параметры управления файлами (file control options)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
fcntl.h — file control options
Синопсис (Synopsis)
#include <fcntl.h>
Описание (Description)
The <fcntl.h> header shall define the following symbolic
constants for the cmd argument used by fcntl(). The values shall
be unique and shall be suitable for use in #if preprocessing
directives.
F_DUPFD Duplicate file descriptor.
F_DUPFD_CLOEXEC
Duplicate file descriptor with the close-on-exec flag
FD_CLOEXEC set.
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.
The <fcntl.h> header shall define the following symbolic constant
used for the fcntl() file descriptor flags, which shall be
suitable for use in #if preprocessing directives.
FD_CLOEXEC Close the file descriptor upon execution of an exec
family function.
The <fcntl.h> header shall also define the following symbolic
constants for the l_type argument used for record locking with
fcntl(). The values shall be unique and shall be suitable for
use in #if preprocessing directives.
F_RDLCK Shared or read lock.
F_UNLCK Unlock.
F_WRLCK Exclusive or write lock.
The <fcntl.h> header shall define the values used for l_whence,
SEEK_SET, SEEK_CUR, and SEEK_END as described in <stdio.h>.
The <fcntl.h> header shall define the following symbolic
constants as file creation flags for use in the oflag value to
open() and openat(). The values shall be bitwise-distinct and
shall be suitable for use in #if preprocessing directives.
O_CLOEXEC The FD_CLOEXEC flag associated with the new
descriptor shall be set to close the file descriptor
upon execution of an exec family function.
O_CREAT Create file if it does not exist.
O_DIRECTORY Fail if file is a non-directory file.
O_EXCL Exclusive use flag.
O_NOCTTY Do not assign controlling terminal.
O_NOFOLLOW Do not follow symbolic links.
O_TRUNC Truncate flag.
O_TTY_INIT Set the termios structure terminal parameters to a
state that provides conforming behavior; see Section
11.2, Parameters that Can be Set.
The O_TTY_INIT flag can have the value zero and in this case it
need not be bitwise-distinct from the other flags.
The <fcntl.h> header shall define the following symbolic
constants for use as file status flags for open(), openat(), and
fcntl(). The values shall be suitable for use in #if
preprocessing directives.
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.
The <fcntl.h> header shall define the following symbolic constant
for use as the mask for file access modes. The value shall be
suitable for use in #if preprocessing directives.
O_ACCMODE Mask for file access modes.
The <fcntl.h> header shall define the following symbolic
constants for use as the file access modes for open(), openat(),
and fcntl(). The values shall be unique, except that O_EXEC and
O_SEARCH may have equal values. The values shall be suitable for
use in #if preprocessing directives.
O_EXEC Open for execute only (non-directory files). The
result is unspecified if this flag is applied to a
directory.
O_RDONLY Open for reading only.
O_RDWR Open for reading and writing.
O_SEARCH Open directory for search only. The result is
unspecified if this flag is applied to a non-
directory file.
O_WRONLY Open for writing only.
The <fcntl.h> header shall define the symbolic constants for file
modes for use as values of mode_t as described in <sys/stat.h>.
The <fcntl.h> header shall define the following symbolic constant
as a special value used in place of a file descriptor for the
*at() functions which take a directory file descriptor as a
parameter:
AT_FDCWD Use the current working directory to determine the
target of relative file paths.
The <fcntl.h> header shall define the following symbolic constant
as a value for the flag used by faccessat():
AT_EACCESS Check access using effective user and group ID.
The <fcntl.h> header shall define the following symbolic constant
as a value for the flag used by fstatat(), fchmodat(),
fchownat(), and utimensat():
AT_SYMLINK_NOFOLLOW
Do not follow symbolic links.
The <fcntl.h> header shall define the following symbolic constant
as a value for the flag used by linkat():
AT_SYMLINK_FOLLOW
Follow symbolic link.
The <fcntl.h> header shall define the following symbolic constant
as a value for the flag used by unlinkat():
AT_REMOVEDIR
Remove directory instead of file.
The <fcntl.h> header shall define the following symbolic
constants for the advice argument used by posix_fadvise():
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.
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_RANDOM
The application expects to access the specified data in a
random order.
POSIX_FADV_SEQUENTIAL
The application expects to access the specified data
sequentially from lower offsets to higher offsets.
POSIX_FADV_WILLNEED
The application expects to access the specified data in the
near future.
The <fcntl.h> header shall define the flock structure describing
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 <fcntl.h> header shall define the mode_t, off_t, and pid_t
types 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 openat(int, const char *, int, ...);
int posix_fadvise(int, off_t, off_t, int);
int posix_fallocate(int, off_t, off_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.
Использование в приложениях (Application usage)
Although no existing implementation defines AT_SYMLINK_FOLLOW and
AT_SYMLINK_NOFOLLOW as the same numeric value, POSIX.1‐2008 does
not prohibit that as the two constants are not used with the same
interfaces.
Обоснование (Rationale)
While many of the symbolic constants introduced in the <fcntl.h>
header do not strictly need to be used in #if preprocessor
directives, widespread historic practice has defined them as
macros that are usable in such constructs, and examination of
existing applications has shown that they are occasionally used
in such a way. Therefore it was decided to retain this
requirement on an implementation in POSIX.1‐2008.
Будущие направления (Future directions)
None.
Смотри также (See also)
stdio.h(0p), sys_stat.h(0p), sys_types.h(0p), unistd.h(0p)
The System Interfaces volume of POSIX.1‐2017, creat(3p),
exec(1p), fcntl(3p), futimens(3p), open(3p), posix_fadvise(3p),
posix_fallocate(3p), posix_madvise(3p)
