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fcntl.h - file control options
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
Duplicate file descriptor.
Get file descriptor flags.
Set file descriptor flags.
Get file status flags and file access modes.
Set file status flags.
Get record locking information.
Set record locking information.
Set record locking information; wait if blocked.
Get process or process group ID to receive SIGURG signals.
Set process or process group ID to receive SIGURG signals.
File descriptor flags used for fcntl() are as follows:
Close the file descriptor upon execution of an exec family
Values for l_type used for record locking with fcntl() (the following
values are unique) are as follows:
Shared or read lock.
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.
Create file if it does not exist.
O_EXCL Exclusive use flag.
Do not assign controlling terminal.
File status flags used for open() and fcntl() are as follows:
Set append mode.
Write according to synchronized I/O data integrity completion.
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:
Mask for file access modes.
File access modes used for open() and fcntl() are as follows:
Open for reading only.
O_RDWR Open for reading and writing.
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:
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.
The application expects to access the specified data
sequentially from lower offsets to higher offsets.
The application expects to access the specified data in a random
The application expects to access the specified data in the near
The application expects that it will not access the specified
data in the near future.
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
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
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.
<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()
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 .