text: #include <linux/module.h>
  #include <linux/string.h>
  #include <linux/bitops.h>
  #include <linux/slab.h>
  #include <linux/init.h>
  #include <linux/log2.h>
  #include <linux/usb.h>
  #include <linux/wait.h>
  #include <linux/usb/hcd.h>
  
  #define to_urb(d) container_of(d, struct urb, kref)
  
  
  static void urb_destroy(struct kref *kref)
  {
  	struct urb *urb = to_urb(kref);
  
  	if (urb->transfer_flags & URB_FREE_BUFFER)
  		kfree(urb->transfer_buffer);
  
  	kfree(urb);
  }
  
  /**
   * usb_init_urb - initializes a urb so that it can be used by a USB driver
   * @urb: pointer to the urb to initialize
   *
   * Initializes a urb so that the USB subsystem can use it properly.
   *
   * If a urb is created with a call to usb_alloc_urb() it is not
   * necessary to call this function.  Only use this if you allocate the
   * space for a struct urb on your own.  If you call this function, be
   * careful when freeing the memory for your urb that it is no longer in
   * use by the USB core.
   *
   * Only use this function if you _really_ understand what you are doing.
   */
  void usb_init_urb(struct urb *urb)
  {
  	if (urb) {
  		memset(urb, 0, sizeof(*urb));
  		kref_init(&urb->kref);
  		INIT_LIST_HEAD(&urb->anchor_list);
  	}
  }
  EXPORT_SYMBOL_GPL(usb_init_urb);
  
  /**
   * usb_alloc_urb - creates a new urb for a USB driver to use
   * @iso_packets: number of iso packets for this urb
   * @mem_flags: the type of memory to allocate, see kmalloc() for a list of
   *	valid options for this.
   *
   * Creates an urb for the USB driver to use, initializes a few internal
   * structures, incrementes the usage counter, and returns a pointer to it.
   *
   * If no memory is available, NULL is returned.
   *
   * If the driver want to use this urb for interrupt, control, or bulk
   * endpoints, pass '0' as the number of iso packets.
   *
   * The driver must call usb_free_urb() when it is finished with the urb.
   */
  struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
  {
  	struct urb *urb;
  
  	urb = kmalloc(sizeof(struct urb) +
  		iso_packets * sizeof(struct usb_iso_packet_descriptor),
  		mem_flags);
  	if (!urb) {
  		printk(KERN_ERR "alloc_urb: kmalloc failed\n");
  		return NULL;
  	}
  	usb_init_urb(urb);
  	return urb;
  }
  EXPORT_SYMBOL_GPL(usb_alloc_urb);
  
  /**
   * usb_free_urb - frees the memory used by a urb when all users of it are finished
   * @urb: pointer to the urb to free, may be NULL
   *
   * Must be called when a user of a urb is finished with it.  When the last user
   * of the urb calls this function, the memory of the urb is freed.
   *
   * Note: The transfer buffer associated with the urb is not freed unless the
   * URB_FREE_BUFFER transfer flag is set.
   */
  void usb_free_urb(struct urb *urb)
  {
  	if (urb)
  		kref_put(&urb->kref, urb_destroy);
  }
  EXPORT_SYMBOL_GPL(usb_free_urb);
  
  /**
   * usb_get_urb - increments the reference count of the urb
   * @urb: pointer to the urb to modify, may be NULL
   *
   * This must be  called whenever a urb is transferred from a device driver to a
   * host controller driver.  This allows proper reference counting to happen
   * for urbs.
   *
   * A pointer to the urb with the incremented reference counter is returned.
   */
  struct urb *usb_get_urb(struct urb *urb)
  {
  	if (urb)
  		kref_get(&urb->kref);
  	return urb;
  }
  EXPORT_SYMBOL_GPL(usb_get_urb);
  
  /**
   * usb_anchor_urb - anchors an URB while it is processed
   * @urb: pointer to the urb to anchor
   * @anchor: pointer to the anchor
   *
   * This can be called to have access to URBs which are to be executed
   * without bothering to track them
   */
  void usb_anchor_urb(struct urb *urb, struct usb_anchor *anchor)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&anchor->lock, flags);
  	usb_get_urb(urb);
  	list_add_tail(&urb->anchor_list, &anchor->urb_list);
  	urb->anchor = anchor;
  
  	if (unlikely(anchor->poisoned)) {
  		atomic_inc(&urb->reject);
  	}
  
  	spin_unlock_irqrestore(&anchor->lock, flags);
  }
  EXPORT_SYMBOL_GPL(usb_anchor_urb);
  
  /* Callers must hold anchor->lock */
  static void __usb_unanchor_urb(struct urb *urb, struct usb_anchor *anchor)
  {
  	urb->anchor = NULL;
  	list_del(&urb->anchor_list);
  	usb_put_urb(urb);
  	if (list_empty(&anchor->urb_list))
  		wake_up(&anchor->wait);
  }
  
  /**
   * usb_unanchor_urb - unanchors an URB
   * @urb: pointer to the urb to anchor
   *
   * Call this to stop the system keeping track of this URB
   */
  void usb_unanchor_urb(struct urb *urb)
  {
  	unsigned long flags;
  	struct usb_anchor *anchor;
  
  	if (!urb)
  		return;
  
  	anchor = urb->anchor;
  	if (!anchor)
  		return;
  
  	spin_lock_irqsave(&anchor->lock, flags);
  	/*
  	 * At this point, we could be competing with another thread which
  	 * has the same intention. To protect the urb from being unanchored
  	 * twice, only the winner of the race gets the job.
  	 */
  	if (likely(anchor == urb->anchor))
  		__usb_unanchor_urb(urb, anchor);
  	spin_unlock_irqrestore(&anchor->lock, flags);
  }
  EXPORT_SYMBOL_GPL(usb_unanchor_urb);
  
  /*-------------------------------------------------------------------*/
  
  /**
   * usb_submit_urb - issue an asynchronous transfer request for an endpoint
   * @urb: pointer to the urb describing the request
   * @mem_flags: the type of memory to allocate, see kmalloc() for a list
   *	of valid options for this.
   *
   * This submits a transfer request, and transfers control of the URB
   * describing that request to the USB subsystem.  Request completion will
   * be indicated later, asynchronously, by calling the completion handler.
   * The three types of completion are success, error, and unlink
   * (a software-induced fault, also called "request cancellation").
   *
   * URBs may be submitted in interrupt context.
   *
   * The caller must have correctly initialized the URB before submitting
   * it.  Functions such as usb_fill_bulk_urb() and usb_fill_control_urb() are
   * available to ensure that most fields are correctly initialized, for
   * the particular kind of transfer, although they will not initialize
   * any transfer flags.
   *
   * Successful submissions return 0; otherwise this routine returns a
   * negative error number.  If the submission is successful, the complete()
   * callback from the URB will be called exactly once, when the USB core and
   * Host Controller Driver (HCD) are finished with the URB.  When the completion
   * function is called, control of the URB is returned to the device
   * driver which issued the request.  The completion handler may then
   * immediately free or reuse that URB.
   *
   * With few exceptions, USB device drivers should never access URB fields
   * provided by usbcore or the HCD until its complete() is called.
   * The exceptions relate to periodic transfer scheduling.  For both
   * interrupt and isochronous urbs, as part of successful URB submission
   * urb->interval is modified to reflect the actual transfer period used
   * (normally some power of two units).  And for isochronous urbs,
   * urb->start_frame is modified to reflect when the URB's transfers were
   * scheduled to start.  Not all isochronous transfer scheduling policies
   * will work, but most host controller drivers should easily handle ISO
   * queues going from now until 10-200 msec into the future.
   *
   * For control endpoints, the synchronous usb_control_msg() call is
   * often used (in non-interrupt context) instead of this call.
   * That is often used through convenience wrappers, for the requests
   * that are standardized in the USB 2.0 specification.  For bulk
   * endpoints, a synchronous usb_bulk_msg() call is available.
   *
   * Request Queuing:
   *
   * URBs may be submitted to endpoints before previous ones complete, to
   * minimize the impact of interrupt latencies and system overhead on data
   * throughput.  With that queuing policy, an endpoint's queue would never
   * be empty.  This is required for continuous isochronous data streams,
   * and may also be required for some kinds of interrupt transfers. Such
   * queuing also maximizes bandwidth utilization by letting USB controllers
   * start work on later requests before driver software has finished the
   * completion processing for earlier (successful) requests.
   *
   * As of Linux 2.6, all USB endpoint transfer queues support depths greater
   * than one.  This was previously a HCD-specific behavior, except for ISO
   * transfers.  Non-isochronous endpoint queues are inactive during cleanup
   * after faults (transfer errors or cancellation).
   *
   * Reserved Bandwidth Transfers:
   *
   * Periodic transfers (interrupt or isochronous) are performed repeatedly,
   * using the interval specified in the urb.  Submitting the first urb to
   * the endpoint reserves the bandwidth necessary to make those transfers.
   * If the USB subsystem can't allocate sufficient bandwidth to perform
   * the periodic request, submitting such a periodic request should fail.
   *
   * For devices under xHCI, the bandwidth is reserved at configuration time, or
   * when the alt setting is selected.  If there is not enough bus bandwidth, the
   * configuration/alt setting request will fail.  Therefore, submissions to
   * periodic endpoints on devices under xHCI should never fail due to bandwidth
   * constraints.
   *
   * Device drivers must explicitly request that repetition, by ensuring that
   * some URB is always on the endpoint's queue (except possibly for short
   * periods during completion callacks).  When there is no longer an urb
   * queued, the endpoint's bandwidth reservation is canceled.  This means
   * drivers can use their completion handlers to ensure they keep bandwidth
   * they need, by reinitializing and resubmitting the just-completed urb
   * until the driver longer needs that periodic bandwidth.
   *
   * Memory Flags:
   *
   * The general rules for how to decide which mem_flags to use
   * are the same as for kmalloc.  There are four
   * different possible values; GFP_KERNEL, GFP_NOFS, GFP_NOIO and
   * GFP_ATOMIC.
   *
   * GFP_NOFS is not ever used, as it has not been implemented yet.
   *
   * GFP_ATOMIC is used when
   *   (a) you are inside a completion handler, an interrupt, bottom half,
   *       tasklet or timer, or
   *   (b) you are holding a spinlock or rwlock (does not apply to
   *       semaphores), or
   *   (c) current->state != TASK_RUNNING, this is the case only after
   *       you've changed it.
   *
   * GFP_NOIO is used in the block io path and error handling of storage
   * devices.
   *
   * All other situations use GFP_KERNEL.
   *
   * Some more specific rules for mem_flags can be inferred, such as
   *  (1) start_xmit, timeout, and receive methods of network drivers must
   *      use GFP_ATOMIC (they are called with a spinlock held);
   *  (2) queuecommand methods of scsi drivers must use GFP_ATOMIC (also
   *      called with a spinlock held);
   *  (3) If you use a kernel thread with a network driver you must use
   *      GFP_NOIO, unless (b) or (c) apply;
   *  (4) after you have done a down() you can use GFP_KERNEL, unless (b) or (c)
   *      apply or your are in a storage driver's block io path;
   *  (5) USB probe and disconnect can use GFP_KERNEL unless (b) or (c) apply; and
   *  (6) changing firmware on a running storage or net device uses
   *      GFP_NOIO, unless b) or c) apply
   *
   */
  int usb_submit_urb(struct urb *urb, gfp_t mem_flags)
  {
  	int				xfertype, max;
  	struct usb_device		*dev;
  	struct usb_host_endpoint	*ep;
  	int				is_out;
  
  	if (!urb || urb->hcpriv || !urb->complete)
  		return -EINVAL;
  	dev = urb->dev;
  	if ((!dev) || (dev->state < USB_STATE_UNAUTHENTICATED))
  		return -ENODEV;
  
  	/* For now, get the endpoint from the pipe.  Eventually drivers
  	 * will be required to set urb->ep directly and we will eliminate
  	 * urb->pipe.
  	 */
  	ep = usb_pipe_endpoint(dev, urb->pipe);
  	if (!ep)
  		return -ENOENT;
  
  	urb->ep = ep;
  	urb->status = -EINPROGRESS;
  	urb->actual_length = 0;
  
  	/* Lots of sanity checks, so HCDs can rely on clean data
  	 * and don't need to duplicate tests
  	 */
  	xfertype = usb_endpoint_type(&ep->desc);
  	if (xfertype == USB_ENDPOINT_XFER_CONTROL) {
  		struct usb_ctrlrequest *setup =
  				(struct usb_ctrlrequest *) urb->setup_packet;
  
  		if (!setup)
  			return -ENOEXEC;
  		is_out = !(setup->bRequestType & USB_DIR_IN) ||
  				!setup->wLength;
  	} else {
  		is_out = usb_endpoint_dir_out(&ep->desc);
  	}
  
  	/* Clear the internal flags and cache the direction for later use */
  	urb->transfer_flags &= ~(URB_DIR_MASK | URB_DMA_MAP_SINGLE |
  			URB_DMA_MAP_PAGE | URB_DMA_MAP_SG | URB_MAP_LOCAL |
  			URB_SETUP_MAP_SINGLE | URB_SETUP_MAP_LOCAL |
  			URB_DMA_SG_COMBINED);
  	urb->transfer_flags |= (is_out ? URB_DIR_OUT : URB_DIR_IN);
  
  	if (xfertype != USB_ENDPOINT_XFER_CONTROL &&
  			dev->state < USB_STATE_CONFIGURED)
  		return -ENODEV;
  
  	max = usb_endpoint_maxp(&ep->desc);
  	if (max <= 0) {
  		dev_dbg(&dev->dev,
  			"bogus endpoint ep%d%s in %s (bad maxpacket %d)\n",
  			usb_endpoint_num(&ep->desc), is_out ? "out" : "in",
  			__func__, max);
  		return -EMSGSIZE;
  	}
  
  	/* periodic transfers limit size per frame/uframe,
  	 * but drivers only control those sizes for ISO.
  	 * while we're checking, initialize return status.
  	 */
  	if (xfertype == USB_ENDPOINT_XFER_ISOC) {
  		int	n, len;
  
  		/* SuperSpeed isoc endpoints have up to 16 bursts of up to
  		 * 3 packets each
  		 */
  		if (dev->speed == USB_SPEED_SUPER) {
  			int     burst = 1 + ep->ss_ep_comp.bMaxBurst;
  			int     mult = USB_SS_MULT(ep->ss_ep_comp.bmAttributes);
  			max *= burst;
  			max *= mult;
  		}
  
  		/* "high bandwidth" mode, 1-3 packets/uframe? */
  		if (dev->speed == USB_SPEED_HIGH) {
  			int	mult = 1 + ((max >> 11) & 0x03);
  			max &= 0x07ff;
  			max *= mult;
  		}
  
  		if (urb->number_of_packets <= 0)
  			return -EINVAL;
  		for (n = 0; n < urb->number_of_packets; n++) {
  			len = urb->iso_frame_desc[n].length;
  			if (len < 0 || len > max)
  				return -EMSGSIZE;
  			urb->iso_frame_desc[n].status = -EXDEV;
  			urb->iso_frame_desc[n].actual_length = 0;
  		}
  	}
  
  	/* the I/O buffer must be mapped/unmapped, except when length=0 */
  	if (urb->transfer_buffer_length > INT_MAX)
  		return -EMSGSIZE;
  
  #ifdef DEBUG
  	/* stuff that drivers shouldn't do, but which shouldn't
  	 * cause problems in HCDs if they get it wrong.
  	 */
  	{
  	unsigned int	allowed;
  	static int pipetypes[4] = {
  		PIPE_CONTROL, PIPE_ISOCHRONOUS, PIPE_BULK, PIPE_INTERRUPT
  	};
  
  	/* Check that the pipe's type matches the endpoint's type */
  	if (usb_pipetype(urb->pipe) != pipetypes[xfertype])
  		dev_WARN(&dev->dev, "BOGUS urb xfer, pipe %x != type %x\n",
  			usb_pipetype(urb->pipe), pipetypes[xfertype]);
  
  	/* Check against a simple/standard policy */
  	allowed = (URB_NO_TRANSFER_DMA_MAP | URB_NO_INTERRUPT | URB_DIR_MASK |
  			URB_FREE_BUFFER);
  	switch (xfertype) {
  	case USB_ENDPOINT_XFER_BULK:
  		if (is_out)
  			allowed |= URB_ZERO_PACKET;
  		/* FALLTHROUGH */
  	case USB_ENDPOINT_XFER_CONTROL:
  		allowed |= URB_NO_FSBR;	/* only affects UHCI */
  		/* FALLTHROUGH */
  	default:			/* all non-iso endpoints */
  		if (!is_out)
  			allowed |= URB_SHORT_NOT_OK;
  		break;
  	case USB_ENDPOINT_XFER_ISOC:
  		allowed |= URB_ISO_ASAP;
  		break;
  	}
  	allowed &= urb->transfer_flags;
  
  	/* warn if submitter gave bogus flags */
  	if (allowed != urb->transfer_flags)
  		dev_WARN(&dev->dev, "BOGUS urb flags, %x --> %x\n",
  			urb->transfer_flags, allowed);
  	}
  #endif
  	/*
  	 * Force periodic transfer intervals to be legal values that are
  	 * a power of two (so HCDs don't need to).
  	 *
  	 * FIXME want bus->{intr,iso}_sched_horizon values here.  Each HC
  	 * supports different values... this uses EHCI/UHCI defaults (and
  	 * EHCI can use smaller non-default values).
  	 */
  	switch (xfertype) {
  	case USB_ENDPOINT_XFER_ISOC:
  	case USB_ENDPOINT_XFER_INT:
  		/* too small? */
  		switch (dev->speed) {
  		case USB_SPEED_WIRELESS:
  			if (urb->interval < 6)
  				return -EINVAL;
  			break;
  		default:
  			if (urb->interval <= 0)
  				return -EINVAL;
  			break;
  		}
  		/* too big? */
  		switch (dev->speed) {
  		case USB_SPEED_SUPER:	/* units are 125us */
  			/* Handle up to 2^(16-1) microframes */
  			if (urb->interval > (1 << 15))
  				return -EINVAL;
  			max = 1 << 15;
  			break;
  		case USB_SPEED_WIRELESS:
  			if (urb->interval > 16)
  				return -EINVAL;
  			break;
  		case USB_SPEED_HIGH:	/* units are microframes */
  			/* NOTE usb handles 2^15 */
  			if (urb->interval > (1024 * 8))
  				urb->interval = 1024 * 8;
  			max = 1024 * 8;
  			break;
  		case USB_SPEED_FULL:	/* units are frames/msec */
  		case USB_SPEED_LOW:
  			if (xfertype == USB_ENDPOINT_XFER_INT) {
  				if (urb->interval > 255)
  					return -EINVAL;
  				/* NOTE ohci only handles up to 32 */
  				max = 128;
  			} else {
  				if (urb->interval > 1024)
  					urb->interval = 1024;
  				/* NOTE usb and ohci handle up to 2^15 */
  				max = 1024;
  			}
  			break;
  		default:
  			return -EINVAL;
  		}
  		if (dev->speed != USB_SPEED_WIRELESS) {
  			/* Round down to a power of 2, no more than max */
  			urb->interval = min(max, 1 << ilog2(urb->interval));
  		}
  	}
  
  	return usb_hcd_submit_urb(urb, mem_flags);
  }
  EXPORT_SYMBOL_GPL(usb_submit_urb);
  
  /*-------------------------------------------------------------------*/
  
  /**
   * usb_unlink_urb - abort/cancel a transfer request for an endpoint
   * @urb: pointer to urb describing a previously submitted request,
   *	may be NULL
   *
   * This routine cancels an in-progress request.  URBs complete only once
   * per submission, and may be canceled only once per submission.
   * Successful cancellation means termination of @urb will be expedited
   * and the completion handler will be called with a status code
   * indicating that the request has been canceled (rather than any other
   * code).
   *
   * Drivers should not call this routine or related routines, such as
   * usb_kill_urb() or usb_unlink_anchored_urbs(), after their disconnect
   * method has returned.  The disconnect function should synchronize with
   * a driver's I/O routines to insure that all URB-related activity has
   * completed before it returns.
   *
   * This request is asynchronous, however the HCD might call the ->complete()
   * callback during unlink. Therefore when drivers call usb_unlink_urb(), they
   * must not hold any locks that may be taken by the completion function.
   * Success is indicated by returning -EINPROGRESS, at which time the URB will
   * probably not yet have been given back to the device driver. When it is
   * eventually called, the completion function will see @urb->status ==
   * -ECONNRESET.
   * Failure is indicated by usb_unlink_urb() returning any other value.
   * Unlinking will fail when @urb is not currently "linked" (i.e., it was
   * never submitted, or it was unlinked before, or the hardware is already
   * finished with it), even if the completion handler has not yet run.
   *
   * The URB must not be deallocated while this routine is running.  In
   * particular, when a driver calls this routine, it must insure that the
   * completion handler cannot deallocate the URB.
   *
   * Unlinking and Endpoint Queues:
   *
   * [The behaviors and guarantees described below do not apply to virtual
   * root hubs but only to endpoint queues for physical USB devices.]
   *
   * Host Controller Drivers (HCDs) place all the URBs for a particular
   * endpoint in a queue.  Normally the queue advances as the controller
   * hardware processes each request.  But when an URB terminates with an
   * error its queue generally stops (see below), at least until that URB's
   * completion routine returns.  It is guaranteed that a stopped queue
   * will not restart until all its unlinked URBs have been fully retired,
   * with their completion routines run, even if that's not until some time
   * after the original completion handler returns.  The same behavior and
   * guarantee apply when an URB terminates because it was unlinked.
   *
   * Bulk and interrupt endpoint queues are guaranteed to stop whenever an
   * URB terminates with any sort of error, including -ECONNRESET, -ENOENT,
   * and -EREMOTEIO.  Control endpoint queues behave the same way except
   * that they are not guaranteed to stop for -EREMOTEIO errors.  Queues
   * for isochronous endpoints are treated differently, because they must
   * advance at fixed rates.  Such queues do not stop when an URB
   * encounters an error or is unlinked.  An unlinked isochronous URB may
   * leave a gap in the stream of packets; it is undefined whether such
   * gaps can be filled in.
   *
   * Note that early termination of an URB because a short packet was
   * received will generate a -EREMOTEIO error if and only if the
   * URB_SHORT_NOT_OK flag is set.  By setting this flag, USB device
   * drivers can build deep queues for large or complex bulk transfers
   * and clean them up reliably after any sort of aborted transfer by
   * unlinking all pending URBs at the first fault.
   *
   * When a control URB terminates with an error other than -EREMOTEIO, it
   * is quite likely that the status stage of the transfer will not take
   * place.
   */
  int usb_unlink_urb(struct urb *urb)
  {
  	if (!urb)
  		return -EINVAL;
  	if (!urb->dev)
  		return -ENODEV;
  	if (!urb->ep)
  		return -EIDRM;
  	return usb_hcd_unlink_urb(urb, -ECONNRESET);
  }
  EXPORT_SYMBOL_GPL(usb_unlink_urb);
  
  /**
   * usb_kill_urb - cancel a transfer request and wait for it to finish
   * @urb: pointer to URB describing a previously submitted request,
   *	may be NULL
   *
   * This routine cancels an in-progress request.  It is guaranteed that
   * upon return all completion handlers will have finished and the URB
   * will be totally idle and available for reuse.  These features make
   * this an ideal way to stop I/O in a disconnect() callback or close()
   * function.  If the request has not already finished or been unlinked
   * the completion handler will see urb->status == -ENOENT.
   *
   * While the routine is running, attempts to resubmit the URB will fail
   * with error -EPERM.  Thus even if the URB's completion handler always
   * tries to resubmit, it will not succeed and the URB will become idle.
   *
   * The URB must not be deallocated while this routine is running.  In
   * particular, when a driver calls this routine, it must insure that the
   * completion handler cannot deallocate the URB.
   *
   * This routine may not be used in an interrupt context (such as a bottom
   * half or a completion handler), or when holding a spinlock, or in other
   * situations where the caller can't schedule().
   *
   * This routine should not be called by a driver after its disconnect
   * method has returned.
   */
  void usb_kill_urb(struct urb *urb)
  {
  	might_sleep();
  	if (!(urb && urb->dev && urb->ep))
  		return;
  	atomic_inc(&urb->reject);
  
  	usb_hcd_unlink_urb(urb, -ENOENT);
  	wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);
  
  	atomic_dec(&urb->reject);
  }
  EXPORT_SYMBOL_GPL(usb_kill_urb);
  
  /**
   * usb_poison_urb - reliably kill a transfer and prevent further use of an URB
   * @urb: pointer to URB describing a previously submitted request,
   *	may be NULL
   *
   * This routine cancels an in-progress request.  It is guaranteed that
   * upon return all completion handlers will have finished and the URB
   * will be totally idle and cannot be reused.  These features make
   * this an ideal way to stop I/O in a disconnect() callback.
   * If the request has not already finished or been unlinked
   * the completion handler will see urb->status == -ENOENT.
   *
   * After and while the routine runs, attempts to resubmit the URB will fail
   * with error -EPERM.  Thus even if the URB's completion handler always
   * tries to resubmit, it will not succeed and the URB will become idle.
   *
   * The URB must not be deallocated while this routine is running.  In
   * particular, when a driver calls this routine, it must insure that the
   * completion handler cannot deallocate the URB.
   *
   * This routine may not be used in an interrupt context (such as a bottom
   * half or a completion handler), or when holding a spinlock, or in other
   * situations where the caller can't schedule().
   *
   * This routine should not be called by a driver after its disconnect
   * method has returned.
   */
  void usb_poison_urb(struct urb *urb)
  {
  	might_sleep();
  	if (!(urb && urb->dev && urb->ep))
  		return;
  	atomic_inc(&urb->reject);
  
  	usb_hcd_unlink_urb(urb, -ENOENT);
  	wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);
  }
  EXPORT_SYMBOL_GPL(usb_poison_urb);
  
  void usb_unpoison_urb(struct urb *urb)
  {
  	if (!urb)
  		return;
  
  	atomic_dec(&urb->reject);
  }
  EXPORT_SYMBOL_GPL(usb_unpoison_urb);
  
  /**
   * usb_kill_anchored_urbs - cancel transfer requests en masse
   * @anchor: anchor the requests are bound to
   *
   * this allows all outstanding URBs to be killed starting
   * from the back of the queue
   *
   * This routine should not be called by a driver after its disconnect
   * method has returned.
   */
  void usb_kill_anchored_urbs(struct usb_anchor *anchor)
  {
  	struct urb *victim;
  
  	spin_lock_irq(&anchor->lock);
  	while (!list_empty(&anchor->urb_list)) {
  		victim = list_entry(anchor->urb_list.prev, struct urb,
  				    anchor_list);
  		/* we must make sure the URB isn't freed before we kill it*/
  		usb_get_urb(victim);
  		spin_unlock_irq(&anchor->lock);
  		/* this will unanchor the URB */
  		usb_kill_urb(victim);
  		usb_put_urb(victim);
  		spin_lock_irq(&anchor->lock);
  	}
  	spin_unlock_irq(&anchor->lock);
  }
  EXPORT_SYMBOL_GPL(usb_kill_anchored_urbs);
  
  
  /**
   * usb_poison_anchored_urbs - cease all traffic from an anchor
   * @anchor: anchor the requests are bound to
   *
   * this allows all outstanding URBs to be poisoned starting
   * from the back of the queue. Newly added URBs will also be
   * poisoned
   *
   * This routine should not be called by a driver after its disconnect
   * method has returned.
   */
  void usb_poison_anchored_urbs(struct usb_anchor *anchor)
  {
  	struct urb *victim;
  
  	spin_lock_irq(&anchor->lock);
  	anchor->poisoned = 1;
  	while (!list_empty(&anchor->urb_list)) {
  		victim = list_entry(anchor->urb_list.prev, struct urb,
  				    anchor_list);
  		/* we must make sure the URB isn't freed before we kill it*/
  		usb_get_urb(victim);
  		spin_unlock_irq(&anchor->lock);
  		/* this will unanchor the URB */
  		usb_poison_urb(victim);
  		usb_put_urb(victim);
  		spin_lock_irq(&anchor->lock);
  	}
  	spin_unlock_irq(&anchor->lock);
  }
  EXPORT_SYMBOL_GPL(usb_poison_anchored_urbs);
  
  /**
   * usb_unpoison_anchored_urbs - let an anchor be used successfully again
   * @anchor: anchor the requests are bound to
   *
   * Reverses the effect of usb_poison_anchored_urbs
   * the anchor can be used normally after it returns
   */
  void usb_unpoison_anchored_urbs(struct usb_anchor *anchor)
  {
  	unsigned long flags;
  	struct urb *lazarus;
  
  	spin_lock_irqsave(&anchor->lock, flags);
  	list_for_each_entry(lazarus, &anchor->urb_list, anchor_list) {
  		usb_unpoison_urb(lazarus);
  	}
  	anchor->poisoned = 0;
  	spin_unlock_irqrestore(&anchor->lock, flags);
  }
  EXPORT_SYMBOL_GPL(usb_unpoison_anchored_urbs);
  /**
   * usb_unlink_anchored_urbs - asynchronously cancel transfer requests en masse
   * @anchor: anchor the requests are bound to
   *
   * this allows all outstanding URBs to be unlinked starting
   * from the back of the queue. This function is asynchronous.
   * The unlinking is just tiggered. It may happen after this
   * function has returned.
   *
   * This routine should not be called by a driver after its disconnect
   * method has returned.
   */
  void usb_unlink_anchored_urbs(struct usb_anchor *anchor)
  {
  	struct urb *victim;
  
  	while ((victim = usb_get_from_anchor(anchor)) != NULL) {
  		usb_unlink_urb(victim);
  		usb_put_urb(victim);
  	}
  }
  EXPORT_SYMBOL_GPL(usb_unlink_anchored_urbs);
  
  /**
   * usb_wait_anchor_empty_timeout - wait for an anchor to be unused
   * @anchor: the anchor you want to become unused
   * @timeout: how long you are willing to wait in milliseconds
   *
   * Call this is you want to be sure all an anchor's
   * URBs have finished
   */
  int usb_wait_anchor_empty_timeout(struct usb_anchor *anchor,
  				  unsigned int timeout)
  {
  	return wait_event_timeout(anchor->wait, list_empty(&anchor->urb_list),
  				  msecs_to_jiffies(timeout));
  }
  EXPORT_SYMBOL_GPL(usb_wait_anchor_empty_timeout);
  
  /**
   * usb_get_from_anchor - get an anchor's oldest urb
   * @anchor: the anchor whose urb you want
   *
   * this will take the oldest urb from an anchor,
   * unanchor and return it
   */
  struct urb *usb_get_from_anchor(struct usb_anchor *anchor)
  {
  	struct urb *victim;
  	unsigned long flags;
  
  	spin_lock_irqsave(&anchor->lock, flags);
  	if (!list_empty(&anchor->urb_list)) {
  		victim = list_entry(anchor->urb_list.next, struct urb,
  				    anchor_list);
  		usb_get_urb(victim);
  		__usb_unanchor_urb(victim, anchor);
  	} else {
  		victim = NULL;
  	}
  	spin_unlock_irqrestore(&anchor->lock, flags);
  
  	return victim;
  }
  
  EXPORT_SYMBOL_GPL(usb_get_from_anchor);
  
  /**
   * usb_scuttle_anchored_urbs - unanchor all an anchor's urbs
   * @anchor: the anchor whose urbs you want to unanchor
   *
   * use this to get rid of all an anchor's urbs
   */
  void usb_scuttle_anchored_urbs(struct usb_anchor *anchor)
  {
  	struct urb *victim;
  	unsigned long flags;
  
  	spin_lock_irqsave(&anchor->lock, flags);
  	while (!list_empty(&anchor->urb_list)) {
  		victim = list_entry(anchor->urb_list.prev, struct urb,
  				    anchor_list);
  		__usb_unanchor_urb(victim, anchor);
  	}
  	spin_unlock_irqrestore(&anchor->lock, flags);
  }
  
  EXPORT_SYMBOL_GPL(usb_scuttle_anchored_urbs);
  
  /**
   * usb_anchor_empty - is an anchor empty
   * @anchor: the anchor you want to query
   *
   * returns 1 if the anchor has no urbs associated with it
   */
  int usb_anchor_empty(struct usb_anchor *anchor)
  {
  	return list_empty(&anchor->urb_list);
  }
  
  EXPORT_SYMBOL_GPL(usb_anchor_empty);
  
  