ioctl -控制設備

內容簡介

#include

int ioctl(intd, intrequest, ...);

描述

Theioctl() function manipulates the underlying device parameters of special files. In particular, many operating characteristics of character special files (e.g. terminals) may be controlled withioctl() requests. The argumentdmust be an open file descriptor.

The second argument is a device-dependent request code. The third argument is an untyped yiibaier 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?outparameter, and the size of the argument?argp?in bytes. Macros and defines used in specifying an?ioctl()?request?are located in the file?.

返回值

Usually, on success zero is returned. A fewioctl() requests use the return value as an output parameter and return a nonnegative value on success. On error, -1 is returned, anderrnois set appropriately.

錯誤

標簽

描述

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.

注意

In order to use this call, one needs an open file descriptor. Often theopen(2) call has unwanted side effects, that can be avoided under Linux by giving it the O_NONBLOCK flag.

遵循于

No single standard. Arguments, returns, and semantics ofioctl(2) 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). Seeioctl_list(2) for a list of many of the knownioctl() calls. Theioctl() function call appeared in Version 7 AT&T Unix.

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