Tribblix: manual page: ioctl.2

IOCTL(2) System Calls IOCTL(2)

NAME

ioctl - control device

SYNOPSIS

#include <unistd.h>
#include <stropts.h>

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

DESCRIPTION

The ioctl() function 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 request
argument and an optional third argument with varying type are passed
to the device file designated by fildes and are interpreted by the
device driver.

For streams files, specific functions are performed by the ioctl()
function as described in streamio(4I).

The fildes argument is an open file descriptor that refers to a
device. The request argument selects the control function to be
performed and depends on the device being addressed. The arg
argument 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 or disk interfaces.) See termio(4I)),
dkio(4I), etc..

RETURN VALUES

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

ERRORS

The ioctl() function will fail for any type of file if:

EBADF
The fildes argument is not a valid open file descriptor.

EINTR
A signal was caught during the execution of the ioctl()
function.

EINVAL
The stream or multiplexer referenced by fildes is linked
(directly or indirectly) downstream from a multiplexer.

The ioctl() function 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. Under the following conditions, requests to
device drivers may fail and set errno to indicate the error

EFAULT
The request argument requires a data transfer to or from a
buffer pointed to by arg, but arg points to an illegal
address.

EINVAL
The request or arg argument is not valid for this device.
Many devices return ENOTTY for an unknown request.

EIO
Some physical I/O error has occurred.

ENOLINK
The fildes argument is on a remote machine and the link to
that machine is no longer active.

ENOTTY
The fildes argument is not associated with a device that
accepts control functions.

The device driver does not know the request command.

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

The device driver does not support the ioctl() function.

ENODEV
The fildes argument refers to a valid streams device, but
the corresponding device driver does not support the
ioctl() function.

Streams errors are described in streamio(4I).