You may come across code that needs modifications or conditional compilation based
upon what version of Unix it is running under. If you need to make such changes to the
code for conditional compilation, make sure you make the changes as general as possible
so that we can back-port code to older FreeBSD systems and cross-port to other BSD
systems such as 4.4BSD from CSRG, BSD/386, 386BSD, NetBSD, and OpenBSD.
The preferred way to tell 4.3BSD/Reno (1990) and newer versions of the BSD code apart
is by using the BSD macro defined in <sys/param.h>. Hopefully that file is already included; if
not, add the code:
#if (defined(__unix__) || defined(unix)) && !defined(USG)
#include <sys/param.h>
#endif
to the proper place in the .c file. We believe that every
system that defines these two symbols has sys/param.h. If you
find a system that does not, we would like to know. Please send mail to the FreeBSD
ports mailing list.
Another way is to use the GNU Autoconf style of doing this:
#ifdef HAVE_SYS_PARAM_H
#include <sys/param.h>
#endif
Do not forget to add -DHAVE_SYS_PARAM_H to the CFLAGS in the Makefile for this
method.
Once you have sys/param.h included, you may use:
#if (defined(BSD) && (BSD >= 199103))
to detect if the code is being compiled on a 4.3 Net2 code base or newer (e.g. FreeBSD
1.x, 4.3/Reno, NetBSD 0.9, 386BSD, BSD/386 1.1 and below).
Use:
#if (defined(BSD) && (BSD >= 199306))
to detect if the code is being compiled on a 4.4 code base or newer (e.g. FreeBSD 2.x,
4.4, NetBSD 1.0, BSD/386 2.0 or above).
The value of the BSD macro is 199506 for the 4.4BSD-Lite2 code base. This is stated for
informational purposes only. It should not be used to distinguish between versions of
FreeBSD based only on 4.4-Lite vs. versions that have merged in changes from 4.4-Lite2.
The __FreeBSD__ macro should be used instead.
Use sparingly:
-
__FreeBSD__ is defined in all versions of FreeBSD. Use it
if the change you are making only
affects FreeBSD. Porting gotchas like the use of sys_errlist[]
vs strerror() are Berkeley-isms, not FreeBSD changes.
-
In FreeBSD 2.x, __FreeBSD__ is defined to be 2. In earlier versions, it is 1. Later
versions always bump it to match their major version number.
-
If you need to tell the difference between a FreeBSD 1.x system and a FreeBSD 2.x or
above system, usually the right answer is to use the BSD
macros described above. If there actually is a FreeBSD specific change (such as special
shared library options when using ld) then it is OK to use __FreeBSD__ and #if __FreeBSD__ > 1
to detect a FreeBSD 2.x and later system. If you need more granularity in detecting
FreeBSD systems since 2.0-RELEASE you can use the following:
#if __FreeBSD__ >= 2
#include <osreldate.h>
# if __FreeBSD_version >= 199504
/* 2.0.5+ release specific code here */
# endif
#endif
In the hundreds of ports that have been done, there have only been one or two cases
where __FreeBSD__ should have been used. Just because an
earlier port screwed up and used it in the wrong place does not mean you should do so
too.
