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Linux-2.6.12-rc2

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Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
This commit is contained in:
Linus Torvalds
2005-04-16 15:20:36 -07:00
commit 1da177e4c3
17291 changed files with 6718755 additions and 0 deletions
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00-INDEX
- this file: info on the kernel build process
kconfig-language.txt
- specification of Config Language, the language in Kconfig files
makefiles.txt
- developer information for linux kernel makefiles
modules.txt
- how to build modules and to install them

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Introduction
------------
The configuration database is collection of configuration options
organized in a tree structure:
+- Code maturity level options
| +- Prompt for development and/or incomplete code/drivers
+- General setup
| +- Networking support
| +- System V IPC
| +- BSD Process Accounting
| +- Sysctl support
+- Loadable module support
| +- Enable loadable module support
| +- Set version information on all module symbols
| +- Kernel module loader
+- ...
Every entry has its own dependencies. These dependencies are used
to determine the visibility of an entry. Any child entry is only
visible if its parent entry is also visible.
Menu entries
------------
Most entries define a config option, all other entries help to organize
them. A single configuration option is defined like this:
config MODVERSIONS
bool "Set version information on all module symbols"
depends MODULES
help
Usually, modules have to be recompiled whenever you switch to a new
kernel. ...
Every line starts with a key word and can be followed by multiple
arguments. "config" starts a new config entry. The following lines
define attributes for this config option. Attributes can be the type of
the config option, input prompt, dependencies, help text and default
values. A config option can be defined multiple times with the same
name, but every definition can have only a single input prompt and the
type must not conflict.
Menu attributes
---------------
A menu entry can have a number of attributes. Not all of them are
applicable everywhere (see syntax).
- type definition: "bool"/"tristate"/"string"/"hex"/"int"
Every config option must have a type. There are only two basic types:
tristate and string, the other types are based on these two. The type
definition optionally accepts an input prompt, so these two examples
are equivalent:
bool "Networking support"
and
bool
prompt "Networking support"
- input prompt: "prompt" <prompt> ["if" <expr>]
Every menu entry can have at most one prompt, which is used to display
to the user. Optionally dependencies only for this prompt can be added
with "if".
- default value: "default" <expr> ["if" <expr>]
A config option can have any number of default values. If multiple
default values are visible, only the first defined one is active.
Default values are not limited to the menu entry, where they are
defined, this means the default can be defined somewhere else or be
overridden by an earlier definition.
The default value is only assigned to the config symbol if no other
value was set by the user (via the input prompt above). If an input
prompt is visible the default value is presented to the user and can
be overridden by him.
Optionally dependencies only for this default value can be added with
"if".
- dependencies: "depends on"/"requires" <expr>
This defines a dependency for this menu entry. If multiple
dependencies are defined they are connected with '&&'. Dependencies
are applied to all other options within this menu entry (which also
accept an "if" expression), so these two examples are equivalent:
bool "foo" if BAR
default y if BAR
and
depends on BAR
bool "foo"
default y
- reverse dependencies: "select" <symbol> ["if" <expr>]
While normal dependencies reduce the upper limit of a symbol (see
below), reverse dependencies can be used to force a lower limit of
another symbol. The value of the current menu symbol is used as the
minimal value <symbol> can be set to. If <symbol> is selected multiple
times, the limit is set to the largest selection.
Reverse dependencies can only be used with boolean or tristate
symbols.
- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
This allows to limit the range of possible input values for int
and hex symbols. The user can only input a value which is larger than
or equal to the first symbol and smaller than or equal to the second
symbol.
- help text: "help" or "---help---"
This defines a help text. The end of the help text is determined by
the indentation level, this means it ends at the first line which has
a smaller indentation than the first line of the help text.
"---help---" and "help" do not differ in behaviour, "---help---" is
used to help visually seperate configuration logic from help within
the file as an aid to developers.
Menu dependencies
-----------------
Dependencies define the visibility of a menu entry and can also reduce
the input range of tristate symbols. The tristate logic used in the
expressions uses one more state than normal boolean logic to express the
module state. Dependency expressions have the following syntax:
<expr> ::= <symbol> (1)
<symbol> '=' <symbol> (2)
<symbol> '!=' <symbol> (3)
'(' <expr> ')' (4)
'!' <expr> (5)
<expr> '&&' <expr> (6)
<expr> '||' <expr> (7)
Expressions are listed in decreasing order of precedence.
(1) Convert the symbol into an expression. Boolean and tristate symbols
are simply converted into the respective expression values. All
other symbol types result in 'n'.
(2) If the values of both symbols are equal, it returns 'y',
otherwise 'n'.
(3) If the values of both symbols are equal, it returns 'n',
otherwise 'y'.
(4) Returns the value of the expression. Used to override precedence.
(5) Returns the result of (2-/expr/).
(6) Returns the result of min(/expr/, /expr/).
(7) Returns the result of max(/expr/, /expr/).
An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
respectively for calculations). A menu entry becomes visible when it's
expression evaluates to 'm' or 'y'.
There are two types of symbols: constant and nonconstant symbols.
Nonconstant symbols are the most common ones and are defined with the
'config' statement. Nonconstant symbols consist entirely of alphanumeric
characters or underscores.
Constant symbols are only part of expressions. Constant symbols are
always surrounded by single or double quotes. Within the quote any
other character is allowed and the quotes can be escaped using '\'.
Menu structure
--------------
The position of a menu entry in the tree is determined in two ways. First
it can be specified explicitly:
menu "Network device support"
depends NET
config NETDEVICES
...
endmenu
All entries within the "menu" ... "endmenu" block become a submenu of
"Network device support". All subentries inherit the dependencies from
the menu entry, e.g. this means the dependency "NET" is added to the
dependency list of the config option NETDEVICES.
The other way to generate the menu structure is done by analyzing the
dependencies. If a menu entry somehow depends on the previous entry, it
can be made a submenu of it. First, the previous (parent) symbol must
be part of the dependency list and then one of these two conditions
must be true:
- the child entry must become invisible, if the parent is set to 'n'
- the child entry must only be visible, if the parent is visible
config MODULES
bool "Enable loadable module support"
config MODVERSIONS
bool "Set version information on all module symbols"
depends MODULES
comment "module support disabled"
depends !MODULES
MODVERSIONS directly depends on MODULES, this means it's only visible if
MODULES is different from 'n'. The comment on the other hand is always
visible when MODULES is visible (the (empty) dependency of MODULES is
also part of the comment dependencies).
Kconfig syntax
--------------
The configuration file describes a series of menu entries, where every
line starts with a keyword (except help texts). The following keywords
end a menu entry:
- config
- menuconfig
- choice/endchoice
- comment
- menu/endmenu
- if/endif
- source
The first five also start the definition of a menu entry.
config:
"config" <symbol>
<config options>
This defines a config symbol <symbol> and accepts any of above
attributes as options.
menuconfig:
"menuconfig" <symbol>
<config options>
This is similiar to the simple config entry above, but it also gives a
hint to front ends, that all suboptions should be displayed as a
separate list of options.
choices:
"choice"
<choice options>
<choice block>
"endchoice"
This defines a choice group and accepts any of above attributes as
options. A choice can only be of type bool or tristate, while a boolean
choice only allows a single config entry to be selected, a tristate
choice also allows any number of config entries to be set to 'm'. This
can be used if multiple drivers for a single hardware exists and only a
single driver can be compiled/loaded into the kernel, but all drivers
can be compiled as modules.
A choice accepts another option "optional", which allows to set the
choice to 'n' and no entry needs to be selected.
comment:
"comment" <prompt>
<comment options>
This defines a comment which is displayed to the user during the
configuration process and is also echoed to the output files. The only
possible options are dependencies.
menu:
"menu" <prompt>
<menu options>
<menu block>
"endmenu"
This defines a menu block, see "Menu structure" above for more
information. The only possible options are dependencies.
if:
"if" <expr>
<if block>
"endif"
This defines an if block. The dependency expression <expr> is appended
to all enclosed menu entries.
source:
"source" <prompt>
This reads the specified configuration file. This file is always parsed.

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In this document you will find information about:
- how to build external modules
- how to make your module use kbuild infrastructure
- how kbuild will install a kernel
- how to install modules in a non-standard location
=== 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
=== 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
=== 6. Module installation
--- 6.1 INSTALL_MOD_PATH
--- 6.2 INSTALL_MOD_DIR
=== 7. Module versioning
=== 8. Tips & Tricks
--- 8.1 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 modules and is used
both during development and for modules that are not planned to be
included in the kernel tree.
What is covered within this file is mainly information to authors
of modules. The author of an external modules should supply
a makefile that hides most of the complexity so one only has to type
'make' to buld the module. A complete example will be present in
chapter ¤. 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.
--- 2.1 Building external modules
Use the following command to build an external module:
make -C <path-to-kernel> M=`pwd`
For the running kernel use:
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
More complex examples later, the above should get you going.
--- 2.2 Available targets
$KDIR refers to path to kernel source top-level 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 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 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 chater.
make -C $KDIR M=$PWD clean
Remove all generated files for the module - the kernel
source directory is not moddified.
make -C $KDIR M=`pwd` help
help will list the available target when building external
modules.
--- 2.3 Available options:
$KDIR refer to path to kernel src
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.
--- 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.
'module_prepare' solely exists as a simple way to prepare
a kernel for building external modules.
Note: modules_prepare will not build Module.symvers even if
CONFIG_MODULEVERSIONING is set.
Therefore a full kernel build needs to be executed to make
module versioning work.
=== 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.
# 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:
cd /home/user/src/module
make -C /usr/src/`uname -r`/source \
O=/lib/modules/`uname-r`/build \
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
If one looks closely you will see that this is the same commands 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.
=== 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.
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.
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
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.
Example 1:
--> filename: Makefile
ifneq ($(KERNELRELEASE),)
# kbuild part of makefile
obj-m := 8123.o
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
else
# Normal Makefile
KERNELDIR := /lib/modules/`uname -r`/build
all::
$(MAKE) -C $KERNELDIR M=`pwd` $@
# Module specific targets
genbin:
echo "X" > 8123_bini.o_shipped
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 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:
Example 2:
--> filename: Kbuild
obj-m := 8123.o
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` $@
# Module specific targets
genbin:
echo "X" > 8123_bin_shipped
In example 2 we are down to two fairly simple files and for simple
files as used in this example the split is questionable. But some
external modules use Makefiles of several hundred lines and here it
really pays off to separate the kbuild part from the rest.
Example 3 shows a backward compatible version.
Example 3:
--> filename: Kbuild
obj-m := 8123.o
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
--> filename: Makefile
ifneq ($(KERNELRELEASE),)
include Kbuild
else
# Normal Makefile
KERNELDIR := /lib/modules/`uname -r`/build
all::
$(MAKE) -C $KERNELDIR M=`pwd` $@
# Module specific targets
genbin:
echo "X" > 8123_bin_shipped
endif
The trick here is to include the Kbuild file from Makefile so
if an older version of kbuild picks up the Makefile the Kbuild
file will be included.
--- 4.2 Binary blobs included in a module
Some external modules needs to include a .o as a blob. kbuild
has support for this, but requires the blob file to be named
<filename>_shipped. In our example the blob is named
8123_bin.o_shipped and when the kbuild rules kick in the file
8123_bin.o is created as a simple copy off the 8213_bin.o_shipped file
with the _shipped part stripped of the filename.
This allows the 8123_bin.o filename to be used in the assignment to
the module.
Example 4:
obj-m := 8123.o
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
In example 4 there is no distinction between the ordinary .c/.h files
and the binary file. But kbuild will pick up different rules to create
the .o file.
=== 5. Include files
Include files are a necessity when a .c file uses something from another .c
files (not strictly in the sense of .c but if good programming practice is
used). Any module that consist of more than one .c file will have a .h file
for one of the .c files.
- If the .h file only describes a module internal interface then the .h file
shall be placed in the same directory as the .c files.
- If the .h files describe an interface used by other parts of the kernel
located in different directories, the .h files shall be located in
include/linux/ or other include/ directories as appropriate.
One exception for this rule is larger subsystems that have their own directory
under include/ such as include/scsi. Another exception is arch-specific
.h files which are located under include/asm-$(ARCH)/*.
External modules have a tendency to locate include files in a separate include/
directory and therefore needs to deal with this in their kbuild file.
--- 5.1 How to include files from the kernel include dir
When a module needs to include a file from include/linux/ then one
just uses:
#include <linux/modules.h>
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.
#include "8123_if.h"
will do the job.
--- 5.2 External modules using an include/ dir
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_$F.o (take effect only for a single file).
In our example if we move 8123_if.h to a subdirectory named include/
the resulting Kbuild file would look like:
--> filename: Kbuild
obj-m := 8123.o
EXTRA_CFLAGS := -Iinclude
8123-y := 8123_if.o 8123_pci.o 8123_bin.o
Note that in the assingment there is no space between -I and the path.
This is a kbuild limitation and no space must be present.
=== 6. Module installation
Modules which are included in the kernel is installed in the directory:
/lib/modules/$(KERNELRELEASE)/kernel
External modules are installed in the directory:
/lib/modules/$(KERNELRELEASE)/extra
--- 6.1 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:
$ make INSTALL_MOD_PATH=/frodo modules_install
=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel
INSTALL_MOD_PATH may be set as an ordinary shell variable or as in the
example above be specified on the commandline when calling make.
INSTALL_MOD_PATH has effect both when installing modules included in
the kernel as well as when installing external modules.
--- 6.2 INSTALL_MOD_DIR
When installing external modules they are default installed in a
directory under /lib/modules/$(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 than 'extra'.
$ make INSTALL_MOD_DIR=gandalf -C KERNELDIR \
M=`pwd` modules_install
=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf
=== 7. Module versioning
Module versioning are enabled by the CONFIG_MODVERSIONS tag.
Module versioning is used as a simple ABI consistency check. The Module
versioning creates a CRC value of the full prototype for an exported symbol and
when a module is loaded/used then the CRC values contained in the kernel are
compared with similar values in the module. If they are not equal then the
kernel refuses to load the module.
During a kernel build a file named Module.symvers will be generated. This
file includes the symbol version of all symbols within the kernel. If the
Module.symvers file is saved from the last full kernel compile one does not
have to do a full kernel compile to build a module version's compatible module.
=== 8. Tips & Tricks
--- 8.1 Testing for CONFIG_FOO_BAR
Modules often needs to check for certain CONFIG_ options to decide if
a specific feature shall be included in the module. When kbuild is used
this is done by referencing the CONFIG_ variable directly.
#fs/ext2/Makefile
obj-$(CONFIG_EXT2_FS) += ext2.o
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.