Recommit: Update libusb 1.0.9 to libusbx 1.0.16

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

Index: third_party/libusb/src/libusb/os/linux_usbfs.c
diff --git a/third_party/libusb/src/libusb/os/linux_usbfs.c b/third_party/libusb/src/libusb/os/linux_usbfs.c
index 02d182d65aa751ee55d9886a77c0f177a2e94709..09288af719cf694fadcf263f28760bcb1f032ac9 100644
--- a/third_party/libusb/src/libusb/os/linux_usbfs.c
+++ b/third_party/libusb/src/libusb/os/linux_usbfs.c
@@ -1,7 +1,9 @@
 /*
- * Linux usbfs backend for libusb
- * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
- * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ * 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
@@ -18,7 +20,9 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#include <config.h>
+#include "config.h"
+
+#include <assert.h>
 #include <ctype.h>
 #include <dirent.h>
 #include <errno.h>
@@ -43,23 +47,23 @@
  *
  * 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 was added in 2.6.23.
- *  - The "busnum" file was added in 2.6.22
+ *  - 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.
- * We assume this is the case if we see the busnum file (indicates 2.6.22+).
  * The busnum file is important as that is the only way we can relate sysfs
  * devices to usbfs nodes.
  *
- * If we also have descriptors, we can obtain the device descriptor and active 
+ * If we also have all descriptors, we can obtain the device descriptor and
  * configuration without touching usbfs at all.
- *
- * The descriptors file originally only contained the active configuration
- * descriptor alongside the device descriptor, but all configurations are
- * included as of Linux 2.6.26.
  */
 
 /* endianness for multi-byte fields:
@@ -67,6 +71,8 @@
  * 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;
@@ -101,21 +107,42 @@ static int supports_flag_zero_packet = -1;
  * systems. appropriate choice made at initialization time. */
 static clockid_t monotonic_clkid = -1;
 
-/* do we have a busnum to relate devices? this also implies that we can read
+/* 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 = 0;
+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, scan-devices, event-thread, and poll */
+usbi_mutex_static_t linux_hotplug_lock = USBI_MUTEX_INITIALIZER;
 
-/* do we have a descriptors file? */
-static int sysfs_has_descriptors = 0;
+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 *dev_descriptor;
-	unsigned char *config_descriptor;
+	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 {
@@ -142,21 +169,43 @@ struct linux_transfer_priv {
 
 	enum reap_action reap_action;
 	int num_urbs;
-	unsigned int num_retired;
+	int num_retired;
 	enum libusb_transfer_status reap_status;
 
 	/* next iso packet in user-supplied transfer to be populated */
 	int iso_packet_offset;
 };
 
-static void _get_usbfs_path(struct libusb_device *dev, char *path)
+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)
@@ -299,22 +348,6 @@ static int kernel_version_ge(int major, int minor, int sublevel)
 	return ksublevel >= sublevel;
 }
 
-/* Return 1 if filename exists inside dirname in sysfs.
-   SYSFS_DEVICE_PATH is assumed to be the beginning of the path. */
-static int sysfs_has_file(const char *dirname, const char *filename)
-{
-	struct stat statbuf;
-	char path[PATH_MAX];
-	int r;
-
-	snprintf(path, PATH_MAX, "%s/%s/%s", SYSFS_DEVICE_PATH, dirname, filename);
-	r = stat(path, &statbuf);
-	if (r == 0 && S_ISREG(statbuf.st_mode))
-		return 1;
-
-	return 0;
-}
-
 static int op_init(struct libusb_context *ctx)
 {
 	struct stat statbuf;
@@ -353,79 +386,103 @@ static int op_init(struct libusb_context *ctx)
 	if (supports_flag_zero_packet)
 		usbi_dbg("zero length packet flag supported");
 
-	r = stat(SYSFS_DEVICE_PATH, &statbuf);
-	if (r == 0 && S_ISDIR(statbuf.st_mode)) {
-		DIR *devices = opendir(SYSFS_DEVICE_PATH);
-		struct dirent *entry;
-
-		usbi_dbg("found usb devices in sysfs");
+	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 (!devices) {
-			usbi_err(ctx, "opendir devices failed errno=%d", errno);
-			return LIBUSB_ERROR_IO;
+	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;
 		}
+	}
 
-		/* Make sure sysfs supports all the required files. If it
-		 * does not, then usbfs will be used instead.  Determine
-		 * this by looping through the directories in
-		 * SYSFS_DEVICE_PATH.  With the assumption that there will
-		 * always be subdirectories of the name usbN (usb1, usb2,
-		 * etc) representing the root hubs, check the usbN
-		 * subdirectories to see if they have all the needed files.
-		 * This algorithm uses the usbN subdirectories (root hubs)
-		 * because a device disconnection will cause a race
-		 * condition regarding which files are available, sometimes
-		 * causing an incorrect result.  The root hubs are used
-		 * because it is assumed that they will always be present.
-		 * See the "sysfs vs usbfs" comment at the top of this file
-		 * for more details.  */
-		while ((entry = readdir(devices))) {
-			int has_busnum=0, has_devnum=0, has_descriptors=0;
-			int has_configuration_value=0;
-
-			/* Only check the usbN directories. */
-			if (strncmp(entry->d_name, "usb", 3) != 0)
-				continue;
+	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;
+		}
+	}
 
-			/* Check for the files libusb needs from sysfs. */
-			has_busnum = sysfs_has_file(entry->d_name, "busnum");
-			has_devnum = sysfs_has_file(entry->d_name, "devnum");
-			has_descriptors = sysfs_has_file(entry->d_name, "descriptors");
-			has_configuration_value = sysfs_has_file(entry->d_name, "bConfigurationValue");
+	if (sysfs_can_relate_devices)
+		usbi_dbg("sysfs can relate devices");
 
-			if (has_busnum && has_devnum && has_configuration_value)
-				sysfs_can_relate_devices = 1;
-			if (has_descriptors)
-				sysfs_has_descriptors = 1;
+	if (sysfs_has_descriptors)
+		usbi_dbg("sysfs has complete descriptors");
+
+	usbi_mutex_static_lock(&linux_hotplug_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_lock);
 
-			/* Only need to check until we've found ONE device which
-			   has all the attributes. */
-			if (sysfs_has_descriptors && sysfs_can_relate_devices)
-				break;
-		}
-		closedir(devices);
+	return r;
+}
 
-		/* Only use sysfs descriptors if the rest of
-		   sysfs will work for libusb. */
-		if (!sysfs_can_relate_devices)
-			sysfs_has_descriptors = 0;
-	} else {
-		usbi_dbg("sysfs usb info not available");
-		sysfs_has_descriptors = 0;
-		sysfs_can_relate_devices = 0;
+static void op_exit(void)
+{
+	usbi_mutex_static_lock(&linux_hotplug_lock);
+	assert(init_count != 0);
+	if (!--init_count) {
+		/* tear down event handler */
+		(void)linux_stop_event_monitor();
 	}
+	usbi_mutex_static_unlock(&linux_hotplug_lock);
+}
 
-	return 0;
+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 usbfs_get_device_descriptor(struct libusb_device *dev,
-	unsigned char *buffer)
+static int linux_stop_event_monitor(void)
 {
-	struct linux_device_priv *priv = _device_priv(dev);
+#if defined(USE_UDEV)
+	return linux_udev_stop_event_monitor();
+#else
+	return linux_netlink_stop_event_monitor();
+#endif
+}
 
-	/* return cached copy */
-	memcpy(buffer, priv->dev_descriptor, DEVICE_DESC_LENGTH);
-	return 0;
+static int linux_scan_devices(struct libusb_context *ctx)
+{
+#if defined(USE_UDEV)
+	return linux_udev_scan_devices(ctx);
+#else
+	return linux_default_scan_devices(ctx);
+#endif
+}
+
+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)
@@ -481,52 +538,14 @@ static int __read_sysfs_attr(struct libusb_context *ctx,
 	return value;
 }
 
-static int sysfs_get_device_descriptor(struct libusb_device *dev,
-	unsigned char *buffer)
-{
-	int fd;
-	ssize_t r;
-
-	/* sysfs provides access to an in-memory copy of the device descriptor,
-	 * so we use that rather than keeping our own copy */
-
-	fd = _open_sysfs_attr(dev, "descriptors");
-	if (fd < 0)
-		return fd;
-
-	r = read(fd, buffer, DEVICE_DESC_LENGTH);;
-	close(fd);
-	if (r < 0) {
-		usbi_err(DEVICE_CTX(dev), "read failed, ret=%d errno=%d", fd, errno);
-		return LIBUSB_ERROR_IO;
-	} else if (r < DEVICE_DESC_LENGTH) {
-		usbi_err(DEVICE_CTX(dev), "short read %d/%d", r, DEVICE_DESC_LENGTH);
-		return LIBUSB_ERROR_IO;
-	}
-
-	return 0;
-}
-
 static int op_get_device_descriptor(struct libusb_device *dev,
 	unsigned char *buffer, int *host_endian)
 {
-	if (sysfs_has_descriptors) {
-		return sysfs_get_device_descriptor(dev, buffer);
-	} else {
-		*host_endian = 1;
-		return usbfs_get_device_descriptor(dev, buffer);
-	}
-}
-
-static int usbfs_get_active_config_descriptor(struct libusb_device *dev,
-	unsigned char *buffer, size_t len)
-{
 	struct linux_device_priv *priv = _device_priv(dev);
-	if (!priv->config_descriptor)
-		return LIBUSB_ERROR_NOT_FOUND; /* device is unconfigured */
 
-	/* retrieve cached copy */
-	memcpy(buffer, priv->config_descriptor, len);
+	*host_endian = sysfs_has_descriptors ? 0 : 1;
+	memcpy(buffer, priv->descriptors, DEVICE_DESC_LENGTH);
+
 	return 0;
 }
 
@@ -573,250 +592,213 @@ static int sysfs_get_active_config(struct libusb_device *dev, int *config)
 	return 0;
 }
 
-/* takes a usbfs/descriptors fd seeked to the start of a configuration, and
- * seeks to the next one. */
-static int seek_to_next_config(struct libusb_context *ctx, int fd,
-	int host_endian)
+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)
 {
-	struct libusb_config_descriptor config;
-	unsigned char tmp[6];
-	off_t off;
-	ssize_t r;
+	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;
+		}
 
-	/* read first 6 bytes of descriptor */
-	r = read(fd, tmp, sizeof(tmp));
-	if (r < 0) {
-		usbi_err(ctx, "read failed ret=%d errno=%d", r, errno);
-		return LIBUSB_ERROR_IO;
-	} else if (r < sizeof(tmp)) {
-		usbi_err(ctx, "short descriptor read %d/%d", r, sizeof(tmp));
-		return LIBUSB_ERROR_IO;
-	}
+		/* 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);
+		}
 
-	/* seek forward to end of config */
-	usbi_parse_descriptor(tmp, "bbwbb", &config, host_endian);
-	off = lseek(fd, config.wTotalLength - sizeof(tmp), SEEK_CUR);
-	if (off < 0) {
-		usbi_err(ctx, "seek failed ret=%d errno=%d", off, errno);
-		return LIBUSB_ERROR_IO;
+		return LIBUSB_SUCCESS;
 	}
 
-	return 0;
+	usbi_dbg("scan %s", sys_name);
+
+	*busnum = __read_sysfs_attr(ctx, sys_name, "busnum");
+	if (0 > *busnum)
+		return *busnum;
+
+	*devaddr = __read_sysfs_attr(ctx, sys_name, "devnum");
+	if (0 > *devaddr)
+		return *devaddr;
+
+	usbi_dbg("bus=%d dev=%d", *busnum, *devaddr);
+	if (*busnum > 255 || *devaddr > 255)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	return LIBUSB_SUCCESS;
 }
 
-static int sysfs_get_active_config_descriptor(struct libusb_device *dev,
-	unsigned char *buffer, size_t len)
+/* 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)
 {
-	int fd;
-	ssize_t r;
-	off_t off;
-	int to_copy;
-	int config;
-	unsigned char tmp[6];
+	struct usb_descriptor_header header;
+	int i;
 
-	r = sysfs_get_active_config(dev, &config);
-	if (r < 0)
-		return r;
-	if (config == -1)
-		return LIBUSB_ERROR_NOT_FOUND;
+	for (i = 0; size >= 0; i += header.bLength, size -= header.bLength) {
+		if (size == 0)
+			return LIBUSB_ERROR_NOT_FOUND;
 
-	usbi_dbg("active configuration %d", config);
+		if (size < 2) {
+			usbi_err(ctx, "short descriptor read %d/2", size);
+			return LIBUSB_ERROR_IO;
+		}
+		usbi_parse_descriptor(buffer + i, "bb", &header, 0);
 
-	/* sysfs provides access to an in-memory copy of the device descriptor,
-	 * so we use that rather than keeping our own copy */
+		if (i && header.bDescriptorType == descriptor_type)
+			return i;
+	}
+	usbi_err(ctx, "bLength overflow by %d bytes", -size);
+	return LIBUSB_ERROR_IO;
+}
 
-	fd = _open_sysfs_attr(dev, "descriptors");
-	if (fd < 0)
-		return fd;
+/* 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;
 
-	/* device might have been unconfigured since we read bConfigurationValue,
-	 * so first check that there is any config descriptor data at all... */
-	off = lseek(fd, 0, SEEK_END);
-	if (off < 1) {
-		usbi_err(DEVICE_CTX(dev), "end seek failed, ret=%d errno=%d",
-			off, errno);
-		close(fd);
-		return LIBUSB_ERROR_IO;
-	} else if (off == DEVICE_DESC_LENGTH) {
-		close(fd);
+	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;
 	}
 
-	off = lseek(fd, DEVICE_DESC_LENGTH, SEEK_SET);
-	if (off < 0) {
-		usbi_err(DEVICE_CTX(dev), "seek failed, ret=%d errno=%d", off, errno);
-		close(fd);
+	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;
 	}
 
-	/* unbounded loop: we expect the descriptor to be present under all
-	 * circumstances */
-	while (1) {
-		r = read(fd, tmp, sizeof(tmp));
-		if (r < 0) {
-			usbi_err(DEVICE_CTX(dev), "read failed, ret=%d errno=%d",
-				fd, errno);
-			return LIBUSB_ERROR_IO;
-		} else if (r < sizeof(tmp)) {
-			usbi_err(DEVICE_CTX(dev), "short read %d/%d", r, sizeof(tmp));
+	/*
+	 * 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;
+	}
+}
 
-		/* check bConfigurationValue */
-		if (tmp[5] == config)
-			break;
+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;
 
-		/* try the next descriptor */
-		off = lseek(fd, 0 - sizeof(tmp), SEEK_CUR);
-		if (off < 0)
-			return LIBUSB_ERROR_IO;
+	*buffer = NULL;
+	/* Unlike the device desc. config descs. are always in raw format */
+	*host_endian = 0;
 
-		r = seek_to_next_config(DEVICE_CTX(dev), fd, 0);
-		if (r < 0)
-			return r;
-	}
+	/* Skip device header */
+	descriptors += DEVICE_DESC_LENGTH;
+	size -= DEVICE_DESC_LENGTH;
 
-	to_copy = (len < sizeof(tmp)) ? len : sizeof(tmp);
-	memcpy(buffer, tmp, to_copy);
-	if (len > sizeof(tmp)) {
-		r = read(fd, buffer + sizeof(tmp), len - sizeof(tmp));
-		if (r < 0) {
-			usbi_err(DEVICE_CTX(dev), "read failed, ret=%d errno=%d",
-				fd, errno);
-			r = LIBUSB_ERROR_IO;
-		} else if (r == 0) {
-			usbi_dbg("device is unconfigured");
-			r = LIBUSB_ERROR_NOT_FOUND;
-		} else if (r < len - sizeof(tmp)) {
-			usbi_err(DEVICE_CTX(dev), "short read %d/%d", r, len);
-			r = LIBUSB_ERROR_IO;
+	/* 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;
 		}
-	} else {
-		r = 0;
+		size -= next;
+		descriptors += next;
 	}
-
-	close(fd);
-	return r;
 }
 
 static int op_get_active_config_descriptor(struct libusb_device *dev,
 	unsigned char *buffer, size_t len, int *host_endian)
 {
-	if (sysfs_has_descriptors) {
-		return sysfs_get_active_config_descriptor(dev, buffer, len);
-	} else {
-		return usbfs_get_active_config_descriptor(dev, buffer, len);
-	}
-}
-
-/* takes a usbfs fd, attempts to find the requested config and copy a certain
- * amount of it into an output buffer. */
-static int get_config_descriptor(struct libusb_context *ctx, int fd,
-	uint8_t config_index, unsigned char *buffer, size_t len)
-{
-	off_t off;
-	ssize_t r;
+	int r, config;
+	unsigned char *config_desc;
 
-	off = lseek(fd, DEVICE_DESC_LENGTH, SEEK_SET);
-	if (off < 0) {
-		usbi_err(ctx, "seek failed ret=%d errno=%d", off, errno);
-		return LIBUSB_ERROR_IO;
-	}
-
-	/* might need to skip some configuration descriptors to reach the
-	 * requested configuration */
-	while (config_index > 0) {
-		r = seek_to_next_config(ctx, fd, 1);
+	if (sysfs_can_relate_devices) {
+		r = sysfs_get_active_config(dev, &config);
 		if (r < 0)
 			return r;
-		config_index--;
+	} else {
+		/* Use cached bConfigurationValue */
+		struct linux_device_priv *priv = _device_priv(dev);
+		config = priv->active_config;
 	}
+	if (config == -1)
+		return LIBUSB_ERROR_NOT_FOUND;
 
-	/* read the rest of the descriptor */
-	r = read(fd, buffer, len);
-	if (r < 0) {
-		usbi_err(ctx, "read failed ret=%d errno=%d", r, errno);
-		return LIBUSB_ERROR_IO;
-	} else if (r < len) {
-		usbi_err(ctx, "short output read %d/%d", r, len);
-		return LIBUSB_ERROR_IO;
-	}
+	r = op_get_config_descriptor_by_value(dev, config, &config_desc,
+					      host_endian);
+	if (r < 0)
+		return r;
 
-	return 0;
+	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)
 {
-	char filename[PATH_MAX];
-	int fd;
-	int r;
-
-	/* always read from usbfs: sysfs only has the active descriptor
-	 * this will involve waking the device up, but oh well! */
-
-	/* FIXME: the above is no longer true, new kernels have all descriptors
-	 * in the descriptors file. but its kinda hard to detect if the kernel
-	 * is sufficiently new. */
-
-	_get_usbfs_path(dev, filename);
-	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;
-	}
+	struct linux_device_priv *priv = _device_priv(dev);
+	unsigned char *descriptors = priv->descriptors;
+	int i, r, size = priv->descriptors_len;
 
-	r = get_config_descriptor(DEVICE_CTX(dev), fd, config_index, buffer, len);
-	close(fd);
-	return r;
-}
+	/* Unlike the device desc. config descs. are always in raw format */
+	*host_endian = 0;
 
-/* cache the active config descriptor in memory. a value of -1 means that
- * we aren't sure which one is active, so just assume the first one. 
- * only for usbfs. */
-static int cache_active_config(struct libusb_device *dev, int fd,
-	int active_config)
-{
-	struct linux_device_priv *priv = _device_priv(dev);
-	struct libusb_config_descriptor config;
-	unsigned char tmp[8];
-	unsigned char *buf;
-	int idx;
-	int r;
+	/* Skip device header */
+	descriptors += DEVICE_DESC_LENGTH;
+	size -= DEVICE_DESC_LENGTH;
 
-	if (active_config == -1) {
-		idx = 0;
-	} else {
-		r = usbi_get_config_index_by_value(dev, active_config, &idx);
+	/* 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 (idx == -1)
-			return LIBUSB_ERROR_NOT_FOUND;
-	}
-
-	r = get_config_descriptor(DEVICE_CTX(dev), fd, idx, tmp, sizeof(tmp));
-	if (r < 0) {
-		usbi_err(DEVICE_CTX(dev), "first read error %d", r);
-		return r;
-	}
-
-	usbi_parse_descriptor(tmp, "bbw", &config, 0);
-	buf = malloc(config.wTotalLength);
-	if (!buf)
-		return LIBUSB_ERROR_NO_MEM;
-
-	r = get_config_descriptor(DEVICE_CTX(dev), fd, idx, buf,
-		config.wTotalLength);
-	if (r < 0) {
-		free(buf);
-		return r;
+		if (i == config_index)
+			break;
+		size -= r;
+		descriptors += r;
 	}
 
-	if (priv->config_descriptor)
-		free(priv->config_descriptor);
-	priv->config_descriptor = buf;
-	return 0;
+	len = MIN(len, r);
+	memcpy(buffer, descriptors, len);
+	return len;
 }
 
 /* send a control message to retrieve active configuration */
@@ -853,11 +835,9 @@ 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);
-	unsigned char *dev_buf;
-	char path[PATH_MAX];
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	int descriptors_size = 512; /* Begin with a 1024 byte alloc */
 	int fd, speed;
-	int active_config = 0;
-	int device_configured = 1;
 	ssize_t r;
 
 	dev->bus_number = busnum;
@@ -884,113 +864,162 @@ static int initialize_device(struct libusb_device *dev, uint8_t busnum,
 		}
 	}
 
+	/* cache descriptors in memory */
 	if (sysfs_has_descriptors)
-		return 0;
-
-	/* cache device descriptor in memory so that we can retrieve it later
-	 * without waking the device up (op_get_device_descriptor) */
+		fd = _open_sysfs_attr(dev, "descriptors");
+	else
+		fd = _get_usbfs_fd(dev, O_RDONLY, 0);
+	if (fd < 0)
+		return fd;
 
-	priv->dev_descriptor = NULL;
-	priv->config_descriptor = NULL;
+	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 (sysfs_can_relate_devices) {
-		int tmp = sysfs_get_active_config(dev, &active_config);
-		if (tmp < 0)
-			return tmp;
-		if (active_config == -1)
-			device_configured = 0;
+	if (priv->descriptors_len < DEVICE_DESC_LENGTH) {
+		usbi_err(ctx, "short descriptor read (%d)",
+			 priv->descriptors_len);
+		return LIBUSB_ERROR_IO;
 	}
 
-	_get_usbfs_path(dev, path);
-	fd = open(path, O_RDWR);
-	if (fd < 0 && errno == EACCES) {
-		fd = open(path, O_RDONLY);
-		/* if we only have read-only access to the device, we cannot
-		 * send a control message to determine the active config. just
-		 * assume the first one is active. */
-		active_config = -1;
-	}
+	if (sysfs_can_relate_devices)
+		return LIBUSB_SUCCESS;
 
+	/* cache active config */
+	fd = _get_usbfs_fd(dev, O_RDWR, 1);
 	if (fd < 0) {
-		usbi_err(DEVICE_CTX(dev), "open failed, ret=%d errno=%d", fd, errno);
-		return LIBUSB_ERROR_IO;
-	}
+		/* 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 */
 
-	if (!sysfs_can_relate_devices) {
-		if (active_config == -1) {
-			/* if we only have read-only access to the device, we cannot
-			 * send a control message to determine the active config. just
-			 * assume the first one is active. */
-			usbi_warn(DEVICE_CTX(dev), "access to %s is read-only; cannot "
-				"determine active configuration descriptor", path);
-		} else {
-			active_config = usbfs_get_active_config(dev, fd);
-			if (active_config == LIBUSB_ERROR_IO) {
-				/* buggy devices sometimes fail to report their active config.
-				 * assume unconfigured and continue the probing */
-				usbi_warn(DEVICE_CTX(dev), "couldn't query active "
-					"configuration, assumung unconfigured");
-				device_configured = 0;
-			} else if (active_config < 0) {
-				close(fd);
-				return active_config;
-			} else if (active_config == 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");
-				device_configured = 0;
-			}
+	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;
 		}
 	}
 
-	dev_buf = malloc(DEVICE_DESC_LENGTH);
-	if (!dev_buf) {
-		close(fd);
-		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);
 
-	r = read(fd, dev_buf, DEVICE_DESC_LENGTH);
-	if (r < 0) {
-		usbi_err(DEVICE_CTX(dev),
-			"read descriptor failed ret=%d errno=%d", fd, errno);
-		free(dev_buf);
-		close(fd);
-		return LIBUSB_ERROR_IO;
-	} else if (r < DEVICE_DESC_LENGTH) {
-		usbi_err(DEVICE_CTX(dev), "short descriptor read (%d)", r);
-		free(dev_buf);
-		close(fd);
-		return LIBUSB_ERROR_IO;
+	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;
 	}
 
-	/* bit of a hack: set num_configurations now because cache_active_config()
-	 * calls usbi_get_config_index_by_value() which uses it */
-	dev->num_configurations = dev_buf[DEVICE_DESC_LENGTH - 1];
+	usbi_dbg("Dev %p (%s) has parent %p (%s) port %d", dev, sysfs_dir,
+		 dev->parent_dev, parent_sysfs_dir, dev->port_number);
 
-	if (device_configured) {
-		r = cache_active_config(dev, fd, active_config);
-		if (r < 0) {
-			close(fd);
-			free(dev_buf);
-			return r;
-		}
-	}
+	free (parent_sysfs_dir);
 
-	close(fd);
-	priv->dev_descriptor = dev_buf;
-	return 0;
+	return LIBUSB_SUCCESS;
 }
 
-static int enumerate_device(struct libusb_context *ctx,
-	struct discovered_devs **_discdevs, uint8_t busnum, uint8_t devaddr,
-	const char *sysfs_dir)
+int linux_enumerate_device(struct libusb_context *ctx,
+	uint8_t busnum, uint8_t devaddr, const char *sysfs_dir)
 {
-	struct discovered_devs *discdevs;
 	unsigned long session_id;
-	int need_unref = 0;
 	struct libusb_device *dev;
 	int r = 0;
 
@@ -1001,48 +1030,73 @@ static int enumerate_device(struct libusb_context *ctx,
 	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) {
-		usbi_dbg("using existing device for %d/%d (session %ld)",
-			busnum, devaddr, session_id);
-	} else {
-		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;
-		need_unref = 1;
-		r = initialize_device(dev, busnum, devaddr, sysfs_dir);
-		if (r < 0)
-			goto out;
-		r = usbi_sanitize_device(dev);
-		if (r < 0)
-			goto out;
+	if (usbi_get_device_by_session_id(ctx, session_id)) {
+		/* device already exists in the context */
+		usbi_dbg("session_id %ld already exists", session_id);
+		return LIBUSB_SUCCESS;
 	}
 
-	discdevs = discovered_devs_append(*_discdevs, dev);
-	if (!discdevs)
-		r = LIBUSB_ERROR_NO_MEM;
-	else
-		*_discdevs = discdevs;
+	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 (need_unref)
+	if (r < 0)
 		libusb_unref_device(dev);
+	else
+		usbi_connect_device(dev);
+
 	return r;
 }
 
-/* open a bus directory and adds all discovered devices to discdevs. on
- * failure (non-zero return) the pre-existing discdevs should be destroyed
- * (and devices freed). on success, the new discdevs pointer should be used
- * as it may have been moved. */
-static int usbfs_scan_busdir(struct libusb_context *ctx,
-	struct discovered_devs **_discdevs, uint8_t busnum)
+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_hotplug_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);
+		} 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;
-	struct discovered_devs *discdevs = *_discdevs;
 	int r = LIBUSB_ERROR_IO;
 
 	snprintf(dirpath, PATH_MAX, "%s/%03d", usbfs_path, busnum);
@@ -1067,7 +1121,7 @@ static int usbfs_scan_busdir(struct libusb_context *ctx,
 			continue;
 		}
 
-		if (enumerate_device(ctx, &discdevs, busnum, (uint8_t) devaddr, NULL)) {
+		if (linux_enumerate_device(ctx, busnum, (uint8_t) devaddr, NULL)) {
 			usbi_dbg("failed to enumerate dir entry %s", entry->d_name);
 			continue;
 		}
@@ -1075,18 +1129,14 @@ static int usbfs_scan_busdir(struct libusb_context *ctx,
 		r = 0;
 	}
 
-	if (!r)
-		*_discdevs = discdevs;
 	closedir(dir);
 	return r;
 }
 
-static int usbfs_get_device_list(struct libusb_context *ctx,
-	struct discovered_devs **_discdevs)
+static int usbfs_get_device_list(struct libusb_context *ctx)
 {
 	struct dirent *entry;
 	DIR *buses = opendir(usbfs_path);
-	struct discovered_devs *discdevs = *_discdevs;
 	int r = 0;
 
 	if (!buses) {
@@ -1095,7 +1145,6 @@ static int usbfs_get_device_list(struct libusb_context *ctx,
 	}
 
 	while ((entry = readdir(buses))) {
-		struct discovered_devs *discdevs_new = discdevs;
 		int busnum;
 
 		if (entry->d_name[0] == '.')
@@ -1106,8 +1155,7 @@ static int usbfs_get_device_list(struct libusb_context *ctx,
 			if (!_is_usbdev_entry(entry, &busnum, &devaddr))
 				continue;
 
-			r = enumerate_device(ctx, &discdevs_new, busnum,
-				(uint8_t) devaddr, NULL);
+			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;
@@ -1119,48 +1167,35 @@ static int usbfs_get_device_list(struct libusb_context *ctx,
 				continue;
 			}
 
-			r = usbfs_scan_busdir(ctx, &discdevs_new, busnum);
+			r = usbfs_scan_busdir(ctx, busnum);
 			if (r < 0)
-				goto out;
+				break;
 		}
-		discdevs = discdevs_new;
 	}
 
-out:
 	closedir(buses);
-	*_discdevs = discdevs;
 	return r;
 
 }
+#endif
 
-static int sysfs_scan_device(struct libusb_context *ctx,
-	struct discovered_devs **_discdevs, const char *devname)
+static int sysfs_scan_device(struct libusb_context *ctx, const char *devname)
 {
-	int busnum;
-	int devaddr;
-
-	usbi_dbg("scan %s", devname);
+	uint8_t busnum, devaddr;
+	int ret;
 
-	busnum = __read_sysfs_attr(ctx, devname, "busnum");
-	if (busnum < 0)
-		return busnum;
-
-	devaddr = __read_sysfs_attr(ctx, devname, "devnum");
-	if (devaddr < 0)
-		return devaddr;
-
-	usbi_dbg("bus=%d dev=%d", busnum, devaddr);
-	if (busnum > 255 || devaddr > 255)
-		return LIBUSB_ERROR_INVALID_PARAM;
+	ret = linux_get_device_address (ctx, 0, &busnum, &devaddr, NULL, devname);
+	if (LIBUSB_SUCCESS != ret) {
+		return ret;
+	}
 
-	return enumerate_device(ctx, _discdevs, busnum & 0xff, devaddr & 0xff,
+	return linux_enumerate_device(ctx, busnum & 0xff, devaddr & 0xff,
 		devname);
 }
 
-static int sysfs_get_device_list(struct libusb_context *ctx,
-	struct discovered_devs **_discdevs)
+#if !defined(USE_UDEV)
+static int sysfs_get_device_list(struct libusb_context *ctx)
 {
-	struct discovered_devs *discdevs = *_discdevs;
 	DIR *devices = opendir(SYSFS_DEVICE_PATH);
 	struct dirent *entry;
 	int r = LIBUSB_ERROR_IO;
@@ -1171,29 +1206,23 @@ static int sysfs_get_device_list(struct libusb_context *ctx,
 	}
 
 	while ((entry = readdir(devices))) {
-		struct discovered_devs *discdevs_new = discdevs;
-
 		if ((!isdigit(entry->d_name[0]) && strncmp(entry->d_name, "usb", 3))
 				|| strchr(entry->d_name, ':'))
 			continue;
 
-		if (sysfs_scan_device(ctx, &discdevs_new, entry->d_name)) {
+		if (sysfs_scan_device(ctx, entry->d_name)) {
 			usbi_dbg("failed to enumerate dir entry %s", entry->d_name);
 			continue;
 		}
 
 		r = 0;
-		discdevs = discdevs_new;
 	}
 
-	if (!r)
-		*_discdevs = discdevs;
 	closedir(devices);
 	return r;
 }
 
-static int op_get_device_list(struct libusb_context *ctx,
-	struct discovered_devs **_discdevs)
+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
@@ -1206,35 +1235,32 @@ static int op_get_device_list(struct libusb_context *ctx,
 	 * adequacy of sysfs and sets sysfs_can_relate_devices.
 	 */
 	if (sysfs_can_relate_devices != 0)
-		return sysfs_get_device_list(ctx, _discdevs);
+		return sysfs_get_device_list(ctx);
 	else
-		return usbfs_get_device_list(ctx, _discdevs);
+		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);
-	char filename[PATH_MAX];
+	int r;
 
-	_get_usbfs_path(handle->dev, filename);
-	usbi_dbg("opening %s", filename);
-	hpriv->fd = open(filename, O_RDWR);
-	if (hpriv->fd < 0) {
-		if (errno == EACCES) {
-			usbi_err(HANDLE_CTX(handle), "libusb couldn't open USB device %s: "
-				"Permission denied.", filename);
-			usbi_err(HANDLE_CTX(handle),
-				"libusb requires write access to USB device nodes.");
-			return LIBUSB_ERROR_ACCESS;
-		} else if (errno == ENOENT) {
-			usbi_err(HANDLE_CTX(handle), "libusb couldn't open USB device %s: "
-				"No such file or directory.", filename);
-			return LIBUSB_ERROR_NO_DEVICE;
-		} else {
-			usbi_err(HANDLE_CTX(handle),
-				"open failed, code %d errno %d", hpriv->fd, errno);
-			return LIBUSB_ERROR_IO;
-		}
+	hpriv->fd = _get_usbfs_fd(handle->dev, O_RDWR, 0);
+	if (hpriv->fd < 0)
+		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);
@@ -1251,10 +1277,13 @@ static int op_get_configuration(struct libusb_device_handle *handle,
 	int *config)
 {
 	int r;
-	if (sysfs_can_relate_devices != 1)
-		return LIBUSB_ERROR_NOT_SUPPORTED;
 
-	r = sysfs_get_active_config(handle->dev, config);
+	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;
 
@@ -1283,25 +1312,13 @@ static int op_set_configuration(struct libusb_device_handle *handle, int config)
 		return LIBUSB_ERROR_OTHER;
 	}
 
-	if (!sysfs_has_descriptors) {
-		/* update our cached active config descriptor */
-		if (config == -1) {
-			if (priv->config_descriptor) {
-				free(priv->config_descriptor);
-				priv->config_descriptor = NULL;
-			}
-		} else {
-			r = cache_active_config(handle->dev, fd, config);
-			if (r < 0)
-				usbi_warn(HANDLE_CTX(handle),
-					"failed to update cached config descriptor, error %d", r);
-		}
-	}
+	/* update our cached active config descriptor */
+	priv->active_config = config;
 
-	return 0;
+	return LIBUSB_SUCCESS;
 }
 
-static int op_claim_interface(struct libusb_device_handle *handle, int iface)
+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);
@@ -1320,7 +1337,7 @@ static int op_claim_interface(struct libusb_device_handle *handle, int iface)
 	return 0;
 }
 
-static int op_release_interface(struct libusb_device_handle *handle, int iface)
+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);
@@ -1391,7 +1408,7 @@ static int op_reset_device(struct libusb_device_handle *handle)
 	   getting bound to the in kernel driver if any). */
 	for (i = 0; i < USB_MAXINTERFACES; i++) {
 		if (handle->claimed_interfaces & (1L << i)) {
-			op_release_interface(handle, i);
+			release_interface(handle, i);
 		}
 	}
 
@@ -1412,11 +1429,18 @@ static int op_reset_device(struct libusb_device_handle *handle)
 	/* And re-claim any interfaces which were claimed before the reset */
 	for (i = 0; i < USB_MAXINTERFACES; i++) {
 		if (handle->claimed_interfaces & (1L << i)) {
-			r = op_claim_interface(handle, 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", i);
+					"failed to re-claim interface %d after reset: %s",
+					i, libusb_error_name(r));
 				handle->claimed_interfaces &= ~(1L << i);
+				ret = LIBUSB_ERROR_NOT_FOUND;
 			}
 		}
 	}
@@ -1445,7 +1469,7 @@ static int op_kernel_driver_active(struct libusb_device_handle *handle,
 		return LIBUSB_ERROR_OTHER;
 	}
 
-	return 1;
+	return (strcmp(getdrv.driver, "usbfs") == 0) ? 0 : 1;
 }
 
 static int op_detach_kernel_driver(struct libusb_device_handle *handle,
@@ -1453,12 +1477,18 @@ static int op_detach_kernel_driver(struct libusb_device_handle *handle,
 {
 	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)
@@ -1508,15 +1538,69 @@ static int op_attach_kernel_driver(struct libusb_device_handle *handle,
 	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 (!sysfs_has_descriptors) {
-		if (priv->dev_descriptor)
-			free(priv->dev_descriptor);
-		if (priv->config_descriptor)
-			free(priv->config_descriptor);
-	}
+	if (priv->descriptors)
+		free(priv->descriptors);
 	if (priv->sysfs_dir)
 		free(priv->sysfs_dir);
 }
@@ -1583,6 +1667,7 @@ static int submit_bulk_transfer(struct usbi_transfer *itransfer,
 	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;
@@ -1590,30 +1675,67 @@ static int submit_bulk_transfer(struct usbi_transfer *itransfer,
 	if (tpriv->urbs)
 		return LIBUSB_ERROR_BUSY;
 
-	if (is_out && transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET &&
-	    !supports_flag_zero_packet)
+	if (is_out && (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET) &&
+			!(dpriv->caps & USBFS_CAP_ZERO_PACKET))
 		return LIBUSB_ERROR_NOT_SUPPORTED;
 
-	/* usbfs places a 16kb limit on bulk 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. */
-	int num_urbs = transfer->length / MAX_BULK_BUFFER_LENGTH;
+	/*
+	 * 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 % MAX_BULK_BUFFER_LENGTH) > 0) {
+	} 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 = malloc(alloc_size);
+	urbs = calloc(1, alloc_size);
 	if (!urbs)
 		return LIBUSB_ERROR_NO_MEM;
-	memset(urbs, 0, alloc_size);
 	tpriv->urbs = urbs;
 	tpriv->num_urbs = num_urbs;
 	tpriv->num_retired = 0;
@@ -1625,17 +1747,18 @@ static int submit_bulk_transfer(struct usbi_transfer *itransfer,
 		urb->usercontext = itransfer;
 		urb->type = urb_type;
 		urb->endpoint = transfer->endpoint;
-		urb->buffer = transfer->buffer + (i * MAX_BULK_BUFFER_LENGTH);
-		if (supports_flag_bulk_continuation && !is_out)
+		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 % MAX_BULK_BUFFER_LENGTH;
+			urb->buffer_length = transfer->length % bulk_buffer_len;
 		else if (transfer->length == 0)
 			urb->buffer_length = 0;
 		else
-			urb->buffer_length = MAX_BULK_BUFFER_LENGTH;
+			urb->buffer_length = bulk_buffer_len;
 
-		if (i > 0 && supports_flag_bulk_continuation)
+		if (i > 0 && use_bulk_continuation)
 			urb->flags |= USBFS_URB_BULK_CONTINUATION;
 
 		/* we have already checked that the flag is supported */
@@ -1667,7 +1790,7 @@ static int submit_bulk_transfer(struct usbi_transfer *itransfer,
 			 * 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
+			 *    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.
@@ -1722,11 +1845,17 @@ static int submit_iso_transfer(struct usbi_transfer *itransfer)
 	/* 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. */
+	 * 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++) {
-		int space_remaining = MAX_ISO_BUFFER_LENGTH - this_urb_len;
+		unsigned int space_remaining = MAX_ISO_BUFFER_LENGTH - this_urb_len;
 		packet_len = transfer->iso_packet_desc[i].length;
 
 		if (packet_len > space_remaining) {
@@ -1739,10 +1868,9 @@ static int submit_iso_transfer(struct usbi_transfer *itransfer)
 	usbi_dbg("need %d 32k URBs for transfer", num_urbs);
 
 	alloc_size = num_urbs * sizeof(*urbs);
-	urbs = malloc(alloc_size);
+	urbs = calloc(1, alloc_size);
 	if (!urbs)
 		return LIBUSB_ERROR_NO_MEM;
-	memset(urbs, 0, alloc_size);
 
 	tpriv->iso_urbs = urbs;
 	tpriv->num_urbs = num_urbs;
@@ -1753,7 +1881,7 @@ static int submit_iso_transfer(struct usbi_transfer *itransfer)
 	/* allocate + initialize each URB with the correct number of packets */
 	for (i = 0; i < num_urbs; i++) {
 		struct usbfs_urb *urb;
-		int space_remaining_in_urb = MAX_ISO_BUFFER_LENGTH;
+		unsigned int space_remaining_in_urb = MAX_ISO_BUFFER_LENGTH;
 		int urb_packet_offset = 0;
 		unsigned char *urb_buffer_orig = urb_buffer;
 		int j;
@@ -1776,12 +1904,11 @@ static int submit_iso_transfer(struct usbi_transfer *itransfer)
 
 		alloc_size = sizeof(*urb)
 			+ (urb_packet_offset * sizeof(struct usbfs_iso_packet_desc));
-		urb = malloc(alloc_size);
+		urb = calloc(1, alloc_size);
 		if (!urb) {
 			free_iso_urbs(tpriv);
 			return LIBUSB_ERROR_NO_MEM;
 		}
-		memset(urb, 0, alloc_size);
 		urbs[i] = urb;
 
 		/* populate packet lengths */
@@ -1825,7 +1952,7 @@ static int submit_iso_transfer(struct usbi_transfer *itransfer)
 			 * 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
+			 *    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.
@@ -1865,10 +1992,9 @@ static int submit_control_transfer(struct usbi_transfer *itransfer)
 	if (transfer->length - LIBUSB_CONTROL_SETUP_SIZE > MAX_CTRL_BUFFER_LENGTH)
 		return LIBUSB_ERROR_INVALID_PARAM;
 
-	urb = malloc(sizeof(struct usbfs_urb));
+	urb = calloc(1, sizeof(struct usbfs_urb));
 	if (!urb)
 		return LIBUSB_ERROR_NO_MEM;
-	memset(urb, 0, sizeof(struct usbfs_urb));
 	tpriv->urbs = urb;
 	tpriv->num_urbs = 1;
 	tpriv->reap_action = NORMAL;
@@ -2001,7 +2127,7 @@ static int handle_bulk_completion(struct usbi_transfer *itransfer,
 		 *
 		 * 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
+		 * (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) {
@@ -2335,7 +2461,7 @@ static int op_handle_events(struct libusb_context *ctx,
 	struct pollfd *fds, POLL_NFDS_TYPE nfds, int num_ready)
 {
 	int r;
-	int i = 0;
+	unsigned int i = 0;
 
 	usbi_mutex_lock(&ctx->open_devs_lock);
 	for (i = 0; i < nfds && num_ready > 0; i++) {
@@ -2359,7 +2485,9 @@ static int op_handle_events(struct libusb_context *ctx,
 			continue;
 		}
 
-		r = reap_for_handle(handle);
+		do {
+			r = reap_for_handle(handle);
+		} while (r == 0);
 		if (r == 1 || r == LIBUSB_ERROR_NO_DEVICE)
 			continue;
 		else if (r < 0)
@@ -2394,12 +2522,15 @@ static clockid_t op_get_timerfd_clockid(void)
 
 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 = NULL,
-	.get_device_list = op_get_device_list,
+	.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,
@@ -2435,4 +2566,3 @@ const struct usbi_os_backend linux_usbfs_backend = {
 	.transfer_priv_size = sizeof(struct linux_transfer_priv),
 	.add_iso_packet_size = 0,
 };
-