ioctl — control device
#include <sys/ioctl.h>
int
ioctl( |
int | d, |
int | request, | |
...) ; |
The ioctl
() function
manipulates the underlying device parameters of special
files. In particular, many operating characteristics of
character special files (e.g. terminals) may be controlled
with ioctl
() requests. The
argument d
must be an
open file descriptor.
The second argument is a device-dependent request code.
The third argument is an untyped pointer to memory. It's
traditionally char *argp
(from the days before
void * was valid C),
and will be so named for this discussion.
An ioctl
() request
has encoded in it
whether the argument is an in
parameter or out
parameter, and the size
of the argument argp
in bytes. Macros and
defines used in specifying an ioctl
() request
are located in the file
<sys/ioctl.h>
.
Usually, on success zero is returned. A few ioctl
() requests use the return value as an
output parameter and return a non-negative value on success.
On error, −1 is returned, and errno
is set appropriately.
d
is not a
valid descriptor.
argp
references an inaccessible memory area.
Request
or
argp
is not
valid.
d
is not
associated with a character special device.
The specified request does not apply to the kind of
object that the descriptor d
references.
In order to use this call, one needs an open file descriptor. Often the open(2) call has unwanted side effects, that can be avoided under Linux by giving it the O_NONBLOCK flag.
No single standard. Arguments, returns, and semantics of
ioctl(2) vary according to
the device driver in question (the call is used as a
catch-all for operations that don't cleanly fit the Unix
stream I/O model). See ioctl_list(2) for a list of
many of the known ioctl
()
calls. The ioctl
() function
call appeared in Version 7 AT&T Unix.
execve(2), fcntl(2), ioctl_list(2), open(2), mt(4), sd(4), tty(4)
|