FCNTL.H(7) Miscellaneous Information Manual FCNTL.H(7)

NAME

fcntl.h — file control options

SYNOPSIS

#include <fcntl.h>

DESCRIPTION

The <fcntl.h> header defines the following requests and arguments for use by the functions fcntl(3) and open(3) .

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

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.

File descriptor flags used for fcntl ():

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):

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 are defined as described in <unistd.h>.

The following four sets of values for oflag used by open () are 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 ():

O_APPEND: Set append mode.
O_DSYNC: Write according to synchronised I/O data integrity completion.
O_NONBLOCK: Non-blocking mode.
O_RSYNC: Synchronised read I/O operations.
O_SYNC: Write according to synchronised I/O file integrity completion.

Mask for use with file access modes:

O_ACCMODE: Mask for file access modes.

File access modes used for open () and fcntl ():

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 are defined as described in <sys/stat.h>.

The structure flock describes a file lock. It includes 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 off_t and pid_t types are defined as described in <sys/types.h>.

The following are declared as functions and may also be defined as macros. Function prototypes must be provided for use with an ISO C compiler. int creat(const char *, mode_t); int fcntl(int, int, ...); int open(const char *, int, ...);

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

APPLICATION USAGE

None.

FUTURE DIRECTIONS