linux-kernel Linux Hello World Device driver Building and running the module

Example

In order to compile the driver, it is necessary to have the Linux Kernel source tree.

Assuming the sources are at /lib/modules/<kernel-version>, the following Makefile will compile the file driver.c into the driver.ko Kernel Object

obj-m := driver.o
KDIR := /lib/modules/$(shell uname -r)/build/
PWD := $(shell pwd)

all:
    $(MAKE) -C $(KDIR) M=$(PWD) modules

Notice how this Makefile calls make in the build directory of the Kernel.

When the compilation step finishes successfully, the src directory of the driver will look somewhat like this:

driver.c  driver.ko  driver.mod.c  driver.mod.o  driver.o  Makefile  modules.order  Module.symvers

In order to "run" the module, it is necessary to insert into the running kernel:

$ insmod driver.ko
$ dmesg | tail -n 1
[133790.762185] Hello, World!

$ rmmod driver.ko
$ dmesg | tail -n 1
[133790.762185] Goodbye, cruel world...