This section describes how you can perform various other operations on
file descriptors, such as inquiring about or setting flags describing
the status of the file descriptor, manipulating record locks, and the
like. All of these operations are performed by the function fcntl.
The second argument to the fcntl function is a command that
specifies which operation to perform. The function and macros that name
various flags that are used with it are declared in the header file
fcntl.h. Many of these flags are also used by the open
function; see Opening and Closing Files.
— Function: int fcntl (int filedes, int command, ...)
The fcntl function performs the operation specified by
command on the file descriptor filedes. Some commands
require additional arguments to be supplied. These additional arguments
and the return value and error conditions are given in the detailed
descriptions of the individual commands.
Briefly, here is a list of what the various commands are.
F_DUPFD
Duplicate the file descriptor (return another file descriptor pointing
to the same open file). See Duplicating Descriptors.
F_GETFD
Get flags associated with the file descriptor. See Descriptor Flags.
F_SETFD
Set flags associated with the file descriptor. See Descriptor Flags.
Like F_SETLK, but wait for completion. See File Locks.
F_GETOWN
Get process or process group ID to receive SIGIO signals.
See Interrupt Input.
F_SETOWN
Set process or process group ID to receive SIGIO signals.
See Interrupt Input.
This function is a cancellation point in multi-threaded programs. This
is a problem if the thread allocates some resources (like memory, file
descriptors, semaphores or whatever) at the time fcntl is
called. If the thread gets canceled these resources stay allocated
until the program ends. To avoid this calls to fcntl should be
protected using cancellation handlers.
Published under the terms of the GNU General Public License
