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Clear up the 'Differentiating Operating Systems and OS Versions' section as it is

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highly unlikely that anyone will be backporting modern applications to CSRG's BSD.
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Eitan Adler 2013-09-21 15:13:46 +00:00
parent 3fb2953044
commit c890716679
Notes: svn2git 2020-12-08 03:00:23 +00:00 
svn path=/head/; revision=42683
1 changed files with 21 additions and 103 deletions
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en_US.ISO8859-1/books/porters-handbook/book.xml
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@ -11463,112 +11463,30 @@ Reference: <http://www.freebsd.org/ports/portaudit/74a9541d-5d6c-11d8-80e3-00
<title>Differentiating Operating Systems and OS Versions</title> <title>Differentiating Operating Systems and OS Versions</title>
<para>You may come across code that needs modifications or <para>You may come across code that needs modifications or
conditional compilation based upon what version of Unix it is conditional compilation based upon what version of &os; Unix it is
running under. If you need to make such changes to the code running under. The preferred way to tell &os; versions apart
for conditional compilation, make sure you make the changes as are the <literal>__FreeBSD_version</literal> and
general as possible so that we can back-port code to older <literal>__FreeBSD__</literal>
FreeBSD systems and cross-port to other BSD systems such as macros defined in <ulink
4.4BSD from CSRG, BSD/386, 386BSD, NetBSD, and OpenBSD.</para>
<para>The preferred way to tell 4.3BSD/Reno (1990) and newer
versions of the BSD code apart is by using the
<literal>BSD</literal> macro defined in <ulink
url="http://svnweb.freebsd.org/base/head/sys/sys/param.h?view=markup">sys/param.h</ulink>. url="http://svnweb.freebsd.org/base/head/sys/sys/param.h?view=markup">sys/param.h</ulink>.
Hopefully that file is already included; if not, add the If this file is not included add the code,</para>
code:</para>
<programlisting>#if (defined(__unix__) || defined(unix)) &amp;&amp; !defined(USG) <programlisting>#include &lt;sys/param.h&gt;</programlisting>
#include &lt;sys/param.h&gt;
<para>to the proper place in the <filename>.c</filename> file.</para>
<para><literal>__FreeBSD__</literal> is defined in all
versions of &os; as their major version number. For
example, in &os; 9.x, <literal>__FreeBSD__</literal> is
defined to be <literal>9</literal>.</para>
<para>
<programlisting>#if __FreeBSD__ &gt;= 9
# if __FreeBSD_version &gt;= 901000
/* 9.1+ release specific code here */
# endif
#endif</programlisting> #endif</programlisting>
</para>
<para>to the proper place in the <filename>.c</filename> file.
We believe that every system that defines these two symbols
has <filename>sys/param.h</filename>. If you find a system
that does not, we would like to know. Please send mail to the
&a.ports;.</para>
<para>Another way is to use the GNU Autoconf style of doing
this:</para>
<programlisting>#ifdef HAVE_SYS_PARAM_H
#include &lt;sys/param.h&gt;
#endif</programlisting>
<para>Do not forget to add <literal>-DHAVE_SYS_PARAM_H</literal>
to the <makevar>CFLAGS</makevar> in the
<filename>Makefile</filename> for this method.</para>
<para>Once you have <filename>sys/param.h</filename> included,
you may use:</para>
<programlisting>#if (defined(BSD) &amp;&amp; (BSD &gt;= 199103))</programlisting>
<para>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).</para>
<para>Use:</para>
<programlisting>#if (defined(BSD) &amp;&amp; (BSD &gt;= 199306))</programlisting>
<para>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).</para>
<para>The value of the <literal>BSD</literal> macro is
<literal>199506</literal> 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 versus versions that have merged in changes from
4.4-Lite2. The <literal>__FreeBSD__</literal> macro should be
used instead.</para>
<para>Use sparingly:</para>
<itemizedlist>
<listitem>
<para><literal>__FreeBSD__</literal> is defined in all
versions of FreeBSD. Use it if the change you are making
<emphasis>only</emphasis> affects FreeBSD. Porting
gotchas like the use of <literal>sys_errlist[]</literal>
versus <function>strerror()</function> are Berkeley-isms,
not FreeBSD changes.</para>
</listitem>
<listitem>
<para>In FreeBSD 2.x, <literal>__FreeBSD__</literal> is
defined to be <literal>2</literal>. In earlier versions,
it is <literal>1</literal>. Later versions always bump it
to match their major version number.</para>
</listitem>
<listitem>
<para>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 <literal>BSD</literal> macros
described above. If there actually is a FreeBSD specific
change (such as special shared library options when using
<command>ld</command>) then it is OK to use
<literal>__FreeBSD__</literal> and
<literal>#if __FreeBSD__ &gt; 1</literal> 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:</para>
<programlisting>#if __FreeBSD__ &gt;= 2
#include &lt;osreldate.h&gt;
# if __FreeBSD_version &gt;= 199504
/* 2.0.5+ release specific code here */
# endif
#endif</programlisting>
</listitem>
</itemizedlist>
<para>In the hundreds of ports that have been done, there have
only been one or two cases where
<literal>__FreeBSD__</literal> 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.</para>
</sect1> </sect1>
<sect1 id="freebsd-versions"> <sect1 id="freebsd-versions">