Update from DSLogic-v0.3.tar.gzHEADmaster

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>

1 files changed, 2608 insertions, 0 deletions

diff --git a/libusbx-1.0.18/libusb/os/linux_usbfs.c b/libusbx-1.0.18/libusb/os/linux_usbfs.c
new file mode 100644
index 0000000..a95d099
--- /dev/null
+++ b/libusbx-1.0.18/libusb/os/linux_usbfs.c
@@ -0,0 +1,2608 @@
+/* -*- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -*- */
+/*
+ * Linux usbfs backend for libusbx
+ * 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>
+ *
+ * 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 "config.h"
+
+#include <assert.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/utsname.h>
+#include <unistd.h>
+
+#include "libusb.h"
+#include "libusbi.h"
+#include "linux_usbfs.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.
+ */
+
+static const char *usbfs_path = NULL;
+
+/* use usbdev*.* device names in /dev instead of the usbfs bus directories */
+static int usbdev_names = 0;
+
+/* Linux 2.6.32 adds support for a bulk continuation URB flag. this basically
+ * allows us to mark URBs as being part of a specific logical transfer when
+ * we submit them to the kernel. then, on any error except a cancellation, all
+ * URBs within that transfer will be cancelled and no more URBs will be
+ * accepted for the transfer, meaning that no more data can creep in.
+ *
+ * The BULK_CONTINUATION flag must be set on all URBs within a bulk transfer
+ * (in either direction) except the first.
+ * For IN transfers, we must also set SHORT_NOT_OK on all URBs except the
+ * last; it means that the kernel should treat a short reply as an error.
+ * For OUT transfers, SHORT_NOT_OK must not be set. it isn't needed (OUT
+ * transfers can't be short unless there's already some sort of error), and
+ * setting this flag is disallowed (a kernel with USB debugging enabled will
+ * reject such URBs).
+ */
+static int supports_flag_bulk_continuation = -1;
+
+/* Linux 2.6.31 fixes support for the zero length packet URB flag. This
+ * allows us to mark URBs that should be followed by a zero length data
+ * packet, which can be required by device- or class-specific protocols.
+ */
+static int supports_flag_zero_packet = -1;
+
+/* clock ID for monotonic clock, as not all clock sources are available on all
+ * systems. appropriate choice made at initialization time. */
+static clockid_t monotonic_clkid = -1;
+
+/* Linux 2.6.22 (commit 83f7d958eab2fbc6b159ee92bf1493924e1d0f72) adds a busnum
+ * to sysfs, so we can relate devices. This also implies that we can read
+ * the active configuration through bConfigurationValue */
+static int sysfs_can_relate_devices = -1;
+
+/* Linux 2.6.26 (commit 217a9081d8e69026186067711131b77f0ce219ed) adds all
+ * config descriptors (rather then just the active config) to the sysfs
+ * descriptors file, so from then on we can use them. */
+static int sysfs_has_descriptors = -1;
+
+/* how many times have we initted (and not exited) ? */
+static volatile int init_count = 0;
+
+/* Serialize hotplug start/stop */
+usbi_mutex_static_t linux_hotplug_startstop_lock = USBI_MUTEX_INITIALIZER;
+/* Serialize scan-devices, event-thread, and poll */
+usbi_mutex_static_t linux_hotplug_lock = USBI_MUTEX_INITIALIZER;
+
+static int linux_start_event_monitor(void);
+static int linux_stop_event_monitor(void);
+static int linux_scan_devices(struct libusb_context *ctx);
+static int sysfs_scan_device(struct libusb_context *ctx, const char *devname);
+static int detach_kernel_driver_and_claim(struct libusb_device_handle *, int);
+
+#if !defined(USE_UDEV)
+static int linux_default_scan_devices (struct libusb_context *ctx);
+#endif
+
+struct linux_device_priv {
+	char *sysfs_dir;
+	unsigned char *descriptors;
+	int descriptors_len;
+	int active_config; /* cache val for !sysfs_can_relate_devices  */
+};
+
+struct linux_device_handle_priv {
+	int fd;
+	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 _get_usbfs_fd(struct libusb_device *dev, mode_t mode, int silent)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	char path[PATH_MAX];
+	int fd;
+
+	if (usbdev_names)
+		snprintf(path, PATH_MAX, "%s/usbdev%d.%d",
+			usbfs_path, dev->bus_number, dev->device_address);
+	else
+		snprintf(path, PATH_MAX, "%s/%03d/%03d",
+			usbfs_path, dev->bus_number, dev->device_address);
+
+	fd = open(path, mode);
+	if (fd != -1)
+		return fd; /* Success */
+
+	if (!silent) {
+		usbi_err(ctx, "libusbx couldn't open USB device %s: %s",
+			 path, strerror(errno));
+		if (errno == EACCES && mode == O_RDWR)
+			usbi_err(ctx, "libusbx 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;
+}
+
+static struct linux_device_priv *_device_priv(struct libusb_device *dev)
+{
+	return (struct linux_device_priv *) dev->os_priv;
+}
+
+static struct linux_device_handle_priv *_device_handle_priv(
+	struct libusb_device_handle *handle)
+{
+	return (struct linux_device_handle_priv *) handle->os_priv;
+}
+
+/* check dirent for a /dev/usbdev%d.%d name
+ * optionally return bus/device on success */
+static int _is_usbdev_entry(struct dirent *entry, int *bus_p, int *dev_p)
+{
+	int busnum, devnum;
+
+	if (sscanf(entry->d_name, "usbdev%d.%d", &busnum, &devnum) != 2)
+		return 0;
+
+	usbi_dbg("found: %s", entry->d_name);
+	if (bus_p != NULL)
+		*bus_p = busnum;
+	if (dev_p != NULL)
+		*dev_p = devnum;
+	return 1;
+}
+
+static int check_usb_vfs(const char *dirname)
+{
+	DIR *dir;
+	struct dirent *entry;
+	int found = 0;
+
+	dir = opendir(dirname);
+	if (!dir)
+		return 0;
+
+	while ((entry = readdir(dir)) != NULL) {
+		if (entry->d_name[0] == '.')
+			continue;
+
+		/* We assume if we find any files that it must be the right place */
+		found = 1;
+		break;
+	}
+
+	closedir(dir);
+	return found;
+}
+
+static const char *find_usbfs_path(void)
+{
+	const char *path = "/dev/bus/usb";
+	const char *ret = NULL;
+
+	if (check_usb_vfs(path)) {
+		ret = path;
+	} else {
+		path = "/proc/bus/usb";
+		if (check_usb_vfs(path))
+			ret = path;
+	}
+
+	/* look for /dev/usbdev*.* if the normal places fail */
+	if (ret == NULL) {
+		struct dirent *entry;
+		DIR *dir;
+
+		path = "/dev";
+		dir = opendir(path);
+		if (dir != NULL) {
+			while ((entry = readdir(dir)) != NULL) {
+				if (_is_usbdev_entry(entry, NULL, NULL)) {
+					/* found one; that's enough */
+					ret = path;
+					usbdev_names = 1;
+					break;
+				}
+			}
+			closedir(dir);
+		}
+	}
+
+	if (ret != NULL)
+		usbi_dbg("found usbfs at %s", ret);
+
+	return ret;
+}
+
+/* the monotonic clock is not usable on all systems (e.g. embedded ones often
+ * seem to lack it). fall back to REALTIME if we have to. */
+static clockid_t find_monotonic_clock(void)
+{
+#ifdef CLOCK_MONOTONIC
+	struct timespec ts;
+	int r;
+
+	/* Linux 2.6.28 adds CLOCK_MONOTONIC_RAW but we don't use it
+	 * because it's not available through timerfd */
+	r = clock_gettime(CLOCK_MONOTONIC, &ts);
+	if (r == 0)
+		return CLOCK_MONOTONIC;
+	usbi_dbg("monotonic clock doesn't work, errno %d", errno);
+#endif
+
+	return CLOCK_REALTIME;
+}
+
+static int kernel_version_ge(int major, int minor, int sublevel)
+{
+	struct utsname uts;
+	int atoms, kmajor, kminor, ksublevel;
+
+	if (uname(&uts) < 0)
+		return -1;
+	atoms = sscanf(uts.release, "%d.%d.%d", &kmajor, &kminor, &ksublevel);
+	if (atoms < 1)
+		return -1;
+
+	if (kmajor > major)
+		return 1;
+	if (kmajor < major)
+		return 0;
+
+	/* kmajor == major */
+	if (atoms < 2)
+		return 0 == minor && 0 == sublevel;
+	if (kminor > minor)
+		return 1;
+	if (kminor < minor)
+		return 0;
+
+	/* kminor == minor */
+	if (atoms < 3)
+		return 0 == sublevel;
+
+	return ksublevel >= sublevel;
+}
+
+static int op_init(struct libusb_context *ctx)
+{
+	struct stat statbuf;
+	int r;
+
+	usbfs_path = find_usbfs_path();
+	if (!usbfs_path) {
+		usbi_err(ctx, "could not find usbfs");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	if (monotonic_clkid == -1)
+		monotonic_clkid = find_monotonic_clock();
+
+	if (supports_flag_bulk_continuation == -1) {
+		/* bulk continuation URB flag available from Linux 2.6.32 */
+		supports_flag_bulk_continuation = kernel_version_ge(2,6,32);
+		if (supports_flag_bulk_continuation == -1) {
+			usbi_err(ctx, "error checking for bulk continuation support");
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	if (supports_flag_bulk_continuation)
+		usbi_dbg("bulk continuation flag supported");
+
+	if (-1 == supports_flag_zero_packet) {
+		/* zero length packet URB flag fixed since Linux 2.6.31 */
+		supports_flag_zero_packet = kernel_version_ge(2,6,31);
+		if (-1 == supports_flag_zero_packet) {
+			usbi_err(ctx, "error checking for zero length packet support");
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	if (supports_flag_zero_packet)
+		usbi_dbg("zero length packet flag supported");
+
+	if (-1 == sysfs_has_descriptors) {
+		/* sysfs descriptors has all descriptors since Linux 2.6.26 */
+		sysfs_has_descriptors = kernel_version_ge(2,6,26);
+		if (-1 == sysfs_has_descriptors) {
+			usbi_err(ctx, "error checking for sysfs descriptors");
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	if (-1 == sysfs_can_relate_devices) {
+		/* sysfs has busnum since Linux 2.6.22 */
+		sysfs_can_relate_devices = kernel_version_ge(2,6,22);
+		if (-1 == sysfs_can_relate_devices) {
+			usbi_err(ctx, "error checking for sysfs busnum");
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	if (sysfs_can_relate_devices || sysfs_has_descriptors) {
+		r = stat(SYSFS_DEVICE_PATH, &statbuf);
+		if (r != 0 || !S_ISDIR(statbuf.st_mode)) {
+			usbi_warn(ctx, "sysfs not mounted");
+			sysfs_can_relate_devices = 0;
+			sysfs_has_descriptors = 0;
+		}
+	}
+
+	if (sysfs_can_relate_devices)
+		usbi_dbg("sysfs can relate devices");
+
+	if (sysfs_has_descriptors)
+		usbi_dbg("sysfs has complete descriptors");
+
+	usbi_mutex_static_lock(&linux_hotplug_startstop_lock);
+	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");
+	usbi_mutex_static_unlock(&linux_hotplug_startstop_lock);
+
+	return r;
+}
+
+static void op_exit(void)
+{
+	usbi_mutex_static_lock(&linux_hotplug_startstop_lock);
+	assert(init_count != 0);
+	if (!--init_count) {
+		/* tear down event handler */
+		(void)linux_stop_event_monitor();
+	}
+	usbi_mutex_static_unlock(&linux_hotplug_startstop_lock);
+}
+
+static int linux_start_event_monitor(void)
+{
+#if defined(USE_UDEV)
+	return linux_udev_start_event_monitor();
+#else
+	return linux_netlink_start_event_monitor();
+#endif
+}
+
+static int linux_stop_event_monitor(void)
+{
+#if defined(USE_UDEV)
+	return linux_udev_stop_event_monitor();
+#else
+	return linux_netlink_stop_event_monitor();
+#endif
+}
+
+static int linux_scan_devices(struct libusb_context *ctx)
+{
+	int ret;
+
+	usbi_mutex_static_lock(&linux_hotplug_lock);
+
+#if defined(USE_UDEV)
+	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)
+{
+#if defined(USE_UDEV)
+	linux_udev_hotplug_poll();
+#else
+	linux_netlink_hotplug_poll();
+#endif
+}
+
+static int _open_sysfs_attr(struct libusb_device *dev, const char *attr)
+{
+	struct linux_device_priv *priv = _device_priv(dev);
+	char filename[PATH_MAX];
+	int fd;
+
+	snprintf(filename, PATH_MAX, "%s/%s/%s",
+		SYSFS_DEVICE_PATH, priv->sysfs_dir, attr);
+	fd = open(filename, O_RDONLY);
+	if (fd < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"open %s failed ret=%d errno=%d", filename, fd, 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 *devname, const char *attr)
+{
+	char filename[PATH_MAX];
+	FILE *f;
+	int r, value;
+
+	snprintf(filename, PATH_MAX, "%s/%s/%s", SYSFS_DEVICE_PATH,
+		 devname, attr);
+	f = fopen(filename, "r");
+	if (f == NULL) {
+		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;
+	}
+
+	r = fscanf(f, "%d", &value);
+	fclose(f);
+	if (r != 1) {
+		usbi_err(ctx, "fscanf %s returned %d, errno=%d", attr, r, errno);
+		return LIBUSB_ERROR_NO_DEVICE; /* For unplug race (trac #70) */
+	}
+	if (value < 0) {
+		usbi_err(ctx, "%s contains a negative value", filename);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return value;
+}
+
+static int op_get_device_descriptor(struct libusb_device *dev,
+	unsigned char *buffer, int *host_endian)
+{
+	struct linux_device_priv *priv = _device_priv(dev);
+
+	*host_endian = sysfs_has_descriptors ? 0 : 1;
+	memcpy(buffer, priv->descriptors, DEVICE_DESC_LENGTH);
+
+	return 0;
+}
+
+/* read the bConfigurationValue for a device */
+static int sysfs_get_active_config(struct libusb_device *dev, int *config)
+{
+	char *endptr;
+	char tmp[5] = {0, 0, 0, 0, 0};
+	long num;
+	int fd;
+	ssize_t r;
+
+	fd = _open_sysfs_attr(dev, "bConfigurationValue");
+	if (fd < 0)
+		return fd;
+
+	r = read(fd, tmp, sizeof(tmp));
+	close(fd);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"read bConfigurationValue failed ret=%d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	} else if (r == 0) {
+		usbi_dbg("device unconfigured");
+		*config = -1;
+		return 0;
+	}
+
+	if (tmp[sizeof(tmp) - 1] != 0) {
+		usbi_err(DEVICE_CTX(dev), "not null-terminated?");
+		return LIBUSB_ERROR_IO;
+	} else if (tmp[0] == 0) {
+		usbi_err(DEVICE_CTX(dev), "no configuration value?");
+		return LIBUSB_ERROR_IO;
+	}
+
+	num = strtol(tmp, &endptr, 10);
+	if (endptr == tmp) {
+		usbi_err(DEVICE_CTX(dev), "error converting '%s' to integer", tmp);
+		return LIBUSB_ERROR_IO;
+	}
+
+	*config = (int) num;
+	return 0;
+}
+
+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 sysfs_attr;
+
+	usbi_dbg("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_can_relate_devices || detached || NULL == sys_name) {
+		if (NULL == 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/%hhd/%hhd", busnum, devaddr);
+		} else if (!strncmp(dev_node, "/proc/bus/usb", 13)) {
+			sscanf (dev_node, "/proc/bus/usb/%hhd/%hhd", busnum, devaddr);
+		}
+
+		return LIBUSB_SUCCESS;
+	}
+
+	usbi_dbg("scan %s", sys_name);
+
+	sysfs_attr = __read_sysfs_attr(ctx, sys_name, "busnum");
+	if (0 > sysfs_attr)
+		return sysfs_attr;
+	if (sysfs_attr > 255)
+		return LIBUSB_ERROR_INVALID_PARAM;
+	*busnum = (uint8_t) sysfs_attr;
+
+	sysfs_attr = __read_sysfs_attr(ctx, sys_name, "devnum");
+	if (0 > sysfs_attr)
+		return sysfs_attr;
+	if (sysfs_attr > 255)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	*devaddr = (uint8_t) sysfs_attr;
+
+	usbi_dbg("bus=%d dev=%d", *busnum, *devaddr);
+
+	return LIBUSB_SUCCESS;
+}
+
+/* Return offset of the next descriptor with the given type */
+static int seek_to_next_descriptor(struct libusb_context *ctx,
+	uint8_t descriptor_type, unsigned char *buffer, int size)
+{
+	struct usb_descriptor_header header;
+	int i;
+
+	for (i = 0; size >= 0; i += header.bLength, size -= header.bLength) {
+		if (size == 0)
+			return LIBUSB_ERROR_NOT_FOUND;
+
+		if (size < 2) {
+			usbi_err(ctx, "short descriptor read %d/2", size);
+			return LIBUSB_ERROR_IO;
+		}
+		usbi_parse_descriptor(buffer + i, "bb", &header, 0);
+
+		if (i && header.bDescriptorType == descriptor_type)
+			return i;
+	}
+	usbi_err(ctx, "bLength overflow by %d bytes", -size);
+	return LIBUSB_ERROR_IO;
+}
+
+/* Return offset to next config */
+static int seek_to_next_config(struct libusb_context *ctx,
+	unsigned char *buffer, int size)
+{
+	struct libusb_config_descriptor config;
+
+	if (size == 0)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	if (size < LIBUSB_DT_CONFIG_SIZE) {
+		usbi_err(ctx, "short descriptor read %d/%d",
+			 size, LIBUSB_DT_CONFIG_SIZE);
+		return LIBUSB_ERROR_IO;
+	}
+
+	usbi_parse_descriptor(buffer, "bbwbbbbb", &config, 0);
+	if (config.bDescriptorType != LIBUSB_DT_CONFIG) {
+		usbi_err(ctx, "descriptor is not a config desc (type 0x%02x)",
+			 config.bDescriptorType);
+		return LIBUSB_ERROR_IO;
+	}
+
+	/*
+	 * In usbfs the config descriptors are config.wTotalLength bytes apart,
+	 * with any short reads from the device appearing as holes in the file.
+	 *
+	 * In sysfs wTotalLength is ignored, instead the kernel returns a
+	 * config descriptor with verified bLength fields, with descriptors
+	 * with an invalid bLength removed.
+	 */
+	if (sysfs_has_descriptors) {
+		int next = seek_to_next_descriptor(ctx, LIBUSB_DT_CONFIG,
+						   buffer, size);
+		if (next == LIBUSB_ERROR_NOT_FOUND)
+			next = size;
+		if (next < 0)
+			return next;
+
+		if (next != config.wTotalLength)
+			usbi_warn(ctx, "config length mismatch wTotalLength "
+				  "%d real %d", config.wTotalLength, next);
+		return next;
+	} else {
+		if (config.wTotalLength < LIBUSB_DT_CONFIG_SIZE) {
+			usbi_err(ctx, "invalid wTotalLength %d",
+				 config.wTotalLength);
+			return LIBUSB_ERROR_IO;
+		} else if (config.wTotalLength > size) {
+			usbi_warn(ctx, "short descriptor read %d/%d",
+				  size, config.wTotalLength);
+			return size;
+		} else
+			return config.wTotalLength;
+	}
+}
+
+static int op_get_config_descriptor_by_value(struct libusb_device *dev,
+	uint8_t value, unsigned char **buffer, int *host_endian)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct linux_device_priv *priv = _device_priv(dev);
+	unsigned char *descriptors = priv->descriptors;
+	int size = priv->descriptors_len;
+	struct libusb_config_descriptor *config;
+
+	*buffer = NULL;
+	/* Unlike the device desc. config descs. are always in raw format */
+	*host_endian = 0;
+
+	/* Skip device header */
+	descriptors += DEVICE_DESC_LENGTH;
+	size -= DEVICE_DESC_LENGTH;
+
+	/* Seek till the config is found, or till "EOF" */
+	while (1) {
+		int next = seek_to_next_config(ctx, descriptors, size);
+		if (next < 0)
+			return next;
+		config = (struct libusb_config_descriptor *)descriptors;
+		if (config->bConfigurationValue == value) {
+			*buffer = descriptors;
+			return next;
+		}
+		size -= next;
+		descriptors += next;
+	}
+}
+
+static int op_get_active_config_descriptor(struct libusb_device *dev,
+	unsigned char *buffer, size_t len, int *host_endian)
+{
+	int r, config;
+	unsigned char *config_desc;
+
+	if (sysfs_can_relate_devices) {
+		r = sysfs_get_active_config(dev, &config);
+		if (r < 0)
+			return r;
+	} else {
+		/* Use cached bConfigurationValue */
+		struct linux_device_priv *priv = _device_priv(dev);
+		config = priv->active_config;
+	}
+	if (config == -1)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = op_get_config_descriptor_by_value(dev, config, &config_desc,
+					      host_endian);
+	if (r < 0)
+		return r;
+
+	len = MIN(len, r);
+	memcpy(buffer, config_desc, len);
+	return len;
+}
+
+static int op_get_config_descriptor(struct libusb_device *dev,
+	uint8_t config_index, unsigned char *buffer, size_t len, int *host_endian)
+{
+	struct linux_device_priv *priv = _device_priv(dev);
+	unsigned char *descriptors = priv->descriptors;
+	int i, r, size = priv->descriptors_len;
+
+	/* Unlike the device desc. config descs. are always in raw format */
+	*host_endian = 0;
+
+	/* Skip device header */
+	descriptors += DEVICE_DESC_LENGTH;
+	size -= DEVICE_DESC_LENGTH;
+
+	/* Seek till the config is found, or till "EOF" */
+	for (i = 0; ; i++) {
+		r = seek_to_next_config(DEVICE_CTX(dev), descriptors, size);
+		if (r < 0)
+			return r;
+		if (i == config_index)
+			break;
+		size -= r;
+		descriptors += r;
+	}
+
+	len = MIN(len, r);
+	memcpy(buffer, descriptors, len);
+	return len;
+}
+
+/* send a control message to retrieve active configuration */
+static int usbfs_get_active_config(struct libusb_device *dev, int fd)
+{
+	unsigned char 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(DEVICE_CTX(dev),
+			"get_configuration failed ret=%d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return active_config;
+}
+
+static int initialize_device(struct libusb_device *dev, uint8_t busnum,
+	uint8_t devaddr, const char *sysfs_dir)
+{
+	struct linux_device_priv *priv = _device_priv(dev);
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	int descriptors_size = 512; /* Begin with a 1024 byte alloc */
+	int fd, speed;
+	ssize_t r;
+
+	dev->bus_number = busnum;
+	dev->device_address = devaddr;
+
+	if (sysfs_dir) {
+		priv->sysfs_dir = malloc(strlen(sysfs_dir) + 1);
+		if (!priv->sysfs_dir)
+			return LIBUSB_ERROR_NO_MEM;
+		strcpy(priv->sysfs_dir, sysfs_dir);
+
+		/* Note speed can contain 1.5, in this case __read_sysfs_attr
+		   will stop parsing at the '.' and return 1 */
+		speed = __read_sysfs_attr(DEVICE_CTX(dev), sysfs_dir, "speed");
+		if (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;
+			default:
+				usbi_warn(DEVICE_CTX(dev), "Unknown device speed: %d Mbps", speed);
+			}
+		}
+	}
+
+	/* cache descriptors in memory */
+	if (sysfs_has_descriptors)
+		fd = _open_sysfs_attr(dev, "descriptors");
+	else
+		fd = _get_usbfs_fd(dev, O_RDONLY, 0);
+	if (fd < 0)
+		return fd;
+
+	do {
+		descriptors_size *= 2;
+		priv->descriptors = usbi_reallocf(priv->descriptors,
+						  descriptors_size);
+		if (!priv->descriptors) {
+			close(fd);
+			return LIBUSB_ERROR_NO_MEM;
+		}
+		/* usbfs has holes in the file */
+		if (!sysfs_has_descriptors) {
+			memset(priv->descriptors + priv->descriptors_len,
+			       0, descriptors_size - priv->descriptors_len);
+		}
+		r = read(fd, priv->descriptors + priv->descriptors_len,
+			 descriptors_size - priv->descriptors_len);
+		if (r < 0) {
+			usbi_err(ctx, "read descriptor failed ret=%d errno=%d",
+				 fd, errno);
+			close(fd);
+			return LIBUSB_ERROR_IO;
+		}
+		priv->descriptors_len += r;
+	} while (priv->descriptors_len == descriptors_size);
+
+	close(fd);
+
+	if (priv->descriptors_len < DEVICE_DESC_LENGTH) {
+		usbi_err(ctx, "short descriptor read (%d)",
+			 priv->descriptors_len);
+		return LIBUSB_ERROR_IO;
+	}
+
+	if (sysfs_can_relate_devices)
+		return LIBUSB_SUCCESS;
+
+	/* cache active config */
+	fd = _get_usbfs_fd(dev, O_RDWR, 1);
+	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->descriptors_len >=
+				(DEVICE_DESC_LENGTH + LIBUSB_DT_CONFIG_SIZE)) {
+			struct libusb_config_descriptor config;
+			usbi_parse_descriptor(
+				priv->descriptors + DEVICE_DESC_LENGTH,
+				"bbwbbbbb", &config, 0);
+			priv->active_config = config.bConfigurationValue;
+		} else
+			priv->active_config = -1; /* No config dt */
+
+		return LIBUSB_SUCCESS;
+	}
+
+	r = usbfs_get_active_config(dev, fd);
+	if (r > 0) {
+		priv->active_config = r;
+		r = LIBUSB_SUCCESS;
+	} else if (r == 0) {
+		/* some buggy devices have a configuration 0, but we're
+		 * reaching into the corner of a corner case here, so let's
+		 * not support buggy devices in these circumstances.
+		 * stick to the specs: a configuration value of 0 means
+		 * unconfigured. */
+		usbi_dbg("active cfg 0? assuming unconfigured device");
+		priv->active_config = -1;
+		r = LIBUSB_SUCCESS;
+	} else if (r == LIBUSB_ERROR_IO) {
+		/* buggy devices sometimes fail to report their active config.
+		 * assume unconfigured and continue the probing */
+		usbi_warn(ctx, "couldn't query active configuration, assuming"
+			       " unconfigured");
+		priv->active_config = -1;
+		r = LIBUSB_SUCCESS;
+	} /* else r < 0, just return the error code */
+
+	close(fd);
+	return r;
+}
+
+static int linux_get_parent_info(struct libusb_device *dev, const char *sysfs_dir)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct libusb_device *it;
+	char *parent_sysfs_dir, *tmp;
+	int ret, add_parent = 1;
+
+	/* XXX -- can we figure out the topology when using usbfs? */
+	if (NULL == sysfs_dir || 0 == 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 (NULL != (tmp = strrchr(parent_sysfs_dir, '.')) ||
+	    NULL != (tmp = strrchr(parent_sysfs_dir, '-'))) {
+	        dev->port_number = atoi(tmp + 1);
+		*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 (NULL == strchr(parent_sysfs_dir, '-')) {
+		tmp = parent_sysfs_dir;
+		ret = asprintf (&parent_sysfs_dir, "usb%s", tmp);
+		free (tmp);
+		if (0 > ret) {
+			return LIBUSB_ERROR_NO_MEM;
+		}
+	}
+
+retry:
+	/* find the parent in the context */
+	usbi_mutex_lock(&ctx->usb_devs_lock);
+	list_for_each_entry(it, &ctx->usb_devs, list, struct libusb_device) {
+		struct linux_device_priv *priv = _device_priv(it);
+		if (0 == 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("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("Dev %p (%s) has parent %p (%s) port %d", dev, sysfs_dir,
+		 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 = 0;
+
+	/* 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("busnum %d devaddr %d session_id %ld", busnum, devaddr,
+		session_id);
+
+	dev = usbi_get_device_by_session_id(ctx, session_id);
+	if (dev) {
+		/* device already exists in the context */
+		usbi_dbg("session_id %ld already exists", session_id);
+		libusb_unref_device(dev);
+		return LIBUSB_SUCCESS;
+	}
+
+	usbi_dbg("allocating new device for %d/%d (session %ld)",
+		 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);
+	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);
+	list_for_each_entry(ctx, &active_contexts_list, list, struct libusb_context) {
+		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, const char *sys_name)
+{
+	struct libusb_context *ctx;
+	struct libusb_device *dev;
+	unsigned long session_id = busnum << 8 | devaddr;
+
+	usbi_mutex_static_lock(&active_contexts_lock);
+	list_for_each_entry(ctx, &active_contexts_list, list, struct libusb_context) {
+		dev = usbi_get_device_by_session_id (ctx, session_id);
+		if (NULL != dev) {
+			usbi_disconnect_device (dev);
+			libusb_unref_device(dev);
+		} else {
+			usbi_dbg("device not found for session %x", session_id);
+		}
+	}
+	usbi_mutex_static_unlock(&active_contexts_lock);
+}
+
+#if !defined(USE_UDEV)
+/* 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[PATH_MAX];
+	struct dirent *entry;
+	int r = LIBUSB_ERROR_IO;
+
+	snprintf(dirpath, PATH_MAX, "%s/%03d", usbfs_path, busnum);
+	usbi_dbg("%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))) {
+		int devaddr;
+
+		if (entry->d_name[0] == '.')
+			continue;
+
+		devaddr = atoi(entry->d_name);
+		if (devaddr == 0) {
+			usbi_dbg("unknown dir entry %s", entry->d_name);
+			continue;
+		}
+
+		if (linux_enumerate_device(ctx, busnum, (uint8_t) devaddr, NULL)) {
+			usbi_dbg("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 = opendir(usbfs_path);
+	int r = 0;
+
+	if (!buses) {
+		usbi_err(ctx, "opendir buses failed errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	while ((entry = readdir(buses))) {
+		int busnum;
+
+		if (entry->d_name[0] == '.')
+			continue;
+
+		if (usbdev_names) {
+			int devaddr;
+			if (!_is_usbdev_entry(entry, &busnum, &devaddr))
+				continue;
+
+			r = linux_enumerate_device(ctx, busnum, (uint8_t) devaddr, NULL);
+			if (r < 0) {
+				usbi_dbg("failed to enumerate dir entry %s", entry->d_name);
+				continue;
+			}
+		} else {
+			busnum = atoi(entry->d_name);
+			if (busnum == 0) {
+				usbi_dbg("unknown dir entry %s", entry->d_name);
+				continue;
+			}
+
+			r = usbfs_scan_busdir(ctx, busnum);
+			if (r < 0)
+				break;
+		}
+	}
+
+	closedir(buses);
+	return r;
+
+}
+#endif
+
+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);
+	if (LIBUSB_SUCCESS != ret) {
+		return ret;
+	}
+
+	return linux_enumerate_device(ctx, busnum & 0xff, devaddr & 0xff,
+		devname);
+}
+
+#if !defined(USE_UDEV)
+static int sysfs_get_device_list(struct libusb_context *ctx)
+{
+	DIR *devices = opendir(SYSFS_DEVICE_PATH);
+	struct dirent *entry;
+	int r = LIBUSB_ERROR_IO;
+
+	if (!devices) {
+		usbi_err(ctx, "opendir devices failed errno=%d", errno);
+		return r;
+	}
+
+	while ((entry = readdir(devices))) {
+		if ((!isdigit(entry->d_name[0]) && strncmp(entry->d_name, "usb", 3))
+				|| strchr(entry->d_name, ':'))
+			continue;
+
+		if (sysfs_scan_device(ctx, entry->d_name)) {
+			usbi_dbg("failed to enumerate dir entry %s", entry->d_name);
+			continue;
+		}
+
+		r = 0;
+	}
+
+	closedir(devices);
+	return r;
+}
+
+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.
+	 *
+	 * as described in the "sysfs vs usbfs" comment at the top of this
+	 * file, sometimes we have sysfs but not enough information to
+	 * relate sysfs devices to usbfs nodes.  op_init() determines the
+	 * adequacy of sysfs and sets sysfs_can_relate_devices.
+	 */
+	if (sysfs_can_relate_devices != 0)
+		return sysfs_get_device_list(ctx);
+	else
+		return usbfs_get_device_list(ctx);
+}
+#endif
+
+static int op_open(struct libusb_device_handle *handle)
+{
+	struct linux_device_handle_priv *hpriv = _device_handle_priv(handle);
+	int r;
+
+	hpriv->fd = _get_usbfs_fd(handle->dev, O_RDWR, 0);
+	if (hpriv->fd < 0) {
+		if (hpriv->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 (handle->dev->attached) {
+				usbi_dbg("open failed with no device, but device still attached");
+				linux_device_disconnected(handle->dev->bus_number,
+						handle->dev->device_address, NULL);
+			}
+			usbi_mutex_static_unlock(&linux_hotplug_lock);
+		}
+		return hpriv->fd;
+	}
+
+	r = ioctl(hpriv->fd, IOCTL_USBFS_GET_CAPABILITIES, &hpriv->caps);
+	if (r < 0) {
+		if (errno == ENOTTY)
+			usbi_dbg("getcap not available");
+		else
+			usbi_err(HANDLE_CTX(handle), "getcap failed (%d)", errno);
+		hpriv->caps = 0;
+		if (supports_flag_zero_packet)
+			hpriv->caps |= USBFS_CAP_ZERO_PACKET;
+		if (supports_flag_bulk_continuation)
+			hpriv->caps |= USBFS_CAP_BULK_CONTINUATION;
+	}
+
+	return usbi_add_pollfd(HANDLE_CTX(handle), hpriv->fd, POLLOUT);
+}
+
+static void op_close(struct libusb_device_handle *dev_handle)
+{
+	int fd = _device_handle_priv(dev_handle)->fd;
+	usbi_remove_pollfd(HANDLE_CTX(dev_handle), fd);
+	close(fd);
+}
+
+static int op_get_configuration(struct libusb_device_handle *handle,
+	int *config)
+{
+	int r;
+
+	if (sysfs_can_relate_devices) {
+		r = sysfs_get_active_config(handle->dev, config);
+	} else {
+		r = usbfs_get_active_config(handle->dev,
+					    _device_handle_priv(handle)->fd);
+	}
+	if (r < 0)
+		return r;
+
+	if (*config == -1) {
+		usbi_err(HANDLE_CTX(handle), "device unconfigured");
+		*config = 0;
+	}
+
+	return 0;
+}
+
+static int op_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	struct linux_device_priv *priv = _device_priv(handle->dev);
+	int fd = _device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_SETCONFIG, &config);
+	if (r) {
+		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(HANDLE_CTX(handle), "failed, error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	/* update our cached active config descriptor */
+	priv->active_config = config;
+
+	return LIBUSB_SUCCESS;
+}
+
+static int claim_interface(struct libusb_device_handle *handle, int iface)
+{
+	int fd = _device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_CLAIMINTF, &iface);
+	if (r) {
+		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(HANDLE_CTX(handle),
+			"claim interface failed, error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return 0;
+}
+
+static int release_interface(struct libusb_device_handle *handle, int iface)
+{
+	int fd = _device_handle_priv(handle)->fd;
+	int r = ioctl(fd, IOCTL_USBFS_RELEASEINTF, &iface);
+	if (r) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"release interface failed, error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return 0;
+}
+
+static int op_set_interface(struct libusb_device_handle *handle, int iface,
+	int altsetting)
+{
+	int fd = _device_handle_priv(handle)->fd;
+	struct usbfs_setinterface setintf;
+	int r;
+
+	setintf.interface = iface;
+	setintf.altsetting = altsetting;
+	r = ioctl(fd, IOCTL_USBFS_SETINTF, &setintf);
+	if (r) {
+		if (errno == EINVAL)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"setintf failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_clear_halt(struct libusb_device_handle *handle,
+	unsigned char endpoint)
+{
+	int fd = _device_handle_priv(handle)->fd;
+	unsigned int _endpoint = endpoint;
+	int r = ioctl(fd, IOCTL_USBFS_CLEAR_HALT, &_endpoint);
+	if (r) {
+		if (errno == ENOENT)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"clear_halt failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_reset_device(struct libusb_device_handle *handle)
+{
+	int fd = _device_handle_priv(handle)->fd;
+	int i, r, ret = 0;
+
+	/* 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 & (1L << i)) {
+			release_interface(handle, i);
+		}
+	}
+
+	usbi_mutex_lock(&handle->lock);
+	r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
+	if (r) {
+		if (errno == ENODEV) {
+			ret = LIBUSB_ERROR_NOT_FOUND;
+			goto out;
+		}
+
+		usbi_err(HANDLE_CTX(handle),
+			"reset failed error %d errno %d", r, 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 & (1L << i)) {
+			/*
+			 * 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(HANDLE_CTX(handle),
+					"failed to re-claim interface %d after reset: %s",
+					i, libusb_error_name(r));
+				handle->claimed_interfaces &= ~(1L << i);
+				ret = LIBUSB_ERROR_NOT_FOUND;
+			}
+		}
+	}
+out:
+	usbi_mutex_unlock(&handle->lock);
+	return ret;
+}
+
+static int op_kernel_driver_active(struct libusb_device_handle *handle,
+	int interface)
+{
+	int fd = _device_handle_priv(handle)->fd;
+	struct usbfs_getdriver getdrv;
+	int r;
+
+	getdrv.interface = interface;
+	r = ioctl(fd, IOCTL_USBFS_GETDRIVER, &getdrv);
+	if (r) {
+		if (errno == ENODATA)
+			return 0;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle),
+			"get driver failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return (strcmp(getdrv.driver, "usbfs") == 0) ? 0 : 1;
+}
+
+static int op_detach_kernel_driver(struct libusb_device_handle *handle,
+	int interface)
+{
+	int fd = _device_handle_priv(handle)->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") == 0)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
+	if (r) {
+		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(HANDLE_CTX(handle),
+			"detach failed error %d errno %d", r, errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_attach_kernel_driver(struct libusb_device_handle *handle,
+	int interface)
+{
+	int fd = _device_handle_priv(handle)->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(HANDLE_CTX(handle),
+			"attach failed error %d errno %d", r, 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,
+	int interface)
+{
+	struct usbfs_disconnect_claim dc;
+	int r, fd = _device_handle_priv(handle)->fd;
+
+	dc.interface = interface;
+	strcpy(dc.driver, "usbfs");
+	dc.flags = USBFS_DISCONNECT_CLAIM_EXCEPT_DRIVER;
+	r = ioctl(fd, IOCTL_USBFS_DISCONNECT_CLAIM, &dc);
+	if (r == 0 || (r != 0 && errno != ENOTTY)) {
+		if (r == 0)
+			return 0;
+
+		switch (errno) {
+		case EBUSY:
+			return LIBUSB_ERROR_BUSY;
+		case EINVAL:
+			return LIBUSB_ERROR_INVALID_PARAM;
+		case ENODEV:
+			return LIBUSB_ERROR_NO_DEVICE;
+		}
+		usbi_err(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, int iface)
+{
+	if (handle->auto_detach_kernel_driver)
+		return detach_kernel_driver_and_claim(handle, iface);
+	else
+		return claim_interface(handle, iface);
+}
+
+static int op_release_interface(struct libusb_device_handle *handle, int iface)
+{
+	int r;
+
+	r = release_interface(handle, iface);
+	if (r)
+		return r;
+
+	if (handle->auto_detach_kernel_driver)
+		op_attach_kernel_driver(handle, iface);
+
+	return 0;
+}
+
+static void op_destroy_device(struct libusb_device *dev)
+{
+	struct linux_device_priv *priv = _device_priv(dev);
+	if (priv->descriptors)
+		free(priv->descriptors);
+	if (priv->sysfs_dir)
+		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 =
+		usbi_transfer_get_os_priv(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		_device_handle_priv(transfer->dev_handle);
+	int i, ret = 0;
+	struct usbfs_urb *urb;
+
+	for (i = last_plus_one - 1; i >= first; i--) {
+		if (LIBUSB_TRANSFER_TYPE_ISOCHRONOUS == transfer->type)
+			urb = tpriv->iso_urbs[i];
+		else
+			urb = &tpriv->urbs[i];
+
+		if (0 == ioctl(dpriv->fd, IOCTL_USBFS_DISCARDURB, urb))
+			continue;
+
+		if (EINVAL == errno) {
+			usbi_dbg("URB not found --> assuming ready to be reaped");
+			if (i == (last_plus_one - 1))
+				ret = LIBUSB_ERROR_NOT_FOUND;
+		} else if (ENODEV == errno) {
+			usbi_dbg("Device not found for URB --> assuming ready to be reaped");
+			ret = LIBUSB_ERROR_NO_DEVICE;
+		} else {
+			usbi_warn(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,
+	unsigned char urb_type)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		_device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb *urbs;
+	int is_out = (transfer->endpoint & LIBUSB_ENDPOINT_DIR_MASK)
+		== LIBUSB_ENDPOINT_OUT;
+	int bulk_buffer_len, use_bulk_continuation;
+	int r;
+	int i;
+	size_t alloc_size;
+
+	if (tpriv->urbs)
+		return LIBUSB_ERROR_BUSY;
+
+	if (is_out && (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET) &&
+			!(dpriv->caps & USBFS_CAP_ZERO_PACKET))
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+
+	/*
+	 * 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 arbritary 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 (dpriv->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 (dpriv->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 (dpriv->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;
+	}
+
+	int num_urbs = transfer->length / bulk_buffer_len;
+	int last_urb_partial = 0;
+
+	if (transfer->length == 0) {
+		num_urbs = 1;
+	} else if ((transfer->length % bulk_buffer_len) > 0) {
+		last_urb_partial = 1;
+		num_urbs++;
+	}
+	usbi_dbg("need %d urbs for new transfer with length %d", num_urbs,
+		transfer->length);
+	alloc_size = num_urbs * sizeof(struct usbfs_urb);
+	urbs = calloc(1, alloc_size);
+	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;
+		urb->type = urb_type;
+		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(dpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
+		if (r < 0) {
+			if (errno == ENODEV) {
+				r = LIBUSB_ERROR_NO_DEVICE;
+			} else {
+				usbi_err(TRANSFER_CTX(transfer),
+					"submiturb failed error %d errno=%d", r, 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("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 libusbx 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 = EREMOTEIO == errno ? 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 (COMPLETED_EARLY == tpriv->reap_action)
+				return 0;
+
+			discard_urbs(itransfer, 0, i);
+
+			usbi_dbg("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 = usbi_transfer_get_os_priv(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		_device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb **urbs;
+	size_t alloc_size;
+	int num_packets = transfer->num_iso_packets;
+	int i;
+	int this_urb_len = 0;
+	int num_urbs = 1;
+	int packet_offset = 0;
+	unsigned int packet_len;
+	unsigned char *urb_buffer = transfer->buffer;
+
+	if (tpriv->iso_urbs)
+		return LIBUSB_ERROR_BUSY;
+
+	/* usbfs places a 32kb limit on iso URBs. we divide up larger requests
+	 * into smaller units to meet such restriction, then fire off all the
+	 * units at once. it would be simpler if we just fired one unit at a time,
+	 * but there is a big performance gain through doing it this way.
+	 *
+	 * Newer kernels lift the 32k limit (USBFS_CAP_NO_PACKET_SIZE_LIM),
+	 * using arbritary large transfers is still be a bad idea though, as
+	 * the kernel needs to allocate physical contiguous memory for this,
+	 * which may fail for large buffers.
+	 */
+
+	/* calculate how many URBs we need */
+	for (i = 0; i < num_packets; i++) {
+		unsigned int space_remaining = MAX_ISO_BUFFER_LENGTH - this_urb_len;
+		packet_len = transfer->iso_packet_desc[i].length;
+
+		if (packet_len > space_remaining) {
+			num_urbs++;
+			this_urb_len = packet_len;
+		} else {
+			this_urb_len += packet_len;
+		}
+	}
+	usbi_dbg("need %d 32k URBs for transfer", num_urbs);
+
+	alloc_size = num_urbs * sizeof(*urbs);
+	urbs = calloc(1, alloc_size);
+	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 */
+	for (i = 0; i < num_urbs; i++) {
+		struct usbfs_urb *urb;
+		unsigned int space_remaining_in_urb = MAX_ISO_BUFFER_LENGTH;
+		int urb_packet_offset = 0;
+		unsigned char *urb_buffer_orig = urb_buffer;
+		int j;
+		int k;
+
+		/* swallow up all the packets we can fit into this URB */
+		while (packet_offset < transfer->num_iso_packets) {
+			packet_len = transfer->iso_packet_desc[packet_offset].length;
+			if (packet_len <= space_remaining_in_urb) {
+				/* throw it in */
+				urb_packet_offset++;
+				packet_offset++;
+				space_remaining_in_urb -= packet_len;
+				urb_buffer += packet_len;
+			} else {
+				/* it can't fit, save it for the next URB */
+				break;
+			}
+		}
+
+		alloc_size = sizeof(*urb)
+			+ (urb_packet_offset * sizeof(struct usbfs_iso_packet_desc));
+		urb = calloc(1, alloc_size);
+		if (!urb) {
+			free_iso_urbs(tpriv);
+			return LIBUSB_ERROR_NO_MEM;
+		}
+		urbs[i] = urb;
+
+		/* populate packet lengths */
+		for (j = 0, k = packet_offset - urb_packet_offset;
+				k < packet_offset; k++, j++) {
+			packet_len = transfer->iso_packet_desc[k].length;
+			urb->iso_frame_desc[j].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 = urb_packet_offset;
+		urb->buffer = urb_buffer_orig;
+	}
+
+	/* submit URBs */
+	for (i = 0; i < num_urbs; i++) {
+		int r = ioctl(dpriv->fd, IOCTL_USBFS_SUBMITURB, urbs[i]);
+		if (r < 0) {
+			if (errno == ENODEV) {
+				r = LIBUSB_ERROR_NO_DEVICE;
+			} else {
+				usbi_err(TRANSFER_CTX(transfer),
+					"submiturb failed error %d errno=%d", r, 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("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 libusbx 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("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 = usbi_transfer_get_os_priv(itransfer);
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_device_handle_priv *dpriv =
+		_device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb *urb;
+	int r;
+
+	if (tpriv->urbs)
+		return LIBUSB_ERROR_BUSY;
+
+	if (transfer->length - LIBUSB_CONTROL_SETUP_SIZE > MAX_CTRL_BUFFER_LENGTH)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	urb = calloc(1, sizeof(struct usbfs_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(dpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
+	if (r < 0) {
+		free(urb);
+		tpriv->urbs = NULL;
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(TRANSFER_CTX(transfer),
+			"submiturb failed error %d errno=%d", r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+	return 0;
+}
+
+static int op_submit_transfer(struct usbi_transfer *itransfer)
+{
+	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:
+		return submit_bulk_transfer(itransfer, USBFS_URB_TYPE_BULK);
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		return submit_bulk_transfer(itransfer, USBFS_URB_TYPE_INTERRUPT);
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return submit_iso_transfer(itransfer);
+	default:
+		usbi_err(TRANSFER_CTX(transfer),
+			"unknown endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+}
+
+static int op_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_priv(itransfer);
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_BULK:
+		if (tpriv->reap_action == ERROR)
+			break;
+		/* else, fall through */
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		tpriv->reap_action = CANCELLED;
+		break;
+	default:
+		usbi_err(TRANSFER_CTX(transfer),
+			"unknown endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	if (!tpriv->urbs)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	return discard_urbs(itransfer, 0, tpriv->num_urbs);
+}
+
+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 = usbi_transfer_get_os_priv(itransfer);
+
+	/* urbs can be freed also in submit_transfer so lock mutex first */
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		usbi_mutex_lock(&itransfer->lock);
+		if (tpriv->urbs)
+			free(tpriv->urbs);
+		tpriv->urbs = NULL;
+		usbi_mutex_unlock(&itransfer->lock);
+		break;
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		usbi_mutex_lock(&itransfer->lock);
+		if (tpriv->iso_urbs)
+			free_iso_urbs(tpriv);
+		usbi_mutex_unlock(&itransfer->lock);
+		break;
+	default:
+		usbi_err(TRANSFER_CTX(transfer),
+			"unknown endpoint type %d", transfer->type);
+	}
+}
+
+static int handle_bulk_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct linux_transfer_priv *tpriv = usbi_transfer_get_os_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("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("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 libusbx 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("received %d bytes of surplus data", urb->actual_length);
+			if (urb->buffer != target) {
+				usbi_dbg("moving surplus data from offset %d to offset %d",
+					(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("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("device removed");
+		tpriv->reap_status = LIBUSB_TRANSFER_NO_DEVICE;
+		goto cancel_remaining;
+	case -EPIPE:
+		usbi_dbg("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("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("low level error %d", urb->status);
+		tpriv->reap_action = ERROR;
+		goto cancel_remaining;
+	default:
+		usbi_warn(ITRANSFER_CTX(itransfer),
+			"unrecognised urb status %d", urb->status);
+		tpriv->reap_action = ERROR;
+		goto cancel_remaining;
+	}
+
+	/* if we're the last urb or we got less data than requested then we're
+	 * done */
+	if (urb_idx == tpriv->num_urbs - 1) {
+		usbi_dbg("last URB in transfer --> complete!");
+		goto completed;
+	} else if (urb->actual_length < urb->buffer_length) {
+		usbi_dbg("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 (ERROR == tpriv->reap_action && LIBUSB_TRANSFER_COMPLETED == tpriv->reap_status)
+		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 CANCELLED == tpriv->reap_action ?
+		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 = usbi_transfer_get_os_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(TRANSFER_CTX(transfer), "could not locate urb!");
+		usbi_mutex_unlock(&itransfer->lock);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg("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++];
+		lib_desc->status = LIBUSB_TRANSFER_COMPLETED;
+		switch (urb_desc->status) {
+		case 0:
+			break;
+		case -ENOENT: /* cancelled */
+		case -ECONNRESET:
+			break;
+		case -ENODEV:
+		case -ESHUTDOWN:
+			usbi_dbg("device removed");
+			lib_desc->status = LIBUSB_TRANSFER_NO_DEVICE;
+			break;
+		case -EPIPE:
+			usbi_dbg("detected endpoint stall");
+			lib_desc->status = LIBUSB_TRANSFER_STALL;
+			break;
+		case -EOVERFLOW:
+			usbi_dbg("overflow error");
+			lib_desc->status = LIBUSB_TRANSFER_OVERFLOW;
+			break;
+		case -ETIME:
+		case -EPROTO:
+		case -EILSEQ:
+		case -ECOMM:
+		case -ENOSR:
+		case -EXDEV:
+			usbi_dbg("low-level USB error %d", urb_desc->status);
+			lib_desc->status = LIBUSB_TRANSFER_ERROR;
+			break;
+		default:
+			usbi_warn(TRANSFER_CTX(transfer),
+				"unrecognised urb status %d", urb_desc->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("CANCEL: urb status %d", urb->status);
+
+		if (tpriv->num_retired == num_urbs) {
+			usbi_dbg("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("device removed");
+		status = LIBUSB_TRANSFER_NO_DEVICE;
+		break;
+	default:
+		usbi_warn(TRANSFER_CTX(transfer),
+			"unrecognised urb status %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	}
+
+	/* if we're the last urb then we're done */
+	if (urb_idx == num_urbs) {
+		usbi_dbg("last URB in transfer --> 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 = usbi_transfer_get_os_priv(itransfer);
+	int status;
+
+	usbi_mutex_lock(&itransfer->lock);
+	usbi_dbg("handling completion status %d", urb->status);
+
+	itransfer->transferred += urb->actual_length;
+
+	if (tpriv->reap_action == CANCELLED) {
+		if (urb->status != 0 && urb->status != -ENOENT)
+			usbi_warn(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("device removed");
+		status = LIBUSB_TRANSFER_NO_DEVICE;
+		break;
+	case -EPIPE:
+		usbi_dbg("unsupported control request");
+		status = LIBUSB_TRANSFER_STALL;
+		break;
+	case -EOVERFLOW:
+		usbi_dbg("control overflow error");
+		status = LIBUSB_TRANSFER_OVERFLOW;
+		break;
+	case -ETIME:
+	case -EPROTO:
+	case -EILSEQ:
+	case -ECOMM:
+	case -ENOSR:
+		usbi_dbg("low-level bus error occurred");
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	default:
+		usbi_warn(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, status);
+}
+
+static int reap_for_handle(struct libusb_device_handle *handle)
+{
+	struct linux_device_handle_priv *hpriv = _device_handle_priv(handle);
+	int r;
+	struct usbfs_urb *urb;
+	struct usbi_transfer *itransfer;
+	struct libusb_transfer *transfer;
+
+	r = ioctl(hpriv->fd, IOCTL_USBFS_REAPURBNDELAY, &urb);
+	if (r == -1 && errno == EAGAIN)
+		return 1;
+	if (r < 0) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "reap failed error %d errno=%d",
+			r, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	itransfer = urb->usercontext;
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	usbi_dbg("urb type=%d 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_INTERRUPT:
+		return handle_bulk_completion(itransfer, urb);
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return handle_control_completion(itransfer, urb);
+	default:
+		usbi_err(HANDLE_CTX(handle), "unrecognised endpoint type %x",
+			transfer->type);
+		return LIBUSB_ERROR_OTHER;
+	}
+}
+
+static int op_handle_events(struct libusb_context *ctx,
+	struct pollfd *fds, POLL_NFDS_TYPE nfds, int num_ready)
+{
+	int r;
+	unsigned int i = 0;
+
+	usbi_mutex_lock(&ctx->open_devs_lock);
+	for (i = 0; i < nfds && num_ready > 0; i++) {
+		struct pollfd *pollfd = &fds[i];
+		struct libusb_device_handle *handle;
+		struct linux_device_handle_priv *hpriv = NULL;
+
+		if (!pollfd->revents)
+			continue;
+
+		num_ready--;
+		list_for_each_entry(handle, &ctx->open_devs, list, struct libusb_device_handle) {
+			hpriv = _device_handle_priv(handle);
+			if (hpriv->fd == pollfd->fd)
+				break;
+		}
+
+		if (pollfd->revents & POLLERR) {
+			usbi_remove_pollfd(HANDLE_CTX(handle), hpriv->fd);
+			usbi_handle_disconnect(handle);
+			/* 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 (handle->dev->attached)
+				linux_device_disconnected(handle->dev->bus_number,
+						handle->dev->device_address, NULL);
+			usbi_mutex_static_unlock(&linux_hotplug_lock);
+			continue;
+		}
+
+		do {
+			r = reap_for_handle(handle);
+		} while (r == 0);
+		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;
+}
+
+static int op_clock_gettime(int clk_id, struct timespec *tp)
+{
+	switch (clk_id) {
+	case USBI_CLOCK_MONOTONIC:
+		return clock_gettime(monotonic_clkid, tp);
+	case USBI_CLOCK_REALTIME:
+		return clock_gettime(CLOCK_REALTIME, tp);
+	default:
+		return LIBUSB_ERROR_INVALID_PARAM;
+  }
+}
+
+#ifdef USBI_TIMERFD_AVAILABLE
+static clockid_t op_get_timerfd_clockid(void)
+{
+	return monotonic_clkid;
+
+}
+#endif
+
+const struct usbi_os_backend linux_usbfs_backend = {
+	.name = "Linux usbfs",
+	.caps = USBI_CAP_HAS_HID_ACCESS|USBI_CAP_SUPPORTS_DETACH_KERNEL_DRIVER,
+	.init = op_init,
+	.exit = op_exit,
+	.get_device_list = NULL,
+	.hotplug_poll = op_hotplug_poll,
+	.get_device_descriptor = op_get_device_descriptor,
+	.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,
+
+	.open = op_open,
+	.close = op_close,
+	.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,
+
+	.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,
+
+	.clock_gettime = op_clock_gettime,
+
+#ifdef USBI_TIMERFD_AVAILABLE
+	.get_timerfd_clockid = op_get_timerfd_clockid,
+#endif
+
+	.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),
+	.add_iso_packet_size = 0,
+};