ioctl — control device
|unsigned long request,|
manipulates the underlying device parameters of special
files. In particular, many operating characteristics of
character special files (e.g., terminals) may be controlled
ioctl() requests. The
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.
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
request are located in the file
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.
references an inaccessible memory area.
argp is not
fd is not
associated with a character special device.
The specified request does not apply to the kind of
object that the file descriptor
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
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
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(#)ioctl.2 6.4 (Berkeley) 3/10/91
Modified 1993-07-23 by Rik Faith <faithcs.unc.edu>
Modified 1996-10-22 by Eric S. Raymond <esrthyrsus.com>
Modified 1999-06-25 by Rachael Munns <vashtidream.org.uk>
Modified 2000-09-21 by Andries Brouwer <aebcwi.nl>