A simple program on linux device driver

Question

include

#include<linux/module.h>
#include<linux/init.h>

int my_init(void){
        printk("<1> Angus : Module Insertion is successful!");
        return 0;
}

void my_cleanup(void){
        printk("<1> Angus : Module unloading successful!");
}

module_init(my_init);
module_cleanup(my_cleanup);

Makefile :

obj-m:=simple.o
aoll:
        make -C /usr/src/linux-headers-3.2.0-25-generic-pae/ M=$(PWD) modules
clean:

        make -C /usr/src/linux-headers-3.2.0-25-generic-pae/ M=$(PWD) clean

make -C => will change to the directory before doing a make, In this path /usr/src/linux-headers-3.2.0-25-generic-pae/ I have Makefile , why is the M=$(PWD) needed ? what does it do, where I can check for $PWD ? The Makefile inside the /usr/src/linux-headers-3.2.0-25-generic-pae/ has the target all:modules and target modules and has the target clean. What is obj-m ?

Claudio Claudio · Accepted Answer · 2013-10-25T10:20:25

You'd better to read the paragraph at page 24 of the book Linux Device Drivers, 3rd edition (freely available at http://oreilly.com/openbook/linuxdrive3/book/index.html).

The -C option makes it change the directory to the one provided. There, it finds the kernel's top-level Makefile. Then, the M= option causes that Makefile to move back to your module source directory before trying to build the modules target ($PWD is a variable containing the path of your current directory).

obj-m is a variable containing the list of kernel modules to be build (see https://www.kernel.org/doc/Documentation/kbuild/makefiles.txt) .

A simple program on linux device driver

include

3 Answers