cpython-withatomic / Doc / libfcntl.tex

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  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 % Manual text by Jaap Vermeulen \section{Built-in module \sectcode{fcntl}} \bimodindex{fcntl} \indexii{UNIX}{file control} \indexii{UNIX}{IO control} This module performs file control and IO control on file descriptors. It is an interface to the \dfn{fcntl()} and \dfn{ioctl()} \UNIX routines. File descriptors can be obtained with the \dfn{fileno()} method of a file or socket object. The module defines the following functions: \renewcommand{\indexsubitem}{(in module struct)} \begin{funcdesc}{fcntl}{fd\, op\optional{\, arg}} Perform the requested operation on file descriptor \code{\var{fd}}. The operation is defined by \code{\var{op}} and is operating system dependent. Typically these codes can be retrieved from the library module \code{FCNTL}. The argument \code{\var{arg}} is optional, and defaults to the integer value \code{0}. When it is present, it can either be an integer value, or a string. With the argument missing or an integer value, the return value of this function is the integer return value of the real \code{fcntl()} call. When the argument is a string it represents a binary structure, e.g. created by \code{struct.pack()}. The binary data is copied to a buffer whose address is passed to the real \code{fcntl()} call. The return value after a successful call is the contents of the buffer, converted to a string object. In the case the \code{fcntl()} fails, an \code{IOError} will be raised. \end{funcdesc} \begin{funcdesc}{ioctl}{fd\, op\, arg} This function is identical to the \code{fcntl()} function, except that the operations are typically defined in the library module \code{IOCTL}. \end{funcdesc} If the library modules \code{FCNTL} or \code{IOCTL} are missing, you can find the opcodes in the C include files \code{sys/fcntl} and \code{sys/ioctl}. You can create the modules yourself with the h2py script, found in the \code{Demo/scripts} directory. Examples (all on a SVR4 compliant system): \bcode\begin{verbatim} import struct, FCNTL file = open(...) rv = fcntl(file.fileno(), FCNTL.O_NDELAY, 1) lockdata = struct.pack('hhllhh', FCNTL.F_WRLCK, 0, 0, 0, 0, 0) rv = fcntl(file.fileno(), FCNTL.F_SETLKW, lockdata) \end{verbatim}\ecode Note that in the first example the return value variable \code{rv} will hold an integer value; in the second example it will hold a string value.