update

README.md

@@ -5,3 +5,5 @@
 1.  [kmod](kmod.md)
 1.  Examples
     1. [Host](host/)
+
+TODO: use Buildroot as in this answer http://stackoverflow.com/a/38813400/895245 to install and test modules on QEMU.

TODO.md

@@ -0,0 +1,7 @@
+# TODO
+
+- build kernel module against a given kernel tree
+- build out of tree kernel module into the kernel image
+    - http://stackoverflow.com/questions/7353851/insert-linux-kernel-module-statically
+    - http://stackoverflow.com/questions/8421970/compiling-a-driver-as-a-part-of-a-kernel-not-as-a-module
+- .ko file format vs .o http://stackoverflow.com/questions/10476990/difference-between-o-and-ko-file

build.md

@@ -2,7 +2,23 @@
 
 The module building system.
 
-Kernel modules are built using a makefile located at:
+Explained at: <https://www.kernel.org/doc/Documentation/kbuild/modules.txt>
+
+Full method: get the kernel, build it to a directory `$KDIR`, and then run:
+
+	make -C "$KDIR" M="$(PWD)" modules
+
+Quick method: no need for a full build, just:
+
+    make modules_prepare
+
+but you lose some functionality. TODO: module insert on host then fails with:
+
+    insmod: ERROR: could not insert module hello.ko: Invalid module format
+
+even though kernel tree was checked out to match the host.
+
+Using your distro's kernel version:
 
 	/lib/modules/$(uname -r)/build
 

host/Makefile

@@ -1,33 +1,16 @@
-OUT_EXT := .ko
-OBJ_EXT := .o
-RUN     := hello
-RUN_EXT := $(RUN)$(OUT_EXT)
-
 obj-m += hello.o
 ccflags-y := -Wno-declaration-after-statement -std=gnu99
 
-.PHONY: clean ins log rm run my-ins
+.PHONY: all clean
 
-all: $(RUN_EXT) ins_rm_mod.out
+all: hello.ko ins_rm_mod.out
 
 hello.ko: hello.c
-	make -C /lib/modules/$(shell uname -r)/build M="$(PWD)" modules
+	make -C '/lib/modules/$(shell uname -r)/build' M='$(PWD)' modules
 
 clean:
-	make -C /lib/modules/$(shell uname -r)/build M="$(PWD)" clean
-	rm -f *.out
+	make -C '/lib/modules/$(shell uname -r)/build' M='$(PWD)' clean
+	rm -f ins_rm_mod.out
 
-ins: all
-	sudo insmod '$(RUN_EXT)'
-
-log:
-	dmesg
-
-rm:
-	if lsmod | grep -Eq '^$(RUN) '; then sudo rmmod '$(RUN_EXT)'; fi
-
-ins_rm_mod.out: ins_rm_mod.c
-	gcc -Wall -std=gnu99 -o '$@' '$<'
-
-ins_rm_run: ins_rm_mod.out $(RUN_EXT)
-	sudo ./ins_rm_mod.out
+ins_rm_mod.out: ins_rm_mod.c hello.c
+	gcc -Wall -std=gnu99 -o ins_rm_mod.out ins_rm_mod.c

host/README.md

@@ -9,7 +9,7 @@ Simple things that can be demonstrated by inserting a module into the currently
 
 This method easier to setup, but it is not recommended for development, as:
 
-- it may break your system.
+- it may break your system
 - you can't control which kernel version to use
 
 Use VMs instead.
@@ -20,15 +20,21 @@ We only use it for super simple examples.
 
 Build, insert and remove a hello world module:
 
-    make ins
-    make rm
-    make log
+    make
 
-The last lines of the log should contain:
+    sudo insmod hello.ko
 
-    init_module
-    cleanup_module
+    # Our module should be there.
+    sudo lsmod | grep hello
 
-Insert and remove a module from a C program:
+    # Last message should be: init_module
+    dmest -T
 
-    make ins_rm_run
+    sudo rmmod hello
+
+    # Last message should be: cleanup_module
+    dmest -T
+
+Insert and remove the `hello.ko` module from a C program with system calls:
+
+	sudo ./ins_rm_mod.out