NAME

ioctl − control device

SYNOPSIS

#include <sys/ioctl.h>

ioctl (fildes, request, arg)
int fildes, request;

DESCRIPTION

Ioctl performs a variety of functions on character special files (devices).  The write-ups of various devices in Section (7) discuss how ioctl applies to them.  The type of arg is dependent on the specific ioctl call, as described in Section (7). 

Request is made up of several fields.  They encode the size and direction of the argument (referenced by arg ), as well as the desired command.  An enumeration of the request fields are:

IOC_IN Argument is read by the driver.  (That is, the argument is copied from the application to the driver.) 

IOC_OUT Argument is written by the driver.  (That is, the argument is copied from the driver to the application.) 

IOCSIZE_MASK Number of bytes in the passed argument.  A nonzero size indicates that arg is a pointer to the passed argument.  A zero size indicates that arg is the passed argument (if the driver wants to use it), and is not treated as a pointer. 

IOCCMD_MASK The request command itself. 

When both IOC_IN and IOC_OUT are zero, it can be assumed that request is not encoded for size and direction, for compatibility purposes.  Requests which do not require any data to be passed and requests which use arg as a value (as opposed to a pointer), have the IOC_IN bit set to one and the IOCSIZE_MASK field set to zero. 

The following macros are used to create the request argument.  X and y are concatenated ((x<<8) | y) to form IOCCMD and shifted into the proper location according to IOCCMD_MASK.  T is the type (e.g. struct hpib_cmd) of the actual argument that the request references, and its size is taken and shifted into the appropriate place according to IOCSIZE_MASK. 

_IOR(x,y,t) Sets IOC_OUT and initializes the values at IOCCMD_MASK and IOCSIZE_MASK accordingly. 

_IOW(x,y,t) Sets IOC_IN and initializes the values at IOCCMD_MASK and IOCSIZE_MASK accordin gly. 

_IOWR(x,y,t) Sets both IOC_IN and IOC_OUT and initializes the values at IOCCMD_MASK and IOCSIZE_MASK. 

Note: any data structure referenced by arg may not contain any pointers. 

RETURNS

If an error has occurred, a value of −1 is returned and errno is set to indicate the error. 

Ioctl will fail if one or more of the following are true:

­[EBADF] Fildes is not a valid open file descriptor. 

­[ENOTTY] The request is not appropriate to the selected device. 

­[EINVAL] Request or arg is not valid. 

­[EINTR] A signal was caught during the ioctl system call. 

­[EPERM] Typically this error indicates that an ioctl request was attempted that is forbidden in some way to the calling process. 

WARNINGS

Check all references to signal(2) for appropriateness on systems that support sigvector(2). Sigvector(2) can affect the behavior described on this page.

HARDWARE DEPENDENCIES

Series 200, 300, 500
Asynchronous I/O is not supported.

AUTHOR

Ioctl was developed by AT&T Bell Laboratories and the Hewlett-Packard Company. 

SEE ALSO

ioctl(5), termio(7). 

Hewlett-Packard Company  —  Version B.1,  April 12, 1993