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

       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 param-
       eter, 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

       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)

       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information    about    reporting    bugs,    can    be    found    at

Linux                                       2000-09-21                                   IOCTL(2)

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