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.
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
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
Page 1 May 1989
IOCTL(2) IOCTL(2)
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.
[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that machine is no longer active.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), 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.
Page 2 May 1989