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HP-UX 11i Version 3: February 2007

Technical documentation

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ioctl — control device


#include <stropts.h>

int ioctl(int fildes, int request, ... /* arg */);


The ANSI C ", ..." construct denotes a variable length argument list whose optional [or required] members are given in the associated comment (/* */).


ioctl() performs a variety of functions on character special files (devices), or regular files and directories on VxFS file systems. The write-ups of various devices in Section (7) discuss how ioctl() applies to them. The type of arg is dependent on the specific ioctl() call, as described in Section (7).

request is made up of several fields which encode the size and direction of the argument (referenced by arg), as well as the desired command. An enumeration of the request fields are:


Argument is read by the driver (meaning that the argument is copied from the application to the driver).


Argument is written by the driver (meaning that the argument is copied from the driver to the application). Ignored if an error occurs.


Number of bytes in the passed argument. A nonzero size indicates that arg is a pointer to the passed argument. A zero size indicates that arg is the passed argument (if the driver wants to use it), and is not treated as a pointer.


The request command itself.

When both IOC_IN and IOC_OUT are zero, it can be assumed that request is not encoded for size and direction, for compatibility purposes. Requests that do not require any data to be passed and requests that use arg as a value (as opposed to a pointer), have the IOC_IN bit set to one and the IOCSIZE_MASK field set to zero.

The following macros are used to create the request argument. x and y are concatenated ((x<<8) | y) to form IOCCMD and shifted into the proper location according to IOCCMD_MASK. t is the type (e.g. struct routeaddrs) of the actual argument that the request references, and its size is taken and shifted into the appropriate place according to IOCSIZE_MASK.


Sets IOC_OUT and initializes the values at IOCCMD_MASK and IOCSIZE_MASK accordingly.


Sets IOC_IN and initializes the values at IOCCMD_MASK and IOCSIZE_MASK accordingly.


Sets both IOC_IN and IOC_OUT and initializes the values at IOCCMD_MASK and IOCSIZE_MASK.

Note: any data structure referenced by arg must not contain any pointers.


If an error has occurred, a value of -1 is returned and errno is set to indicate the error.

ioctl() fails if one or more of the following are true: IOC_OUT is ignored if an error occurs.


fildes is not a valid open file descriptor.


The request is not appropriate to the selected device.


request or arg is not valid.


A signal was caught during the ioctl() system call.


Typically this error indicates that an ioctl request was attempted that is forbidden in some way to the calling process.


ioctl() was developed by AT&T and HP.


ioctl(): SVID2, SVID3, XPG2

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