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.


F_DUP2FD
Similar to F_DUPFD, but always returns arg.


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)).


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_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_NDELAY
Non-blocking mode.


O_NONBLOCK
Non-blocking mode (POSIX; see standards(5)).


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(5) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|Standard | See standards(5). |
+--------------------+-------------------+

SEE ALSO


creat(2), exec(2), fcntl(2), open(2), fdatasync(3C), fsync(3C),
fsattr(5), attributes(5), standards(5)

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.


April 9, 2016 FCNTL.H(3HEAD)