Merge git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input

[linux-2.6] / Documentation / kbuild / modules.txt

diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt
index 1c0db652b3661f01d36d8dffa53d9947e1e5c55b..7e77f93634ea507569e3554434fe7978767d7fba 100644 (file)
--- a/Documentation/kbuild/modules.txt
+++ b/Documentation/kbuild/modules.txt
@@ -18,6 +18,7 @@ In this document you will find information about:
        === 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
@@ -344,6 +345,45 @@ directory and therefore needs to deal with this in their kbuild file.
        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.
 
+--- 5.3 External modules using several directories
+
+       If an external module does not follow the usual kernel style but
+       decide to spread files over several directories then kbuild can
+       support this too.
+
+       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
+       kbuild file:
+
+       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
+
+
+       kbuild knows how to handle .o files located in another directory -
+       although this is NOT reccommended practice. The syntax is to specify
+       the directory relative to the directory where the 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 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