = usbi_get_config_index_by_value(dev, bConfigurationValue, &idx);
+ if (r < 0)
+ return r;
+ else if (idx == -1)
+ return LIBUSB_ERROR_NOT_FOUND;
+ else
+ return libusb_get_config_descriptor(dev, (uint8_t) idx, config);
+}
+
+/** \ingroup desc
+ * Free a configuration descriptor obtained from
+ * libusb_get_active_config_descriptor() or libusb_get_config_descriptor().
+ * It is safe to call this function with a NULL config parameter, in which
+ * case the function simply returns.
+ *
+ * \param config the configuration descriptor to free
+ */
+void API_EXPORTED libusb_free_config_descriptor(
+ struct libusb_config_descriptor *config)
+{
+ if (!config)
+ return;
+
+ clear_configuration(config);
+ free(config);
+}
+
+/** \ingroup desc
+ * Retrieve a string descriptor in C style ASCII.
+ *
+ * Wrapper around libusb_get_string_descriptor(). Uses the first language
+ * supported by the device.
+ *
+ * \param dev a device handle
+ * \param desc_index the index of the descriptor to retrieve
+ * \param data output buffer for ASCII string descriptor
+ * \param length size of data buffer
+ * \returns number of bytes returned in data, or LIBUSB_ERROR code on failure
+ */
+int API_EXPORTED libusb_get_string_descriptor_ascii(libusb_device_handle *dev,
+ uint8_t desc_index, unsigned char *data, int length)
+{
+ unsigned char tbuf[255]; /* Some devices choke on size > 255 */
+ int r, si, di;
+ uint16_t langid;
+
+ /* Asking for the zero'th index is special - it returns a string
+ * descriptor that contains all the language IDs supported by the device.
+ * Typically there aren't many - often only one. The language IDs are 16
+ * bit numbers, and they start at the third byte in the descriptor. See
+ * USB 2.0 specification section 9.6.7 for more information. */
+ r = libusb_get_string_descriptor(dev, 0, 0, tbuf, sizeof(tbuf));
+ if (r < 0)
+ return r;
+
+ if (r < 4)
+ return LIBUSB_ERROR_IO;
+
+ langid = tbuf[2] | (tbuf[3] << 8);
+
+ r = libusb_get_string_descriptor(dev, desc_index, langid, tbuf,
+ sizeof(tbuf));
+ if (r < 0)
+ return r;
+
+ if (tbuf[1] != LIBUSB_DT_STRING)
+ return LIBUSB_ERROR_IO;
+
+ if (tbuf[0] > r)
+ return LIBUSB_ERROR_IO;
+
+ for (di = 0, si = 2; si < tbuf[0]; si += 2) {
+ if (di >= (length - 1))
+ break;
+
+ if (tbuf[si + 1]) /* high byte */
+ data[di++] = '?';
+ else
+ data[di++] = tbuf[si];
+ }
+
+ data[di] = 0;
+ return di;
+}
+