File control.

#include <fcntl.h>

int
fcntl(int fd, int cmd, ...);

Description

The fcntl() system call provides for control over descriptors. The argument fd is a descriptor to be operated on by cmd as described below. Depending on the value of cmd, fcntl() can take an additional third argument int arg.

F_GETFL	Get descriptor status flags, as described below (arg is ignored).
F_SETFL	Set descriptor status flags to arg.

The flags for the F_GETFL and F_SETFL flags are as follows:

O_NONBLOCK

Non-blocking I/O; if no data is available to a read() system call, or if a write() operation would block, the read or write call returns -1 with the error EAGAIN.

Return Values

Upon successful completion, the value returned depends on cmd as follows:

F_GETFL	Value of flags.
Other	Value other than -1.

The fcntl() system call will fail if:

EBADF	The fd argument is not a valid open file descriptor.
EINVAL	The specified cmd is invalid.

Requirements