[Bug 191] Add kernel header explanation

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@1316 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter01/changelog.xml

@@ -23,6 +23,10 @@
 
 </para></listitem>
 
+<listitem><para>October 12th, 2001 [markh]: Chapter 5 - Kernel: Added
+explanation as to why we copy the kernel headers rather than symlink
+them.</para></listitem>
+
 <listitem><para>October 12th, 2001 [markh]: Appendix A - Gzip: Added
 uncompress to the gunzip description as it was
 missing.</para></listitem>

chapter05/kernel-exp-headers.xml

@@ -0,0 +1,35 @@
+<sect2>
+<title>Why we copy the kernel headers and don't symlink them</title>
+
+<para>In the past, it was common practise for people to symlink the
+/usr/include/linux and asm directories to /usr/src/linux/include/linux
+and asm respectively.  This is a <emphasis>bad</emphasis> idea as 
+this extract from a post by Linus Torvalds to the Linux Kernel 
+Mailing List points out:</para>
+
+<screen>I would suggest that people who compile new kernels should: 
+
+ - not have a single symbolic link in sight (except the one that the 
+   kernel build itself sets up, namely the "linux/include/asm" symlink 
+   that is only used for the internal kernel compile itself) 
+
+And yes, this is what I do. My /usr/src/linux still has the old 2.2.13 
+header files, even though I haven't run a 2.2.13 kernel in a _loong_ 
+time. But those headers were what glibc was compiled against, so those 
+headers are what matches the library object files. 
+
+And this is actually what has been the suggested environment for at 
+least the last five years. I don't know why the symlink business keeps 
+on living on, like a bad zombie. Pretty much every distribution still 
+has that broken symlink, and people still remember that the linux 
+sources should go into "/usr/src/linux" even though that hasn't been 
+true in a _loong_ time.</screen>
+
+<para>The relevant part here is where he states that the headers should
+be the ones which <emphasis>glibc was compiled against</emphasis>.  These are 
+the headers which should remain accessable and so by copying them, we ensure
+that we follow these guidelines.  Also note that as long as you don't have 
+those symlinks, it is perfectly alright to have the kernel sources 
+in <filename>/usr/src/linux</filename>.</para>
+
+</sect2>

chapter05/kernel.xml

@@ -7,6 +7,7 @@ Estimated required disk space:  &kernel-compsize-static;</screen>
 
 &c5-kernel-inst;
 &c5-kernel-exp;
+&c5-kernel-exp-headers;
 &aa-kernel-desc;
 &ab-kernel-dep;
 

index.xml

@@ -164,6 +164,7 @@
 <!ENTITY c5-kernel SYSTEM "chapter5/kernel.xml">
 <!ENTITY c5-kernel-inst SYSTEM "chapter5/kernel-inst.xml">
 <!ENTITY c5-kernel-exp SYSTEM "chapter5/kernel-exp.xml">
+<!ENTITY c5-kernel-exp-headers SYSTEM "chapter5/kernel-exp-headers.xml">
 <!ENTITY c5-make SYSTEM "chapter5/make.xml">
 <!ENTITY c5-make-inst SYSTEM "chapter5/make-inst.xml">
 <!ENTITY c5-mawk SYSTEM "chapter5/mawk.xml">