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74 lines
2.9 KiB
TeX
74 lines
2.9 KiB
TeX
% Manual text by Jaap Vermeulen
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\section{Built-in Module \sectcode{fcntl}}
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\label{module-fcntl}
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\bimodindex{fcntl}
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\indexii{UNIX@\UNIX{}}{file control}
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\indexii{UNIX@\UNIX{}}{I/O control}
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This module performs file control and I/O control on file descriptors.
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It is an interface to the \dfn{fcntl()} and \dfn{ioctl()} \UNIX{} routines.
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File descriptors can be obtained with the \dfn{fileno()} method of a
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file or socket object.
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The module defines the following functions:
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\setindexsubitem{(in module struct)}
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\begin{funcdesc}{fcntl}{fd\, op\optional{\, arg}}
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Perform the requested operation on file descriptor \code{\var{fd}}.
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The operation is defined by \code{\var{op}} and is operating system
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dependent. Typically these codes can be retrieved from the library
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module \code{FCNTL}. The argument \code{\var{arg}} is optional, and
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defaults to the integer value \code{0}. When
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it is present, it can either be an integer value, or a string. With
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the argument missing or an integer value, the return value of this
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function is the integer return value of the real \code{fcntl()}
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call. When the argument is a string it represents a binary
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structure, e.g.\ created by \code{struct.pack()}. The binary data is
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copied to a buffer whose address is passed to the real \code{fcntl()}
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call. The return value after a successful call is the contents of
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the buffer, converted to a string object. In case the
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\code{fcntl()} fails, an \code{IOError} will be raised.
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\end{funcdesc}
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\begin{funcdesc}{ioctl}{fd\, op\, arg}
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This function is identical to the \code{fcntl()} function, except
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that the operations are typically defined in the library module
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\code{IOCTL}.
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\end{funcdesc}
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\begin{funcdesc}{flock}{fd\, op}
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Perform the lock operation \var{op} on file descriptor \var{fd}.
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See the \UNIX{} manual for details. (On some systems, this function is
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emulated using \code{fcntl()}.)
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\end{funcdesc}
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\begin{funcdesc}{lockf}{fd\, code\, \optional{len\, \optional{start\, \optional{whence}}}}
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This is a wrapper around the \code{F_SETLK} and \code{F_SETLKW}
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\code{fcntl()} calls. See the \UNIX{} manual for details.
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\end{funcdesc}
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If the library modules \code{FCNTL} or \code{IOCTL} are missing, you
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can find the opcodes in the C include files \file{sys/fcntl.h} and
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\file{sys/ioctl.h}. You can create the modules yourself with the h2py
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script, found in the \file{Tools/scripts} directory.
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\refstmodindex{FCNTL}
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\refstmodindex{IOCTL}
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Examples (all on a SVR4 compliant system):
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\begin{verbatim}
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import struct, FCNTL
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file = open(...)
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rv = fcntl(file.fileno(), FCNTL.O_NDELAY, 1)
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lockdata = struct.pack('hhllhh', FCNTL.F_WRLCK, 0, 0, 0, 0, 0)
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rv = fcntl(file.fileno(), FCNTL.F_SETLKW, lockdata)
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\end{verbatim}
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%
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Note that in the first example the return value variable \code{rv} will
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hold an integer value; in the second example it will hold a string
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value. The structure lay-out for the \var{lockadata} variable is
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system dependent -- therefore using the \code{flock()} call may be
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better.
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