man/man2/ioctl.2

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 IOCTL 2 "June 18, 2020"
 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).
 ATTRIBUTES
See attributes(7) for descriptions of the following attributes:


ATTRIBUTE TYPE ATTRIBUTE VALUE
Interface Stability Standard


 SEE ALSO
 streamio (4I),  termio (4I),  attributes (7),  standards (7)