/src/libusb/libusb/os/linux_usbfs.c

Source
/* -*- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -*- */
/*
 * Linux usbfs backend for libusb
 * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
 * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
 * Copyright © 2013 Nathan Hjelm <hjelmn@mac.com>
 * Copyright © 2012-2013 Hans de Goede <hdegoede@redhat.com>
 * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later
 *
 * 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 "libusbi.h"
#include "linux_usbfs.h"

#include <alloca.h>
#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/utsname.h>
#include <sys/vfs.h>
#include <unistd.h>

/* sysfs vs usbfs:
 * opening a usbfs node causes the device to be resumed, so we attempt to
 * avoid this during enumeration.
 *
 * sysfs allows us to read the kernel's in-memory copies of device descriptors
 * and so forth, avoiding the need to open the device:
 *  - The binary "descriptors" file contains all config descriptors since
 *    2.6.26, commit 217a9081d8e69026186067711131b77f0ce219ed
 *  - The binary "descriptors" file was added in 2.6.23, commit
 *    69d42a78f935d19384d1f6e4f94b65bb162b36df, but it only contains the
 *    active config descriptors
 *  - The "busnum" file was added in 2.6.22, commit
 *    83f7d958eab2fbc6b159ee92bf1493924e1d0f72
 *  - The "devnum" file has been present since pre-2.6.18
 *  - the "bConfigurationValue" file has been present since pre-2.6.18
 *
 * If we have bConfigurationValue, busnum, and devnum, then we can determine
 * the active configuration without having to open the usbfs node in RDWR mode.
 * The busnum file is important as that is the only way we can relate sysfs
 * devices to usbfs nodes.
 *
 * If we also have all descriptors, we can obtain the device descriptor and
 * configuration without touching usbfs at all.
 */

/* endianness for multi-byte fields:
 *
 * Descriptors exposed by usbfs have the multi-byte fields in the device
 * descriptor as host endian. Multi-byte fields in the other descriptors are
 * bus-endian. The kernel documentation says otherwise, but it is wrong.
 *
 * In sysfs all descriptors are bus-endian.
 */

#define USBDEV_PATH   "/dev"
#define USB_DEVTMPFS_PATH "/dev/bus/usb"

/* use usbdev*.* device names in /dev instead of the usbfs bus directories */
static int usbdev_names = 0;

/* Linux has changed the maximum length of an individual isochronous packet
 * over time.  Initially this limit was 1,023 bytes, but Linux 2.6.18
 * (commit 3612242e527eb47ee4756b5350f8bdf791aa5ede) increased this value to
 * 8,192 bytes to support higher bandwidth devices.  Linux 3.10
 * (commit e2e2f0ea1c935edcf53feb4c4c8fdb4f86d57dd9) further increased this
 * value to 49,152 bytes to support super speed devices.  Linux 5.2
 * (commit 8a1dbc8d91d3d1602282c7e6b4222c7759c916fa) even further increased
 * this value to 98,304 bytes to support super speed plus devices.
 */
static unsigned int max_iso_packet_len = 0;

/* is sysfs available (mounted) ? */
static int sysfs_available = -1;

/* how many times have we initted (and not exited) ? */
static int init_count = 0;

/* Serialize scan-devices, event-thread, and poll */
usbi_mutex_static_t linux_hotplug_lock = USBI_MUTEX_INITIALIZER;

static int open_sysfs_attr(struct libusb_context *ctx,
  const char *sysfs_dir, const char *attr);
static int read_sysfs_attr(struct libusb_context *ctx,
  const char *sysfs_dir, const char *attr, int max_value, int *value_p);
static int linux_scan_devices(struct libusb_context *ctx);
static int detach_kernel_driver_and_claim(struct libusb_device_handle *, uint8_t);
static int sysfs_get_active_config(struct libusb_device *dev, int *config);

#if !defined(HAVE_LIBUDEV)
static int linux_default_scan_devices(struct libusb_context *ctx);
#endif

struct kernel_version {
  int major;
  int minor;
  int sublevel;
};

struct config_descriptor {
  struct usbi_configuration_descriptor *desc;
  size_t actual_len;
};

struct linux_context_priv {
  /* no enumeration or hot-plug detection */
  int no_device_discovery;
};

struct linux_device_priv {
  char *sysfs_dir;
  void *descriptors;
  size_t descriptors_len;
  struct config_descriptor *config_descriptors;
  int active_config; /* cache val for !sysfs_available  */
};

struct linux_device_handle_priv {
  int fd;
  int fd_removed;
  int fd_keep;
  uint32_t caps;
};

enum reap_action {
  NORMAL = 0,
  /* submission failed after the first URB, so await cancellation/completion
   * of all the others */
  SUBMIT_FAILED,

  /* cancelled by user or timeout */
  CANCELLED,

  /* completed multi-URB transfer in non-final URB */
  COMPLETED_EARLY,

  /* one or more urbs encountered a low-level error */
  ERROR,
};

struct linux_transfer_priv {
  union {
    struct usbfs_urb *urbs;
    struct usbfs_urb **iso_urbs;
  };

  enum reap_action reap_action;
  int num_urbs;
  int num_retired;
  enum libusb_transfer_status reap_status;

  /* next iso packet in user-supplied transfer to be populated */
  int iso_packet_offset;
};

static int dev_has_config0(struct libusb_device *dev)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct config_descriptor *config;
  uint8_t idx;

  for (idx = 0; idx < dev->device_descriptor.bNumConfigurations; idx++) {
    config = &priv->config_descriptors[idx];
    if (config->desc->bConfigurationValue == 0)
      return 1;
  }

  return 0;
}

static int get_usbfs_fd(struct libusb_device *dev, int access_mode, int silent)
{
  struct libusb_context *ctx = usbi_device_ctx(dev);
  char path[24];
  int fd;

  if (usbdev_names)
    snprintf(path, sizeof(path), USBDEV_PATH "/usbdev%u.%u",
      dev->bus_number, dev->device_address);
  else
    snprintf(path, sizeof(path), USB_DEVTMPFS_PATH "/%03u/%03u",
      dev->bus_number, dev->device_address);

  fd = open(path, access_mode | O_CLOEXEC);
  if (fd != -1)
    return fd; /* Success */

  /* TODO: fix race between netlink and usbfs https://github.com/libusb/libusb/issues/1691 */
  if (errno == ENOENT) {
    const long delay_ms = 10L;
    const struct timespec delay_ts = { 0L, delay_ms * 1000L * 1000L };
    uint8_t retry = 3;

    while (retry-- > 0) {
      if (!silent)
        usbi_err(ctx, "File doesn't exist, wait %ld ms and try again", delay_ms);

      /* Wait 10ms for USB device path creation.*/
      nanosleep(&delay_ts, NULL);

      fd = open(path, access_mode | O_CLOEXEC);
      if (fd != -1)
        return fd; /* Success */
      if (errno != ENOENT)
        break;
    }
  }

  if (!silent) {
    usbi_err(ctx, "libusb couldn't open USB device %s, errno=%d", path, errno);
    if (errno == EACCES && access_mode == O_RDWR)
      usbi_err(ctx, "libusb requires write access to USB device nodes");
  }

  if (errno == EACCES)
    return LIBUSB_ERROR_ACCESS;
  if (errno == ENOENT)
    return LIBUSB_ERROR_NO_DEVICE;
  return LIBUSB_ERROR_IO;
}

/* check dirent for a /dev/usbdev%d.%d name
 * optionally return bus/device on success */
static int is_usbdev_entry(const char *name, uint8_t *bus_p, uint8_t *dev_p)
{
  int busnum, devnum;

  if (sscanf(name, "usbdev%d.%d", &busnum, &devnum) != 2)
    return 0;
  if (busnum < 0 || busnum > UINT8_MAX || devnum < 0 || devnum > UINT8_MAX) {
    usbi_dbg(NULL, "invalid usbdev format '%s'", name);
    return 0;
  }

  usbi_dbg(NULL, "found: %s", name);
  if (bus_p)
    *bus_p = (uint8_t)busnum;
  if (dev_p)
    *dev_p = (uint8_t)devnum;
  return 1;
}

static const char *find_usbfs_path(void)
{
  const char *path;
  DIR *dir;
  struct dirent *entry;

  path = USB_DEVTMPFS_PATH;
  dir = opendir(path);
  if (dir) {
    while ((entry = readdir(dir))) {
      if (entry->d_name[0] == '.')
        continue;

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

    closedir(dir);

    if (entry)
      return path;
  }

  /* look for /dev/usbdev*.* if the normal place fails */
  path = USBDEV_PATH;
  dir = opendir(path);
  if (dir) {
    while ((entry = readdir(dir))) {
      if (entry->d_name[0] == '.')
        continue;

      if (is_usbdev_entry(entry->d_name, NULL, NULL)) {
        /* found one; that's enough */
        break;
      }
    }

    closedir(dir);

    if (entry) {
      usbdev_names = 1;
      return path;
    }
  }

  return NULL;
}

static int get_kernel_version(struct libusb_context *ctx,
  struct kernel_version *ver)
{
  struct utsname uts;
  int atoms;

  if (uname(&uts) < 0) {
    usbi_err(ctx, "uname failed, errno=%d", errno);
    return -1;
  }

  atoms = sscanf(uts.release, "%d.%d.%d", &ver->major, &ver->minor, &ver->sublevel);
  if (atoms < 2) {
    usbi_err(ctx, "failed to parse uname release '%s'", uts.release);
    return -1;
  }

  if (atoms < 3)
    ver->sublevel = -1;

  usbi_dbg(ctx, "reported kernel version is %s", uts.release);

  return 0;
}

static int kernel_version_ge(const struct kernel_version *ver,
  int major, int minor, int sublevel)
{
  if (ver->major > major)
    return 1;
  else if (ver->major < major)
    return 0;

  /* kmajor == major */
  if (ver->minor > minor)
    return 1;
  else if (ver->minor < minor)
    return 0;

  /* kminor == minor */
  if (ver->sublevel == -1)
    return sublevel == 0;

  return ver->sublevel >= sublevel;
}

static int op_init(struct libusb_context *ctx)
{
  struct kernel_version kversion;
  const char *usbfs_path;
  int r;
  struct linux_context_priv *cpriv = (struct linux_context_priv *)usbi_get_context_priv(ctx);

  if (get_kernel_version(ctx, &kversion) < 0)
    return LIBUSB_ERROR_OTHER;

  if (!kernel_version_ge(&kversion, 2, 6, 32)) {
    usbi_err(ctx, "kernel version is too old (reported as %d.%d.%d)",
       kversion.major, kversion.minor,
       kversion.sublevel != -1 ? kversion.sublevel : 0);
    return LIBUSB_ERROR_NOT_SUPPORTED;
  }

  usbfs_path = find_usbfs_path();
  if (!usbfs_path) {
    /* On udev based systems without any usb devices /dev/bus/usb will not
    * exist. On android and other systems SELinux policies might block us
    * from reading /dev. Nonetheless it's the default for most modern linux
    systems including those using udev alternatives such as busybox's mdev. */
    usbfs_path = USB_DEVTMPFS_PATH;
    usbi_dbg(ctx, "could not find usbfs, defaulting to %s", usbfs_path);
  } else {
    usbi_dbg(ctx, "found usbfs at %s", usbfs_path);
  }

  if (!max_iso_packet_len) {
    if (kernel_version_ge(&kversion, 5, 2, 0))
      max_iso_packet_len = 98304;
    else if (kernel_version_ge(&kversion, 3, 10, 0))
      max_iso_packet_len = 49152;
    else
      max_iso_packet_len = 8192;
  }

  usbi_dbg(ctx, "max iso packet length is (likely) %u bytes", max_iso_packet_len);

  if (sysfs_available == -1) {
    struct statfs statfsbuf;

    r = statfs(SYSFS_MOUNT_PATH, &statfsbuf);
    if (r == 0 && statfsbuf.f_type == SYSFS_MAGIC) {
      usbi_dbg(ctx, "sysfs is available");
      sysfs_available = 1;
    } else {
      usbi_warn(ctx, "sysfs not mounted");
      sysfs_available = 0;
    }
  }

  if (cpriv->no_device_discovery) {
    return LIBUSB_SUCCESS;
  }

  r = LIBUSB_SUCCESS;
  if (init_count == 0) {
    /* start up hotplug event handler */
    r = linux_start_event_monitor();
  }
  if (r == LIBUSB_SUCCESS) {
    r = linux_scan_devices(ctx);
    if (r == LIBUSB_SUCCESS)
      init_count++;
    else if (init_count == 0)
      linux_stop_event_monitor();
  } else {
    usbi_err(ctx, "error starting hotplug event monitor");
  }

  return r;
}

static void op_exit(struct libusb_context *ctx)
{
  struct linux_context_priv *cpriv = (struct linux_context_priv *)usbi_get_context_priv(ctx);

  if (cpriv->no_device_discovery) {
    return;
  }

  assert(init_count != 0);
  if (!--init_count) {
    /* tear down event handler */
    linux_stop_event_monitor();
  }
}

static int op_set_option(struct libusb_context *ctx, enum libusb_option option, va_list ap)
{
  UNUSED(ap);

  if (option == LIBUSB_OPTION_NO_DEVICE_DISCOVERY) {
    struct linux_context_priv *cpriv = (struct linux_context_priv *)usbi_get_context_priv(ctx);

    usbi_dbg(ctx, "no device discovery will be performed");
    cpriv->no_device_discovery = 1;
    return LIBUSB_SUCCESS;
  }

  return LIBUSB_ERROR_NOT_SUPPORTED;
}

/* Read an already-open sysfs attribute fd into buffer as a NUL-terminated
 * string, strip the trailing newline and close fd.  Returns the length of
 * the string in buffer, including the terminating NUL, or a negative
 * LIBUSB_ERROR code. */
static int read_sysfs_attr_fd(struct libusb_context *ctx, int fd,
  const char *attr, char *buffer, int length)
{
  ssize_t r;
  int e;

  UNUSED(attr);  /* only referenced by usbi_err(), a no-op without logging */

  if (length <= 0) {
    close(fd);
    return LIBUSB_ERROR_INVALID_PARAM;
  }

  r = read(fd, buffer, length - 1);  // leave space for null terminator
  if (r < 0) {
    e = errno;
    close(fd);
    if (e == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;
    usbi_err(ctx, "attribute %s read failed, errno=%d", attr, e);
    return LIBUSB_ERROR_IO;
  }
  close(fd);
  buffer[r] = 0;  // add null terminator
  while (r && ((buffer[r] == 0) || (buffer[r] == '\n'))) {
    buffer[r--] = 0;
  }
  return (int)strlen(buffer) + 1;
}

static int op_get_device_string(struct libusb_device *dev,
    enum libusb_device_string_type string_type, char *buffer, int length)
{
  int fd;
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct libusb_context* ctx = usbi_device_ctx(dev);
  const char * attr;

  switch (string_type) {
    case LIBUSB_DEVICE_STRING_MANUFACTURER: attr = "manufacturer"; break;
    case LIBUSB_DEVICE_STRING_PRODUCT: attr = "product"; break;
    case LIBUSB_DEVICE_STRING_SERIAL_NUMBER: attr = "serial"; break;
    case LIBUSB_DEVICE_STRING_COUNT:
      /* intentional fall-through, avoid -Wswitch-enum */
    default:
      return LIBUSB_ERROR_INVALID_PARAM;
  }
  fd = open_sysfs_attr(ctx, priv->sysfs_dir, attr);
  if (fd < 0)
    return LIBUSB_ERROR_IO;

  return read_sysfs_attr_fd(ctx, fd, attr, buffer, length);
}

/* Read a textual sysfs attribute into buffer as a UTF-8 string.  A missing
 * file maps to LIBUSB_ERROR_NOT_FOUND (no such string), not a disconnect. */
static int read_sysfs_string_attr(struct libusb_context *ctx,
  const char *sysfs_dir, const char *attr, char *buffer, int length)
{
  char filename[256];
  int fd, e, r;

  if (length <= 0)
    return LIBUSB_ERROR_INVALID_PARAM;
  if (sysfs_dir == NULL)
    return LIBUSB_ERROR_NOT_SUPPORTED;

  r = snprintf(filename, sizeof(filename), SYSFS_DEVICE_PATH "/%s/%s", sysfs_dir, attr);
  if (r < 0 || r >= (int)sizeof(filename)) {
    usbi_err(ctx, "sysfs attribute path %s/%s too long", sysfs_dir, attr);
    return LIBUSB_ERROR_OTHER;
  }
  fd = open(filename, O_RDONLY | O_CLOEXEC);
  if (fd < 0) {
    e = errno;
    if (e == ENOENT)
      return LIBUSB_ERROR_NOT_FOUND;
    usbi_err(ctx, "open %s failed, errno=%d", filename, e);
    return LIBUSB_ERROR_IO;
  }

  return read_sysfs_attr_fd(ctx, fd, attr, buffer, length);
}

static int op_get_config_string(struct libusb_device *dev,
    uint8_t config_value, char *buffer, int length)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct libusb_context* ctx = usbi_device_ctx(dev);
  uint8_t string_index = 0;
  int r;

  assert(NULL != buffer && length > 0);  /* guaranteed by the core */

  if (priv->sysfs_dir == NULL)
    return LIBUSB_ERROR_NOT_SUPPORTED;

  /* Resolve iConfiguration from the cached descriptors first, so that a
   * missing string (index 0), a nonexistent configuration or an
   * unconfigured device fails the same way as on other backends. */
  r = usbi_get_config_string_index(dev, config_value, &string_index);
  if (r < 0)
    return r;
  if (0 == string_index)
    return LIBUSB_ERROR_NOT_FOUND;

  /* sysfs only exposes the iConfiguration string of the active
   * configuration.  String descriptors are device-global, however, so
   * that string is also the requested one whenever the requested
   * configuration shares its iConfiguration index with the active one;
   * anything else cannot be read without opening the device. */
  if (config_value != 0) {
    int active = 0;
    r = sysfs_get_active_config(dev, &active);
    if (r < 0)
      return r;
    if (active != (int)config_value) {
      uint8_t active_index = 0;
      if (active <= 0 ||
          usbi_get_config_string_index(dev, (uint8_t)active, &active_index) < 0 ||
          active_index != string_index)
        return LIBUSB_ERROR_NOT_SUPPORTED;
    }
  }

  return read_sysfs_string_attr(ctx, priv->sysfs_dir, "configuration", buffer, length);
}

static int op_get_interface_string(struct libusb_device *dev,
    uint8_t config_value, uint8_t interface_number, uint8_t alt_setting,
    char *buffer, int length)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct libusb_context* ctx = usbi_device_ctx(dev);
  char intf_dir[256];
  uint8_t string_index = 0;
  int active = 0;
  int cur_alt = 0;
  int r;

  assert(NULL != buffer && length > 0);  /* guaranteed by the core */

  if (priv->sysfs_dir == NULL)
    return LIBUSB_ERROR_NOT_SUPPORTED;

  /* Resolve iInterface from the cached descriptors first, so that a
   * nonexistent interface/alternate setting or a missing string (index 0)
   * returns NOT_FOUND, the same way as on other backends. */
  r = usbi_get_interface_string_index(dev, config_value, interface_number,
    alt_setting, &string_index);
  if (r < 0)
    return r;
  if (0 == string_index)
    return LIBUSB_ERROR_NOT_FOUND;

  /* sysfs exposes interfaces only for the active configuration */
  r = sysfs_get_active_config(dev, &active);
  if (r < 0)
    return r;
  if (active <= 0)
    return LIBUSB_ERROR_NOT_FOUND;  /* device not configured */

  /* The interface's sysfs directory is a sibling of the device directory,
   * named "<device>:<bConfigurationValue>.<bInterfaceNumber>". */
  r = snprintf(intf_dir, sizeof(intf_dir), "%s:%d.%u", priv->sysfs_dir, active,
    (unsigned)interface_number);
  if (r < 0 || r >= (int)sizeof(intf_dir)) {
    usbi_err(ctx, "interface sysfs directory name %s:%d.%u too long",
      priv->sysfs_dir, active, (unsigned)interface_number);
    return LIBUSB_ERROR_OTHER;
  }

  r = read_sysfs_attr(ctx, intf_dir, "bAlternateSetting", UINT8_MAX, &cur_alt);
  if (r < 0) {
    /* When a non-active configuration was requested the interface may
     * legitimately not exist in the active one: that is a limit of
     * sysfs, not a nonexistent interface (already ruled out above). */
    if (config_value != 0 && (int)config_value != active)
      return LIBUSB_ERROR_NOT_SUPPORTED;
    return (r == LIBUSB_ERROR_NO_DEVICE) ? LIBUSB_ERROR_NOT_FOUND : r;
  }

  /* sysfs only exposes the string of the currently selected alternate
   * setting in the active configuration.  String descriptors are
   * device-global, however, so that string is also the requested one
   * whenever the requested interface/alternate setting shares its
   * iInterface index with the current one; anything else cannot be read
   * without opening the device. */
  if ((config_value != 0 && (int)config_value != active) ||
      cur_alt != (int)alt_setting) {
    uint8_t cur_index = 0;
    if (cur_alt < 0 ||
        usbi_get_interface_string_index(dev, (uint8_t)active, interface_number,
                (uint8_t)cur_alt, &cur_index) < 0 ||
        cur_index != string_index)
      return LIBUSB_ERROR_NOT_SUPPORTED;
  }

  return read_sysfs_string_attr(ctx, intf_dir, "interface", buffer, length);
}

static int linux_scan_devices(struct libusb_context *ctx)
{
  int ret;

  usbi_mutex_static_lock(&linux_hotplug_lock);

#if defined(HAVE_LIBUDEV)
  ret = linux_udev_scan_devices(ctx);
#else
  ret = linux_default_scan_devices(ctx);
#endif

  usbi_mutex_static_unlock(&linux_hotplug_lock);

  return ret;
}

static void op_hotplug_poll(void)
{
  linux_hotplug_poll();
}

static int open_sysfs_attr(struct libusb_context *ctx,
  const char *sysfs_dir, const char *attr)
{
  char filename[256];
  int fd;

  snprintf(filename, sizeof(filename), SYSFS_DEVICE_PATH "/%s/%s", sysfs_dir, attr);
  fd = open(filename, O_RDONLY | O_CLOEXEC);
  if (fd < 0) {
    if (errno == ENOENT) {
      /* File doesn't exist. Assume the device has been
         disconnected (see trac ticket #70). */
      return LIBUSB_ERROR_NO_DEVICE;
    }
    usbi_err(ctx, "open %s failed, errno=%d", filename, errno);
    return LIBUSB_ERROR_IO;
  }

  return fd;
}

/* Note only suitable for attributes which always read >= 0, < 0 is error */
static int read_sysfs_attr(struct libusb_context *ctx,
  const char *sysfs_dir, const char *attr, int max_value, int *value_p)
{
  char buf[20], *endptr;
  long value;
  ssize_t r;
  int fd;

  fd = open_sysfs_attr(ctx, sysfs_dir, attr);
  if (fd < 0)
    return fd;

  r = read(fd, buf, sizeof(buf) - 1);
  if (r < 0) {
    r = errno;
    close(fd);
    if (r == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;
    usbi_err(ctx, "attribute %s read failed, errno=%zd", attr, r);
    return LIBUSB_ERROR_IO;
  }
  close(fd);

  if (r == 0) {
    /* Certain attributes (e.g. bConfigurationValue) are not
     * populated if the device is not configured. */
    *value_p = -1;
    return 0;
  }

  /* The kernel does *not* NUL-terminate the string, but every attribute
   * should be terminated with a newline character. */
  if (buf[r - 1] != '\n') {
    usbi_warn(ctx, "attribute %s doesn't end with newline?", attr);
  } else {
    /* Remove the terminating newline character */
    r--;
  }
  buf[r] = '\0';

  errno = 0;
  value = strtol(buf, &endptr, 10);
  if (buf == endptr) {
    /* strtol() returns buf == endptr when a error occurs and
     * value == 0 for a non-numeric value, first check if the
     * error was because of a non-numeric value,
     * before general errors */
    usbi_err(ctx, "attribute %s doesn't have numeric value?", attr);
    return LIBUSB_ERROR_IO;
  } else if (value < 0 || value > (long)max_value || errno) {
    usbi_err(ctx, "attribute %s contains an invalid value: '%s'", attr, buf);
    return LIBUSB_ERROR_INVALID_PARAM;
  } else if (*endptr != '\0') {
    /* Consider the value to be valid if the remainder is a '.'
     * character followed by numbers.  This occurs, for example,
     * when reading the "speed" attribute for a low-speed device
     * (e.g. "1.5") */
    if (*endptr == '.' && isdigit(*(endptr + 1))) {
      endptr++;
      while (isdigit(*endptr))
        endptr++;
    }
    if (*endptr != '\0') {
      usbi_err(ctx, "attribute %s contains an invalid value: '%s'", attr, buf);
      return LIBUSB_ERROR_INVALID_PARAM;
    }
  }

  *value_p = (int)value;
  return 0;
}

static int sysfs_scan_device(struct libusb_context *ctx, const char *devname)
{
  uint8_t busnum, devaddr;
  int ret;

  ret = linux_get_device_address(ctx, 0, &busnum, &devaddr, NULL, devname, -1);
  if (ret != LIBUSB_SUCCESS)
    return ret;

  return linux_enumerate_device(ctx, busnum, devaddr, devname);
}

/* read the bConfigurationValue for a device */
static int sysfs_get_active_config(struct libusb_device *dev, int *config)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);

  return read_sysfs_attr(usbi_device_ctx(dev), priv->sysfs_dir, "bConfigurationValue",
      UINT8_MAX, config);
}

int linux_get_device_address(struct libusb_context *ctx, int detached,
  uint8_t *busnum, uint8_t *devaddr, const char *dev_node,
  const char *sys_name, int fd)
{
  int sysfs_val;
  int r;

  usbi_dbg(ctx, "getting address for device: %s detached: %d", sys_name, detached);
  /* can't use sysfs to read the bus and device number if the
   * device has been detached */
  if (!sysfs_available || detached || !sys_name) {
    if (!dev_node && fd >= 0) {
      char *fd_path = (char *)alloca(PATH_MAX);
      char proc_path[32];

      /* try to retrieve the device node from fd */
      snprintf(proc_path, sizeof(proc_path), "/proc/self/fd/%d", fd);
      r = readlink(proc_path, fd_path, PATH_MAX - 1);
      if (r > 0) {
        fd_path[r] = '\0';
        dev_node = fd_path;
      }
    }

    if (!dev_node)
      return LIBUSB_ERROR_OTHER;

    /* will this work with all supported kernel versions? */
    if (!strncmp(dev_node, "/dev/bus/usb", 12))
      sscanf(dev_node, "/dev/bus/usb/%hhu/%hhu", busnum, devaddr);
    else
      return LIBUSB_ERROR_OTHER;

    return LIBUSB_SUCCESS;
  }

  usbi_dbg(ctx, "scan %s", sys_name);

  r = read_sysfs_attr(ctx, sys_name, "busnum", UINT8_MAX, &sysfs_val);
  if (r < 0)
    return r;
  *busnum = (uint8_t)sysfs_val;

  r = read_sysfs_attr(ctx, sys_name, "devnum", UINT8_MAX, &sysfs_val);
  if (r < 0)
    return r;
  *devaddr = (uint8_t)sysfs_val;

  usbi_dbg(ctx, "bus=%u dev=%u", *busnum, *devaddr);

  return LIBUSB_SUCCESS;
}

/* Return offset of the next config descriptor */
static int seek_to_next_config(struct libusb_context *ctx,
  uint8_t *buffer, size_t len)
{
  struct usbi_descriptor_header *header;
  int offset;

  /* Start seeking past the config descriptor */
  offset = LIBUSB_DT_CONFIG_SIZE;
  buffer += LIBUSB_DT_CONFIG_SIZE;
  len -= LIBUSB_DT_CONFIG_SIZE;

  while (len > 0) {
    if (len < 2) {
      usbi_err(ctx, "remaining descriptor length too small %zu/2", len);
      return LIBUSB_ERROR_IO;
    }

    header = (struct usbi_descriptor_header *)buffer;
    if (header->bDescriptorType == LIBUSB_DT_CONFIG)
      return offset;

    if (header->bLength < 2) {
      usbi_err(ctx, "invalid descriptor bLength %hhu", header->bLength);
      return LIBUSB_ERROR_IO;
    }

    if (len < header->bLength) {
      usbi_err(ctx, "bLength overflow by %zu bytes",
         (size_t)header->bLength - len);
      return LIBUSB_ERROR_IO;
    }

    offset += header->bLength;
    buffer += header->bLength;
    len -= header->bLength;
  }

  usbi_err(ctx, "config descriptor not found");
  return LIBUSB_ERROR_IO;
}

static int parse_config_descriptors(struct libusb_device *dev)
{
  struct libusb_context *ctx = usbi_device_ctx(dev);
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct usbi_device_descriptor *device_desc;
  uint8_t idx, num_configs;
  uint8_t *buffer;
  size_t remaining;

  device_desc = (struct usbi_device_descriptor *)priv->descriptors;
  num_configs = device_desc->bNumConfigurations;

  if (num_configs == 0)
    return 0; /* no configurations? */

  priv->config_descriptors = (struct config_descriptor *)malloc(num_configs * sizeof(priv->config_descriptors[0]));
  if (!priv->config_descriptors)
    return LIBUSB_ERROR_NO_MEM;

  buffer = (uint8_t *)priv->descriptors + LIBUSB_DT_DEVICE_SIZE;
  remaining = priv->descriptors_len - LIBUSB_DT_DEVICE_SIZE;

  for (idx = 0; idx < num_configs; idx++) {
    struct usbi_configuration_descriptor *config_desc;
    uint16_t config_len;

    if (remaining < LIBUSB_DT_CONFIG_SIZE) {
      usbi_err(ctx, "short descriptor read %zu/%d",
         remaining, LIBUSB_DT_CONFIG_SIZE);
      return LIBUSB_ERROR_IO;
    }

    config_desc = (struct usbi_configuration_descriptor *)buffer;
    if (config_desc->bDescriptorType != LIBUSB_DT_CONFIG) {
      usbi_err(ctx, "descriptor is not a config desc (type 0x%02x)",
         config_desc->bDescriptorType);
      return LIBUSB_ERROR_IO;
    } else if (config_desc->bLength < LIBUSB_DT_CONFIG_SIZE) {
      usbi_err(ctx, "invalid descriptor bLength %u",
         config_desc->bLength);
      return LIBUSB_ERROR_IO;
    }

    config_len = libusb_le16_to_cpu(config_desc->wTotalLength);
    if (config_len < LIBUSB_DT_CONFIG_SIZE) {
      usbi_err(ctx, "invalid wTotalLength %u", config_len);
      return LIBUSB_ERROR_IO;
    }

    if (priv->sysfs_dir) {
      /*
       * In sysfs wTotalLength is ignored, instead the kernel returns a
       * config descriptor with verified bLength fields, with descriptors
       * with an invalid bLength removed.
       */
      uint16_t sysfs_config_len;
      int offset;

      if (num_configs > 1 && idx < num_configs - 1) {
        offset = seek_to_next_config(ctx, buffer, remaining);
        if (offset < 0)
          return offset;
        sysfs_config_len = (uint16_t)offset;
      } else {
        sysfs_config_len = (uint16_t)remaining;
      }

      if (config_len != sysfs_config_len) {
        usbi_warn(ctx, "config length mismatch wTotalLength %u real %u",
            config_len, sysfs_config_len);
        config_len = sysfs_config_len;
      }
    } else {
      /*
       * In usbfs the config descriptors are wTotalLength bytes apart,
       * with any short reads from the device appearing as holes in the file.
       */
      if (config_len > remaining) {
        usbi_warn(ctx, "short descriptor read %zu/%u", remaining, config_len);
        config_len = (uint16_t)remaining;
      }
    }

    if (config_desc->bConfigurationValue == 0)
      usbi_warn(ctx, "device has configuration 0");

    priv->config_descriptors[idx].desc = config_desc;
    priv->config_descriptors[idx].actual_len = config_len;

    buffer += config_len;
    remaining -= config_len;
  }

  return LIBUSB_SUCCESS;
}

static int op_get_config_descriptor_by_value(struct libusb_device *dev,
  uint8_t value, void **buffer)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct config_descriptor *config;
  uint8_t idx;

  for (idx = 0; idx < dev->device_descriptor.bNumConfigurations; idx++) {
    config = &priv->config_descriptors[idx];
    if (config->desc->bConfigurationValue == value) {
      *buffer = config->desc;
      return (int)config->actual_len;
    }
  }

  return LIBUSB_ERROR_NOT_FOUND;
}

static int op_get_active_config_descriptor(struct libusb_device *dev,
  void *buffer, size_t len)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  void *config_desc;
  int active_config;
  int r;

  if (priv->sysfs_dir) {
    r = sysfs_get_active_config(dev, &active_config);
    if (r < 0)
      return r;
  } else {
    /* Use cached bConfigurationValue */
    active_config = priv->active_config;
  }

  if (active_config == -1) {
    usbi_err(usbi_device_ctx(dev), "device unconfigured");
    return LIBUSB_ERROR_NOT_FOUND;
  }

  r = op_get_config_descriptor_by_value(dev, (uint8_t)active_config, &config_desc);
  if (r < 0)
    return r;

  len = MIN(len, (size_t)r);
  memcpy(buffer, config_desc, len);
  return len;
}

static int op_get_config_descriptor(struct libusb_device *dev,
  uint8_t config_index, void *buffer, size_t len)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct config_descriptor *config;

  if (config_index >= dev->device_descriptor.bNumConfigurations)
    return LIBUSB_ERROR_NOT_FOUND;

  config = &priv->config_descriptors[config_index];
  len = MIN(len, config->actual_len);
  memcpy(buffer, config->desc, len);
  return len;
}

/* send a control message to retrieve active configuration */
static int usbfs_get_active_config(struct libusb_device *dev, int fd)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  uint8_t active_config = 0;
  int r;

  struct usbfs_ctrltransfer ctrl = {
    .bmRequestType = LIBUSB_ENDPOINT_IN,
    .bRequest = LIBUSB_REQUEST_GET_CONFIGURATION,
    .wValue = 0,
    .wIndex = 0,
    .wLength = 1,
    .timeout = 1000,
    .data = &active_config
  };

  r = ioctl(fd, IOCTL_USBFS_CONTROL, &ctrl);
  if (r < 0) {
    if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    /* we hit this error path frequently with buggy devices :( */
    usbi_warn(usbi_device_ctx(dev), "get configuration failed, errno=%d", errno);

    /* assume the current configuration is the first one if we have
     * the configuration descriptors, otherwise treat the device
     * as unconfigured. */
    if (priv->config_descriptors)
      priv->active_config = (int)priv->config_descriptors[0].desc->bConfigurationValue;
    else
      priv->active_config = -1;
  } else if (active_config == 0) {
    if (dev_has_config0(dev)) {
      /* some buggy devices have a configuration 0, but we're
       * reaching into the corner of a corner case here. */
      priv->active_config = 0;
    } else {
      priv->active_config = -1;
    }
  } else {
    priv->active_config = (int)active_config;
  }

  return LIBUSB_SUCCESS;
}

static enum libusb_speed usbfs_get_speed(struct libusb_context *ctx, int fd)
{
  int r;

  r = ioctl(fd, IOCTL_USBFS_GET_SPEED, NULL);
  switch (r) {
  case USBFS_SPEED_UNKNOWN: return LIBUSB_SPEED_UNKNOWN;
  case USBFS_SPEED_LOW:   return LIBUSB_SPEED_LOW;
  case USBFS_SPEED_FULL:   return LIBUSB_SPEED_FULL;
  case USBFS_SPEED_HIGH:   return LIBUSB_SPEED_HIGH;
  case USBFS_SPEED_WIRELESS: return LIBUSB_SPEED_HIGH;
  case USBFS_SPEED_SUPER:   return LIBUSB_SPEED_SUPER;
  case USBFS_SPEED_SUPER_PLUS: return LIBUSB_SPEED_SUPER_PLUS;
  default:
    usbi_warn(ctx, "Error getting device speed: %d", r);
  }

  return LIBUSB_SPEED_UNKNOWN;
}

static int initialize_device(struct libusb_device *dev, uint8_t busnum,
  uint8_t devaddr, const char *sysfs_dir, int wrapped_fd)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);
  struct libusb_context *ctx = usbi_device_ctx(dev);
  size_t alloc_len;
  int fd, speed, r;
  ssize_t nb;

  dev->bus_number = busnum;
  dev->device_address = devaddr;

  if (sysfs_dir) {
    priv->sysfs_dir = strdup(sysfs_dir);
    if (!priv->sysfs_dir)
      return LIBUSB_ERROR_NO_MEM;

    /* Note speed can contain 1.5, in this case read_sysfs_attr()
       will stop parsing at the '.' and return 1 */
    if (read_sysfs_attr(ctx, sysfs_dir, "speed", INT_MAX, &speed) == 0) {
      switch (speed) {
      case     1: dev->speed = LIBUSB_SPEED_LOW; break;
      case    12: dev->speed = LIBUSB_SPEED_FULL; break;
      case   480: dev->speed = LIBUSB_SPEED_HIGH; break;
      case  5000: dev->speed = LIBUSB_SPEED_SUPER; break;
      case 10000: dev->speed = LIBUSB_SPEED_SUPER_PLUS; break;
      case 20000: dev->speed = LIBUSB_SPEED_SUPER_PLUS_X2; break;
      default:
        usbi_warn(ctx, "unknown device speed: %d Mbps", speed);
      }
    }
  } else if (wrapped_fd >= 0) {
    dev->speed = usbfs_get_speed(ctx, wrapped_fd);
  }

  /* cache descriptors in memory */
  if (sysfs_dir) {
    fd = open_sysfs_attr(ctx, sysfs_dir, "descriptors");
  } else if (wrapped_fd < 0) {
    fd = get_usbfs_fd(dev, O_RDONLY, 0);
  } else {
    fd = wrapped_fd;
    r = lseek(fd, 0, SEEK_SET);
    if (r < 0) {
      usbi_err(ctx, "lseek failed, errno=%d", errno);
      return LIBUSB_ERROR_IO;
    }
  }
  if (fd < 0)
    return fd;

  alloc_len = 0;
  do {
    const size_t desc_read_length = 256;
    uint8_t *read_ptr;

    alloc_len += desc_read_length;
    priv->descriptors = usbi_reallocf(priv->descriptors, alloc_len);
    if (!priv->descriptors) {
      if (fd != wrapped_fd)
        close(fd);
      return LIBUSB_ERROR_NO_MEM;
    }
    read_ptr = (uint8_t *)priv->descriptors + priv->descriptors_len;
    /* usbfs has holes in the file */
    if (!sysfs_dir)
      memset(read_ptr, 0, desc_read_length);
    nb = read(fd, read_ptr, desc_read_length);
    if (nb < 0) {
      usbi_err(ctx, "read descriptor failed, errno=%d", errno);
      if (fd != wrapped_fd)
        close(fd);
      return LIBUSB_ERROR_IO;
    }
    priv->descriptors_len += (size_t)nb;
  } while (priv->descriptors_len == alloc_len);

  if (fd != wrapped_fd)
    close(fd);

  if (priv->descriptors_len < LIBUSB_DT_DEVICE_SIZE) {
    usbi_err(ctx, "short descriptor read (%zu)", priv->descriptors_len);
    return LIBUSB_ERROR_IO;
  }

  r = parse_config_descriptors(dev);
  if (r < 0)
    return r;

  memcpy(&dev->device_descriptor, priv->descriptors, LIBUSB_DT_DEVICE_SIZE);

  if (sysfs_dir) {
    /* sysfs descriptors are in bus-endian format */
    usbi_localize_device_descriptor(&dev->device_descriptor);
    return LIBUSB_SUCCESS;
  }

  /* cache active config */
  if (wrapped_fd < 0)
    fd = get_usbfs_fd(dev, O_RDWR, 1);
  else
    fd = wrapped_fd;
  if (fd < 0) {
    /* cannot send a control message to determine the active
     * config. just assume the first one is active. */
    usbi_warn(ctx, "Missing rw usbfs access; cannot determine "
             "active configuration descriptor");
    if (priv->config_descriptors)
      priv->active_config = (int)priv->config_descriptors[0].desc->bConfigurationValue;
    else
      priv->active_config = -1; /* No config dt */

    return LIBUSB_SUCCESS;
  }

  r = usbfs_get_active_config(dev, fd);
  if (fd != wrapped_fd)
    close(fd);

  return r;
}

static int linux_get_parent_info(struct libusb_device *dev, const char *sysfs_dir)
{
  struct libusb_context *ctx = usbi_device_ctx(dev);
  struct libusb_device *it;
  char *parent_sysfs_dir, *tmp, *end;
  int ret, add_parent = 1;

  /* XXX -- can we figure out the topology when using usbfs? */
  if (!sysfs_dir || !strncmp(sysfs_dir, "usb", 3)) {
    /* either using usbfs or finding the parent of a root hub */
    return LIBUSB_SUCCESS;
  }

  parent_sysfs_dir = strdup(sysfs_dir);
  if (!parent_sysfs_dir)
    return LIBUSB_ERROR_NO_MEM;

  if ((tmp = strrchr(parent_sysfs_dir, '.')) ||
      (tmp = strrchr(parent_sysfs_dir, '-'))) {
    const char *start = tmp + 1;
    long port_number = strtol(start, &end, 10);
    if (port_number < 0 || port_number > INT_MAX || start == end || '\0' != *end) {
      usbi_warn(ctx, "Can not parse sysfs_dir: %s, unexpected parent info",
        parent_sysfs_dir);
      free(parent_sysfs_dir);
      return LIBUSB_ERROR_OTHER;
    } else {
      dev->port_number = (int)port_number;
    }
    *tmp = '\0';
  } else {
    usbi_warn(ctx, "Can not parse sysfs_dir: %s, no parent info",
        parent_sysfs_dir);
    free(parent_sysfs_dir);
    return LIBUSB_SUCCESS;
  }

  /* is the parent a root hub? */
  if (!strchr(parent_sysfs_dir, '-')) {
    tmp = parent_sysfs_dir;
    ret = asprintf(&parent_sysfs_dir, "usb%s", tmp);
    free(tmp);
    if (ret < 0)
      return LIBUSB_ERROR_NO_MEM;
  }

retry:
  /* find the parent in the context */
  usbi_mutex_lock(&ctx->usb_devs_lock);
  for_each_device(ctx, it) {
    struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(it);

    if (priv->sysfs_dir) {
      if (!strcmp(priv->sysfs_dir, parent_sysfs_dir)) {
        dev->parent_dev = libusb_ref_device(it);
        break;
      }
    }
  }
  usbi_mutex_unlock(&ctx->usb_devs_lock);

  if (!dev->parent_dev && add_parent) {
    usbi_dbg(ctx, "parent_dev %s not enumerated yet, enumerating now",
       parent_sysfs_dir);
    sysfs_scan_device(ctx, parent_sysfs_dir);
    add_parent = 0;
    goto retry;
  }

  usbi_dbg(ctx, "dev %p (%s) has parent %p (%s) port %u",
     (void *) dev, sysfs_dir, (void *) dev->parent_dev,
     parent_sysfs_dir, dev->port_number);

  free(parent_sysfs_dir);

  return LIBUSB_SUCCESS;
}

int linux_enumerate_device(struct libusb_context *ctx,
  uint8_t busnum, uint8_t devaddr, const char *sysfs_dir)
{
  unsigned long session_id;
  struct libusb_device *dev;
  int r;

  /* FIXME: session ID is not guaranteed unique as addresses can wrap and
   * will be reused. instead we should add a simple sysfs attribute with
   * a session ID. */
  session_id = busnum << 8 | devaddr;
  usbi_dbg(ctx, "busnum %u devaddr %u session_id %lu", busnum, devaddr, session_id);

  dev = usbi_get_device_by_session_id(ctx, session_id);
  if (dev) {
    /* device already exists in the context */
    usbi_dbg(ctx, "session_id %lu already exists", session_id);
    libusb_unref_device(dev);
    return LIBUSB_SUCCESS;
  }

  usbi_dbg(ctx, "allocating new device for %u/%u (session %lu)",
     busnum, devaddr, session_id);
  dev = usbi_alloc_device(ctx, session_id);
  if (!dev)
    return LIBUSB_ERROR_NO_MEM;

  r = initialize_device(dev, busnum, devaddr, sysfs_dir, -1);
  if (r < 0)
    goto out;
  r = usbi_sanitize_device(dev);
  if (r < 0)
    goto out;

  r = linux_get_parent_info(dev, sysfs_dir);
  if (r < 0)
    goto out;
out:
  if (r < 0)
    libusb_unref_device(dev);
  else
    usbi_connect_device(dev);

  return r;
}

void linux_hotplug_enumerate(uint8_t busnum, uint8_t devaddr, const char *sys_name)
{
  struct libusb_context *ctx;

  usbi_mutex_static_lock(&active_contexts_lock);
  for_each_context(ctx) {
    linux_enumerate_device(ctx, busnum, devaddr, sys_name);
  }
  usbi_mutex_static_unlock(&active_contexts_lock);
}

void linux_device_disconnected(uint8_t busnum, uint8_t devaddr)
{
  struct libusb_context *ctx;
  struct libusb_device *dev;
  unsigned long session_id = busnum << 8 | devaddr;

  usbi_mutex_static_lock(&active_contexts_lock);
  for_each_context(ctx) {
    dev = usbi_get_device_by_session_id(ctx, session_id);
    if (dev) {
      usbi_disconnect_device(dev);
      libusb_unref_device(dev);
    } else {
      usbi_dbg(ctx, "device not found for session %lx", session_id);
    }
  }
  usbi_mutex_static_unlock(&active_contexts_lock);
}

#if !defined(HAVE_LIBUDEV)
static int parse_u8(const char *str, uint8_t *val_p)
{
  char *endptr;
  long num;

  errno = 0;
  num = strtol(str, &endptr, 10);
  if (num < 0 || num > UINT8_MAX || errno)
    return 0;
  if (endptr == str || *endptr != '\0')
    return 0;

  *val_p = (uint8_t)num;
  return 1;
}

/* open a bus directory and adds all discovered devices to the context */
static int usbfs_scan_busdir(struct libusb_context *ctx, uint8_t busnum)
{
  DIR *dir;
  char dirpath[20];
  struct dirent *entry;
  int r = LIBUSB_ERROR_IO;

  snprintf(dirpath, sizeof(dirpath), USB_DEVTMPFS_PATH "/%03u", busnum);
  usbi_dbg(ctx, "%s", dirpath);
  dir = opendir(dirpath);
  if (!dir) {
    usbi_err(ctx, "opendir '%s' failed, errno=%d", dirpath, errno);
    /* FIXME: should handle valid race conditions like hub unplugged
     * during directory iteration - this is not an error */
    return r;
  }

  while ((entry = readdir(dir))) {
    uint8_t devaddr;

    if (entry->d_name[0] == '.')
      continue;

    if (!parse_u8(entry->d_name, &devaddr)) {
      usbi_dbg(ctx, "unknown dir entry %s", entry->d_name);
      continue;
    }

    if (linux_enumerate_device(ctx, busnum, devaddr, NULL)) {
      usbi_dbg(ctx, "failed to enumerate dir entry %s", entry->d_name);
      continue;
    }

    r = 0;
  }

  closedir(dir);
  return r;
}

static int usbfs_get_device_list(struct libusb_context *ctx)
{
  struct dirent *entry;
  DIR *buses;
  uint8_t busnum, devaddr;
  int r = 0;

  if (usbdev_names)
    buses = opendir(USBDEV_PATH);
  else
    buses = opendir(USB_DEVTMPFS_PATH);

  if (!buses) {
    if (!usbdev_names && errno == ENOENT) {
      /* The path does not exist if there are no devices plugged in */
      return LIBUSB_SUCCESS;
    }
    usbi_err(ctx, "opendir buses failed, errno=%d", errno);
    return LIBUSB_ERROR_IO;
  }

  while ((entry = readdir(buses))) {
    if (entry->d_name[0] == '.')
      continue;

    if (usbdev_names) {
      if (!is_usbdev_entry(entry->d_name, &busnum, &devaddr))
        continue;

      r = linux_enumerate_device(ctx, busnum, devaddr, NULL);
      if (r < 0) {
        usbi_dbg(ctx, "failed to enumerate dir entry %s", entry->d_name);
        continue;
      }
    } else {
      if (!parse_u8(entry->d_name, &busnum)) {
        usbi_dbg(ctx, "unknown dir entry %s", entry->d_name);
        continue;
      }

      r = usbfs_scan_busdir(ctx, busnum);
      if (r < 0)
        break;
    }
  }

  closedir(buses);
  return r;

}

static int sysfs_get_device_list(struct libusb_context *ctx)
{
  DIR *devices = opendir(SYSFS_DEVICE_PATH);
  struct dirent *entry;
  int num_devices = 0;
  int num_enumerated = 0;

  if (!devices) {
    usbi_err(ctx, "opendir devices failed, errno=%d", errno);
    return LIBUSB_ERROR_IO;
  }

  while ((entry = readdir(devices))) {
    if ((!isdigit(entry->d_name[0]) && strncmp(entry->d_name, "usb", 3))
        || strchr(entry->d_name, ':'))
      continue;

    num_devices++;

    if (sysfs_scan_device(ctx, entry->d_name)) {
      usbi_dbg(ctx, "failed to enumerate dir entry %s", entry->d_name);
      continue;
    }

    num_enumerated++;
  }

  closedir(devices);

  /* successful if at least one device was enumerated or no devices were found */
  if (num_enumerated || !num_devices)
    return LIBUSB_SUCCESS;
  else
    return LIBUSB_ERROR_IO;
}

static int linux_default_scan_devices(struct libusb_context *ctx)
{
  /* we can retrieve device list and descriptors from sysfs or usbfs.
   * sysfs is preferable, because if we use usbfs we end up resuming
   * any autosuspended USB devices. however, sysfs is not available
   * everywhere, so we need a usbfs fallback too.
   */
  if (sysfs_available && sysfs_get_device_list(ctx) == LIBUSB_SUCCESS)
    return LIBUSB_SUCCESS;

  return usbfs_get_device_list(ctx);
}
#endif

static int initialize_handle(struct libusb_device_handle *handle, int fd)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int r;

  hpriv->fd = fd;

  r = ioctl(fd, IOCTL_USBFS_GET_CAPABILITIES, &hpriv->caps);
  if (r < 0) {
    if (errno == ENOTTY)
      usbi_dbg(usbi_handle_ctx(handle), "getcap not available");
    else
      usbi_err(usbi_handle_ctx(handle), "getcap failed, errno=%d", errno);
    hpriv->caps = USBFS_CAP_BULK_CONTINUATION;
  }

  return usbi_add_event_source(usbi_handle_ctx(handle), hpriv->fd, POLLOUT);
}

static int op_wrap_sys_device(struct libusb_context *ctx,
  struct libusb_device_handle *handle, intptr_t sys_dev)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = (int)sys_dev;
  uint8_t busnum, devaddr;
  struct usbfs_connectinfo ci;
  struct libusb_device *dev;
  int r;

  r = linux_get_device_address(ctx, 1, &busnum, &devaddr, NULL, NULL, fd);
  if (r < 0) {
    r = ioctl(fd, IOCTL_USBFS_CONNECTINFO, &ci);
    if (r < 0) {
      usbi_err(ctx, "connectinfo failed, errno=%d", errno);
      return LIBUSB_ERROR_IO;
    }
    /* There is no ioctl to get the bus number. We choose 0 here
     * as linux starts numbering buses from 1. */
    busnum = 0;
    devaddr = ci.devnum;
  }

  /* Session id is unused as we do not add the device to the list of
   * connected devices. */
  usbi_dbg(ctx, "allocating new device for fd %d", fd);
  dev = usbi_alloc_device(ctx, 0);
  if (!dev)
    return LIBUSB_ERROR_NO_MEM;

  r = initialize_device(dev, busnum, devaddr, NULL, fd);
  if (r < 0)
    goto out;
  r = usbi_sanitize_device(dev);
  if (r < 0)
    goto out;
  /* Consider the device as connected, but do not add it to the managed
   * device list. */
  usbi_atomic_store(&dev->attached, 1);
  handle->dev = dev;

  r = initialize_handle(handle, fd);
  hpriv->fd_keep = 1;

out:
  if (r < 0)
    libusb_unref_device(dev);
  return r;
}

static int op_open(struct libusb_device_handle *handle)
{
  int fd, r;

  fd = get_usbfs_fd(handle->dev, O_RDWR, 0);
  if (fd < 0) {
    if (fd == LIBUSB_ERROR_NO_DEVICE) {
      /* device will still be marked as attached if hotplug monitor thread
       * hasn't processed remove event yet */
      usbi_mutex_static_lock(&linux_hotplug_lock);
      if (usbi_atomic_load(&handle->dev->attached)) {
        usbi_dbg(usbi_handle_ctx(handle), "open failed with no device, but device still attached");
        linux_device_disconnected(handle->dev->bus_number,
                handle->dev->device_address);
      }
      usbi_mutex_static_unlock(&linux_hotplug_lock);
    }
    return fd;
  }

  r = initialize_handle(handle, fd);
  if (r < 0)
    close(fd);

  return r;
}

static void op_close(struct libusb_device_handle *dev_handle)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(dev_handle);

  /* fd may have already been removed by POLLERR condition in op_handle_events() */
  if (!hpriv->fd_removed)
    usbi_remove_event_source(usbi_handle_ctx(dev_handle), hpriv->fd);
  if (!hpriv->fd_keep)
    close(hpriv->fd);
}

static int op_get_configuration(struct libusb_device_handle *handle,
  uint8_t *config)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(handle->dev);
  int active_config = -1; /* to please compiler */
  int r;

  if (priv->sysfs_dir) {
    r = sysfs_get_active_config(handle->dev, &active_config);
  } else {
    struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);

    r = usbfs_get_active_config(handle->dev, hpriv->fd);
    if (r == LIBUSB_SUCCESS)
      active_config = priv->active_config;
  }
  if (r < 0)
    return r;

  if (active_config == -1) {
    usbi_warn(usbi_handle_ctx(handle), "device unconfigured");
    active_config = 0;
  }

  *config = (uint8_t)active_config;

  return 0;
}

static int op_set_configuration(struct libusb_device_handle *handle, int config)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(handle->dev);
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  int r = ioctl(fd, IOCTL_USBFS_SETCONFIGURATION, &config);

  if (r < 0) {
    if (errno == EINVAL)
      return LIBUSB_ERROR_NOT_FOUND;
    else if (errno == EBUSY)
      return LIBUSB_ERROR_BUSY;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "set configuration failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }

  /* if necessary, update our cached active config descriptor */
  if (!priv->sysfs_dir) {
    if (config == 0 && !dev_has_config0(handle->dev))
      config = -1;

    priv->active_config = config;
  }

  return LIBUSB_SUCCESS;
}

static int claim_interface(struct libusb_device_handle *handle, unsigned int iface)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  int r = ioctl(fd, IOCTL_USBFS_CLAIMINTERFACE, &iface);

  if (r < 0) {
    if (errno == ENOENT)
      return LIBUSB_ERROR_NOT_FOUND;
    else if (errno == EBUSY)
      return LIBUSB_ERROR_BUSY;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "claim interface failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }
  return 0;
}

static int release_interface(struct libusb_device_handle *handle, unsigned int iface)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  int r = ioctl(fd, IOCTL_USBFS_RELEASEINTERFACE, &iface);

  if (r < 0) {
    if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "release interface failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }
  return 0;
}

static int op_set_interface(struct libusb_device_handle *handle, uint8_t interface,
  uint8_t altsetting)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  struct usbfs_setinterface setintf;
  int r;

  setintf.interface = interface;
  setintf.altsetting = altsetting;
  r = ioctl(fd, IOCTL_USBFS_SETINTERFACE, &setintf);
  if (r < 0) {
    if (errno == EINVAL)
      return LIBUSB_ERROR_NOT_FOUND;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "set interface failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }

  return 0;
}

static int op_clear_halt(struct libusb_device_handle *handle,
  unsigned char endpoint)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  unsigned int _endpoint = endpoint;
  int r = ioctl(fd, IOCTL_USBFS_CLEAR_HALT, &_endpoint);

  if (r < 0) {
    if (errno == ENOENT)
      return LIBUSB_ERROR_NOT_FOUND;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "clear halt failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }

  return 0;
}

static int op_reset_device(struct libusb_device_handle *handle)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  int r, ret = 0;
  uint8_t i;

  /* Doing a device reset will cause the usbfs driver to get unbound
   * from any interfaces it is bound to. By voluntarily unbinding
   * the usbfs driver ourself, we stop the kernel from rebinding
   * the interface after reset (which would end up with the interface
   * getting bound to the in kernel driver if any). */
  for (i = 0; i < USB_MAXINTERFACES; i++) {
    if (handle->claimed_interfaces & (1UL << i))
      release_interface(handle, i);
  }

  usbi_mutex_lock(&handle->lock);
  r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
  if (r < 0) {
    if (errno == ENODEV) {
      ret = LIBUSB_ERROR_NOT_FOUND;
      goto out;
    }

    usbi_err(usbi_handle_ctx(handle), "reset failed, errno=%d", errno);
    ret = LIBUSB_ERROR_OTHER;
    goto out;
  }

  /* And re-claim any interfaces which were claimed before the reset */
  for (i = 0; i < USB_MAXINTERFACES; i++) {
    if (!(handle->claimed_interfaces & (1UL << i)))
      continue;
    /*
     * A driver may have completed modprobing during
     * IOCTL_USBFS_RESET, and bound itself as soon as
     * IOCTL_USBFS_RESET released the device lock
     */
    r = detach_kernel_driver_and_claim(handle, i);
    if (r) {
      usbi_warn(usbi_handle_ctx(handle), "failed to re-claim interface %u after reset: %s",
          i, libusb_error_name(r));
      handle->claimed_interfaces &= ~(1UL << i);
      ret = LIBUSB_ERROR_NOT_FOUND;
    }
  }
out:
  usbi_mutex_unlock(&handle->lock);
  return ret;
}

static int do_streams_ioctl(struct libusb_device_handle *handle,
  unsigned long req, uint32_t num_streams, unsigned char *endpoints,
  int num_endpoints)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int r, fd = hpriv->fd;
  struct usbfs_streams *streams;

  if (num_endpoints > 30) /* Max 15 in + 15 out eps */
    return LIBUSB_ERROR_INVALID_PARAM;

  streams = (struct usbfs_streams *)malloc(sizeof(*streams) + num_endpoints);
  if (!streams)
    return LIBUSB_ERROR_NO_MEM;

  streams->num_streams = num_streams;
  streams->num_eps = num_endpoints;
  memcpy(streams->eps, endpoints, num_endpoints);

  r = ioctl(fd, req, streams);

  free(streams);

  if (r < 0) {
    if (errno == ENOTTY)
      return LIBUSB_ERROR_NOT_SUPPORTED;
    else if (errno == EINVAL)
      return LIBUSB_ERROR_INVALID_PARAM;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "streams-ioctl failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }
  return r;
}

static int op_alloc_streams(struct libusb_device_handle *handle,
  uint32_t num_streams, unsigned char *endpoints, int num_endpoints)
{
  return do_streams_ioctl(handle, IOCTL_USBFS_ALLOC_STREAMS,
        num_streams, endpoints, num_endpoints);
}

static int op_free_streams(struct libusb_device_handle *handle,
    unsigned char *endpoints, int num_endpoints)
{
  return do_streams_ioctl(handle, IOCTL_USBFS_FREE_STREAMS, 0,
        endpoints, num_endpoints);
}

static void *op_dev_mem_alloc(struct libusb_device_handle *handle, size_t len)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  void *buffer;

  buffer = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, hpriv->fd, 0);
  if (buffer == MAP_FAILED) {
    usbi_err(usbi_handle_ctx(handle), "alloc dev mem failed, errno=%d", errno);
    return NULL;
  }
  return buffer;
}

static int op_dev_mem_free(struct libusb_device_handle *handle, void *buffer,
  size_t len)
{
  if (munmap(buffer, len) != 0) {
    usbi_err(usbi_handle_ctx(handle), "free dev mem failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  } else {
    return LIBUSB_SUCCESS;
  }
}

static int op_kernel_driver_active(struct libusb_device_handle *handle,
  uint8_t interface)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  struct usbfs_getdriver getdrv;
  int r;

  getdrv.interface = interface;
  r = ioctl(fd, IOCTL_USBFS_GETDRIVER, &getdrv);
  if (r < 0) {
    if (errno == ENODATA)
      return 0;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "get driver failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }

  return strcmp(getdrv.driver, "usbfs") != 0;
}

static int op_detach_kernel_driver(struct libusb_device_handle *handle,
  uint8_t interface)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  struct usbfs_ioctl command;
  struct usbfs_getdriver getdrv;
  int r;

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

  getdrv.interface = interface;
  r = ioctl(fd, IOCTL_USBFS_GETDRIVER, &getdrv);
  if (r == 0 && !strcmp(getdrv.driver, "usbfs"))
    return LIBUSB_ERROR_NOT_FOUND;

  r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
  if (r < 0) {
    if (errno == ENODATA)
      return LIBUSB_ERROR_NOT_FOUND;
    else if (errno == EINVAL)
      return LIBUSB_ERROR_INVALID_PARAM;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "detach failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }

  return 0;
}

static int op_attach_kernel_driver(struct libusb_device_handle *handle,
  uint8_t interface)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int fd = hpriv->fd;
  struct usbfs_ioctl command;
  int r;

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

  r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
  if (r < 0) {
    if (errno == ENODATA)
      return LIBUSB_ERROR_NOT_FOUND;
    else if (errno == EINVAL)
      return LIBUSB_ERROR_INVALID_PARAM;
    else if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;
    else if (errno == EBUSY)
      return LIBUSB_ERROR_BUSY;

    usbi_err(usbi_handle_ctx(handle), "attach failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  } else if (r == 0) {
    return LIBUSB_ERROR_NOT_FOUND;
  }

  return 0;
}

static int detach_kernel_driver_and_claim(struct libusb_device_handle *handle,
  uint8_t interface)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  struct usbfs_disconnect_claim dc;
  int r, fd = hpriv->fd;

  dc.interface = interface;
  snprintf(dc.driver, sizeof(dc.driver), "%s", "usbfs");
  dc.flags = USBFS_DISCONNECT_CLAIM_EXCEPT_DRIVER;
  r = ioctl(fd, IOCTL_USBFS_DISCONNECT_CLAIM, &dc);
  if (r == 0)
    return 0;
  switch (errno) {
  case ENOTTY:
    break;
  case EBUSY:
    return LIBUSB_ERROR_BUSY;
  case EINVAL:
    return LIBUSB_ERROR_INVALID_PARAM;
  case ENODEV:
    return LIBUSB_ERROR_NO_DEVICE;
  default:
    usbi_err(usbi_handle_ctx(handle), "disconnect-and-claim failed, errno=%d", errno);
    return LIBUSB_ERROR_OTHER;
  }

  /* Fallback code for kernels which don't support the
     disconnect-and-claim ioctl */
  r = op_detach_kernel_driver(handle, interface);
  if (r != 0 && r != LIBUSB_ERROR_NOT_FOUND)
    return r;

  return claim_interface(handle, interface);
}

static int op_claim_interface(struct libusb_device_handle *handle, uint8_t interface)
{
  if (handle->auto_detach_kernel_driver)
    return detach_kernel_driver_and_claim(handle, interface);
  else
    return claim_interface(handle, interface);
}

static int op_release_interface(struct libusb_device_handle *handle, uint8_t interface)
{
  int r;

  r = release_interface(handle, interface);
  if (r)
    return r;

  if (handle->auto_detach_kernel_driver)
    op_attach_kernel_driver(handle, interface);

  return 0;
}

static void op_destroy_device(struct libusb_device *dev)
{
  struct linux_device_priv *priv = (struct linux_device_priv *)usbi_get_device_priv(dev);

  free(priv->config_descriptors);
  free(priv->descriptors);
  free(priv->sysfs_dir);
}

/* URBs are discarded in reverse order of submission to avoid races. */
static int discard_urbs(struct usbi_transfer *itransfer, int first, int last_plus_one)
{
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  struct linux_device_handle_priv *hpriv =
    (struct linux_device_handle_priv *)usbi_get_device_handle_priv(transfer->dev_handle);
  int i, ret = 0;
  struct usbfs_urb *urb;

  for (i = last_plus_one - 1; i >= first; i--) {
    if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS)
      urb = tpriv->iso_urbs[i];
    else
      urb = &tpriv->urbs[i];

    if (ioctl(hpriv->fd, IOCTL_USBFS_DISCARDURB, urb) == 0)
      continue;

    if (errno == EINVAL) {
      usbi_dbg(usbi_transfer_ctx(transfer), "URB not found --> assuming ready to be reaped");
      if (i == (last_plus_one - 1))
        ret = LIBUSB_ERROR_NOT_FOUND;
    } else if (errno == ENODEV) {
      usbi_dbg(usbi_transfer_ctx(transfer), "Device not found for URB --> assuming ready to be reaped");
      ret = LIBUSB_ERROR_NO_DEVICE;
    } else {
      usbi_warn(usbi_transfer_ctx(transfer), "unrecognised discard errno %d", errno);
      ret = LIBUSB_ERROR_OTHER;
    }
  }
  return ret;
}

static void free_iso_urbs(struct linux_transfer_priv *tpriv)
{
  int i;

  for (i = 0; i < tpriv->num_urbs; i++) {
    struct usbfs_urb *urb = tpriv->iso_urbs[i];

    if (!urb)
      break;
    free(urb);
  }

  free(tpriv->iso_urbs);
  tpriv->iso_urbs = NULL;
}

static int submit_bulk_transfer(struct usbi_transfer *itransfer)
{
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  struct linux_device_handle_priv *hpriv =
    (struct linux_device_handle_priv *)usbi_get_device_handle_priv(transfer->dev_handle);
  struct usbfs_urb *urbs;
  int is_out = usbi_is_xferout(transfer);
  int bulk_buffer_len, use_bulk_continuation;
  int num_urbs;
  int last_urb_partial = 0;
  int r;
  int i;

  /*
   * Older versions of usbfs place a 16kb limit on bulk URBs. We work
   * around this by splitting large transfers into 16k blocks, and then
   * submit all urbs at once. it would be simpler to submit one urb at
   * a time, but there is a big performance gain doing it this way.
   *
   * Newer versions lift the 16k limit (USBFS_CAP_NO_PACKET_SIZE_LIM),
   * using arbitrary large transfers can still be a bad idea though, as
   * the kernel needs to allocate physical contiguous memory for this,
   * which may fail for large buffers.
   *
   * The kernel solves this problem by splitting the transfer into
   * blocks itself when the host-controller is scatter-gather capable
   * (USBFS_CAP_BULK_SCATTER_GATHER), which most controllers are.
   *
   * Last, there is the issue of short-transfers when splitting, for
   * short split-transfers to work reliable USBFS_CAP_BULK_CONTINUATION
   * is needed, but this is not always available.
   */
  if (hpriv->caps & USBFS_CAP_BULK_SCATTER_GATHER) {
    /* Good! Just submit everything in one go */
    bulk_buffer_len = transfer->length ? transfer->length : 1;
    use_bulk_continuation = 0;
  } else if (hpriv->caps & USBFS_CAP_BULK_CONTINUATION) {
    /* Split the transfers and use bulk-continuation to
       avoid issues with short-transfers */
    bulk_buffer_len = MAX_BULK_BUFFER_LENGTH;
    use_bulk_continuation = 1;
  } else if (hpriv->caps & USBFS_CAP_NO_PACKET_SIZE_LIM) {
    /* Don't split, assume the kernel can alloc the buffer
       (otherwise the submit will fail with -ENOMEM) */
    bulk_buffer_len = transfer->length ? transfer->length : 1;
    use_bulk_continuation = 0;
  } else {
    /* Bad, splitting without bulk-continuation, short transfers
       which end before the last urb will not work reliable! */
    /* Note we don't warn here as this is "normal" on kernels <
       2.6.32 and not a problem for most applications */
    bulk_buffer_len = MAX_BULK_BUFFER_LENGTH;
    use_bulk_continuation = 0;
  }

  num_urbs = transfer->length / bulk_buffer_len;

  if (transfer->length == 0) {
    num_urbs = 1;
  } else if ((transfer->length % bulk_buffer_len) > 0) {
    last_urb_partial = 1;
    num_urbs++;
  }
  usbi_dbg(usbi_transfer_ctx(transfer), "need %d urbs for new transfer with length %d", num_urbs, transfer->length);
  urbs = (struct usbfs_urb *)calloc(num_urbs, sizeof(*urbs));
  if (!urbs)
    return LIBUSB_ERROR_NO_MEM;
  tpriv->urbs = urbs;
  tpriv->num_urbs = num_urbs;
  tpriv->num_retired = 0;
  tpriv->reap_action = NORMAL;
  tpriv->reap_status = LIBUSB_TRANSFER_COMPLETED;

  for (i = 0; i < num_urbs; i++) {
    struct usbfs_urb *urb = &urbs[i];

    urb->usercontext = itransfer;
    switch (transfer->type) {
    case LIBUSB_TRANSFER_TYPE_BULK:
      urb->type = USBFS_URB_TYPE_BULK;
      urb->stream_id = 0;
      break;
    case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
      urb->type = USBFS_URB_TYPE_BULK;
      urb->stream_id = itransfer->stream_id;
      break;
    case LIBUSB_TRANSFER_TYPE_INTERRUPT:
      urb->type = USBFS_URB_TYPE_INTERRUPT;
      break;
    }
    urb->endpoint = transfer->endpoint;
    urb->buffer = transfer->buffer + (i * bulk_buffer_len);

    /* don't set the short not ok flag for the last URB */
    if (use_bulk_continuation && !is_out && (i < num_urbs - 1))
      urb->flags = USBFS_URB_SHORT_NOT_OK;

    if (i == num_urbs - 1 && last_urb_partial)
      urb->buffer_length = transfer->length % bulk_buffer_len;
    else if (transfer->length == 0)
      urb->buffer_length = 0;
    else
      urb->buffer_length = bulk_buffer_len;

    if (i > 0 && use_bulk_continuation)
      urb->flags |= USBFS_URB_BULK_CONTINUATION;

    /* we have already checked that the flag is supported */
    if (is_out && i == num_urbs - 1 &&
        (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET))
      urb->flags |= USBFS_URB_ZERO_PACKET;

    r = ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
    if (r == 0)
      continue;

    if (errno == ENODEV) {
      r = LIBUSB_ERROR_NO_DEVICE;
    } else if (errno == ENOMEM) {
      r = LIBUSB_ERROR_NO_MEM;
    } else {
      usbi_err(usbi_transfer_ctx(transfer), "submiturb failed, errno=%d", errno);
      r = LIBUSB_ERROR_IO;
    }

    /* if the first URB submission fails, we can simply free up and
     * return failure immediately. */
    if (i == 0) {
      usbi_dbg(usbi_transfer_ctx(transfer), "first URB failed, easy peasy");
      free(urbs);
      tpriv->urbs = NULL;
      return r;
    }

    /* if it's not the first URB that failed, the situation is a bit
     * tricky. we may need to discard all previous URBs. there are
     * complications:
     *  - discarding is asynchronous - discarded urbs will be reaped
     *    later. the user must not have freed the transfer when the
     *    discarded URBs are reaped, otherwise libusb will be using
     *    freed memory.
     *  - the earlier URBs may have completed successfully and we do
     *    not want to throw away any data.
     *  - this URB failing may be no error; EREMOTEIO means that
     *    this transfer simply didn't need all the URBs we submitted
     * so, we report that the transfer was submitted successfully and
     * in case of error we discard all previous URBs. later when
     * the final reap completes we can report error to the user,
     * or success if an earlier URB was completed successfully.
     */
    tpriv->reap_action = errno == EREMOTEIO ? COMPLETED_EARLY : SUBMIT_FAILED;

    /* The URBs we haven't submitted yet we count as already
     * retired. */
    tpriv->num_retired += num_urbs - i;

    /* If we completed short then don't try to discard. */
    if (tpriv->reap_action == COMPLETED_EARLY)
      return 0;

    discard_urbs(itransfer, 0, i);

    usbi_dbg(usbi_transfer_ctx(transfer), "reporting successful submission but waiting for %d "
       "discards before reporting error", i);
    return 0;
  }

  return 0;
}

static int submit_iso_transfer(struct usbi_transfer *itransfer)
{
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  struct linux_device_handle_priv *hpriv =
    (struct linux_device_handle_priv *)usbi_get_device_handle_priv(transfer->dev_handle);
  struct usbfs_urb **urbs;
  int num_packets = transfer->num_iso_packets;
  int num_packets_remaining;
  int i, j;
  int num_urbs;
  unsigned int packet_len;
  unsigned int total_len = 0;
  unsigned char *urb_buffer = transfer->buffer;

  if (num_packets < 1)
    return LIBUSB_ERROR_INVALID_PARAM;

  /* usbfs places arbitrary limits on iso URBs. this limit has changed
   * at least three times, but we attempt to detect this limit during
   * init and check it here. if the kernel rejects the request due to
   * its size, we return an error indicating such to the user.
   */
  for (i = 0; i < num_packets; i++) {
    packet_len = transfer->iso_packet_desc[i].length;

    if (packet_len > max_iso_packet_len) {
      usbi_warn(usbi_transfer_ctx(transfer),
          "iso packet length of %u bytes exceeds maximum of %u bytes",
          packet_len, max_iso_packet_len);
      return LIBUSB_ERROR_INVALID_PARAM;
    }

    total_len += packet_len;
  }

  if (transfer->length < (int)total_len)
    return LIBUSB_ERROR_INVALID_PARAM;

  /* usbfs limits the number of iso packets per URB */
  num_urbs = (num_packets + (MAX_ISO_PACKETS_PER_URB - 1)) / MAX_ISO_PACKETS_PER_URB;

  usbi_dbg(usbi_transfer_ctx(transfer), "need %d urbs for new transfer with length %d", num_urbs, transfer->length);

  urbs = (struct usbfs_urb **)calloc(num_urbs, sizeof(*urbs));
  if (!urbs)
    return LIBUSB_ERROR_NO_MEM;

  tpriv->iso_urbs = urbs;
  tpriv->num_urbs = num_urbs;
  tpriv->num_retired = 0;
  tpriv->reap_action = NORMAL;
  tpriv->iso_packet_offset = 0;

  /* allocate + initialize each URB with the correct number of packets */
  num_packets_remaining = num_packets;
  for (i = 0, j = 0; i < num_urbs; i++) {
    int num_packets_in_urb = MIN(num_packets_remaining, MAX_ISO_PACKETS_PER_URB);
    struct usbfs_urb *urb;
    size_t alloc_size;
    int k;

    alloc_size = sizeof(*urb)
      + (num_packets_in_urb * sizeof(struct usbfs_iso_packet_desc));
    urb = (struct usbfs_urb *)calloc(1, alloc_size);
    if (!urb) {
      free_iso_urbs(tpriv);
      return LIBUSB_ERROR_NO_MEM;
    }
    urbs[i] = urb;

    /* populate packet lengths */
    for (k = 0; k < num_packets_in_urb; j++, k++) {
      packet_len = transfer->iso_packet_desc[j].length;
      urb->buffer_length += packet_len;
      urb->iso_frame_desc[k].length = packet_len;
    }

    urb->usercontext = itransfer;
    urb->type = USBFS_URB_TYPE_ISO;
    /* FIXME: interface for non-ASAP data? */
    urb->flags = USBFS_URB_ISO_ASAP;
    urb->endpoint = transfer->endpoint;
    urb->number_of_packets = num_packets_in_urb;
    urb->buffer = urb_buffer;

    urb_buffer += urb->buffer_length;
    num_packets_remaining -= num_packets_in_urb;
  }

  /* submit URBs */
  for (i = 0; i < num_urbs; i++) {
    int r = ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urbs[i]);

    if (r == 0)
      continue;

    if (errno == ENODEV) {
      r = LIBUSB_ERROR_NO_DEVICE;
    } else if (errno == EINVAL) {
      usbi_warn(usbi_transfer_ctx(transfer), "submiturb failed, transfer too large");
      r = LIBUSB_ERROR_INVALID_PARAM;
    } else if (errno == EMSGSIZE) {
      usbi_warn(usbi_transfer_ctx(transfer), "submiturb failed, iso packet length too large");
      r = LIBUSB_ERROR_INVALID_PARAM;
    } else {
      usbi_err(usbi_transfer_ctx(transfer), "submiturb failed, errno=%d", errno);
      r = LIBUSB_ERROR_IO;
    }

    /* if the first URB submission fails, we can simply free up and
     * return failure immediately. */
    if (i == 0) {
      usbi_dbg(usbi_transfer_ctx(transfer), "first URB failed, easy peasy");
      free_iso_urbs(tpriv);
      return r;
    }

    /* if it's not the first URB that failed, the situation is a bit
     * tricky. we must discard all previous URBs. there are
     * complications:
     *  - discarding is asynchronous - discarded urbs will be reaped
     *    later. the user must not have freed the transfer when the
     *    discarded URBs are reaped, otherwise libusb will be using
     *    freed memory.
     *  - the earlier URBs may have completed successfully and we do
     *    not want to throw away any data.
     * so, in this case we discard all the previous URBs BUT we report
     * that the transfer was submitted successfully. then later when
     * the final discard completes we can report error to the user.
     */
    tpriv->reap_action = SUBMIT_FAILED;

    /* The URBs we haven't submitted yet we count as already
     * retired. */
    tpriv->num_retired = num_urbs - i;
    discard_urbs(itransfer, 0, i);

    usbi_dbg(usbi_transfer_ctx(transfer), "reporting successful submission but waiting for %d "
       "discards before reporting error", i);
    return 0;
  }

  return 0;
}

static int submit_control_transfer(struct usbi_transfer *itransfer)
{
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  struct linux_device_handle_priv *hpriv =
    (struct linux_device_handle_priv *)usbi_get_device_handle_priv(transfer->dev_handle);
  struct usbfs_urb *urb;
  int r;

  if (transfer->length - LIBUSB_CONTROL_SETUP_SIZE > MAX_CTRL_BUFFER_LENGTH)
    return LIBUSB_ERROR_INVALID_PARAM;

  urb = (struct usbfs_urb *)calloc(1, sizeof(*urb));
  if (!urb)
    return LIBUSB_ERROR_NO_MEM;
  tpriv->urbs = urb;
  tpriv->num_urbs = 1;
  tpriv->reap_action = NORMAL;

  urb->usercontext = itransfer;
  urb->type = USBFS_URB_TYPE_CONTROL;
  urb->endpoint = transfer->endpoint;
  urb->buffer = transfer->buffer;
  urb->buffer_length = transfer->length;

  r = ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
  if (r < 0) {
    free(urb);
    tpriv->urbs = NULL;
    if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_transfer_ctx(transfer), "submiturb failed, errno=%d", errno);
    return LIBUSB_ERROR_IO;
  }
  return 0;
}

static int op_submit_transfer(struct usbi_transfer *itransfer) REQUIRES(itransfer->lock)
{
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);

  switch (transfer->type) {
  case LIBUSB_TRANSFER_TYPE_CONTROL:
    return submit_control_transfer(itransfer);
  case LIBUSB_TRANSFER_TYPE_BULK:
  case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
    return submit_bulk_transfer(itransfer);
  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
    return submit_bulk_transfer(itransfer);
  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
    return submit_iso_transfer(itransfer);
  default:
    usbi_err(usbi_transfer_ctx(transfer), "unknown transfer type %u", transfer->type);
    return LIBUSB_ERROR_INVALID_PARAM;
  }
}

static int op_cancel_transfer(struct usbi_transfer *itransfer)
{
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  int r;

  if (!tpriv->urbs)
    return LIBUSB_ERROR_NOT_FOUND;

  r = discard_urbs(itransfer, 0, tpriv->num_urbs);
  if (r != 0)
    return r;

  switch (transfer->type) {
  case LIBUSB_TRANSFER_TYPE_BULK:
  case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
    if (tpriv->reap_action == ERROR)
      break;
    /* else, fall through */
  default:
    tpriv->reap_action = CANCELLED;
  }

  return 0;
}

static void op_clear_transfer_priv(struct usbi_transfer *itransfer)
{
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);

  switch (transfer->type) {
  case LIBUSB_TRANSFER_TYPE_CONTROL:
  case LIBUSB_TRANSFER_TYPE_BULK:
  case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
    if (tpriv->urbs) {
      free(tpriv->urbs);
      tpriv->urbs = NULL;
    }
    break;
  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
    if (tpriv->iso_urbs) {
      free_iso_urbs(tpriv);
      tpriv->iso_urbs = NULL;
    }
    break;
  default:
    usbi_err(usbi_transfer_ctx(transfer), "unknown transfer type %u", transfer->type);
  }
}

static int handle_bulk_completion(struct usbi_transfer *itransfer,
  struct usbfs_urb *urb)
{
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  struct libusb_transfer *transfer = usbi_transfer_to_libusb_transfer(itransfer);
  int urb_idx = urb - tpriv->urbs;

  usbi_mutex_lock(&itransfer->lock);
  usbi_dbg(usbi_transfer_ctx(transfer), "handling completion status %d of bulk urb %d/%d", urb->status,
     urb_idx + 1, tpriv->num_urbs);

  tpriv->num_retired++;

  if (tpriv->reap_action != NORMAL) {
    /* cancelled, submit_fail, or completed early */
    usbi_dbg(usbi_transfer_ctx(transfer), "abnormal reap: urb status %d", urb->status);

    /* even though we're in the process of cancelling, it's possible that
     * we may receive some data in these URBs that we don't want to lose.
     * examples:
     * 1. while the kernel is cancelling all the packets that make up an
     *    URB, a few of them might complete. so we get back a successful
     *    cancellation *and* some data.
     * 2. we receive a short URB which marks the early completion condition,
     *    so we start cancelling the remaining URBs. however, we're too
     *    slow and another URB completes (or at least completes partially).
     *    (this can't happen since we always use BULK_CONTINUATION.)
     *
     * When this happens, our objectives are not to lose any "surplus" data,
     * and also to stick it at the end of the previously-received data
     * (closing any holes), so that libusb reports the total amount of
     * transferred data and presents it in a contiguous chunk.
     */
    if (urb->actual_length > 0) {
      unsigned char *target = transfer->buffer + itransfer->transferred;

      usbi_dbg(usbi_transfer_ctx(transfer), "received %d bytes of surplus data", urb->actual_length);
      if (urb->buffer != target) {
        usbi_dbg(usbi_transfer_ctx(transfer), "moving surplus data from offset %zu to offset %zu",
           (unsigned char *)urb->buffer - transfer->buffer,
           target - transfer->buffer);
        memmove(target, urb->buffer, urb->actual_length);
      }
      itransfer->transferred += urb->actual_length;
    }

    if (tpriv->num_retired == tpriv->num_urbs) {
      usbi_dbg(usbi_transfer_ctx(transfer), "abnormal reap: last URB handled, reporting");
      if (tpriv->reap_action != COMPLETED_EARLY &&
          tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
        tpriv->reap_status = LIBUSB_TRANSFER_ERROR;
      goto completed;
    }
    goto out_unlock;
  }

  itransfer->transferred += urb->actual_length;

  /* Many of these errors can occur on *any* urb of a multi-urb
   * transfer.  When they do, we tear down the rest of the transfer.
   */
  switch (urb->status) {
  case 0:
    break;
  case -EREMOTEIO: /* short transfer */
    break;
  case -ENOENT: /* cancelled */
  case -ECONNRESET:
    break;
  case -ENODEV:
  case -ESHUTDOWN:
    usbi_dbg(usbi_transfer_ctx(transfer), "device removed");
    tpriv->reap_status = LIBUSB_TRANSFER_NO_DEVICE;
    goto cancel_remaining;
  case -EPIPE:
    usbi_dbg(usbi_transfer_ctx(transfer), "detected endpoint stall");
    if (tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
      tpriv->reap_status = LIBUSB_TRANSFER_STALL;
    goto cancel_remaining;
  case -EOVERFLOW:
    /* overflow can only ever occur in the last urb */
    usbi_dbg(usbi_transfer_ctx(transfer), "overflow, actual_length=%d", urb->actual_length);
    if (tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
      tpriv->reap_status = LIBUSB_TRANSFER_OVERFLOW;
    goto completed;
  case -ETIME:
  case -EPROTO:
  case -EILSEQ:
  case -ECOMM:
  case -ENOSR:
    usbi_dbg(usbi_transfer_ctx(transfer), "low-level bus error %d", urb->status);
    tpriv->reap_action = ERROR;
    goto cancel_remaining;
  default:
    usbi_warn(usbi_itransfer_ctx(itransfer), "unrecognised urb status %d", urb->status);
    tpriv->reap_action = ERROR;
    goto cancel_remaining;
  }

  /* if we've reaped all urbs or we got less data than requested then we're
   * done */
  if (tpriv->num_retired == tpriv->num_urbs) {
    usbi_dbg(usbi_transfer_ctx(transfer), "all URBs in transfer reaped --> complete!");
    goto completed;
  } else if (urb->actual_length < urb->buffer_length) {
    usbi_dbg(usbi_transfer_ctx(transfer), "short transfer %d/%d --> complete!",
       urb->actual_length, urb->buffer_length);
    if (tpriv->reap_action == NORMAL)
      tpriv->reap_action = COMPLETED_EARLY;
  } else {
    goto out_unlock;
  }

cancel_remaining:
  if (tpriv->reap_action == ERROR && tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
    tpriv->reap_status = LIBUSB_TRANSFER_ERROR;

  if (tpriv->num_retired == tpriv->num_urbs) /* nothing to cancel */
    goto completed;

  /* cancel remaining urbs and wait for their completion before
   * reporting results */
  discard_urbs(itransfer, urb_idx + 1, tpriv->num_urbs);

out_unlock:
  usbi_mutex_unlock(&itransfer->lock);
  return 0;

completed:
  free(tpriv->urbs);
  tpriv->urbs = NULL;
  usbi_mutex_unlock(&itransfer->lock);
  return tpriv->reap_action == CANCELLED ?
    usbi_handle_transfer_cancellation(itransfer) :
    usbi_handle_transfer_completion(itransfer, tpriv->reap_status);
}

static int handle_iso_completion(struct usbi_transfer *itransfer,
  struct usbfs_urb *urb)
{
  struct libusb_transfer *transfer =
    usbi_transfer_to_libusb_transfer(itransfer);
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  int num_urbs = tpriv->num_urbs;
  int urb_idx = 0;
  int i;
  enum libusb_transfer_status status = LIBUSB_TRANSFER_COMPLETED;

  usbi_mutex_lock(&itransfer->lock);
  for (i = 0; i < num_urbs; i++) {
    if (urb == tpriv->iso_urbs[i]) {
      urb_idx = i + 1;
      break;
    }
  }
  if (urb_idx == 0) {
    usbi_err(usbi_transfer_ctx(transfer), "could not locate urb!");
    usbi_mutex_unlock(&itransfer->lock);
    return LIBUSB_ERROR_NOT_FOUND;
  }

  usbi_dbg(usbi_transfer_ctx(transfer), "handling completion status %d of iso urb %d/%d", urb->status,
     urb_idx, num_urbs);

  /* copy isochronous results back in */

  for (i = 0; i < urb->number_of_packets; i++) {
    struct usbfs_iso_packet_desc *urb_desc = &urb->iso_frame_desc[i];
    struct libusb_iso_packet_descriptor *lib_desc =
      &transfer->iso_packet_desc[tpriv->iso_packet_offset++];
    /* usbfs writes negative errno values to this unsigned UAPI field. */
    int packet_status = (int)urb_desc->status;

    lib_desc->status = LIBUSB_TRANSFER_COMPLETED;
    switch (packet_status) {
    case 0:
      break;
    case -ENOENT: /* cancelled */
    case -ECONNRESET:
      break;
    case -ENODEV:
    case -ESHUTDOWN:
      usbi_dbg(usbi_transfer_ctx(transfer), "packet %d - device removed", i);
      lib_desc->status = LIBUSB_TRANSFER_NO_DEVICE;
      break;
    case -EPIPE:
      usbi_dbg(usbi_transfer_ctx(transfer), "packet %d - detected endpoint stall", i);
      lib_desc->status = LIBUSB_TRANSFER_STALL;
      break;
    case -EOVERFLOW:
      usbi_dbg(usbi_transfer_ctx(transfer), "packet %d - overflow error", i);
      lib_desc->status = LIBUSB_TRANSFER_OVERFLOW;
      break;
    case -ETIME:
    case -EPROTO:
    case -EILSEQ:
    case -ECOMM:
    case -ENOSR:
    case -EXDEV:
      usbi_dbg(usbi_transfer_ctx(transfer), "packet %d - low-level USB error %d", i, packet_status);
      lib_desc->status = LIBUSB_TRANSFER_ERROR;
      break;
    default:
      usbi_warn(usbi_transfer_ctx(transfer), "packet %d - unrecognised urb status %d",
          i, packet_status);
      lib_desc->status = LIBUSB_TRANSFER_ERROR;
      break;
    }
    lib_desc->actual_length = urb_desc->actual_length;
  }

  tpriv->num_retired++;

  if (tpriv->reap_action != NORMAL) { /* cancelled or submit_fail */
    usbi_dbg(usbi_transfer_ctx(transfer), "CANCEL: urb status %d", urb->status);

    if (tpriv->num_retired == num_urbs) {
      usbi_dbg(usbi_transfer_ctx(transfer), "CANCEL: last URB handled, reporting");
      free_iso_urbs(tpriv);
      if (tpriv->reap_action == CANCELLED) {
        usbi_mutex_unlock(&itransfer->lock);
        return usbi_handle_transfer_cancellation(itransfer);
      } else {
        usbi_mutex_unlock(&itransfer->lock);
        return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_ERROR);
      }
    }
    goto out;
  }

  switch (urb->status) {
  case 0:
    break;
  case -ENOENT: /* cancelled */
  case -ECONNRESET:
    break;
  case -ESHUTDOWN:
    usbi_dbg(usbi_transfer_ctx(transfer), "device removed");
    status = LIBUSB_TRANSFER_NO_DEVICE;
    break;
  default:
    usbi_warn(usbi_transfer_ctx(transfer), "unrecognised urb status %d", urb->status);
    status = LIBUSB_TRANSFER_ERROR;
    break;
  }

  /* if we've reaped all urbs then we're done */
  if (tpriv->num_retired == num_urbs) {
    usbi_dbg(usbi_transfer_ctx(transfer), "all URBs in transfer reaped --> complete!");
    free_iso_urbs(tpriv);
    usbi_mutex_unlock(&itransfer->lock);
    return usbi_handle_transfer_completion(itransfer, status);
  }

out:
  usbi_mutex_unlock(&itransfer->lock);
  return 0;
}

static int handle_control_completion(struct usbi_transfer *itransfer,
  struct usbfs_urb *urb)
{
  struct linux_transfer_priv *tpriv = (struct linux_transfer_priv *)usbi_get_transfer_priv(itransfer);
  int status;

  usbi_mutex_lock(&itransfer->lock);
  usbi_dbg(usbi_itransfer_ctx(itransfer), "handling completion status %d", urb->status);

  itransfer->transferred += urb->actual_length;

  if (tpriv->reap_action == CANCELLED) {
    if (urb->status && urb->status != -ENOENT)
      usbi_warn(usbi_itransfer_ctx(itransfer), "cancel: unrecognised urb status %d",
          urb->status);
    free(tpriv->urbs);
    tpriv->urbs = NULL;
    usbi_mutex_unlock(&itransfer->lock);
    return usbi_handle_transfer_cancellation(itransfer);
  }

  switch (urb->status) {
  case 0:
    status = LIBUSB_TRANSFER_COMPLETED;
    break;
  case -ENOENT: /* cancelled */
    status = LIBUSB_TRANSFER_CANCELLED;
    break;
  case -ENODEV:
  case -ESHUTDOWN:
    usbi_dbg(usbi_itransfer_ctx(itransfer), "device removed");
    status = LIBUSB_TRANSFER_NO_DEVICE;
    break;
  case -EPIPE:
    usbi_dbg(usbi_itransfer_ctx(itransfer), "unsupported control request");
    status = LIBUSB_TRANSFER_STALL;
    break;
  case -EOVERFLOW:
    usbi_dbg(usbi_itransfer_ctx(itransfer), "overflow, actual_length=%d", urb->actual_length);
    status = LIBUSB_TRANSFER_OVERFLOW;
    break;
  case -ETIME:
  case -EPROTO:
  case -EILSEQ:
  case -ECOMM:
  case -ENOSR:
    usbi_dbg(usbi_itransfer_ctx(itransfer), "low-level bus error %d", urb->status);
    status = LIBUSB_TRANSFER_ERROR;
    break;
  default:
    usbi_warn(usbi_itransfer_ctx(itransfer), "unrecognised urb status %d", urb->status);
    status = LIBUSB_TRANSFER_ERROR;
    break;
  }

  free(tpriv->urbs);
  tpriv->urbs = NULL;
  usbi_mutex_unlock(&itransfer->lock);
  return usbi_handle_transfer_completion(itransfer, (enum libusb_transfer_status)status);
}

static int reap_for_handle(struct libusb_device_handle *handle)
{
  struct linux_device_handle_priv *hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
  int r;
  struct usbfs_urb *urb = NULL;
  struct usbi_transfer *itransfer;
  struct libusb_transfer *transfer;

  r = ioctl(hpriv->fd, IOCTL_USBFS_REAPURBNDELAY, &urb);
  if (r < 0) {
    if (errno == EAGAIN)
      return 1;
    if (errno == ENODEV)
      return LIBUSB_ERROR_NO_DEVICE;

    usbi_err(usbi_handle_ctx(handle), "reap failed, errno=%d", errno);
    return LIBUSB_ERROR_IO;
  }

  itransfer = (struct usbi_transfer *)urb->usercontext;
  transfer = usbi_transfer_to_libusb_transfer(itransfer);

  usbi_dbg(usbi_handle_ctx(handle), "urb type=%u status=%d transferred=%d", urb->type, urb->status, urb->actual_length);

  switch (transfer->type) {
  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
    return handle_iso_completion(itransfer, urb);
  case LIBUSB_TRANSFER_TYPE_BULK:
  case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
    return handle_bulk_completion(itransfer, urb);
  case LIBUSB_TRANSFER_TYPE_CONTROL:
    return handle_control_completion(itransfer, urb);
  default:
    usbi_err(usbi_handle_ctx(handle), "unrecognised transfer type %u", transfer->type);
    return LIBUSB_ERROR_OTHER;
  }
}

static int op_handle_events(struct libusb_context *ctx,
  void *event_data, unsigned int count, unsigned int num_ready)
{
  struct pollfd *fds = (struct pollfd *)event_data;
  unsigned int n;
  int r;

  usbi_mutex_lock(&ctx->open_devs_lock);
  for (n = 0; n < count && num_ready > 0; n++) {
    struct pollfd *pollfd = &fds[n];
    struct libusb_device_handle *handle;
    struct linux_device_handle_priv *hpriv = NULL;
    int reap_count;

    if (!pollfd->revents)
      continue;

    num_ready--;
    for_each_open_device(ctx, handle) {
      hpriv = (struct linux_device_handle_priv *)usbi_get_device_handle_priv(handle);
      if (hpriv->fd == pollfd->fd)
        break;
    }

    if (!hpriv || hpriv->fd != pollfd->fd) {
      usbi_err(ctx, "cannot find handle for fd %d",
         pollfd->fd);
      continue;
    }

    if (pollfd->revents & POLLERR) {
      /* remove the fd from the pollfd set so that it doesn't continuously
       * trigger an event, and flag that it has been removed so op_close()
       * doesn't try to remove it a second time */
      usbi_remove_event_source(usbi_handle_ctx(handle), hpriv->fd);
      hpriv->fd_removed = 1;

      /* device will still be marked as attached if hotplug monitor thread
       * hasn't processed remove event yet */
      usbi_mutex_static_lock(&linux_hotplug_lock);
      if (usbi_atomic_load(&handle->dev->attached))
        linux_device_disconnected(handle->dev->bus_number,
                handle->dev->device_address);
      usbi_mutex_static_unlock(&linux_hotplug_lock);

      if (hpriv->caps & USBFS_CAP_REAP_AFTER_DISCONNECT) {
        do {
          r = reap_for_handle(handle);
        } while (r == 0);
      }

      usbi_handle_disconnect(ctx, handle);
      continue;
    }

    reap_count = 0;
    do {
      r = reap_for_handle(handle);
    } while (r == 0 && ++reap_count <= 25);

    if (r == 1 || r == LIBUSB_ERROR_NO_DEVICE)
      continue;
    else if (r < 0)
      goto out;
  }

  r = 0;
out:
  usbi_mutex_unlock(&ctx->open_devs_lock);
  return r;
}

const struct usbi_os_backend usbi_backend = {
  .name = "Linux usbfs",
  .caps = USBI_CAP_HAS_HID_ACCESS|USBI_CAP_SUPPORTS_DETACH_KERNEL_DRIVER,
  .init = op_init,
  .exit = op_exit,
  .set_option = op_set_option,
  .get_device_string = op_get_device_string,
  .get_config_string = op_get_config_string,
  .get_interface_string = op_get_interface_string,
  .hotplug_poll = op_hotplug_poll,
  .wrap_sys_device = op_wrap_sys_device,
  .open = op_open,
  .close = op_close,

  .get_active_config_descriptor = op_get_active_config_descriptor,
  .get_config_descriptor = op_get_config_descriptor,
  .get_config_descriptor_by_value = op_get_config_descriptor_by_value,
  .get_configuration = op_get_configuration,
  .set_configuration = op_set_configuration,
  .claim_interface = op_claim_interface,
  .release_interface = op_release_interface,

  .set_interface_altsetting = op_set_interface,
  .clear_halt = op_clear_halt,
  .reset_device = op_reset_device,

  .alloc_streams = op_alloc_streams,
  .free_streams = op_free_streams,

  .dev_mem_alloc = op_dev_mem_alloc,
  .dev_mem_free = op_dev_mem_free,

  .kernel_driver_active = op_kernel_driver_active,
  .detach_kernel_driver = op_detach_kernel_driver,
  .attach_kernel_driver = op_attach_kernel_driver,

  .destroy_device = op_destroy_device,

  .submit_transfer = op_submit_transfer,
  .cancel_transfer = op_cancel_transfer,
  .clear_transfer_priv = op_clear_transfer_priv,

  .handle_events = op_handle_events,

  .context_priv_size = sizeof(struct linux_context_priv),
  .device_priv_size = sizeof(struct linux_device_priv),
  .device_handle_priv_size = sizeof(struct linux_device_handle_priv),
  .transfer_priv_size = sizeof(struct linux_transfer_priv),
};

Coverage Report

Created: 2026-09-03 07:15