ioctl(2)

NAME

ioctl − control device

SYNOPSIS

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

For STREAMS files, specific functions are performed by the ioctl() call as described in streamio(7I).

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, generic functions are provided by more than one device driver, for example, the general terminal interface (see termio(7I)).

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

ioctl() fails for any type of file if one or more of the following are true:

EBADF fildes is not a valid open file descriptor.

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

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

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:

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

EINVAL request or arg is not valid for this device.

EIO Some physical I/O error has occurred.

ENOLINK fildes is on a remote machine and the link to that machine is no longer active.

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

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

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(7I).

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