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58 lines
2.3 KiB
TeX
58 lines
2.3 KiB
TeX
% Manual text by Jaap Vermeulen
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\section{Built-in module \sectcode{fcntl}}
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\bimodindex{fcntl}
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\indexii{UNIX}{file control}
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\indexii{UNIX}{IO control}
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This module performs file control and IO 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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\renewcommand{\indexsubitem}{(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 the 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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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 \code{sys/fcntl} and
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\code{sys/ioctl}. You can create the modules yourself with the h2py
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script, found in the \code{Demo/scripts} directory.
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Examples (all on a SVR4 compliant system):
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\bcode\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}\ecode
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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.
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