ioctl(2) [freebsd man page]
IOCTL(2) BSD System Calls Manual IOCTL(2) NAME
ioctl -- control device LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/ioctl.h> int ioctl(int fd, unsigned long request, ...); DESCRIPTION
The ioctl() system call 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 fd must be an open file descriptor. The third argument to ioctl() is traditionally named char *argp. Most uses of ioctl(), however, require the third argument to be a caddr_t or an int. An ioctl() request has encoded in it whether the argument is an ``in'' argument or ``out'' argument, 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>. GENERIC IOCTLS
Some generic ioctls are not implemented for all types of file descriptors. These include: FIONREAD int Get the number of bytes that are immediately available for reading. FIONWRITE int Get the number of bytes in the descriptor's send queue. These bytes are data which has been written to the descriptor but which are being held by the kernel for further processing. The nature of the required processing depends on the underlying device. For TCP sockets, these bytes have not yet been acknowledged by the other side of the connection. FIONSPACE int Get the free space in the descriptor's send queue. This value is the size of the send queue minus the number of bytes being held in the queue. Note: while this value represents the number of bytes that may be added to the queue, other resource limitations may cause a write not larger than the send queue's space to be blocked. One such limitation would be a lack of network buffers for a write to a network connection. RETURN VALUES
If an error has occurred, a value of -1 is returned and errno is set to indicate the error. ERRORS
The ioctl() system call will fail if: [EBADF] The fd argument is not a valid descriptor. [ENOTTY] The fd argument is not associated with a character special device. [ENOTTY] The specified request does not apply to the kind of object that the descriptor fd references. [EINVAL] The request or argp argument is not valid. [EFAULT] The argp argument points outside the process's allocated address space. SEE ALSO
execve(2), fcntl(2), intro(4), tty(4) HISTORY
The ioctl() function appeared in Version 7 AT&T UNIX. BSD
September 11, 2013 BSD
Check Out this Related Man Page
ioctl(2) System Calls Manual ioctl(2) NAME
ioctl - Controls devices SYNOPSIS
#include <stropts.h> int ioctl( int fildes, int request, ... /* arg */); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: ioctl(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Specifies the file descriptor of the requested device. Specifies the ioctl command to be performed on the device. Specifies parameters for this request. The type of arg is dependent on the specific ioctl() request and device to which the ioctl is targeted. See the appro- priate Section 7 reference page or the documentation accompanying the device for more information. 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 and arg parameters are passed to the file designated by fildes and are inter- preted by the device driver. This control is occasionally used on non-STREAMS devices, with the basic input/output functions performed through the read() and write() system calls. An ioctl() request has encoded in it whether the parameter is an "in" parameter or "out" parameter, and the size of the arg parameter in bytes. Macros and defines used to specify an ioctl() request are located in the <stropts.h> header file. For STREAMS files, specific functions are performed by the ioctl() function as described in streamio(7). STREAMS errors are described in streamio(7). RETURN VALUES
Upon successful completion, the ioctl() function returns a value other than -1 that depends upon the STREAMS device control function. If an error occurs, a value of -1 is returned and errno is set to indicate the error. ERRORS
The ioctl() function sets errno to the specified values for the following general conditions: The fildes parameter is not a valid open file descriptor. A signal was caught during the ioctl() operation. The STREAM or multiplexer referenced by fildes is linked (directly or indi- rectly) downstream from a multiplexer. If an underlying device driver detects an error, errno may be set to one of the following values: Either the request or arg parameter is not valid. Some physical I/O error has occurred. The fildes parameter is not associated with a STREAMS device that accepts control func- tions. (Defined for Issue 4 Version 2 and higher issues of the XSH specification.) [Tru64 UNIX] The fildes parameter is not associated with a character special device, or the specified request does not apply to the kind of object that the fildes parameter references. The request and arg parameters are valid for this device driver, but the service requested cannot be performed on the particular subdevice. The fildes parameter refers to a valid STREAMS device, but the corresponding device driver does not support the ioctl() function. RELATED INFORMATION
Functions: exec(2), fcntl(2) Files: tty(7), streamio(7) Standards: standards(5) delim off ioctl(2)