Omit needless words and sentences; reorganize and tighten sentence structure;
swap sections 2.2 and 2.3 for a more logical flow; and cleanup some of the
inconsistency with the margin width.
Signed-off-by: matt mooney <mfm@xxxxxxxxxxxxx>
---
A couple of notes:
I chose to use the environment variable $PWD in the examples for both the commandline
and Makefile; however, I was wondering if I should have set PWD in the Makefile and
used $(PWD) instead. Also, the $@ variable was removed from the 'make' command within
the Makefile. I did not understand the purpose of this for building kernel modules and
it would break my test build.
Documentation/kbuild/modules.txt | 264 ++++++++++++++++++-------------------
1 files changed, 128 insertions(+), 136 deletions(-)
diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt
index 0767cf6..42d7329 100644
--- a/Documentation/kbuild/modules.txt
+++ b/Documentation/kbuild/modules.txt
@@ -10,8 +10,8 @@ In this document you will find information about:
=== 1 Introduction
=== 2 How to build external modules
--- 2.1 Building external modules
- --- 2.2 Available targets
- --- 2.3 Available options
+ --- 2.2 Options
+ --- 2.3 Targets
--- 2.4 Preparing the kernel tree for module build
--- 2.5 Building separate files for a module
=== 3. Example commands
@@ -34,128 +34,123 @@ In this document you will find information about:
=== 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 that is used by the Linux kernel. It includes
+functionality for building modules both inside and outside of the kernel
+source tree. The latter is usually referred to as an external or
+"out-of-tree" module. This is commonly used during development, and for a
+module that is not planned for inclusion within the kernel 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 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 section 4, "Creating a
+kbuild file for an external module".
=== 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 pre-built kernel available with
+full source. If you are using a distribution kernel, there will be a package
+containing the source for their kernel build.
--- 2.1 Building external modules
Use the following command to build an external module:
- make -C <path-to-kernel> M=`pwd`
+ make -C <path-to-kernel> M=$PWD
For the running kernel use:
- make -C /lib/modules/`uname -r`/build M=`pwd`
+ make -C /lib/modules/`uname -r`/build M=$PWD
For the above command to succeed, the kernel must have been
built with modules enabled.
To install the modules that were just built:
- make -C <path-to-kernel> M=`pwd` modules_install
+ make -C <path-to-kernel> M=$PWD modules_install
More complex examples will be shown later, the above should
be enough to get you started.
---- 2.2 Available targets
+--- 2.2 Options
- $KDIR refers to the path to the kernel source top-level directory
+ $KDIR is the path to the kernel source directory.
- 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.
+ make -C $KDIR
+ -C is used to specify where to find the kernel source.
+ 'make' will actually change to the specified directory
+ when executing and will change back when finished.
- 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
+ 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.
- 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.
+ make -C $KDIR SUBDIRS=$PWD
+ Same as M=. The SUBDIRS= syntax is kept for backwards
+ compatibility, but its usage is deprecated.
- make -C $KDIR M=`pwd` clean
- Remove all generated files for the module - the kernel
- source directory is not modified.
+--- 2.3 Targets
- make -C $KDIR M=`pwd` help
- help will list the available target when building external
- modules.
+ When building an external module, only a subset of the 'make'
+ targets are available.
---- 2.3 Available options:
+ make -C $KDIR M=$PWD
+ Build the module(s) located in the current directory; 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.
- $KDIR refers to the path to the kernel source top-level directory
+ make -C $KDIR M=$PWD modules
+ modules is the default target, it has the same functionality
+ as if no target was specified. See description above.
- 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.
-
- 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.
-
- make -C $KDIR SUBDIRS=`pwd`
- Same as M=. The SUBDIRS= syntax is kept for backwards
- compatibility.
+ make -C $KDIR M=$PWD modules_install
+ Install the external module(s). The default location is
+ /lib/modules/<kernel-version>/extra, but a prefix may be
+ added with INSTALL_MOD_PATH (discussed in section 6).
+
+ make -C $KDIR M=$PWD clean
+ Remove all generated files in the module directory only.
+
+ make -C $KDIR M=$PWD help
+ help will list the available targets when building external
+ modules.
--- 2.4 Preparing the kernel tree for module build
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.
+ 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
+ CONFIG_MODVERSIONS is set; therefore, a full kernel build
needs to be executed to make module versioning work.
--- 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
+
+ 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.
- 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` /
+
+ Example (The module foo.ko, consist of bar.o and baz.o):
+ make -C $KDIR M=$PWD bar.o
+ make -C $KDIR M=$PWD baz.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.
+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;
+however, the example will also work when the source and the output files
+are mixed in the same directory, provided the links exist.
# Kernel source
/lib/modules/<kernel-version>/source -> /usr/src/linux-<version>
@@ -164,39 +159,36 @@ when the source and the output files are mixed in the same directory.
/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:
+the following command to build the module:
+
+ cd /home/<username>/src/module
- cd /home/user/src/module
make -C /usr/src/`uname -r`/source \
O=/lib/modules/`uname-r`/build \
- M=`pwd`
+ M=$PWD
Then, to install the module use the following command:
make -C /usr/src/`uname -r`/source \
O=/lib/modules/`uname-r`/build \
- M=`pwd` \
+ M=$PWD \
modules_install
-If you look closely you will see that this is the same command as
-listed before - with the directories spelled out.
-
-The above are rather long commands, and the following chapter
-lists a few tricks to make it all easier.
+Since the commands above are rather long, the subsequent section lists a
+few tricks to make it easier.
=== 4. Creating a kbuild file for an external module
-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.
+External modules must use kbuild to stay compatible with changes in the
+build system and to pick up the right flags to gcc. As you will soon learn,
+this can be done by using a separate Kbuild file or by using a conditional
+branch within a Makefile. 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 Makefile 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
@@ -204,26 +196,24 @@ following files:
--- 4.1 Shared Makefile for module and kernel
- 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. The Makefile
+ provided may include additional functionality, such as test targets,
+ that will be filtered out from kbuild due to possible name clashes.
Example 1:
--> filename: Makefile
ifneq ($(KERNELRELEASE),)
- # kbuild part of makefile
+ # kbuild part of Makefile
obj-m := 8123.o
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
else
# Normal Makefile
+ KDIR := /lib/modules/`uname -r`/build
- KERNELDIR := /lib/modules/`uname -r`/build
all::
- $(MAKE) -C $(KERNELDIR) M=`pwd` $@
+ $(MAKE) -C $(KDIR) M=$$PWD
# Module specific targets
genbin:
@@ -231,15 +221,14 @@ following files:
endif
- In example 1, the check for KERNELRELEASE is used to separate
- the two parts of the Makefile. kbuild will only see the two
- assignments whereas make will see everything except the two
- kbuild assignments.
+ In example 1, the check for KERNELRELEASE is used to separate the
+ two parts of the Makefile. kbuild will only see the two assignments
+ whereas 'make' will see everything except the two kbuild assignments.
- In recent versions of the kernel, kbuild will look for a file named
- Kbuild and as second option look for a file named Makefile.
- Utilising the Kbuild file makes us split up the Makefile in example 1
- into two files as shown in example 2:
+ In newer versions of the kernel, kbuild will first look for a file
+ named Kbuild and only if that is not found, will it look for a
+ Makefile. Utilizing a Kbuild file allows us to split up the Makefile
+ from example 1 into two files:
Example 2:
--> filename: Kbuild
@@ -247,20 +236,21 @@ following files:
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
--> filename: Makefile
- KERNELDIR := /lib/modules/`uname -r`/build
+ KDIR := /lib/modules/`uname -r`/build
+
all::
- $(MAKE) -C $(KERNELDIR) M=`pwd` $@
+ $(MAKE) -C $(KDIR) M=$$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 +259,14 @@ following files:
--> filename: Makefile
ifneq ($(KERNELRELEASE),)
+ # kbuild part of Makefile
include Kbuild
else
# Normal Makefile
+ KDIR := /lib/modules/`uname -r`/build
- KERNELDIR := /lib/modules/`uname -r`/build
all::
- $(MAKE) -C $(KERNELDIR) M=`pwd` $@
+ $(MAKE) -C $(KDIR) M=$$PWD
# Module specific targets
genbin:
@@ -283,28 +274,29 @@ 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
- 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>. The 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 to create
+ the object file.
=== 5. Include files
--
1.7.2.1
--
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