Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild-2.6

* 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild-2.6: (39 commits)
  Revert "namespace: add source file location exceptions"
  Coccinelle: Add contextual message
  Coccinelle: Fix documentation
  Coccinelle: Find doubled arguments to boolean or bit operators.
  Coccinelle: Find nested lock+irqsave functions that use the same flags variables.
  namespace: add source file location exceptions
  scripts/extract-ikconfig: add support for bzip2, lzma and lzo
  kbuild: check return value of asprintf()
  scripts/namespace.pl: improve to get more correct results
  scripts/namespace.pl: some bug fixes
  scripts/namespace.pl: update file exclusion list
  scripts/namespace.pl: fix wrong source path
  Coccinelle: Use the -no_show_diff option for org and report mode
  Coccinelle: Add a new mode named 'chain'
  Coccinelle: Use new comment format to explain kfree.cocci
  Coccinelle: Improve user information with a new kind of comment
  Coccinelle: Update documentation
  MAINTAINERS: Coccinelle: Update email address
  Documentation/kbuild: modules.txt cleanup
  Documentation/kbuild: major edit of modules.txt sections 5-8
  ...

2 files changed, 400 insertions, 383 deletions

diff --git a/Documentation/coccinelle.txt b/Documentation/coccinelle.txt
index cd2b02837066..4a276ea7001c 100644
--- a/Documentation/coccinelle.txt
+++ b/Documentation/coccinelle.txt
@@ -24,6 +24,9 @@ of many distributions, e.g. :
 You can get the latest version released from the Coccinelle homepage at
 http://coccinelle.lip6.fr/
 
+Information and tips about Coccinelle are also provided on the wiki
+pages at http://cocci.ekstranet.diku.dk/wiki/doku.php
+
 Once you have it, run the following command:
 
      	./configure
@@ -41,20 +44,22 @@ A Coccinelle-specific target is defined in the top level
 Makefile. This target is named 'coccicheck' and calls the 'coccicheck'
 front-end in the 'scripts' directory.
 
-Four modes are defined: report, patch, context, and org. The mode to
+Four modes are defined: patch, report, context, and org. The mode to
 use is specified by setting the MODE variable with 'MODE=<mode>'.
 
+'patch' proposes a fix, when possible.
+
 'report' generates a list in the following format:
   file:line:column-column: message
 
-'patch' proposes a fix, when possible.
-
 'context' highlights lines of interest and their context in a
 diff-like style.Lines of interest are indicated with '-'.
 
 'org' generates a report in the Org mode format of Emacs.
 
-Note that not all semantic patches implement all modes.
+Note that not all semantic patches implement all modes. For easy use
+of Coccinelle, the default mode is "chain" which tries the previous
+modes in the order above until one succeeds.
 
 To make a report for every semantic patch, run the following command:
 
@@ -68,9 +73,9 @@ To produce patches, run:
 
 
 The coccicheck target applies every semantic patch available in the
-subdirectories of 'scripts/coccinelle' to the entire Linux kernel.
+sub-directories of 'scripts/coccinelle' to the entire Linux kernel.
 
-For each semantic patch, a changelog message is proposed.  It gives a
+For each semantic patch, a commit message is proposed.  It gives a
 description of the problem being checked by the semantic patch, and
 includes a reference to Coccinelle.
 
@@ -93,12 +98,35 @@ or
 	make coccicheck COCCI=<my_SP.cocci> MODE=report
 
 
+ Using Coccinelle on (modified) files
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To apply Coccinelle on a file basis, instead of a directory basis, the
+following command may be used:
+
+    make C=1 CHECK="scripts/coccicheck"
+
+To check only newly edited code, use the value 2 for the C flag, i.e.
+
+    make C=2 CHECK="scripts/coccicheck"
+
+This runs every semantic patch in scripts/coccinelle by default. The
+COCCI variable may additionally be used to only apply a single
+semantic patch as shown in the previous section.
+
+The "chain" mode is the default. You can select another one with the
+MODE variable explained above.
+
+In this mode, there is no information about semantic patches
+displayed, and no commit message proposed.
+
+
  Proposing new semantic patches
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 New semantic patches can be proposed and submitted by kernel
 developers. For sake of clarity, they should be organized in the
-subdirectories of 'scripts/coccinelle/'.
+sub-directories of 'scripts/coccinelle/'.
 
 
  Detailed description of the 'report' mode
@@ -111,7 +139,7 @@ Example:
 
 Running
 
-	make coccicheck MODE=report COCCI=scripts/coccinelle/err_cast.cocci
+	make coccicheck MODE=report COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script.
 
@@ -149,7 +177,7 @@ identified.
 Example:
 
 Running
-	make coccicheck MODE=patch COCCI=scripts/coccinelle/err_cast.cocci
+	make coccicheck MODE=patch COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script.
 
@@ -193,7 +221,7 @@ NOTE: The diff-like output generated is NOT an applicable patch. The
 Example:
 
 Running
-	make coccicheck MODE=context COCCI=scripts/coccinelle/err_cast.cocci
+	make coccicheck MODE=context COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script.
 
@@ -228,7 +256,7 @@ diff -u -p /home/user/linux/crypto/ctr.c /tmp/nothing
 Example:
 
 Running
-	make coccicheck MODE=org COCCI=scripts/coccinelle/err_cast.cocci
+	make coccicheck MODE=org COCCI=scripts/coccinelle/api/err_cast.cocci
 
 will execute the following part of the SmPL script.
 
diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt
index 0767cf69c69e..3fb39e0116b4 100644
--- a/Documentation/kbuild/modules.txt
+++ b/Documentation/kbuild/modules.txt
@@ -1,215 +1,185 @@
+Building External Modules
 
-In this document you will find information about:
-- how to build external modules
-- how to make your module use the kbuild infrastructure
-- how kbuild will install a kernel
-- how to install modules in a non-standard location
+This document describes how to build an out-of-tree kernel module.
 
 === Table of Contents
 
 	=== 1 Introduction
-	=== 2 How to build external modules
-	   --- 2.1 Building external modules
-	   --- 2.2 Available targets
-	   --- 2.3 Available options
-	   --- 2.4 Preparing the kernel tree for module build
-	   --- 2.5 Building separate files for a module
-	=== 3. Example commands
-	=== 4. Creating a kbuild file for an external module
-	=== 5. Include files
-	   --- 5.1 How to include files from the kernel include dir
-	   --- 5.2 External modules using an include/ dir
-	   --- 5.3 External modules using several directories
-	=== 6. Module installation
-	   --- 6.1 INSTALL_MOD_PATH
-	   --- 6.2 INSTALL_MOD_DIR
-	=== 7. Module versioning & Module.symvers
-	   --- 7.1 Symbols from the kernel (vmlinux + modules)
-	   --- 7.2 Symbols and external modules
-	   --- 7.3 Symbols from another external module
-	=== 8. Tips & Tricks
-	   --- 8.1 Testing for CONFIG_FOO_BAR
+	=== 2 How to Build External Modules
+	   --- 2.1 Command Syntax
+	   --- 2.2 Options
+	   --- 2.3 Targets
+	   --- 2.4 Building Separate Files
+	=== 3. Creating a Kbuild File for an External Module
+	   --- 3.1 Shared Makefile
+	   --- 3.2 Separate Kbuild file and Makefile
+	   --- 3.3 Binary Blobs
+	   --- 3.4 Building Multiple Modules
+	=== 4. Include Files
+	   --- 4.1 Kernel Includes
+	   --- 4.2 Single Subdirectory
+	   --- 4.3 Several Subdirectories
+	=== 5. Module Installation
+	   --- 5.1 INSTALL_MOD_PATH
+	   --- 5.2 INSTALL_MOD_DIR
+	=== 6. Module Versioning
+	   --- 6.1 Symbols From the Kernel (vmlinux + modules)
+	   --- 6.2 Symbols and External Modules
+	   --- 6.3 Symbols From Another External Module
+	=== 7. Tips & Tricks
+	   --- 7.1 Testing for CONFIG_FOO_BAR
 
 
 
 === 1. Introduction
 
-kbuild includes functionality for building modules both
-within the kernel source tree and outside the kernel source tree.
-The latter is usually referred to as external or "out-of-tree"
-modules and is used both during development and for modules that
-are not planned to be included in the kernel tree.
+"kbuild" is the build system used by the Linux kernel. Modules must use
+kbuild to stay compatible with changes in the build infrastructure and
+to pick up the right flags to "gcc." Functionality for building modules
+both in-tree and out-of-tree is provided. The method for building
+either is similar, and all modules are initially developed and built
+out-of-tree.
 
-What is covered within this file is mainly information to authors
-of modules. The author of an external module should supply
-a makefile that hides most of the complexity, so one only has to type
-'make' to build the module. A complete example will be presented in
-chapter 4, "Creating a kbuild file for an external module".
+Covered in this document is information aimed at developers interested
+in building out-of-tree (or "external") modules. The author of an
+external module should supply a makefile that hides most of the
+complexity, so one only has to type "make" to build the module. This is
+easily accomplished, and a complete example will be presented in
+section 3.
 
 
-=== 2. How to build external modules
+=== 2. How to Build External Modules
 
-kbuild offers functionality to build external modules, with the
-prerequisite that there is a pre-built kernel available with full source.
-A subset of the targets available when building the kernel is available
-when building an external module.
+To build external modules, you must have a prebuilt kernel available
+that contains the configuration and header files used in the build.
+Also, the kernel must have been built with modules enabled. If you are
+using a distribution kernel, there will be a package for the kernel you
+are running provided by your distribution.
 
---- 2.1 Building external modules
+An alternative is to use the "make" target "modules_prepare." This will
+make sure the kernel contains the information required. The target
+exists solely as a simple way to prepare a kernel source tree for
+building external modules.
 
-	Use the following command to build an external module:
+NOTE: "modules_prepare" will not build Module.symvers even if
+CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be
+executed to make module versioning work.
 
-		make -C <path-to-kernel> M=`pwd`
+--- 2.1 Command Syntax
 
-	For the running kernel use:
+	The command to build an external module is:
 
-		make -C /lib/modules/`uname -r`/build M=`pwd`
+		$ make -C <path_to_kernel_src> M=$PWD
 
-	For the above command to succeed, the kernel must have been
-	built with modules enabled.
+	The kbuild system knows that an external module is being built
+	due to the "M=<dir>" option given in the command.
 
-	To install the modules that were just built:
+	To build against the running kernel use:
 
-		make -C <path-to-kernel> M=`pwd` modules_install
+		$ make -C /lib/modules/`uname -r`/build M=$PWD
 
-	More complex examples will be shown later, the above should
-	be enough to get you started.
+	Then to install the module(s) just built, add the target
+	"modules_install" to the command:
 
---- 2.2 Available targets
+		$ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
 
-	$KDIR refers to the path to the kernel source top-level directory
+--- 2.2 Options
 
-	make -C $KDIR M=`pwd`
-		Will build the module(s) located in current directory.
-		All output files will be located in the same directory
-		as the module source.
-		No attempts are made to update the kernel source, and it is
-		a precondition that a successful make has been executed
-		for the kernel.
+	($KDIR refers to the path of the kernel source directory.)
 
-	make -C $KDIR M=`pwd` modules
-		The modules target is implied when no target is given.
-		Same functionality as if no target was specified.
-		See description above.
+	make -C $KDIR M=$PWD
 
-	make -C $KDIR M=`pwd` modules_install
-		Install the external module(s).
-		Installation default is in /lib/modules/<kernel-version>/extra,
-		but may be prefixed with INSTALL_MOD_PATH - see separate
-		chapter.
+	-C $KDIR
+		The directory where the kernel source is located.
+		"make" will actually change to the specified directory
+		when executing and will change back when finished.
 
-	make -C $KDIR M=`pwd` clean
-		Remove all generated files for the module - the kernel
-		source directory is not modified.
+	M=$PWD
+		Informs kbuild that an external module is being built.
+		The value given to "M" is the absolute path of the
+		directory where the external module (kbuild file) is
+		located.
 
-	make -C $KDIR M=`pwd` help
-		help will list the available target when building external
-		modules.
+--- 2.3 Targets
 
---- 2.3 Available options:
+	When building an external module, only a subset of the "make"
+	targets are available.
 
-	$KDIR refers to the path to the kernel source top-level directory
+	make -C $KDIR M=$PWD [target]
 
-	make -C $KDIR
-		Used to specify where to find the kernel source.
-		'$KDIR' represent the directory where the kernel source is.
-		Make will actually change directory to the specified directory
-		when executed but change back when finished.
+	The default will build the module(s) located in the current
+	directory, so a target does not need to be specified. All
+	output files will also be generated in this directory. No
+	attempts are made to update the kernel source, and it is a
+	precondition that a successful "make" has been executed for the
+	kernel.
 
-	make -C $KDIR M=`pwd`
-		M= is used to tell kbuild that an external module is
-		being built.
-		The option given to M= is the directory where the external
-		module (kbuild file) is located.
-		When an external module is being built only a subset of the
-		usual targets are available.
+	modules
+		The default target for external modules. It has the
+		same functionality as if no target was specified. See
+		description above.
 
-	make -C $KDIR SUBDIRS=`pwd`
-		Same as M=. The SUBDIRS= syntax is kept for backwards
-		compatibility.
+	modules_install
+		Install the external module(s). The default location is
+		/lib/modules/<kernel_release>/extra/, but a prefix may
+		be added with INSTALL_MOD_PATH (discussed in section 5).
 
---- 2.4 Preparing the kernel tree for module build
+	clean
+		Remove all generated files in the module directory only.
 
-	To make sure the kernel contains the information required to
-	build external modules the target 'modules_prepare' must be used.
-	'modules_prepare' exists solely as a simple way to prepare
-	a kernel source tree for building external modules.
-	Note: modules_prepare will not build Module.symvers even if
-	CONFIG_MODVERSIONS is set. Therefore a full kernel build
-	needs to be executed to make module versioning work.
+	help
+		List the available targets for external modules.
 
---- 2.5 Building separate files for a module
-	It is possible to build single files which are part of a module.
-	This works equally well for the kernel, a module and even for
-	external modules.
-	Examples (module foo.ko, consist of bar.o, baz.o):
-		make -C $KDIR M=`pwd` bar.lst
-		make -C $KDIR M=`pwd` bar.o
-		make -C $KDIR M=`pwd` foo.ko
-		make -C $KDIR M=`pwd` /
-
-
-=== 3. Example commands
-
-This example shows the actual commands to be executed when building
-an external module for the currently running kernel.
-In the example below, the distribution is supposed to use the
-facility to locate output files for a kernel compile in a different
-directory than the kernel source - but the examples will also work
-when the source and the output files are mixed in the same directory.
+--- 2.4 Building Separate Files
 
-# Kernel source
-/lib/modules/<kernel-version>/source -> /usr/src/linux-<version>
-
-# Output from kernel compile
-/lib/modules/<kernel-version>/build -> /usr/src/linux-<version>-up
-
-Change to the directory where the kbuild file is located and execute
-the following commands to build the module:
+	It is possible to build single files that are part of a module.
+	This works equally well for the kernel, a module, and even for
+	external modules.
 
-	cd /home/user/src/module
-	make -C /usr/src/`uname -r`/source            \
-	        O=/lib/modules/`uname-r`/build        \
-	        M=`pwd`
+	Example (The module foo.ko, consist of bar.o and baz.o):
+		make -C $KDIR M=$PWD bar.lst
+		make -C $KDIR M=$PWD baz.o
+		make -C $KDIR M=$PWD foo.ko
+		make -C $KDIR M=$PWD /
 
-Then, to install the module use the following command:
 
-	make -C /usr/src/`uname -r`/source            \
-	        O=/lib/modules/`uname-r`/build        \
-	        M=`pwd`                               \
-		modules_install
+=== 3. Creating a Kbuild File for an External Module
 
-If you look closely you will see that this is the same command as
-listed before - with the directories spelled out.
+In the last section we saw the command to build a module for the
+running kernel. The module is not actually built, however, because a
+build file is required. Contained in this file will be the name of
+the module(s) being built, along with the list of requisite source
+files. The file may be as simple as a single line:
 
-The above are rather long commands, and the following chapter
-lists a few tricks to make it all easier.
+	obj-m := <module_name>.o
 
+The kbuild system will build <module_name>.o from <module_name>.c,
+and, after linking, will result in the kernel module <module_name>.ko.
+The above line can be put in either a "Kbuild" file or a "Makefile."
+When the module is built from multiple sources, an additional line is
+needed listing the files:
 
-=== 4. Creating a kbuild file for an external module
+	<module_name>-y := <src1>.o <src2>.o ...
 
-kbuild is the build system for the kernel, and external modules
-must use kbuild to stay compatible with changes in the build system
-and to pick up the right flags to gcc etc.
+NOTE: Further documentation describing the syntax used by kbuild is
+located in Documentation/kbuild/makefiles.txt.
 
-The kbuild file used as input shall follow the syntax described
-in Documentation/kbuild/makefiles.txt. This chapter will introduce a few
-more tricks to be used when dealing with external modules.
+The examples below demonstrate how to create a build file for the
+module 8123.ko, which is built from the following files:
 
-In the following a Makefile will be created for a module with the
-following files:
 	8123_if.c
 	8123_if.h
 	8123_pci.c
 	8123_bin.o_shipped	<= Binary blob
 
---- 4.1 Shared Makefile for module and kernel
+--- 3.1 Shared Makefile
 
-	An external module always includes a wrapper Makefile supporting
-	building the module using 'make' with no arguments.
-	The Makefile provided will most likely include additional
-	functionality such as test targets etc. and this part shall
-	be filtered away from kbuild since it may impact kbuild if
-	name clashes occurs.
+	An external module always includes a wrapper makefile that
+	supports building the module using "make" with no arguments.
+	This target is not used by kbuild; it is only for convenience.
+	Additional functionality, such as test targets, can be included
+	but should be filtered out from kbuild due to possible name
+	clashes.
 
 	Example 1:
 		--> filename: Makefile
@@ -219,11 +189,11 @@ following files:
 		8123-y := 8123_if.o 8123_pci.o 8123_bin.o
 
 		else
-		# Normal Makefile
+		# normal makefile
+		KDIR ?= /lib/modules/`uname -r`/build
 
-		KERNELDIR := /lib/modules/`uname -r`/build
-		all::
-			$(MAKE) -C $(KERNELDIR) M=`pwd` $@
+		default:
+			$(MAKE) -C $(KDIR) M=$$PWD
 
 		# Module specific targets
 		genbin:
@@ -231,15 +201,20 @@ following files:
 
 		endif
 
-	In example 1, the check for KERNELRELEASE is used to separate
-	the two parts of the Makefile. kbuild will only see the two
-	assignments whereas make will see everything except the two
-	kbuild assignments.
+	The check for KERNELRELEASE is used to separate the two parts
+	of the makefile. In the example, kbuild will only see the two
+	assignments, whereas "make" will see everything except these
+	two assignments. This is due to two passes made on the file:
+	the first pass is by the "make" instance run on the command
+	line; the second pass is by the kbuild system, which is
+	initiated by the parameterized "make" in the default target.
+
+--- 3.2 Separate Kbuild File and Makefile
 
-	In recent versions of the kernel, kbuild will look for a file named
-	Kbuild and as second option look for a file named Makefile.
-	Utilising the Kbuild file makes us split up the Makefile in example 1
-	into two files as shown in example 2:
+	In newer versions of the kernel, kbuild will first look for a
+	file named "Kbuild," and only if that is not found, will it
+	then look for a makefile. Utilizing a "Kbuild" file allows us
+	to split up the makefile from example 1 into two files:
 
 	Example 2:
 		--> filename: Kbuild
@@ -247,20 +222,21 @@ following files:
 		8123-y := 8123_if.o 8123_pci.o 8123_bin.o
 
 		--> filename: Makefile
-		KERNELDIR := /lib/modules/`uname -r`/build
-		all::
-			$(MAKE) -C $(KERNELDIR) M=`pwd` $@
+		KDIR ?= /lib/modules/`uname -r`/build
+
+		default:
+			$(MAKE) -C $(KDIR) M=$$PWD
 
 		# Module specific targets
 		genbin:
 			echo "X" > 8123_bin.o_shipped
 
+	The split in example 2 is questionable due to the simplicity of
+	each file; however, some external modules use makefiles
+	consisting of several hundred lines, and here it really pays
+	off to separate the kbuild part from the rest.
 
-	In example 2, we are down to two fairly simple files and for simple
-	files as used in this example the split is questionable. But some
-	external modules use Makefiles of several hundred lines and here it
-	really pays off to separate the kbuild part from the rest.
-	Example 3 shows a backward compatible version.
+	The next example shows a backward compatible version.
 
 	Example 3:
 		--> filename: Kbuild
@@ -269,13 +245,15 @@ following files:
 
 		--> filename: Makefile
 		ifneq ($(KERNELRELEASE),)
+		# kbuild part of makefile
 		include Kbuild
+
 		else
-		# Normal Makefile
+		# normal makefile
+		KDIR ?= /lib/modules/`uname -r`/build
 
-		KERNELDIR := /lib/modules/`uname -r`/build
-		all::
-			$(MAKE) -C $(KERNELDIR) M=`pwd` $@
+		default:
+			$(MAKE) -C $(KDIR) M=$$PWD
 
 		# Module specific targets
 		genbin:
@@ -283,260 +261,271 @@ following files:
 
 		endif
 
-	The trick here is to include the Kbuild file from Makefile, so
-	if an older version of kbuild picks up the Makefile, the Kbuild
-	file will be included.
+	Here the "Kbuild" file is included from the makefile. This
+	allows an older version of kbuild, which only knows of
+	makefiles, to be used when the "make" and kbuild parts are
+	split into separate files.
 
---- 4.2 Binary blobs included in a module
+--- 3.3 Binary Blobs
 
-	Some external modules needs to include a .o as a blob. kbuild
-	has support for this, but requires the blob file to be named
-	<filename>_shipped. In our example the blob is named
-	8123_bin.o_shipped and when the kbuild rules kick in the file
-	8123_bin.o is created as a simple copy off the 8213_bin.o_shipped file
-	with the _shipped part stripped of the filename.
-	This allows the 8123_bin.o filename to be used in the assignment to
-	the module.
+	Some external modules need to include an object file as a blob.
+	kbuild has support for this, but requires the blob file to be
+	named <filename>_shipped. When the kbuild rules kick in, a copy
+	of <filename>_shipped is created with _shipped stripped off,
+	giving us <filename>. This shortened filename can be used in
+	the assignment to the module.
+
+	Throughout this section, 8123_bin.o_shipped has been used to
+	build the kernel module 8123.ko; it has been included as
+	8123_bin.o.
 
-	Example 4:
-		obj-m  := 8123.o
 		8123-y := 8123_if.o 8123_pci.o 8123_bin.o
 
-	In example 4, there is no distinction between the ordinary .c/.h files
-	and the binary file. But kbuild will pick up different rules to create
-	the .o file.
+	Although there is no distinction between the ordinary source
+	files and the binary file, kbuild will pick up different rules
+	when creating the object file for the module.
+
+--- 3.4 Building Multiple Modules
 
+	kbuild supports building multiple modules with a single build
+	file. For example, if you wanted to build two modules, foo.ko
+	and bar.ko, the kbuild lines would be:
 
-=== 5. Include files
+		obj-m := foo.o bar.o
+		foo-y := <foo_srcs>
+		bar-y := <bar_srcs>
 
-Include files are a necessity when a .c file uses something from other .c
-files (not strictly in the sense of C, but if good programming practice is
-used). Any module that consists of more than one .c file will have a .h file
-for one of the .c files.
+	It is that simple!
 
-- If the .h file only describes a module internal interface, then the .h file
-  shall be placed in the same directory as the .c files.
-- If the .h files describe an interface used by other parts of the kernel
-  located in different directories, the .h files shall be located in
-  include/linux/ or other include/ directories as appropriate.
 
-One exception for this rule is larger subsystems that have their own directory
-under include/ such as include/scsi. Another exception is arch-specific
-.h files which are located under include/asm-$(ARCH)/*.
+=== 4. Include Files
 
-External modules have a tendency to locate include files in a separate include/
-directory and therefore need to deal with this in their kbuild file.
+Within the kernel, header files are kept in standard locations
+according to the following rule:
 
---- 5.1 How to include files from the kernel include dir
+	* If the header file only describes the internal interface of a
+	  module, then the file is placed in the same directory as the
+	  source files.
+	* If the header file describes an interface used by other parts
+	  of the kernel that are located in different directories, then
+	  the file is placed in include/linux/.
 
-	When a module needs to include a file from include/linux/, then one
-	just uses:
+	  NOTE: There are two notable exceptions to this rule: larger
+	  subsystems have their own directory under include/, such as
+	  include/scsi; and architecture specific headers are located
+	  under arch/$(ARCH)/include/.
 
-		#include <linux/modules.h>
+--- 4.1 Kernel Includes
 
-	kbuild will make sure to add options to gcc so the relevant
-	directories are searched.
-	Likewise for .h files placed in the same directory as the .c file.
+	To include a header file located under include/linux/, simply
+	use:
 
-		#include "8123_if.h"
+		#include <linux/module.h>
 
-	will do the job.
+	kbuild will add options to "gcc" so the relevant directories
+	are searched.
 
---- 5.2 External modules using an include/ dir
+--- 4.2 Single Subdirectory
 
-	External modules often locate their .h files in a separate include/
-	directory although this is not usual kernel style. When an external
-	module uses an include/ dir then kbuild needs to be told so.
-	The trick here is to use either EXTRA_CFLAGS (take effect for all .c
-	files) or CFLAGS_$F.o (take effect only for a single file).
+	External modules tend to place header files in a separate
+	include/ directory where their source is located, although this
+	is not the usual kernel style. To inform kbuild of the
+	directory, use either ccflags-y or CFLAGS_<filename>.o.
 
-	In our example, if we move 8123_if.h to a subdirectory named include/
-	the resulting Kbuild file would look like:
+	Using the example from section 3, if we moved 8123_if.h to a
+	subdirectory named include, the resulting kbuild file would
+	look like:
 
 		--> filename: Kbuild
-		obj-m  := 8123.o
+		obj-m := 8123.o
 
-		EXTRA_CFLAGS := -Iinclude
+		ccflags-y := -Iinclude
 		8123-y := 8123_if.o 8123_pci.o 8123_bin.o
 
-	Note that in the assignment there is no space between -I and the path.
-	This is a kbuild limitation:  there must be no space present.
+	Note that in the assignment there is no space between -I and
+	the path. This is a limitation of kbuild: there must be no
+	space present.
 
---- 5.3 External modules using several directories
-
-	If an external module does not follow the usual kernel style, but
-	decides to spread files over several directories, then kbuild can
-	handle this too.
+--- 4.3 Several Subdirectories
 
+	kbuild can handle files that are spread over several directories.
 	Consider the following example:
 
-	|
-	+- src/complex_main.c
-	|   +- hal/hardwareif.c
-	|   +- hal/include/hardwareif.h
-	+- include/complex.h
-
-	To build a single module named complex.ko, we then need the following
+	.
+	|__ src
+	|   |__ complex_main.c
+	|   |__ hal
+	|	|__ hardwareif.c
+	|	|__ include
+	|	    |__ hardwareif.h
+	|__ include
+	    |__ complex.h
+
+	To build the module complex.ko, we then need the following
 	kbuild file:
 
-	Kbuild:
+		--> filename: Kbuild
 		obj-m := complex.o
 		complex-y := src/complex_main.o
 		complex-y += src/hal/hardwareif.o
 
-		EXTRA_CFLAGS := -I$(src)/include
-		EXTRA_CFLAGS += -I$(src)src/hal/include
+		ccflags-y := -I$(src)/include
+		ccflags-y += -I$(src)/src/hal/include
 
+	As you can see, kbuild knows how to handle object files located
+	in other directories. The trick is to specify the directory
+	relative to the kbuild file's location. That being said, this
+	is NOT recommended practice.
 
-	kbuild knows how to handle .o files located in another directory -
-	although this is NOT recommended practice. The syntax is to specify
-	the directory relative to the directory where the Kbuild file is
-	located.
+	For the header files, kbuild must be explicitly told where to
+	look. When kbuild executes, the current directory is always the
+	root of the kernel tree (the argument to "-C") and therefore an
+	absolute path is needed. $(src) provides the absolute path by
+	pointing to the directory where the currently executing kbuild
+	file is located.
 
-	To find the .h files, we have to explicitly tell kbuild where to look
-	for the .h files. When kbuild executes, the current directory is always
-	the root of the kernel tree (argument to -C) and therefore we have to
-	tell kbuild how to find the .h files using absolute paths.
-	$(src) will specify the absolute path to the directory where the
-	Kbuild file are located when being build as an external module.
-	Therefore -I$(src)/ is used to point out the directory of the Kbuild
-	file and any additional path are just appended.
 
-=== 6. Module installation
+=== 5. Module Installation
 
-Modules which are included in the kernel are installed in the directory:
+Modules which are included in the kernel are installed in the
+directory:
 
-	/lib/modules/$(KERNELRELEASE)/kernel
+	/lib/modules/$(KERNELRELEASE)/kernel/
 
-External modules are installed in the directory:
+And external modules are installed in:
 
-	/lib/modules/$(KERNELRELEASE)/extra
+	/lib/modules/$(KERNELRELEASE)/extra/
 
---- 6.1 INSTALL_MOD_PATH
+--- 5.1 INSTALL_MOD_PATH
 
-	Above are the default directories, but as always, some level of
-	customization is possible. One can prefix the path using the variable
-	INSTALL_MOD_PATH:
+	Above are the default directories but as always some level of
+	customization is possible. A prefix can be added to the
+	installation path using the variable INSTALL_MOD_PATH:
 
 		$ make INSTALL_MOD_PATH=/frodo modules_install
-		=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel
-
-	INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the
-	example above, can be specified on the command line when calling make.
-	INSTALL_MOD_PATH has effect both when installing modules included in
-	the kernel as well as when installing external modules.
+		=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
 
---- 6.2 INSTALL_MOD_DIR
+	INSTALL_MOD_PATH may be set as an ordinary shell variable or,
+	as shown above, can be specified on the command line when
+	calling "make." This has effect when installing both in-tree
+	and out-of-tree modules.
 
-	When installing external modules they are by default installed to a
-	directory under /lib/modules/$(KERNELRELEASE)/extra, but one may wish
-	to locate modules for a specific functionality in a separate
-	directory. For this purpose, one can use INSTALL_MOD_DIR to specify an
-	alternative name to 'extra'.
+--- 5.2 INSTALL_MOD_DIR
 
-		$ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \
-			M=`pwd` modules_install
-		=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf
+	External modules are by default installed to a directory under
+	/lib/modules/$(KERNELRELEASE)/extra/, but you may wish to
+	locate modules for a specific functionality in a separate
+	directory. For this purpose, use INSTALL_MOD_DIR to specify an
+	alternative name to "extra."
 
+		$ make INSTALL_MOD_DIR=gandalf -C $KDIR \
+		       M=$PWD modules_install
+		=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
 
-=== 7. Module versioning & Module.symvers
 
-Module versioning is enabled by the CONFIG_MODVERSIONS tag.
+=== 6. Module Versioning
 
-Module versioning is used as a simple ABI consistency check. The Module
-versioning creates a CRC value of the full prototype for an exported symbol and
-when a module is loaded/used then the CRC values contained in the kernel are
-compared with similar values in the module. If they are not equal, then the
-kernel refuses to load the module.
+Module versioning is enabled by the CONFIG_MODVERSIONS tag, and is used
+as a simple ABI consistency check. A CRC value of the full prototype
+for an exported symbol is created. When a module is loaded/used, the
+CRC values contained in the kernel are compared with similar values in
+the module; if they are not equal, the kernel refuses to load the
+module.
 
-Module.symvers contains a list of all exported symbols from a kernel build.
+Module.symvers contains a list of all exported symbols from a kernel
+build.
 
---- 7.1 Symbols from the kernel (vmlinux + modules)
+--- 6.1 Symbols From the Kernel (vmlinux + modules)
 
-	During a kernel build, a file named Module.symvers will be generated.
-	Module.symvers contains all exported symbols from the kernel and
-	compiled modules. For each symbols, the corresponding CRC value
-	is stored too.
+	During a kernel build, a file named Module.symvers will be
+	generated. Module.symvers contains all exported symbols from
+	the kernel and compiled modules. For each symbol, the
+	corresponding CRC value is also stored.
 
 	The syntax of the Module.symvers file is:
-		<CRC>       <Symbol>           <module>
-	Sample:
+		<CRC>	    <Symbol>	       <module>
+
 		0x2d036834  scsi_remove_host   drivers/scsi/scsi_mod
 
-	For a kernel build without CONFIG_MODVERSIONS enabled, the crc
-	would read: 0x00000000
+	For a kernel build without CONFIG_MODVERSIONS enabled, the CRC
+	would read 0x00000000.
 
 	Module.symvers serves two purposes:
-	1) It lists all exported symbols both from vmlinux and all modules
-	2) It lists the CRC if CONFIG_MODVERSIONS is enabled
-
---- 7.2 Symbols and external modules
-
-	When building an external module, the build system needs access to
-	the symbols from the kernel to check if all external symbols are
-	defined. This is done in the MODPOST step and to obtain all
-	symbols, modpost reads Module.symvers from the kernel.
-	If a Module.symvers file is present in the directory where
-	the external module is being built, this file will be read too.
-	During the MODPOST step, a new Module.symvers file will be written
-	containing all exported symbols that were not defined in the kernel.
-
---- 7.3 Symbols from another external module
-
-	Sometimes, an external module uses exported symbols from another
-	external module. Kbuild needs to have full knowledge on all symbols
-	to avoid spitting out warnings about undefined symbols.
-	Three solutions exist to let kbuild know all symbols of more than
-	one external module.
-	The method with a top-level kbuild file is recommended but may be
-	impractical in certain situations.
-
-	Use a top-level Kbuild file
-		If you have two modules: 'foo' and 'bar', and 'foo' needs
-		symbols from 'bar', then one can use a common top-level kbuild
-		file so both modules are compiled in same build.
-
-		Consider following directory layout:
-		./foo/ <= contains the foo module
-		./bar/ <= contains the bar module
-		The top-level Kbuild file would then look like:
-
-		#./Kbuild: (this file may also be named Makefile)
+	1) It lists all exported symbols from vmlinux and all modules.
+	2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
+
+--- 6.2 Symbols and External Modules
+
+	When building an external module, the build system needs access
+	to the symbols from the kernel to check if all external symbols
+	are defined. This is done in the MODPOST step. modpost obtains
+	the symbols by reading Module.symvers from the kernel source
+	tree. If a Module.symvers file is present in the directory
+	where the external module is being built, this file will be
+	read too. During the MODPOST step, a new Module.symvers file
+	will be written containing all exported symbols that were not
+	defined in the kernel.
+
+--- 6.3 Symbols From Another External Module
+
+	Sometimes, an external module uses exported symbols from
+	another external module. kbuild needs to have full knowledge of
+	all symbols to avoid spitting out warnings about undefined
+	symbols. Three solutions exist for this situation.
+
+	NOTE: The method with a top-level kbuild file is recommended
+	but may be impractical in certain situations.
+
+	Use a top-level kbuild file
+		If you have two modules, foo.ko and bar.ko, where
+		foo.ko needs symbols from bar.ko, you can use a
+		common top-level kbuild file so both modules are
+		compiled in the same build. Consider the following
+		directory layout:
+
+		./foo/ <= contains foo.ko
+		./bar/ <= contains bar.ko
+
+		The top-level kbuild file would then look like:
+
+		#./Kbuild (or ./Makefile):
 			obj-y := foo/ bar/
 
-		Executing:
-			make -C $KDIR M=`pwd`
+		And executing
+
+			$ make -C $KDIR M=$PWD
 
-		will then do the expected and compile both modules with full
-		knowledge on symbols from both modules.
+		will then do the expected and compile both modules with
+		full knowledge of symbols from either module.
 
 	Use an extra Module.symvers file
-		When an external module is built, a Module.symvers file is
-		generated containing all exported symbols which are not
-		defined in the kernel.
-		To get access to symbols from module 'bar', one can copy the
-		Module.symvers file from the compilation of the 'bar' module
-		to the directory where the 'foo' module is built.
-		During the module build, kbuild will read the Module.symvers
-		file in the directory of the external module and when the
-		build is finished, a new Module.symvers file is created
-		containing the sum of all symbols defined and not part of the
-		kernel.
-
-	Use make variable KBUILD_EXTRA_SYMBOLS in the Makefile
-		If it is impractical to copy Module.symvers from another
-		module, you can assign a space separated list of files to
-		KBUILD_EXTRA_SYMBOLS in your Makfile. These files will be
-		loaded by modpost during the initialisation of its symbol
-		tables.
-
-=== 8. Tips & Tricks
-
---- 8.1 Testing for CONFIG_FOO_BAR
-
-	Modules often need to check for certain CONFIG_ options to decide if
-	a specific feature shall be included in the module. When kbuild is used
-	this is done by referencing the CONFIG_ variable directly.
+		When an external module is built, a Module.symvers file
+		is generated containing all exported symbols which are
+		not defined in the kernel. To get access to symbols
+		from bar.ko, copy the Module.symvers file from the
+		compilation of bar.ko to the directory where foo.ko is
+		built. During the module build, kbuild will read the
+		Module.symvers file in the directory of the external
+		module, and when the build is finished, a new
+		Module.symvers file is created containing the sum of
+		all symbols defined and not part of the kernel.
+
+	Use "make" variable KBUILD_EXTRA_SYMBOLS
+		If it is impractical to copy Module.symvers from
+		another module, you can assign a space separated list
+		of files to KBUILD_EXTRA_SYMBOLS in your build file.
+		These files will be loaded by modpost during the
+		initialization of its symbol tables.
+
+
+=== 7. Tips & Tricks
+
+--- 7.1 Testing for CONFIG_FOO_BAR
+
+	Modules often need to check for certain CONFIG_ options to
+	decide if a specific feature is included in the module. In
+	kbuild this is done by referencing the CONFIG_ variable
+	directly.
 
 		#fs/ext2/Makefile
 		obj-$(CONFIG_EXT2_FS) += ext2.o
@@ -544,9 +533,9 @@ Module.symvers contains a list of all exported symbols from a kernel build.
 		ext2-y := balloc.o bitmap.o dir.o
 		ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
 
-	External modules have traditionally used grep to check for specific
-	CONFIG_ settings directly in .config. This usage is broken.
-	As introduced before, external modules shall use kbuild when building
-	and therefore can use the same methods as in-kernel modules when
-	testing for CONFIG_ definitions.
+	External modules have traditionally used "grep" to check for
+	specific CONFIG_ settings directly in .config. This usage is
+	broken. As introduced before, external modules should use
+	kbuild for building and can therefore use the same methods as
+	in-tree modules when testing for CONFIG_ definitions.