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 section Opening and Closing Files.
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
F_GETFD
F_SETFD
F_GETFL
F_SETFL
F_GETLK
F_SETLK
F_SETLKW
F_SETLK
, but wait for completion. See section File Locks.
F_GETOWN
SIGIO
signals.
See section Interrupt-Driven Input.
F_SETOWN
SIGIO
signals.
See section Interrupt-Driven 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 cancelled these resources stay allocated
until the program ends. To avoid this calls to fcntl
should be
protected using cancellation handlers.
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