ioctl(2) [linux man page]
IOCTL(2) Linux Programmer's Manual IOCTL(2) NAME
ioctl - control device SYNOPSIS
#include <sys/ioctl.h> int ioctl(int d, int request, ...); DESCRIPTION
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 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>. RETURN VALUE
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. ERRORS
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. CONFORMING TO
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. NOTES
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. SEE ALSO
execve(2), fcntl(2), ioctl_list(2), open(2), sd(4), tty(4) COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2000-09-21 IOCTL(2)
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ioctl(2) System Calls ioctl(2) NAME
ioctl - control device SYNOPSIS
#include <unistd.h> #include <stropts.h> int ioctl(int fildes, int request, /* arg */ ...); DESCRIPTION
The ioctl() function performs a variety of control functions on devices and STREAMS. For non-STREAMS files, the functions performed by this call are device-specific control functions. The request argument and an optional third argument with varying type are passed to the file designated by fildes and are interpreted by the device driver. For STREAMS files, specific functions are performed by the ioctl() function as described in streamio(7I). The fildes argument is an open file descriptor that refers to a device. The request argument selects the control function to be performed and depends on the device being addressed. The arg argument represents a third argument that has additional information that is needed by this specific device to perform the requested function. The data type of arg depends upon the particular control request, but it is either an int or a pointer to a device-specific data structure. In addition to device-specific and STREAMS functions, generic functions are provided by more than one device driver (for example, the gen- eral terminal interface.) See termio(7I)). RETURN VALUES
Upon successful completion, the value returned depends upon the device control function, but must be a non-negative integer. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The ioctl() function will fail for any type of file if: EBADF The fildes argument is not a valid open file descriptor. EINTR A signal was caught during the execution of the ioctl() function. EINVAL The STREAM or multiplexer referenced by fildes is linked (directly or indirectly) downstream from a multiplexer. The ioctl() function will also fail if the device driver detects an error. In this case, the error is passed through ioctl() without change to the caller. A particular driver might not have all of the following error cases. Under the following conditions, requests to device drivers may fail and set errno to indicate the error EFAULT The request argument requires a data transfer to or from a buffer pointed to by arg, but arg points to an illegal address. EINVAL The request or arg argument is not valid for this device. EIO Some physical I/O error has occurred. ENOLINK The fildes argument is on a remote machine and the link to that machine is no longer active. ENOTTY The fildes argument is not associated with a STREAMS device that accepts control functions. ENXIO The request and arg arguments are valid for this device driver, but the service requested can not be performed on this par- ticular subdevice. ENODEV The fildes argument refers to a valid STREAMS device, but the corresponding device driver does not support the ioctl() function. STREAMS errors are described in streamio(7I). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
attributes(5), standards(5), streamio(7I), termio(7I) SunOS 5.10 15 Feb 1996 ioctl(2)