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).

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)

June 18, 2020 IOCTL(2)