POSIX.1B(9) BSD Kernel Developer's Manual POSIX.1B(9)NAME
posix1b — Posix P1003-1B extensions
DESCRIPTION
POSIX.1B adds real time extensions and some commonly used Berkeley exten‐
sions to POSIX.1. This section contains preliminary information about
avoiding conflicts and adding support for the required ability to specify
the interface version.
STATUS
March 28, 1998: _POSIX_PRIORITY_SCHEDULING works with these kernel
options in your configuration:
options "P1003_1B"
options "_KPOSIX_PRIORITY_SCHEDULING"
SPECIFYING THE VERSION
There are three manifest constants that set the version and programming
interface for POSIX.1B.
_POSIX_VERSION
specifies the system for which the system is built. The default is
POSIX.1 and is 199009L. POSIX.1B is 199309L. This defines the base fea‐
tures of the operating system.
_POSIX_SOURCE
is a macro from POSIX.1 that can be defined to specify that only POSIX
and ANSI functionality should occur in the name space.
_POSIX_C_SOURCE
is a macro from POSIX.1B that can be defined to specify that only POSIX
and ANSI functionality from a specific POSIX version should occur in the
name space, i.e., if _POSIX_VERSION is 199309L (POSIX.1B) but
_POSIX_C_SOURCE is 199009L (POSIX.1) then only POSIX.1 features should
appear.
PROPERLY HIDING EXTENSIONS
The following test macros are set up in <sys/_posix.h>. They should used
by system header files to avoid the kind of tests you see in
<sys/_posix.h>. Source programs should not use these DragonFly specific
implementation details and should test _POSIX_VERSION, _POSIX_SOURCE and
_POSIX_C_SOURCE. These should not be used in the kernel though - the
kernel should be immune to the user land setting of _POSIX_VERSION. The
P1003_1B option can be used in the kernel to limit inclusion of new code,
but make sure things work properly when a POSIX.1B program is run on a
kernel without the P1003_1B option.
_P1003_1B_VISIBLE
is a test macro that sorts out when extensions should be visible. It is
defined in <sys/_posix.h>.
In normal C program development only _POSIX_VERSION is set, permitting
BSD extensions to appear to the programs. However, when adding new func‐
tionality mandated by POSIX.1B, it is important to satisfy the require‐
ments added by the new _POSIX_C_SOURCE macro. _P1003_1B_VISIBLE (not a
standard feature test macro) is defined in <sys/unistd.h> when the combi‐
nation of _POSIX_VERSION, _POSIX_SOURCE, and _POSIX_C_SOURCE indicate
that the extensions are in scope.
_P1003_1B_VISIBLE_HISTORICALLY
is present to conditionalize POSIX.1B extensions that were historically
in the system. These are visible when _POSIX_SOURCE and _POSIX_C_SOURCE
are not set at all or when _POSIX_C_SOURCE enables POSIX.1B features.
The intent of this feature test is to permit hiding the new extensions
while still letting BSD extensions show up to avoid breaking existing
programs without trying to use the "big hammer" of _POSIX_C_SOURCE.
Some recent additions to header files are new enough that they should be
changed to be dependent on _P1003_1B_VISIBLE instead of _HISTORICALLY.
Traditional BSD headers (e.g., mmap.h) now specified in POSIX.1B can
include <sys/_posix.h> and conditionalize BSD extensions on
_P1003_1B_VISIBLE_HISTORICALLY.
NON STANDARD TEST MACROS
_P1003_1B_INCLUDE_MAYBES
when set before the inclusion of any other header file requests that all
header files that the POSIX.1B spec says a standard header may include
should be included. Normally no non-required headers are included. Set‐
ting this pre-processor definition should make any compliant program com‐
pile without issues of header file inclusion.
P1003_1B
is a config option to build in POSIX.1B support in the kernel.
HISTORY
The posix1b section manual page appeared in FreeBSD 3.0.
BSD March 1, 1998 BSD
