133 lines
5.5 KiB
Groff
133 lines
5.5 KiB
Groff
.\" Copyright (c) 1998 HD Associates, Inc.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $Id: posix4.9,v 1.1 1998/03/04 10:23:50 dufault Exp $
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.Dd March 1, 1998
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.Dt POSIX.4 9
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.Os FreeBSD 3.0
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.Sh NAME
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.Nm posix4
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.Nd "POSIX.4 extensions"
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.Sh DESCRIPTION
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POSIX.4 adds real time extensions and some commonly used
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Berkeley extensions to POSIX.1
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This section contains preliminary information about avoiding conflicts
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and adding support for the required ability to specify the interface
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version.
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.Sh STATUS
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March 7, 1998: adding header file changes to 3.0. There should be no
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visible differences as long as _POSIX_VERSION is left undefined.
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Defining _POSIX_VERSION, even to the current value of 199009L, will
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change the behavior of the system per the POSIX spec: if you define
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_POSIX_VERSION to be 199009L then any extensions
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already added to the system (for example,
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John Dyson's aio work) may no longer be visible - this is happening
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slowly.
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.Pp
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In spite of what I said at first, don't set _POSIX_VERSION into the
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future until I say it is working.
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.Pp
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Since this only brings in the headers I'm only explaining the feature
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test options.
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.Sh SPECIFYING THE VERSION
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There are three manifest constants that set the version and programming interface
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for POSIX.4.
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.Bd -literal -offset 0i
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_POSIX_VERSION
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.Ed
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specifies the system for which the system is built. The default
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is POSIX.1 and is 199009L. POSIX.4 is 199309L. This defines
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the base features of the operating system.
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.Bd -literal -offset 0i
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_POSIX_SOURCE
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.Ed
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is a macro from POSIX.1 that can
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be defined to specify that only POSIX and ANSI functionality should occur
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in the name space.
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.Bd -literal -offset 0i
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_POSIX_C_SOURCE
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.Ed
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is a macro from POSIX.4 that can be defined to specify that only
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POSIX and ANSI functionality from a specific POSIX version should occur
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in the name space, i.e., if _POSIX_VERSION is 199309L (POSIX.4) but
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_POSIX_C_SOURCE is 199009L (POSIX.1) then only POSIX.1 features should
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appear.
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.Sh PROPERLY HIDING EXTENSIONS
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The following test macros are set up in <sys/_posix.h>. They should
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used by system header files to avoid the kind of tests you see in
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<sys/_posix.h>. Source programs should not use these FreeBSD specific
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implementation details and should test _POSIX_VERSION.
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These should not be used in the kernel either - the kernel should be
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immune to the user land setting of _POSIX_VERSION. The POSIX4 option can
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be used in the kernel to limit inclusion of new code, but make sure
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things work properly when a POSIX.4 program is run on a kernel without
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the POSIX4 option.
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.Bd -literal -offset 0i
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_POSIX4_VISIBLE
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.Ed
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is a test macro that sorts out when extensions should be
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visible. It is defined in <sys/_posix.h>.
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.Pp
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In normal C program development
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only _POSIX_VERSION is set, permitting BSD extensions to
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appear to the programs. However, when adding new functionality mandated
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by POSIX.4, it
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is important to satisfy the requirements added by the
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new _POSIX_C_SOURCE macro. _POSIX4_VISIBLE (not a standard feature test macro)
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is defined in sys/unistd.h when the combination of _POSIX_VERSION,
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_POSIX_SOURCE, and _POSIX_C_SOURCE indicate that the extensions are in scope.
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.Bd -literal -offset 0i
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_POSIX4_VISIBLE_HISTORICALLY
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is present to conditionalize POSIX.4 extensions that were historically
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in the system. These are visible when _POSIX_SOURCE and _POSIX_C_SOURCE
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are not set at all or when _POSIX_C_SOURCE enables POSIX.4 features.
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.Pp
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Some of these are new enough that they should be changed to
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be dependent on _POSIX4_VISIBLE instead.
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.Pp
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Traditional BSD headers (e.g., mmap.h) that are now specified
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in POSIX.4 should include <sys/_posix.h> and conditionalize
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BSD extensions on _POSIX4_VISIBLE_HISTORICALLY.
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.Sh NON STANDARD TEST MACROS
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.Bd -literal -offset 0i
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_POSIX4_INCLUDE_MAYBES
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.Ed
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when set before the inclusion of any other header file
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requests that all header files that the POSIX.4 spec says a standard
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header may include should be included. Normally no non-required
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headers are included. Setting this pre-processor definition should
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make any compliant program compile without issues of header file
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inclusion.
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.Bd -literal -offset 0i
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POSIX4
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.Ed
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is a config option and (currently) a request to build POSIX.4 by
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setting the _POSIX_VERSION to 199309L in sys/unistd.h.
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.Sh SEE ALSO
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.Sh HISTORY
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The
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.Nm posix4
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section manual page appeared in
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.Fx 3.0 .
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