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       ioctl - control device


       #include <sys/ioctl.h>

       int ioctl(int d, int 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 d 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  d is not a valid descriptor.

       EFAULT argp references an inaccessible memory area.

       EINVAL Request or argp is not valid.

       ENOTTY d is not associated with a character special device.

       ENOTTY The specified request does not apply to the kind of object  that
              the descriptor d 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_list(2), open(2), sd(4), tty(4)


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