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Diffstat (limited to 'chapter06/kernel-headers.xml')
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diff --git a/chapter06/kernel-headers.xml b/chapter06/kernel-headers.xml new file mode 100644 index 000000000..14d73d992 --- /dev/null +++ b/chapter06/kernel-headers.xml @@ -0,0 +1,74 @@ +<sect1 id="ch-system-kernel-headers"> +<title>Installing Linux-&kernel-version; headers</title> +<?dbhtml filename="kernelheaders.html" dir="chapter06"?> + +<screen>&buildtime; &kernel-time-headers; +&diskspace; &kernel-compsize-headers;</screen> + +<sect2><title> </title><para> </para></sect2> + +<sect2> +<title>Installation of the kernel headers</title> + +<para>We won't be compiling a new kernel yet -- we'll do that when we have +finished the installation of all the packages. But the libraries installed in +the next section need to refer to the kernel header files in order to know how +to interface with the kernel. Instead of unpacking the kernel sources again, +making the version file and the symlinks and so on, we will simply copy the +headers from the temporary tools directory in one swoop:</para> + +<screen><userinput>cp -a /tools/include/{asm,asm-generic,linux} /usr/include</userinput></screen> + +<para>A few kernel header files refer to the <filename>autoconf.h</filename> +header file. Since we have not yet configured the kernel, we need to create +this file ourselves in order to avoid a compilation failure of Sysklogd. +Create an empty <filename>autoconf.h</filename> file with:</para> + +<screen><userinput>touch /usr/include/linux/autoconf.h</userinput></screen> + +</sect2> + +<sect2><title> </title><para> </para></sect2> + +<sect2> +<title>Why we copy the kernel headers</title> + +<para>In the past it was common practice to symlink the +<filename class="directory">/usr/include/{linux,asm}</filename> directories +to <filename class="directory">/usr/src/linux/include/{linux,asm}</filename>. +This was a <emphasis>bad</emphasis> practice, as the following 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 essential part is where Linus states that the header files should be +<emphasis>the ones which Glibc was compiled against</emphasis>. These are +the headers that should be used when you later compile other packages, as they +are the ones that match the object-code library files. By copying the headers, +we ensure that they remain available if later you upgrade your kernel.</para> + +<para>Note, by the way, that it is perfectly all right to have the kernel sources +in <filename class="directory">/usr/src/linux</filename>, as long as you don't +have the <filename class="directory">/usr/include/{linux,asm}</filename> +symlinks.</para> + +</sect2> + +</sect1> + |