FCNTL.H(3HEAD) Headers FCNTL.H(3HEAD)
NAME
fcntl.h, fcntl - file control options
SYNOPSIS
#include <fcntl.h>
DESCRIPTION
The
<fcntl.h> header defines the following requests and arguments for
use by the functions
fcntl(2),
open(2), and
openat(2).
Values for
cmd used by
fcntl() (the following values are unique):
F_DUPFD Duplicate file descriptor. File descriptor flags
cleared on duplicate.
F_DUP2FD Similar to
F_DUPFD, but always returns
arg. File
descriptor flags cleared on duplicate.
F_DUP3FD Similar to
F_DUP2FD, but takes a fourth
int argument
which specifies the file descriptor flags (
FD_CLOEXEC and
FD_CLOFORK).
F_DUPFD_CLOEXEC Similar to
F_DUPFD, but the
FD_CLOEXEC flag is set on
the returned descriptor.
F_DUPFD_CLOFORK Similar to
F_DUPFD, but the
FD_CLOFORK flag is set on
the returned descriptor.
F_DUP2FD_CLOEXEC Similar to
F_DUP2FD, but the
FD_CLOEXEC flag is set on
the returned descriptor.
F_DUP2FD_CLOFORK Similar to
F_DUP2FD, but the
FD_CLOFORK flag is set on
the returned descriptor.
F_GETFD Get file descriptor flags.
F_SETFD Set file descriptor flags.
F_GETFL Get file status flags.
F_SETFL Set file status flags.
F_GETOWN Get process or process group
ID to receive
SIGURG signals.
F_SETOWN Set process or process group
ID to receive
SIGURG signals.
F_FREESP Free storage space associated with a section of the
ordinary file
fildes.
F_ALLOCSP Allocate space for a section of the ordinary file
fildes.
F_ALLOCSP64 Equivalent to
F_ALLOCSP, but takes a
struct flock64 argument rather than a
struct flock argument.
F_GETLK Get record locking information.
F_GETLK64 Equivalent to
F_GETLK, but takes a
struct flock64 argument rather than a
struct flock argument.
F_SETLK Set record locking information.
F_SETLK64 Equivalent to
F_SETLK, but takes a
struct flock64 argument rather than a
struct flock argument.
F_SETLKW Set record locking information; wait if blocked.
F_SETLKW64 Equivalent to
F_SETLKW, but takes a
struct flock64 argument rather than a
struct flock argument.
F_SHARE Set share reservation.
F_UNSHARE Remove share reservation.
File descriptor flags used for
fcntl():
FD_CLOEXEC Close the file descriptor upon execution of an
exec function (see
exec(2)).
FD_CLOFORK Close the file descriptor in any child process created
with the
fork(2) family functions.
Values for
l_type used for record locking with
fcntl() (the following
values are unique):
F_RDLCK Shared or read lock.
F_UNLCK Unlock.
F_WRLCK Exclusive or write lock.
Values for
f_access used for share reservations with
fcntl() (the
following values are unique):
F_RDACC Read-only share reservation.
F_WRACC Write-only share reservation.
F_RWACC Read and write share reservation.
Values for
f_deny used for share reservations with
fcntl() (the
following values are unique):
F_COMPAT Compatibility mode share reservation.
F_RDDNY Deny other read access share reservations.
F_WRDNY Deny other write access share reservations.
F_RWDNY Deny other read or write access share reservations.
F_NODNY Do not deny other read or write access share
reservations.
File creation and assignment flags are used in the
oflag argument by
open() and
openat(). All of these values are bitwise distinct:
O_CREAT Create file if it does not exist.
O_DIRECTORY Fail unless the path is a directory.
O_EXCL Exclusive use flag.
O_NOCTTY Do not assign controlling tty.
O_TRUNC Truncate flag.
O_XATTR When opening a file, this flag affects the way in which
relative paths are resolved by
open() and
openat(). With
this flag set, the
path argument is resolved as an
extended attribute reference on either the current
working directory (if open) or of the file referenced by
the file descriptor argument of
openat().
File status flags used for
fcntl(),
open(), and
open():
O_APPEND Set append mode.
O_CLOEXEC The file should be closed on any calls to
exec(2).
O_CLOFORK The file will be closed in any child processes created
with calls to
fork(2).
O_NDELAY Non-blocking mode.
O_NONBLOCK Non-blocking mode (POSIX; see
standards(7)).
O_DSYNC Write I/O operations on the file descriptor complete as
defined by synchronized I/O data integrity completion.
O_RSYNC Read I/O operations on the file descriptor complete at
the same level of integrity as specified by the
O_DSYNC and
O_SYNC flags. If both
O_DSYNC and
O_RSYNC are set
in
oflag, all I/O operations on the file descriptor
complete as defined by synchronized I/O data integrity
completion. If both
O_SYNC and
O_RSYNC are set in
oflag, all I/O operations on the file descriptor
complete as defined by synchronized I/O file integrity
completion.
O_SYNC When opening a regular file, this flag affects
subsequent writes. If set, each
write(2) will wait for
both the file data and file status to be physically
updated. Write I/O operations on the file descriptor
complete as defined by synchronized I/O file integrity
completion.
Mask for use with file access modes:
O_ACCMODE Mask for file access modes.
File access modes used for
fcntl(),
open(), and
openat():
O_RDONLY Open for reading only.
O_RDWR Open for reading and writing.
O_WRONLY Open for writing only.
The following constants are used by system calls capable of resolving
paths relative to a provided open file descriptor:
AT_FDCWD Special value to pass in place of a file
descriptor to inform the called routine that
relative path arguments should be resolved
from the current working directory.
AT_SYMLINK_NOFOLLOW Flag passed to
fstatat(2) and
fchownat(2) to
change the behavior of these functions when
they are given a file as an argument that is a
symbolic link. In this case the functions
operate on the symbolic link file rather than
the file the link references.
AT_REMOVEDIR Flag passed to
unlinkat(2) to tell it to
assume that its path argument refers to a
directory and to attempt to remove this
directory.
The
flock structure describes a file lock. It includes the following
members:
short l_type; /* Type of lock */
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 */
long l_sysid; /* Returned with F_GETLK */
pid_t l_pid; /* Returned with F_GETLK */
The structure
fshare describes a file share reservation. It includes
the following members:
short f_access; /* Type of reservation */
short f_deny; /* Type of reservations to deny */
long f_id; /* Process unique identifier */
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|Standard | See
standards(7). |
+--------------------+-------------------+
SEE ALSO
creat(2),
exec(2),
fcntl(2),
fork(2),
open(2),
fdatasync(3C),
fsync(3C),
attributes(7),
fsattr(7),
standards(7)NOTES
Data is successfully transferred for a write operation to a regular
file when the system ensures that all data written is readable on any
subsequent open of the file (even one that follows a system or power
failure) in the absence of a failure of the physical storage medium.
Data is successfully transferred for a read operation when an image
of the data on the physical storage medium is available to the
requesting process.
Synchronized I/O data integrity completion (see
fdatasync(3C)):
o For reads, the operation has been completed or diagnosed
if unsuccessful. The read is complete only when an image
of the data has been successfully transferred to the
requesting process. If there were any pending write
requests affecting the data to be read at the time that
the synchronized read operation was requested, these write
requests will be successfully transferred prior to reading
the data.
o For writes, the operation has been completed or diagnosed
if unsuccessful. The write is complete only when the data
specified in the write request is successfully
transferred, and all file system information required to
retrieve the data is successfully transferred.
File attributes that are not necessary for data retrieval (access
time, modification time, status change time) need not be successfully
transferred prior to returning to the calling process.
Synchronized I/O file integrity completion (see
fsync(3C)):
o Identical to a synchronized I/O data integrity completion
with the addition that all file attributes relative to the
I/O operation (including access time, modification time,
status change time) will be successfully transferred prior
to returning to the calling process.
June 21, 2024 FCNTL.H(3HEAD)
