IOCTL(2) Linux Programmer's Manual IOCTL(2)
ioctl - control device
int ioctl(int fd, unsigned long request, ...);
The ioctl() function manipulates the underlying device parameters of
special files. In particular, many operating characteristics of char-
acter 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 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 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_fat(2), ioctl_list(2), open(2), con-
sole_ioctl(4), tty_ioctl(4), sd(4), tty(4)
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Linux 2015-05-07 IOCTL(2)
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