ioctl(), vioctl()

Synopsis:

#include <sys/ioctl.h> 

int ioctl( int fd, 
           int request, 
           ... );

int vioctl( int fd, 
            int request, 
            va_list arg );

Arguments:

fd: An open file descriptor for the file or device that you want to manipulate.
request: What you want to do to the file or device; see below for a summary. The macros and definitions that you use in specifying a request are located in the file <sys/ioctl.h>.
arg: A variable-argument list of the additional arguments, which you must have initialized with the va_start() macro. Used with vioctl() only.
Additional arguments: As required by the request.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The ioctl() function manipulates the underlying parameters of files. In particular, it can be used to control many of the operating attributes of files (such as the attributes of terminals).

The vioctl() function is a "varargs" version of ioctl().

The request argument determines whether the subsequent arguments are an “in” or “out” parameter; it also specifies the size of the arguments in bytes.

I/O control commands

Use these macros to set up the I/O control commands:

_IO(class, cmd): A command with no associated data.
_IOR(class, cmd, data): Get information from the device.
_IOW(class, cmd, data): Pass information to the device.
_IOWR(class, cmd, data): Pass some information to the device, and get some from it.

The arguments to these macros are:

class: A single character that denotes the major category for the command.
cmd: An integer that identifies the command in the class.
data: The type of data to pass to and/or from the device. The additional argument to ioctl() must be a pointer to this type of data.
Note: The size of the structure that's passed as the last field to the __IO* macros must be less than 2^14 == 16 KB. Anything larger than this interferes with the upper two directional bits.

How ioctl() commands map to other commands

Some ioctl() commands map to calls to fcntl(), tcgetattr(), tcsetattr(), and tcsetsid(). Other commands are transformed into devctl() commands, and the rest are simply passed to devctl(). Here's a summary (for details, see the Devctl and Ioctl Commands reference):

ioctl() command	Description	Maps to:
CIO*, CRIOGET	Handle cryptography operations	These commands are used by the legacy devcrypto system driver interface. The preferred cryptography mechanism is the newer qcrypto library; for more information, see “Cryptography for developers” in the System Security Guide.
FIOASYNC	Set or clear asynchronous I/O	fcntl(): F_GETFL (which becomes a devctl() DCMD_ALL_GETFLAGS), followed by fcntl(): F_SETFL (which becomes a devctl() DCMD_ALL_SETFLAGS), setting or clearing O_ASYNC
FIOCLEX	Set “close on exec” on a file descriptor	fcntl(): F_SETFD with FD_CLOEXEC
FIOGETOWN	Get the owner	fcntl(): F_GETOWN
FIONBIO	Set or clear non-blocking I/O	fcntl(): F_GETFL (which becomes a devctl() DCMD_ALL_GETFLAGS), followed by fcntl(): F_SETFL (which becomes a devctl() DCMD_ALL_SETFLAGS), setting or clearing O_NONBLOCK
FIONCLEX	Remove “close on exec”	fcntl(): F_SETFD with ~FD_CLOEXEC
FIONREAD	Get the number of bytes to read	devctl(): DCMD_CHR_ISCHARS
FIOSETOWN	Set the owner	fcntl(): F_SETOWN
NOSIOCGIFCONF	Get ifnet list	Passed to devctl()
SIOCADDMULTI	Add multicast address	Passed to devctl()
SIOCADDRT	Add route	Passed to devctl()
SIOCAIFADDR	Add or change an interface alias	Passed to devctl()
SIOCALIFADDR	Add interface address	Passed to devctl()
SIOCATMARK	At out-of-band mark?	Passed to devctl()
SIOCDELMULTI	Delete multicast address	Passed to devctl()
SIOCDELRT	Delete route	Passed to devctl()
SIOCDIFADDR	Delete interface address	Passed to devctl()
SIOCDIFPHYADDR	Delete gif addresses	Passed to devctl()
SIOCDLIFADDR	Delete interface address	Passed to devctl()
SIOCGDRVSPEC	Get driver-specific parameters	Passed to devctl()
SIOCGETSGCNT	Get the source group packet count	Passed to devctl()
SIOCGETVIFCNT	Get the packet count for a virtual interface	Passed to devctl()
SIOCGHIWAT	Get high watermark	Passed to devctl()
SIOCGIFADDR	Get the interface address	Passed to devctl()
SIOCGIFALIAS	Get interface alias	Passed to devctl()
SIOCGIFASYNCMAP	Get ppp asyncmap	Passed to devctl()
SIOCGIFBRDADDR	Get broadcast address	Passed to devctl()
SIOCGIFCAP	Get capabilities	Passed to devctl()
SIOCGIFCONF	Return a list of interface (transport layer) addresses	Passed to devctl()
SIOCGIFDLT	Get data link type	Passed to devctl()
SIOCGIFDSTADDR	Get point-to-point address	Passed to devctl()
SIOCGIFFLAGS	Get ifnet flags	Passed to devctl()
SIOCGIFGENERIC	Generic interface get op	Passed to devctl()
SIOCGIFMEDIA	Get net media	Passed to devctl()
SIOCGIFMETRIC	Get interface metric	Passed to devctl()
SIOCGIFMTU	Get ifnet MTU	Passed to devctl()
SIOCGIFNETMASK	Get net address mask	Passed to devctl()
SIOCGIFPDSTADDR	Get gif pdst address	Passed to devctl()
SIOCGIFPSRCADDR	Get gif psrc address	Passed to devctl()
SIOCGLIFADDR	Get interface address	Passed to devctl()
SIOCGLIFPHYADDR	Get gif addresses	Passed to devctl()
SIOCGLOWAT	Get low watermark	Passed to devctl()
SIOCGPGRP	Get process group	fcntl(): F_GETOWN
SIOCIFCREATE	Create clone interface	Passed to devctl()
SIOCIFDESTROY	Destroy clone interface	Passed to devctl()
SIOCIFGCLONERS	Get cloners	Passed to devctl()
SIOCSDRVSPEC	Set driver-specific parameters	Passed to devctl()
SIOCSHIWAT	Set high watermark	Passed to devctl()
SIOCSIFADDR	Set ifnet address	Passed to devctl()
SIOCSIFASYNCMAP	Set ppp asyncmap	Passed to devctl()
SIOCSIFBRDADDR	Set broadcast address	Passed to devctl()
SIOCSIFCAP	Set capabilities	Passed to devctl()
SIOCSIFDSTADDR	Set point-to-point address	Passed to devctl()
SIOCSIFFLAGS	Set ifnet flags	Passed to devctl()
SIOCSIFGENERIC	Generic interface set op	Passed to devctl()
SIOCSIFMEDIA	Set net media	Passed to devctl()
SIOCSIFMETRIC	Set interface metric	Passed to devctl()
SIOCSIFMTU	Set ifnet MTU	Passed to devctl()
SIOCSIFNETMASK	Set net address mask	Passed to devctl()
SIOCSIFPHYADDR	Set gif address	Passed to devctl()
SIOCSLIFPHYADDR	Set gif addresses	Passed to devctl()
SIOCSLOWAT	Set low watermark	Passed to devctl()
SIOCSPGRP	Set process group	fcntl(): F_SETOWN
TCFLSH	Flush buffers	Passed to devctl()
TCGETA	Get the terminal's properties in a termio structure	tcgetattr()
TCGETS	Get the terminal's properties in a termios structure	tcgetattr()
TCSBRK	Send a break for a period of time	devctl() : DCMD_CHR_SERCTL
TCSETA	Set the terminal's properties	tcsetattr()
TCSETAF	Set the terminal's properties, waiting until all currently written data has been transmitted, and discarding any received but unread data	tcsetattr()
TCSETAW	Set the terminal's properties, waiting until all currently written data has been transmitted	tcsetattr()
TCSETS	Set the terminal's properties from a termios structure	devctl() : DCMD_CHR_TCSETATTR
TCSETSF	Drain the output, flush the input, and set	Passed to devctl()
TCSETSW	Drain output, set	Passed to devctl()
TCXONC	Perform a flow-control operation on a data stream	devctl(): DCMD_CHR_TCFLOW
TIOCCBRK	Clear the break bit	tcsetattr()
TIOCCDTR	Clear the Data Terminal Ready line	devctl() : DCMD_CHR_LINESTATUS, followed by DCMD_CHR_SERCTL
TIOCDRAIN	Wait until output has drained	devctl(): DCMD_CHR_TCDRAIN
TIOCEXCL	Set exclusive use of tty	fcntl(): F_SETLK
TIOCFLUSH	Flush buffers	devctl(): DCMD_CHR_TCFLUSH
TIOCGETA	Get the terminal's properties in a termios structure	devctl() : DCMD_CHR_TCGETATTR
TIOCGETC	Get special characters	tcgetattr()
TIOCGETP	Get the terminal's parameters in a sgttyb structure	tcgetattr()
TIOCGETPGRP	Get the process group of the tty (POSIX)	Passed to devctl()
TIOCGLTC	Get local special characters	tcgetattr()
TIOCGPGRP	Get the process group of the tty	devctl(): DCMD_CHR_TCGETPGRP
TIOCGSIZE	Get window size	devctl(): DCMD_CHR_GETSIZE
TIOCGWINSZ	Get window size	devctl(): DCMD_CHR_GETSIZE
TIOCHPCL	Hang up on last close	tcsetattr()
TIOCLGET	Get local modes	tcgetattr()
TIOCLSET	Set entire local mode word	tcsetattr()
TIOCMBIC	Clear modem port B interrupt	devctl() : DCMD_CHR_LINESTATUS, followed by DCMD_CHR_SERCTL
TIOCMBIS	Set modem port B interrupt	devctl() : DCMD_CHR_LINESTATUS, followed by DCMD_CHR_SERCTL
TIOCMGET	Get the state of the modem lines	devctl() : DCMD_CHR_SERCTL
TIOCMSET	Set all modem bits	Passed to devctl()
TIOCNOTTY	Make this terminal not be the controlling terminal for the process	tcsetsid()
TIOCNXCL	Reset exclusive use of tty	fcntl(): F_SETLK
TIOCOUTQ	Output queue size	devctl(): DCMD_CHR_OSCHARS
TIOCPKT	Pty: set/clear packet mode	Passed to devctl()
TIOCSBRK	Set break bit	Passed to devctl()
TIOCSCTTY	Make the terminal become the controlling tty	tcsetsid()
TIOCSDTR	Set the Data Terminal Ready line	devctl() : DCMD_CHR_LINESTATUS, followed by DCMD_CHR_SERCTL
TIOCSETA	Set the terminal's properties from a termios structure	devctl() : DCMD_CHR_TCSETATTR
TIOCSETAF	Drain the output, flush the input, and set	devctl(): DCMD_CHR_TCSETATTRF
TIOCSETAW	Drain output, set	devctl(): DCMD_CHR_TCSETATTRD
TIOCSETC	Set special characters	tcsetattr()
TIOCSETN	Similar to TIOCSETP, but the changes are made immediately without discarding any data.	tcsetattr()
TIOCSETP	Set the terminal's parameters in a sgttyb structure. No change is made until all currently written data has been transmitted, at which point any received but unread data is discarded.	tcsetattr()
TIOCSETPGRP	Set the process group of the tty (POSIX)	Passed to devctl()
TIOCSINUSE	Set exclusive use of tty	fcntl(): F_SETLK
TIOCSLTC	Set local special characters	tcsetattr()
TIOCSPGRP	Set the process group of the tty	devctl(): DCMD_CHR_TCSETPGRP
TIOCSSIZE	Set the window size	devctl(): DCMD_CHR_SETSIZE
TIOCSTART	Start output, like Ctrl–Q	Passed to devctl()
TIOCSTI	Simulate terminal input	devctl(): DCMD_CHR_TCINJECTC
TIOCSTOP	Stop output, like Ctrl–S	Passed to devctl()
TIOCSWINSZ	Set window size	devctl(): DCMD_CHR_SETSIZE
UIOCCMD()	User control operator `n`	Passed to devctl()

Note: If you're writing a resource manager, note that the iofunc_devctl_default() function handles the DCMD_ALL_GETFLAGS and DCMD_ALL_SETFLAGS commands; your resource manager will need to handle all other devctl commands that apply to it.

Registering an I/O control handler

An ioctl() command with data to pass is often passed to devctl(). However, this mechanism is not supported for commands that pass data using pointers to data buffers. For these types of ioctl() commands, you can register an I/O control handler that serializes the data. For more information, see _register_ioctl_handler() and _unregister_ioctl_handler().

Returns:

A value based on the request, or -1 if an error occurs (errno is set).

Errors:

EBADF: Invalid descriptor fd.
EINVAL: The request or optional variables aren't valid.
ENOBUFS: There wasn't enough memory available to allocate for data referred to by embedded pointers.
ENOTTY: The fd argument isn't associated with a character-special device; the specified request doesn't apply to the kind of object that the descriptor fd references.

Classification:

ioctl() is POSIX 1003.1 OB XSR; vioctl() is QNX Neutrino. The ioctl() function is marked as obsolescent, and may be removed from a future version of the standard.

Safety:
Cancellation point	Yes
Interrupt handler	No
Signal handler	No
Thread	No

Caveats:

The ioctl() function is a Unix function that varies greatly from platform to platform.