HP-UX Reference (11i v2 04/09) - 2 System Calls (vol 5)

f
fcntl(2) fcntl(2)
NAME
fcntl - file control
SYNOPSIS
#include <fcntl.h>
int fcntl(int fildes, int cmd, ... /* arg */);
Remarks
The ANSI C ", ..." construct denotes a variable length argument list whose optional [or required]
members are given in the associated comment (
/* */).
DESCRIPTION
fcntl() provides for control over open files. fildes is an open file descriptor.
The following are possible values for the cmd argument:
F_DUPFD Return a new file descriptor having the following characteristics:
• Lowest numbered available file descriptor greater than or equal to the
third argument, arg, taken as an integer of type
int.
• Same open file (or pipe) as the original file.
• Same file pointer as the original file (that is, both file descriptors share one
file pointer).
• Same access mode (read, write or read/write).
• Same file status flags (that is, both file descriptors share the same file
status flags).
• The close-on-exec flag associated with the new file descriptor is set to
remain open across exec(2) system calls.
F_GETFD Get the close-on-exec flag associated with the file descriptor fildes . If the low-order
bit is
0 the file will remain open across exec (2), otherwise the file will be closed
upon execution of exec (2).
F_SETFD Set the close-on-exec flag associated with fildes to the low-order bit of the third
argument, arg , taken as an integer of type
int (see F_GETFD).
F_GETFL Get file status flags and access modes; see fcntl (5).
F_SETFL Set file status flags to the third argument, arg, taken as an integer of type
int.
Only certain flags can be set; see fcntl (5). It is not possible to set both
O_NDELAY
and O_NONBLOCK.
F_GETLK Get the first lock that blocks the lock described by the variable of type
struct
flock
pointed to by the third argument, arg, taken as a pointer to type struct
flock. The information retrieved overwrites the information passed to fcntl()
in the flock structure. If no lock is found that would prevent this lock from being
created, the structure is passed back unchanged, except that the lock type is set to
F_UNLCK.
F_SETLK Set or clear a file segment lock according to the variable of type struct flock
pointed to by the third argument, arg, taken as a pointer to type struct flock
(see fcntl (5)). The cmd F_SETLK is used to establish read ( F_RDLCK ) and write
( F_WRLCK ) locks, as well as to remove either type of lock ( F_UNLCK ). If a read or
write lock cannot be set, fcntl() returns immediately with an error value of −1.
F_SETLKW This cmd is the same as F_SETLK except that if a read or write lock is blocked by
other locks, the process will sleep until the segment is free to be locked.
F_GETOWN If fildes refers to a socket, fcntl() returns the process or process group ID
specified to receive SIGURG signals when out-of-band data is available. Positive
values indicate a process ID; negative values, other than -1, indicate a process
group ID.
F_SETOWN If fildes refers to a socket, fcntl() sets the process or process group ID specified
to receive SIGURG signals when out-of-band data is available, using the value of
the third argument, arg, taken as type int. Positive values indicate a process ID;
Section 2−−68 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: September 2004