I got the feeling that this question has been asked many times on lkml
now so I wrote this quick summary.
Anyone with additional comments or is it complete rubbish?
Sam
diff --git a/Documentation/kbuild/modules.txt b/Documentation/kbuild/modules.txt
index 1c0db65..7e77f93 100644
--- a/Documentation/kbuild/modules.txt
+++ b/Documentation/kbuild/modules.txt
@@ -18,6 +18,7 @@ In this document you will find informati
=== 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 wi
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
-
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