adb/usb_linux.c - AOSPA/android_system_core - Gitiles

 /*
  * Copyright (C) 2007 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>

 #include <usbhost/usbhost.h>
 #include <linux/usbdevice_fs.h>
 #include <linux/version.h>
 #if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 20)
 #include <linux/usb/ch9.h>
 #else
 #include <linux/usb_ch9.h>
 #endif

 #include "sysdeps.h"

 #define   TRACE_TAG  TRACE_USB
 #include "adb.h"


 /* usb scan debugging is waaaay too verbose */
 #define DBGX(x...)

 static adb_mutex_t usb_lock = ADB_MUTEX_INITIALIZER;

 struct usb_handle
 {
     usb_handle *prev;
     usb_handle *next;

     struct usb_device *device;
     struct usb_endpoint *ep_in;
     struct usb_endpoint *ep_out;

     adb_cond_t notify_in;
     adb_cond_t notify_out;
     adb_mutex_t lock;

     int read_result, write_result;
     int zero_mask;
     int dead;

     // Thread ID for our reaper thread
     pthread_t reaper_thread;
 };

 static usb_handle handle_list = {
     .prev = &handle_list,
     .next = &handle_list,
 };

 static int known_device(const char *dev_name)
 {
     usb_handle *usb;

     adb_mutex_lock(&usb_lock);
     for (usb = handle_list.next; usb != &handle_list; usb = usb->next) {
         if (!strcmp(usb_device_get_name(usb->device), dev_name)) {
             adb_mutex_unlock(&usb_lock);
             return 1;
         }
     }
     adb_mutex_unlock(&usb_lock);
     return 0;
 }

 static void kick_disconnected_device(const char *devname)
 {
     usb_handle *usb;

     adb_mutex_lock(&usb_lock);
     /* kick the device if it is in our list */
     for (usb = handle_list.next; usb != &handle_list; usb = usb->next) {
         if (!strcmp(devname, usb_device_get_name(usb->device)))
             usb_kick(usb);
     }
     adb_mutex_unlock(&usb_lock);

 }

 static void* reaper_thread(void* arg)
 {
     struct usb_handle* h = (struct usb_handle *)arg;
     int ep_in = usb_endpoint_number(h->ep_in);
     int ep_out = usb_endpoint_number(h->ep_out);
     int reaped_ep, res;

     while (1) {
         D("[ reap urb - wait ]\n");
         adb_mutex_unlock(&h->lock);
         res = usb_endpoint_wait(h->device, &reaped_ep);
         adb_mutex_lock(&h->lock);
         if(h->dead) {
             res = -1;
             break;
         }

         D("[ reaped ep %d ret = %d ]\n", reaped_ep, res);

         if (reaped_ep == ep_in) {
             D("[ reap urb - IN complete ]\n");
             h->read_result = res;
             adb_cond_broadcast(&h->notify_in);
         }
         if (reaped_ep == ep_out) {
             D("[ reap urb - OUT compelete ]\n");
             h->write_result = res;
             adb_cond_broadcast(&h->notify_out);
         }
     }

     return NULL;
 }

 static void register_device(struct usb_device *device, int interface,
         struct usb_endpoint *ep_in, struct usb_endpoint *ep_out)
 {
     usb_handle* usb = 0;
     int ret = 0;
     int writeable;
     char *serial;
     pthread_attr_t   attr;
     const char* dev_name = usb_device_get_name(device);

         /* Since Linux will not reassign the device ID (and dev_name)
         ** as long as the device is open, we can add to the list here
         ** once we open it and remove from the list when we're finally
         ** closed and everything will work out fine.
         **
         ** If we have a usb_handle on the list 'o handles with a matching
         ** name, we have no further work to do.
         */
     adb_mutex_lock(&usb_lock);
     for (usb = handle_list.next; usb != &handle_list; usb = usb->next) {
         if (!strcmp(usb_device_get_name(usb->device), dev_name)) {
             adb_mutex_unlock(&usb_lock);
             return;
         }
     }
     adb_mutex_unlock(&usb_lock);

     usb = calloc(1, sizeof(usb_handle));
     adb_cond_init(&usb->notify_in, 0);
     adb_cond_init(&usb->notify_out, 0);
     adb_mutex_init(&usb->lock, 0);

     usb->device = device;
     usb->ep_in = ep_in;
     usb->ep_out = ep_out;
     usb->zero_mask = usb_endpoint_max_packet(usb->ep_out) - 1;

     D("[ usb open %s ]\n", dev_name);
     writeable = usb_device_is_writeable(device);
     if (writeable) {
         ret = usb_device_claim_interface(device, interface);
         if(ret != 0) goto fail;
     }

         /* add to the end of the active handles */
     adb_mutex_lock(&usb_lock);
     usb->next = &handle_list;
     usb->prev = handle_list.prev;
     usb->prev->next = usb;
     usb->next->prev = usb;
     adb_mutex_unlock(&usb_lock);

     pthread_attr_init(&attr);
     pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
     pthread_create(&usb->reaper_thread, &attr, reaper_thread, usb);

     serial = usb_device_get_serial(device);
     register_usb_transport(usb, serial, writeable);
     if (serial)
         free(serial);
     return;

 fail:
     D("[ usb open %s error=%d, err_str = %s]\n",
         dev_name,  errno, strerror(errno));
     if (usb->ep_in)
         usb_endpoint_close(usb->ep_in);
     if (usb->ep_out)
         usb_endpoint_close(usb->ep_out);
     if(device) {
         usb_device_close(device);
     }
     free(usb);
 }

 static void check_usb_device(const char *devname) {
     struct usb_device *device;
     struct usb_descriptor_iter iter;
     struct usb_descriptor_header* header;
     struct usb_interface_descriptor* interface;
     struct usb_endpoint_descriptor *ep1, *ep2;
     struct usb_endpoint *ep_in = NULL, *ep_out = NULL;
     uint16_t vid, pid;

     if(known_device(devname)) {
         DBGX("skipping %s\n", devname);
         return;
     }

     device = usb_device_open(devname);
     if (!device) return;

     vid = usb_device_get_vendor_id(device);
     pid = usb_device_get_product_id(device);
     DBGX("[ %s is V:%04x P:%04x ]\n", devname, vid, pid);

     // loop through all the descriptors and look for the ADB interface
     usb_descriptor_iter_init(device, &iter);

     while ((header = usb_descriptor_iter_next(&iter)) != NULL) {
         if (header->bDescriptorType == USB_DT_INTERFACE) {
             interface = (struct usb_interface_descriptor *)header;

             DBGX("bInterfaceClass: %d,  bInterfaceSubClass: %d,"
                  "bInterfaceProtocol: %d, bNumEndpoints: %d\n",
                  interface->bInterfaceClass, interface->bInterfaceSubClass,
                  interface->bInterfaceProtocol, interface->bNumEndpoints);

             if (interface->bNumEndpoints == 2 &&
                     is_adb_interface(vid, pid, interface->bInterfaceClass,
                     interface->bInterfaceSubClass, interface->bInterfaceProtocol))  {

                 DBGX("looking for bulk endpoints\n");
                     // looks like ADB...
                 ep1 = (struct usb_endpoint_descriptor *)usb_descriptor_iter_next(&iter);
                 ep2 = (struct usb_endpoint_descriptor *)usb_descriptor_iter_next(&iter);

                 if (!ep1 || !ep2 ||
                     ep1->bDescriptorType != USB_DT_ENDPOINT ||
                     ep2->bDescriptorType != USB_DT_ENDPOINT) {
                     D("endpoints not found\n");
                     continue;
                 }

                     // both endpoints should be bulk
                 if (ep1->bmAttributes != USB_ENDPOINT_XFER_BULK ||
                     ep2->bmAttributes != USB_ENDPOINT_XFER_BULK) {
                     D("bulk endpoints not found\n");
                     continue;
                 }

                     // we have a match.  now we just need to figure out which is in and which is out.
                 if (ep1->bEndpointAddress & USB_ENDPOINT_DIR_MASK) {
                     ep_in = usb_endpoint_open(device, ep1);
                     ep_out = usb_endpoint_open(device, ep2);
                 } else {
                     ep_in = usb_endpoint_open(device, ep2);
                     ep_out = usb_endpoint_open(device, ep1);
                 }

                 register_device(device, interface->bInterfaceNumber, ep_in, ep_out);
                 // so we don't free it at the bottom
                 device = NULL;
                 break;
             }
         }
     } // end of while

     if (device)
         usb_device_close(device);
 }

 void usb_cleanup()
 {
 }

 static int usb_bulk_write(usb_handle *h, const void *data, int len)
 {
     struct usb_endpoint *ep = h->ep_out;
     int res;

     D("++ write ++\n");

     adb_mutex_lock(&h->lock);
     if(h->dead) {
         res = -1;
         goto fail;
     }
     res = usb_endpoint_queue(ep, (void *)data, len);
     if(res < 0) {
         goto fail;
     }

     res = pthread_cond_wait(&h->notify_out, &h->lock);
     if (!res)
         res = h->write_result;

 fail:
     adb_mutex_unlock(&h->lock);
     D("-- write --\n");
     return res;
 }

 static int usb_bulk_read(usb_handle *h, void *data, int len)
 {
     struct usb_endpoint *ep = h->ep_in;
     int res;

     adb_mutex_lock(&h->lock);
     if(h->dead) {
         res = -1;
         goto fail;
     }
     res = usb_endpoint_queue(ep, data, len);
     if (res < 0) {
         goto fail;
     }
     res = pthread_cond_wait(&h->notify_in, &h->lock);
     if (!res)
         res = h->read_result;

 fail:
     adb_mutex_unlock(&h->lock);
     return res;
 }

 int usb_write(usb_handle *h, const void *_data, int len)
 {
     unsigned char *data = (unsigned char*) _data;
     int n;
     int need_zero = 0;

     if(h->zero_mask) {
             /* if we need 0-markers and our transfer
             ** is an even multiple of the packet size,
             ** we make note of it
             */
         if(!(len & h->zero_mask)) {
             need_zero = 1;
         }
     }

     while(len > 0) {
         int xfer = (len > 4096) ? 4096 : len;

         n = usb_bulk_write(h, data, xfer);
         if(n != xfer) {
             D("ERROR: n = %d, errno = %d (%s)\n",
                 n, errno, strerror(errno));
             return -1;
         }

         len -= xfer;
         data += xfer;
     }

     if(need_zero) {
         n = usb_bulk_write(h, _data, 0);
         return n;
     }

     return 0;
 }

 int usb_read(usb_handle *h, void *_data, int len)
 {
     unsigned char *data = (unsigned char*) _data;
     int n;

     D("++ usb_read ++\n");
     while(len > 0) {
         int xfer = (len > 4096) ? 4096 : len;

         n = usb_bulk_read(h, data, xfer);
         if(n != xfer) {
             if(errno == ETIMEDOUT && h->device) {
                 D("[ timeout ]\n");
                 if(n > 0){
                     data += n;
                     len -= n;
                 }
                 continue;
             }
             D("ERROR: n = %d, errno = %d (%s)\n",
                 n, errno, strerror(errno));
             return -1;
         }

         len -= xfer;
         data += xfer;
     }

     D("-- usb_read --\n");
     return 0;
 }

 void usb_kick(usb_handle *h)
 {
     D("[ kicking %p (fd = %s) ]\n", h, usb_device_get_name(h->device));
     adb_mutex_lock(&h->lock);
     if(h->dead == 0) {
         h->dead = 1;

         if (usb_device_is_writeable(h->device)) {
             /* HACK ALERT!
             ** Sometimes we get stuck in ioctl(USBDEVFS_REAPURB).
             ** This is a workaround for that problem.
             */
             if (h->reaper_thread) {
                 pthread_kill(h->reaper_thread, SIGALRM);
             }

             /* cancel any pending transactions
             ** these will quietly fail if the txns are not active,
             ** but this ensures that a reader blocked on REAPURB
             ** will get unblocked
             */
             usb_endpoint_cancel(h->ep_in);
             usb_endpoint_cancel(h->ep_out);
             adb_cond_broadcast(&h->notify_in);
             adb_cond_broadcast(&h->notify_out);
         } else {
             unregister_usb_transport(h);
         }
     }
     adb_mutex_unlock(&h->lock);
 }

 int usb_close(usb_handle *h)
 {
     D("[ usb close ... ]\n");
     adb_mutex_lock(&usb_lock);
     h->next->prev = h->prev;
     h->prev->next = h->next;
     h->prev = 0;
     h->next = 0;

     usb_device_close(h->device);
     D("[ usb closed %p ]\n", h);
     adb_mutex_unlock(&usb_lock);

     free(h);
     return 0;
 }

 static void sigalrm_handler(int signo)
 {
     // don't need to do anything here
 }

 void usb_init()
 {
     struct sigaction    actions;

     if (usb_host_init(check_usb_device, kick_disconnected_device))
         fatal_errno("usb_host_init failed\n");

     memset(&actions, 0, sizeof(actions));
     sigemptyset(&actions.sa_mask);
     actions.sa_flags = 0;
     actions.sa_handler = sigalrm_handler;
     sigaction(SIGALRM,& actions, NULL);
 }
	/*
	* Copyright (C) 2007 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <string.h>

	#include <usbhost/usbhost.h>
	#include <linux/usbdevice_fs.h>
	#include <linux/version.h>
	#if LINUX_VERSION_CODE > KERNEL_VERSION(2, 6, 20)
	#include <linux/usb/ch9.h>
	#else
	#include <linux/usb_ch9.h>
	#endif

	#include "sysdeps.h"

	#define TRACE_TAG TRACE_USB
	#include "adb.h"


	/* usb scan debugging is waaaay too verbose */
	#define DBGX(x...)

	static adb_mutex_t usb_lock = ADB_MUTEX_INITIALIZER;

	struct usb_handle
	{
	usb_handle *prev;
	usb_handle *next;

	struct usb_device *device;
	struct usb_endpoint *ep_in;
	struct usb_endpoint *ep_out;

	adb_cond_t notify_in;
	adb_cond_t notify_out;
	adb_mutex_t lock;

	int read_result, write_result;
	int zero_mask;
	int dead;

	// Thread ID for our reaper thread
	pthread_t reaper_thread;
	};

	static usb_handle handle_list = {
	.prev = &handle_list,
	.next = &handle_list,
	};

	static int known_device(const char *dev_name)
	{
	usb_handle *usb;

	adb_mutex_lock(&usb_lock);
	for (usb = handle_list.next; usb != &handle_list; usb = usb->next) {
	if (!strcmp(usb_device_get_name(usb->device), dev_name)) {
	adb_mutex_unlock(&usb_lock);
	return 1;
	}
	}
	adb_mutex_unlock(&usb_lock);
	return 0;
	}

	static void kick_disconnected_device(const char *devname)
	{
	usb_handle *usb;

	adb_mutex_lock(&usb_lock);
	/* kick the device if it is in our list */
	for (usb = handle_list.next; usb != &handle_list; usb = usb->next) {
	if (!strcmp(devname, usb_device_get_name(usb->device)))
	usb_kick(usb);
	}
	adb_mutex_unlock(&usb_lock);

	}

	static void* reaper_thread(void* arg)
	{
	struct usb_handle* h = (struct usb_handle *)arg;
	int ep_in = usb_endpoint_number(h->ep_in);
	int ep_out = usb_endpoint_number(h->ep_out);
	int reaped_ep, res;

	while (1) {
	D("[ reap urb - wait ]\n");
	adb_mutex_unlock(&h->lock);
	res = usb_endpoint_wait(h->device, &reaped_ep);
	adb_mutex_lock(&h->lock);
	if(h->dead) {
	res = -1;
	break;
	}

	D("[ reaped ep %d ret = %d ]\n", reaped_ep, res);

	if (reaped_ep == ep_in) {
	D("[ reap urb - IN complete ]\n");
	h->read_result = res;
	adb_cond_broadcast(&h->notify_in);
	}
	if (reaped_ep == ep_out) {
	D("[ reap urb - OUT compelete ]\n");
	h->write_result = res;
	adb_cond_broadcast(&h->notify_out);
	}
	}

	return NULL;
	}

	static void register_device(struct usb_device *device, int interface,
	struct usb_endpoint ep_in, struct usb_endpoint ep_out)
	{
	usb_handle* usb = 0;
	int ret = 0;
	int writeable;
	char *serial;
	pthread_attr_t attr;
	const char* dev_name = usb_device_get_name(device);

	/* Since Linux will not reassign the device ID (and dev_name)
	** as long as the device is open, we can add to the list here
	** once we open it and remove from the list when we're finally
	** closed and everything will work out fine.
	**
	** If we have a usb_handle on the list 'o handles with a matching
	** name, we have no further work to do.
	*/
	adb_mutex_lock(&usb_lock);
	for (usb = handle_list.next; usb != &handle_list; usb = usb->next) {
	if (!strcmp(usb_device_get_name(usb->device), dev_name)) {
	adb_mutex_unlock(&usb_lock);
	return;
	}
	}
	adb_mutex_unlock(&usb_lock);

	usb = calloc(1, sizeof(usb_handle));
	adb_cond_init(&usb->notify_in, 0);
	adb_cond_init(&usb->notify_out, 0);
	adb_mutex_init(&usb->lock, 0);

	usb->device = device;
	usb->ep_in = ep_in;
	usb->ep_out = ep_out;
	usb->zero_mask = usb_endpoint_max_packet(usb->ep_out) - 1;

	D("[ usb open %s ]\n", dev_name);
	writeable = usb_device_is_writeable(device);
	if (writeable) {
	ret = usb_device_claim_interface(device, interface);
	if(ret != 0) goto fail;
	}

	/* add to the end of the active handles */
	adb_mutex_lock(&usb_lock);
	usb->next = &handle_list;
	usb->prev = handle_list.prev;
	usb->prev->next = usb;
	usb->next->prev = usb;
	adb_mutex_unlock(&usb_lock);

	pthread_attr_init(&attr);
	pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
	pthread_create(&usb->reaper_thread, &attr, reaper_thread, usb);

	serial = usb_device_get_serial(device);
	register_usb_transport(usb, serial, writeable);
	if (serial)
	free(serial);
	return;

	fail:
	D("[ usb open %s error=%d, err_str = %s]\n",
	dev_name, errno, strerror(errno));
	if (usb->ep_in)
	usb_endpoint_close(usb->ep_in);
	if (usb->ep_out)
	usb_endpoint_close(usb->ep_out);
	if(device) {
	usb_device_close(device);
	}
	free(usb);
	}

	static void check_usb_device(const char *devname) {
	struct usb_device *device;
	struct usb_descriptor_iter iter;
	struct usb_descriptor_header* header;
	struct usb_interface_descriptor* interface;
	struct usb_endpoint_descriptor ep1, ep2;
	struct usb_endpoint ep_in = NULL, ep_out = NULL;
	uint16_t vid, pid;

	if(known_device(devname)) {
	DBGX("skipping %s\n", devname);
	return;
	}

	device = usb_device_open(devname);
	if (!device) return;

	vid = usb_device_get_vendor_id(device);
	pid = usb_device_get_product_id(device);
	DBGX("[ %s is V:%04x P:%04x ]\n", devname, vid, pid);

	// loop through all the descriptors and look for the ADB interface
	usb_descriptor_iter_init(device, &iter);

	while ((header = usb_descriptor_iter_next(&iter)) != NULL) {
	if (header->bDescriptorType == USB_DT_INTERFACE) {
	interface = (struct usb_interface_descriptor *)header;

	DBGX("bInterfaceClass: %d, bInterfaceSubClass: %d,"
	"bInterfaceProtocol: %d, bNumEndpoints: %d\n",
	interface->bInterfaceClass, interface->bInterfaceSubClass,
	interface->bInterfaceProtocol, interface->bNumEndpoints);

	if (interface->bNumEndpoints == 2 &&
	is_adb_interface(vid, pid, interface->bInterfaceClass,
	interface->bInterfaceSubClass, interface->bInterfaceProtocol)) {

	DBGX("looking for bulk endpoints\n");
	// looks like ADB...
	ep1 = (struct usb_endpoint_descriptor *)usb_descriptor_iter_next(&iter);
	ep2 = (struct usb_endpoint_descriptor *)usb_descriptor_iter_next(&iter);

	if (!ep1 \|\| !ep2 \|\|
	ep1->bDescriptorType != USB_DT_ENDPOINT \|\|
	ep2->bDescriptorType != USB_DT_ENDPOINT) {
	D("endpoints not found\n");
	continue;
	}

	// both endpoints should be bulk
	if (ep1->bmAttributes != USB_ENDPOINT_XFER_BULK \|\|
	ep2->bmAttributes != USB_ENDPOINT_XFER_BULK) {
	D("bulk endpoints not found\n");
	continue;
	}

	// we have a match. now we just need to figure out which is in and which is out.
	if (ep1->bEndpointAddress & USB_ENDPOINT_DIR_MASK) {
	ep_in = usb_endpoint_open(device, ep1);
	ep_out = usb_endpoint_open(device, ep2);
	} else {
	ep_in = usb_endpoint_open(device, ep2);
	ep_out = usb_endpoint_open(device, ep1);
	}

	register_device(device, interface->bInterfaceNumber, ep_in, ep_out);
	// so we don't free it at the bottom
	device = NULL;
	break;
	}
	}
	} // end of while

	if (device)
	usb_device_close(device);
	}

	void usb_cleanup()
	{
	}

	static int usb_bulk_write(usb_handle h, const void data, int len)
	{
	struct usb_endpoint *ep = h->ep_out;
	int res;

	D("++ write ++\n");

	adb_mutex_lock(&h->lock);
	if(h->dead) {
	res = -1;
	goto fail;
	}
	res = usb_endpoint_queue(ep, (void *)data, len);
	if(res < 0) {
	goto fail;
	}

	res = pthread_cond_wait(&h->notify_out, &h->lock);
	if (!res)
	res = h->write_result;

	fail:
	adb_mutex_unlock(&h->lock);
	D("-- write --\n");
	return res;
	}

	static int usb_bulk_read(usb_handle h, void data, int len)
	{
	struct usb_endpoint *ep = h->ep_in;
	int res;

	adb_mutex_lock(&h->lock);
	if(h->dead) {
	res = -1;
	goto fail;
	}
	res = usb_endpoint_queue(ep, data, len);
	if (res < 0) {
	goto fail;
	}
	res = pthread_cond_wait(&h->notify_in, &h->lock);
	if (!res)
	res = h->read_result;

	fail:
	adb_mutex_unlock(&h->lock);
	return res;
	}

	int usb_write(usb_handle h, const void _data, int len)
	{
	unsigned char data = (unsigned char) _data;
	int n;
	int need_zero = 0;

	if(h->zero_mask) {
	/* if we need 0-markers and our transfer
	** is an even multiple of the packet size,
	** we make note of it
	*/
	if(!(len & h->zero_mask)) {
	need_zero = 1;
	}
	}

	while(len > 0) {
	int xfer = (len > 4096) ? 4096 : len;

	n = usb_bulk_write(h, data, xfer);
	if(n != xfer) {
	D("ERROR: n = %d, errno = %d (%s)\n",
	n, errno, strerror(errno));
	return -1;
	}

	len -= xfer;
	data += xfer;
	}

	if(need_zero) {
	n = usb_bulk_write(h, _data, 0);
	return n;
	}

	return 0;
	}

	int usb_read(usb_handle h, void _data, int len)
	{
	unsigned char data = (unsigned char) _data;
	int n;

	D("++ usb_read ++\n");
	while(len > 0) {
	int xfer = (len > 4096) ? 4096 : len;

	n = usb_bulk_read(h, data, xfer);
	if(n != xfer) {
	if(errno == ETIMEDOUT && h->device) {
	D("[ timeout ]\n");
	if(n > 0){
	data += n;
	len -= n;
	}
	continue;
	}
	D("ERROR: n = %d, errno = %d (%s)\n",
	n, errno, strerror(errno));
	return -1;
	}

	len -= xfer;
	data += xfer;
	}

	D("-- usb_read --\n");
	return 0;
	}

	void usb_kick(usb_handle *h)
	{
	D("[ kicking %p (fd = %s) ]\n", h, usb_device_get_name(h->device));
	adb_mutex_lock(&h->lock);
	if(h->dead == 0) {
	h->dead = 1;

	if (usb_device_is_writeable(h->device)) {
	/* HACK ALERT!
	** Sometimes we get stuck in ioctl(USBDEVFS_REAPURB).
	** This is a workaround for that problem.
	*/
	if (h->reaper_thread) {
	pthread_kill(h->reaper_thread, SIGALRM);
	}

	/* cancel any pending transactions
	** these will quietly fail if the txns are not active,
	** but this ensures that a reader blocked on REAPURB
	** will get unblocked
	*/
	usb_endpoint_cancel(h->ep_in);
	usb_endpoint_cancel(h->ep_out);
	adb_cond_broadcast(&h->notify_in);
	adb_cond_broadcast(&h->notify_out);
	} else {
	unregister_usb_transport(h);
	}
	}
	adb_mutex_unlock(&h->lock);
	}

	int usb_close(usb_handle *h)
	{
	D("[ usb close ... ]\n");
	adb_mutex_lock(&usb_lock);
	h->next->prev = h->prev;
	h->prev->next = h->next;
	h->prev = 0;
	h->next = 0;

	usb_device_close(h->device);
	D("[ usb closed %p ]\n", h);
	adb_mutex_unlock(&usb_lock);

	free(h);
	return 0;
	}

	static void sigalrm_handler(int signo)
	{
	// don't need to do anything here
	}

	void usb_init()
	{
	struct sigaction actions;

	if (usb_host_init(check_usb_device, kick_disconnected_device))
	fatal_errno("usb_host_init failed\n");

	memset(&actions, 0, sizeof(actions));
	sigemptyset(&actions.sa_mask);
	actions.sa_flags = 0;
	actions.sa_handler = sigalrm_handler;
	sigaction(SIGALRM,& actions, NULL);
	}