IOCTL(2) INTERACTIVE UNIX System IOCTL(2)
NAME
ioctl - control device
SYNOPSIS
int ioctl (fildes, request, arg)
int fildes, request;
DESCRIPTION
The ioctl system call performs a variety of control func-
tions 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 dev-
ice 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, gen-
eric functions are provided by more than one device driver,
for example, the general terminal interface [see termio(7)].
The ioctl system call will fail for any type of file if one
or more of the following is true:
[EBADF] Fildes is not a valid open file descriptor.
[ENOTTY] Fildes is not associated with a device driver
that accepts control functions.
[EINTR] A signal was caught during the ioctl system
call.
The ioctl system call 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 is true:
[EFAULT] Request requires a data transfer to or from a
buffer pointed to by arg, but some part of
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IOCTL(2) INTERACTIVE UNIX System IOCTL(2)
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 cannot 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that machine is no longer active.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 INTERACTIVE UNIX System
User's/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.
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