ioctl(2)                  SYSTEM CALLS                   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,  gen-
     eric  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  fol-
     lowing 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:




                                                                1

ioctl(2)                  SYSTEM CALLS                   ioctl(2)



     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.

     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.




























                                                                2