NAME¶

fcntl.h - file control options

SYNOPSIS¶

#include <fcntl.h>

DESCRIPTION¶

The <fcntl.h> header shall define the following requests and arguments for use by the functions fcntl() and open().

Values for cmd used by fcntl() (the following values are unique) are as follows:

F_DUPFD

Duplicate file descriptor.

F_GETFD

Get file descriptor flags.

F_SETFD

Set file descriptor flags.

F_GETFL

Get file status flags and file access modes.

F_SETFL

Set file status flags.

F_GETLK

Get record locking information.

F_SETLK

Set record locking information.

F_SETLKW

Set record locking information; wait if blocked.

F_GETOWN

Get process or process group ID to receive SIGURG signals.

F_SETOWN

Set process or process group ID to receive SIGURG signals.

File descriptor flags used for fcntl() are as follows:

FD_CLOEXEC

Close the file descriptor upon execution of an exec family function.

Values for l_type used for record locking with fcntl() (the following values are unique) are as follows:

F_RDLCK

Shared or read lock.

F_UNLCK

Unlock.

F_WRLCK

Exclusive or write lock.

The values used for l_whence, SEEK_SET, SEEK_CUR, and SEEK_END shall be defined as described in <unistd.h> .

The following values are file creation flags and are used in the oflag value to open(). They shall be bitwise-distinct.

O_CREAT

Create file if it does not exist.

O_EXCL

Exclusive use flag.

O_NOCTTY

Do not assign controlling terminal.

O_TRUNC

Truncate flag.

File status flags used for open() and fcntl() are as follows:

O_APPEND

Set append mode.

O_DSYNC

Write according to synchronized I/O data integrity completion.

O_NONBLOCK

Non-blocking mode.

O_RSYNC

Synchronized read I/O operations.

O_SYNC

Write according to synchronized I/O file integrity completion.

Mask for use with file access modes is as follows:

O_ACCMODE

Mask for file access modes.

File access modes used for open() and fcntl() are as follows:

O_RDONLY

Open for reading only.

O_RDWR

Open for reading and writing.

O_WRONLY

Open for writing only.

The symbolic names for file modes for use as values of mode_t shall be defined as described in <sys/stat.h> .

Values for advice used by posix_fadvise() are as follows:

POSIX_FADV_NORMAL

The application has no advice to give on its behavior with respect to the specified data. It is the default characteristic if no advice is given for an open file.

POSIX_FADV_SEQUENTIAL

The application expects to access the specified data sequentially from lower offsets to higher offsets.

POSIX_FADV_RANDOM

The application expects to access the specified data in a random order.

POSIX_FADV_WILLNEED

The application expects to access the specified data in the near future.

POSIX_FADV_DONTNEED

The application expects that it will not access the specified data in the near future.

POSIX_FADV_NOREUSE

The application expects to access the specified data once and then not reuse it thereafter.

The structure flock describes a file lock. It shall include the following members:

short  l_type   Type of lock; F_RDLCK, F_WRLCK, F_UNLCK. 
short  l_whence Flag for starting offset. 
off_t  l_start  Relative offset in bytes. 
off_t  l_len    Size; if 0 then until EOF. 
pid_t  l_pid    Process ID of the process holding the lock; returned with F_GETLK. 

The mode_t, off_t, and pid_t types shall be defined as described in <sys/types.h> .

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

int  creat(const char *, mode_t);
int  fcntl(int, int, ...);
int  open(const char *, int, ...);
int  posix_fadvise(int, off_t, size_t, int);
int  posix_fallocate(int, off_t, size_t);

Inclusion of the <fcntl.h> header may also make visible all symbols from <sys/stat.h> and <unistd.h>.

The following sections are informative.

APPLICATION USAGE¶

None.

RATIONALE¶

None.

FUTURE DIRECTIONS¶

None.

SEE ALSO¶

<sys/stat.h>, <sys/types.h>, <unistd.h>, the System Interfaces volume of IEEE Std 1003.1-2001, creat(), exec, fcntl(), open(), posix_fadvise(), posix_fallocate(), posix_madvise()

COPYRIGHT¶

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .