ioctl(2)                         UNIX System V                         ioctl(2)


NAME
      ioctl - control device

SYNOPSIS
      #include <unistd.h>

      int ioctl (int fildes, int request, ... /* arg */);

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.  request and an optional third argument with
      varying type are passed to the file designated by fildes and are
      interpreted by the device driver.  This control is not frequently used on
      non-STREAMS devices, where the basic input/output functions are usually
      performed through the read(2) and write(2) system calls.

      For STREAMS files, specific functions are performed by the ioctl call as
      described in streamio(7).

      fildes is an open file descriptor that refers to a device.  request
      selects the control function to be performed and depends on the device
      being addressed.  arg represents a third argument that has 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 int 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 fails 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 also fails 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.  Under
      the following conditions, requests to device drivers may fail and set
      errno to:

      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)                         UNIX System V                         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.

      STREAMS errors are described in streamio(7).

SEE ALSO
      streamio(7) in the Programmer's Guide: STREAMS.
      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.

































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