ioctl — control device
#include <sys/ioctl.h>
int
ioctl( |
int fd, |
| unsigned long 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 fd 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 nonnegative value on success.
On error, −1 is returned, and errno is set appropriately.
fd is not a
valid file descriptor.
argp
references an inaccessible memory area.
request or
argp is not
valid.
fd is not
associated with a character special device.
The specified request does not apply to the kind of
object that the file descriptor fd references.
No single standard. Arguments, returns, and semantics of
ioctl() 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.
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.
execve(2), fcntl(2), ioctl_fideduperange(2), ioctl_fat(2), ioctl_ficlonerange(2), ioctl_list(2), open(2), console_ioctl(4), tty_ioctl(4), sd(4), tty(4)
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
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