================================================================
  HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices
  ================================================================

  
  The hidraw driver provides a raw interface to USB and Bluetooth Human
  Interface Devices (HIDs).  It differs from hiddev in that reports sent and
  received are not parsed by the HID parser, but are sent to and received from
  the device unmodified.
  
  Hidraw should be used if the userspace application knows exactly how to
  communicate with the hardware device, and is able to construct the HID
  reports manually.  This is often the case when making userspace drivers for
  custom HID devices.
  
  Hidraw is also useful for communicating with non-conformant HID devices
  which send and receive data in a way that is inconsistent with their report
  descriptors.  Because hiddev parses reports which are sent and received
  through it, checking them against the device's report descriptor, such
  communication with these non-conformant devices is impossible using hiddev.
  Hidraw is the only alternative, short of writing a custom kernel driver, for
  these non-conformant devices.
  
  A benefit of hidraw is that its use by userspace applications is independent
  of the underlying hardware type.  Currently, Hidraw is implemented for USB
  and Bluetooth.  In the future, as new hardware bus types are developed which
  use the HID specification, hidraw will be expanded to add support for these
  new bus types.
  
  Hidraw uses a dynamic major number, meaning that udev should be relied on to
  create hidraw device nodes.  Udev will typically create the device nodes
  directly under /dev (eg: /dev/hidraw0).  As this location is distribution-
  and udev rule-dependent, applications should use libudev to locate hidraw
  devices attached to the system.  There is a tutorial on libudev with a
  working example at:

  	http://www.signal11.us/oss/udev/
  
  The HIDRAW API
  ---------------
  
  read()
  -------
  read() will read a queued report received from the HID device. On USB
  devices, the reports read using read() are the reports sent from the device
  on the INTERRUPT IN endpoint.  By default, read() will block until there is
  a report available to be read.  read() can be made non-blocking, by passing
  the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using
  fcntl().
  
  On a device which uses numbered reports, the first byte of the returned data
  will be the report number; the report data follows, beginning in the second
  byte.  For devices which do not use numbered reports, the report data
  will begin at the first byte.
  
  write()

  -------

  The write() function will write a report to the device. For USB devices, if
  the device has an INTERRUPT OUT endpoint, the report will be sent on that
  endpoint. If it does not, the report will be sent over the control endpoint,
  using a SET_REPORT transfer.
  
  The first byte of the buffer passed to write() should be set to the report
  number.  If the device does not use numbered reports, the first byte should
  be set to 0. The report data itself should begin at the second byte.
  
  ioctl()

  -------

  Hidraw supports the following ioctls:

  HIDIOCGRDESCSIZE:
  	Get Report Descriptor Size

  This ioctl will get the size of the device's report descriptor.

  HIDIOCGRDESC:
  	Get Report Descriptor

  This ioctl returns the device's report descriptor using a
  hidraw_report_descriptor struct.  Make sure to set the size field of the
  hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.

  HIDIOCGRAWINFO:
  	Get Raw Info

  This ioctl will return a hidraw_devinfo struct containing the bus type, the
  vendor ID (VID), and product ID (PID) of the device. The bus type can be one

  of::
  
  	- BUS_USB
  	- BUS_HIL
  	- BUS_BLUETOOTH
  	- BUS_VIRTUAL

  which are defined in uapi/linux/input.h.

  HIDIOCGRAWNAME(len):
  	Get Raw Name

  This ioctl returns a string containing the vendor and product strings of
  the device.  The returned string is Unicode, UTF-8 encoded.

  HIDIOCGRAWPHYS(len):
  	Get Physical Address

  This ioctl returns a string representing the physical address of the device.
  For USB devices, the string contains the physical path to the device (the
  USB controller, hubs, ports, etc).  For Bluetooth devices, the string
  contains the hardware (MAC) address of the device.

  HIDIOCSFEATURE(len):
  	Send a Feature Report

  This ioctl will send a feature report to the device.  Per the HID
  specification, feature reports are always sent using the control endpoint.
  Set the first byte of the supplied buffer to the report number.  For devices
  which do not use numbered reports, set the first byte to 0. The report data
  begins in the second byte. Make sure to set len accordingly, to one more
  than the length of the report (to account for the report number).

  HIDIOCGFEATURE(len):
  	Get a Feature Report

  This ioctl will request a feature report from the device using the control
  endpoint.  The first byte of the supplied buffer should be set to the report
  number of the requested report.  For devices which do not use numbered
  reports, set the first byte to 0.  The report will be returned starting at
  the first byte of the buffer (ie: the report number is not returned).
  
  Example

  -------

  In samples/, find hid-example.c, which shows examples of read(), write(),
  and all the ioctls for hidraw.  The code may be used by anyone for any
  purpose, and can serve as a starting point for developing applications using
  hidraw.
  
  Document by:

  	Alan Ott <alan@signal11.us>, Signal 11 Software