ioctl - control device
#include <sys/ioctl.h>
int ioctl(int fd, unsigned long request,
...);
The
ioctl() system call 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.
- EBADF
- fd is not a valid file descriptor.
- EFAULT
- argp references an inaccessible memory area.
- EINVAL
- request or argp is not valid.
- ENOTTY
- fd is not associated with a character special device.
- ENOTTY
- 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() system 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_console(2),
ioctl_fat(2),
ioctl_ficlonerange(2),
ioctl_fideduperange(2),
ioctl_getfsmap(2),
ioctl_iflags(2),
ioctl_list(2),
ioctl_ns(2),
ioctl_tty(2),
ioctl_userfaultfd(2),
open(2),
sd(4),
tty(4)