IOCTL(2)                   Linux Programmer's Manual                  IOCTL(2)

       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  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  ar-
       gument  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 pa-
       rameter 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_ficlon-
       erange(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)

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Linux                             2017-05-03                          IOCTL(2)
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