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() and open().

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

None.

SEE ALSO

creat(), exec, fcntl(), open(), <sys/stat.h>, <sys/types.h>, <unistd.h>.