IOCTL(2)                                                 IOCTL(2)



     NAME
          ioctl - control device

     SYNOPSIS
          int ioctl (fildes, request, arg)
          int fildes, request;

     DESCRIPTION
          ioctl performs a variety of control functions on devices and
          STREAMS.  For non-STREAMS files, the functions performed by
          this call are device-specific control functions.  The
          arguments request and arg are passed to the file designated
          by fildes and are interpreted by the device driver.  This
          control is infrequently used on non-STREAMS devices, with
          the basic input/output functions performed through the
          read(2) and write(2) system calls.

          Fildes is an open file descriptor that refers to a device.
          Request selects the control function to be performed and
          will depend on the device being addressed.  Arg represents
          additional information that is needed by this specific
          device to perform the requested function.  The data type of
          arg depends upon the particular control request, but it is
          either an integer or a pointer to a device-specific data
          structure.

          In addition to device-specific and STREAMS functions,
          generic functions are provided by more than one device
          driver, for example, the general terminal interface [see
          termio(7)].

          ioctl will fail for any type of file if one or more of the
          following are true:

          [EBADF]        Fildes is not a valid open file descriptor.

          [ENOTTY]       Fildes is not associated with a device driver
                         that accepts control functions.

          [EINTR]        A signal was caught during the ioctl system
                         call.

          ioctl will also fail if the device driver detects an error.
          In this case, the error is passed through ioctl without
          change to the caller.  A particular driver might not have
          all of the following error cases.  Other requests to device
          drivers will fail if one or more of the following are true:

          [EFAULT]       Request requires a data transfer to or from a
                         buffer pointed to by arg, but some part of
                         the buffer is outside the process's allocated
                         space.



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     IOCTL(2)                                                 IOCTL(2)



          [EINVAL]       Request or arg is not valid for this device.

          [EIO]          Some physical I/O error has occurred.

          [ENXIO]        The request and arg are valid for this device
                         driver, but the service requested can not be
                         performed on this particular subdevice.

          [ENOLINK]      Fildes is on a remote machine and the link to
                         that machine is no longer active.

     SEE ALSO
          termio(7) in the System Administrator's Reference Manual.

     DIAGNOSTICS
          Upon successful completion, the value returned depends upon
          the device control function, but must be a non-negative
          integer. Otherwise, a value of -1 is returned and errno is
          set to indicate the error.

     ORIGIN
          AT&T V.3

































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