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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)						      BSD System Calls Manual							  IOCTL(2)

NAME
ioctl -- control device LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/ioctl.h> int ioctl(int d, unsigned long request, ...); DESCRIPTION
The ioctl() function manipulates the underlying device parameters of special files. In particular, many operating characteristics of charac- ter special files (e.g. terminals) may be controlled with ioctl() requests. The argument d must be an open file descriptor. An ioctl() request has encoded in it whether the argument is an ``in'', ``out'', or ``inout'' parameter, and the size of the first variadic argument in bytes. Note that there can be only one variadic argument but cannot be represented as a void * argument in the prototype because this would require a cast to pass integral types without warnings. Macros and defines used in specifying an ioctl() request are located in the header <sys/ioctl.h>. GENERIC IOCTLS
Some ioctls are applicable to any file descriptor. These include: FIOCLEX Set close-on-exec flag. The file will be closed when exec(3) is invoked (This is equivalent to fcntl() F_SETFD FD_CLOEXEC and the fcntl() form should be preferred). FIONCLEX Clear close-on-exec flag. The file will remain open across exec(3) (This is equivalent to fcntl() F_SETFD 0 and the fcntl() form should be preferred). 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 tty devices, these bytes are typically queued for delivery to the tty hardware. For TCP sockets, these bytes have not yet been acknowl- edged by the other side of the connection. For files, this operation always returns zero as files do not have send queues. 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. FIONBIO int Set non-blocking I/O mode if the argument is non-zero. In non-blocking mode, read(2) or write(2) calls return -1 and set errno to EAGAIN immediately when no data is available (This is equivalent to fcntl() F_SETFL O_NONBLOCK and the fcntl() form should be pre- ferred). FIOASYNC int Set asynchronous I/O mode if the argument is non-zero (This is equivalent to fcntl() F_SETFL O_ASYNC and the fcntl() form should be preferred). In asynchronous mode, the process or process group specified by FIOSETOWN will start receiving SIGIO signals when data is available. The SIGIO signal will be delivered when data is available on the file descriptor. FIOSETOWN, FIOGETOWN int Set/get the process or the process group (if negative) that should receive SIGIO signals when data is available (This is equivalent to fcntl() F_SETOWN pid_t and the fcntl form should be preferred). RETURN VALUES
If an error has occurred, a value of -1 is returned and errno is set to indicate the error. ERRORS
ioctl() will fail if: [EBADF] d is not a valid descriptor. [EFAULT] argp points outside the process's allocated address space. [EINVAL] request or argp is not valid. [ENOTTY] d is not associated with a character special device; or the specified request does not apply to the kind of object that the descriptor d references. SEE ALSO
mt(1), execve(2), fcntl(2), intro(4), tty(4) HISTORY
An ioctl() function call appeared in Version 7 AT&T UNIX. BSD
December 19, 2010 BSD
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