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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

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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 3.44 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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