LDP
/
LDP
mirror of https://github.com/tLDP/LDP
0
1
Fork 0
Code Releases Activity

updated

This commit is contained in:
gferg 2005-07-20 16:20:51 +00:00
parent aa593058de
commit 1acf0d8ad7
4 changed files with 86 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
LDP/howto/docbook/HOWTO-INDEX/howtoChap.sgml
View File

@ -2956,7 +2956,7 @@ This HOWTO has been removed for review. </Para>
Module-HOWTO</ULink>,
<CiteTitle>Linux Loadable Kernel Module HOWTO</CiteTitle>
</Para><Para>
<CiteTitle>Updated: Jan 2005</CiteTitle>.
<CiteTitle>Updated: Jul 2005</CiteTitle>.
Explains what Linux loadable kernel modules (LKMs) are,
and how to use and create them. </Para>
</ListItem>

2
LDP/howto/docbook/HOWTO-INDEX/osSect.sgml
View File

@ -527,7 +527,7 @@ Crash Dump) package. </Para>
Module-HOWTO</ULink>,
<CiteTitle>Linux Loadable Kernel Module HOWTO</CiteTitle>
</Para><Para>
<CiteTitle>Updated: Jan 2005</CiteTitle>.
<CiteTitle>Updated: Jul 2005</CiteTitle>.
Explains what Linux loadable kernel modules (LKMs) are,
and how to use and create them. </Para>
</ListItem>

2
LDP/howto/docbook/HOWTO-INDEX/programmSect.sgml
View File

@ -335,7 +335,7 @@ point for more information. </Para>
Module-HOWTO</ULink>,
<CiteTitle>Linux Loadable Kernel Module HOWTO</CiteTitle>
</Para><Para>
<CiteTitle>Updated: Jan 2005</CiteTitle>.
<CiteTitle>Updated: Jul 2005</CiteTitle>.
Explains what Linux loadable kernel modules (LKMs) are,
and how to use and create them. </Para>
</ListItem>

104
LDP/howto/docbook/Module-HOWTO.sgml
View File

@ -17,9 +17,19 @@
</author>
<pubdate>January 12, 2005</pubdate>
<pubdate>2005-07-20</pubdate>
<revhistory>
<revision>
<revnumber>v1.07</revnumber>
<date>2005-07-20</date>
<authorinitials>bjh</authorinitials>
<revremark>
Add some 2.6 info and disclaimers.
Update references to Linux Device Drivers
book, Linux Kernel Module Programming Guide.
</revremark>
</revision>
<revision>
<revnumber>v1.06</revnumber>
<date>2005-01-12</date>
@ -550,6 +560,15 @@ If it does work, though, the way to prove to yourself that you know what
you're doing is to look at <filename>/proc/modules</filename> as
described in <xref linkend="procmodules">.
</para>
<para>
Note that the examples in this section are from Linux 2.4. In Linux 2.6,
the technical aspects of loading LKMs are considerably different, and
the most visible manifestation of this is that the LKM file has a suffix
of &quot;.ko&quot; instead of &quot;.o&quot;. From the user point of
view, it looks quite similar, though.
</para>
<para>
Now lets look at a more difficult insertion. If you try
<screen>
@ -574,6 +593,12 @@ to list every symbol that is exported by the kernel (i.e. available
for binding to LKMs). You will see that 'fat_date_unix2dos' is
nowhere in the list.
</para>
<para>(In Linux 2.6, there is no <filename>/proc/ksyms</filename>. Use
<filename>/proc/kallsyms</filename> instead; the format is like the
output of <command>nm</command>: look for symbols labelled &quot;t&quot;).
</para>
<para>
How do you get it into the list? By loading another LKM, one which
defines those symbols and exports them. In this case, it is the LKM
@ -888,9 +913,9 @@ Kernel Module Loader
</title>
<para>
There is some documentation of the kernel module loader in the file
<filename>Documentation/kmod.txt</filename> in the Linux source tree.
As of this writing, this section is more complete and accurate than
that file. You can also look at its source code in
<filename>Documentation/kmod.txt</filename> in the Linux 2.4 source
tree. This section is more complete and accurate than that file. You
can also look at its source code in
<filename>kernel/kmod.c</filename>.
</para>
<para>
@ -1665,7 +1690,21 @@ base kernel's <function>register_chrdev</function> subroutine. This
is not a system call, but an ordinary subroutine bound into the base
kernel. Calling it means branching to its address. So how does our
LKM, which was not compiled anywhere near the base kernel, know that
address? The answer to this is <command>insmod</command> relocation.
address? The answer to this is the relocation that happens at
<command>insmod</command> time.
</para>
<para>
How that relocation happens is fundamentally different between Linux
2.4 and Linux 2.6. In 2.6, <command>insmod</command> pretty much just
passes the verbatim contents of the LKM file (.ko file) to the kernel
and the kernel does the relocation. In 2.4, <command>insmod</command> does
the relocation and passes a fully linked module image, ready to stuff
into kernel memory, to the kernel. <emphasis>The description below
covers the 2.4 case.</emphasis>
</para>
<para>
<command>insmod</command> functions as a relocating linker/loader.
The LKM object file contains an external reference to the symbol
<varname>register_chrdev</varname>. <command>insmod</command> does a
@ -1804,9 +1843,10 @@ kernel, in hexadecimal.
<para>
<command>ksymoops</command> looks at the hexadecimal addresses, looks
them up in the kernel symbol table (which you see in
<filename>/proc/ksyms</filename>, and translates the addresses in the
oops message to symbolic addresses, which you might be able to look
up in an assembler listing.
<filename>/proc/ksyms</filename> (Linux 2.4) or
<filename>/proc/kallsyms</filename> (Linux 2.6), and translates the
addresses in the oops message to symbolic addresses, which you might
be able to look up in an assembler listing.
</para>
<para>
So lets say you have an LKM crash on you. The oops message contains
@ -1822,9 +1862,9 @@ get the loadpoints and lengths of the various sections of the LKM from
the kernel symbol table.
</para>
<para>
Well, <command>insmod</command> knows those addresses, so it just
creates symbols for them and includes them in the symbols it loads
with the LKM.
Well, in Linux 2.4, <command>insmod</command> knows those addresses,
so it just creates symbols for them and includes them in the symbols
it loads with the LKM.
</para>
<para>
In particular, those symbols are named (and you can see this for
@ -1880,6 +1920,9 @@ in Linux's <filename>linux/version.h</filename> file. For example,
The value of this symbol is meaningless.
</para>
<para>
In Linux 2.6, it works differently. (I haven't figured out how yet).
</para>
</sect2>
@ -2063,13 +2106,19 @@ Writing Your Own Loadable Kernel Module
</title>
<para>
<ulink url="http://tldp.org/LDP/lkmpg"><citetitle>The Linux Kernel
Module Programming Guide</citetitle></ulink> by Ori Pomerantz (Lkmpg) is a
complete explanation of writing your own LKM. This book is also
available in print.
Module Programming Guide</citetitle></ulink> by Peter J Salzman,
Michael Burian, and Ori Pomerantz is a complete explanation of writing
your own LKM. This book is also available in print. There are two
versions of it: one for Linux 2.4, and another for 2.6.
</para>
<para>
We will not duplicate information in that document, but here are
Here are a few things about writing an LKM that aren't in there.
At one time, the Linux 2.4 version of this document was rather out of
date and contained an error or two.
</para>
<para>
Here are a few things about writing an LKM that, at least at one time,
weren't in there. Let the author of the LKM HOWTO know if it's still
true. If not, he can remove this section from the LKM HOWTO.
</para>
<sect2>
@ -2220,12 +2269,12 @@ changes.
<sect2>
<title>
Rubini &amp Corbet: Linux Device Drivers
Rubini: Linux Device Drivers
</title>
<para>
The most popular book on writing device drivers is O'Reilly's
<citetitle>Linux Device Drivers</citetitle> by Alessandro
Rubini and Jonathan Corbet.
Rubini, Jonathan Corbet, and Greg Kroah-Hartman.
</para>
<para>
Even if you're writing an LKM that isn't a device driver, you can learn
@ -2234,12 +2283,27 @@ a lot from this book that will help you.
<para>
The first edition of this book covers Linux 2.0, with notes about
differences in 2.2. The second edition (June 2001) covers Linux 2.4.
The third edition (April 2005) covers Linux 2.6. Of course, if you know
anything about Linux, you know that a book like this doesn't perfectly
cover any release, because Linux changes frequently. Linux 2.6 as was
current a month after the Third Edition was released had significant
differences from the Linux 2.6 about which the book was written.
</para>
<para>
This book is available under the FDL. You can read it at
The second edition of this book is available under the FDL. You can
read it at
<ulink URL="http://www.xml.com/ldd/chapter/book/">
http://www.xml.com/ldd/chapter/book/</ulink>.
The third edition is available under the terms of the Creative Commons
Attribution-ShareAlike license, and you'll find it at
<ulink URL="http://lwn.net/Kernel/LDD3/">
http://lwn.net/Kernel/LDD3/</ulink>.
</para>
<para>
This book is also available in print in any decent technical book store.
</para>
</sect2>
@ -6987,5 +7051,3 @@ Copyright <trademark class="copyright">2001</trademark>.
</sect1>
</Article>