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Lab 7: Build a Custom Driver

In this lab you'll build a custom device driver from source. 

Introduction

Git is a source control management (SCM) tool that is popular with open source projects. Git gives you a way to download source code for a program, keep up with updates and contribute your own features and fixes to the authors. Once you have a driver's source code you must compile it to yield a loadable kernel module. 
Using Git to get the Source Code
In this lab you'll use a kernel driver that is an example in the excellent book Linux Device Drivers. The book was published in 2005 so some of the example code needs a bit of fixups. I maintain a Git repository that fixes some compilation problems. You can checkout the code with the following command: 

$ git clone https://github.com/mike-matera/ldd3.git 

That will create an "ldd3" directory in the current directory. There are several drivers in that directory, the "scull" driver compiles and can be inserted into your kernel. 

$ cd ldd3/scull 

Once you're in the directory you invoke the "make" command to build the source:

$ make 

This creates scull.ko. The *.ko extension is used for kernel modules. You can insert the kernel module with the insmod command: 

$ sudo insmod scull.ko 

Check to verify that your module is inserted: 

$ lsmod 
$ lsmod | grep scull 

Most drivers print a banner to the kernel log when they are inserted. Look at the kernel message buffer to see what the scull driver reported:

$ dmesg | tail 
$ tail /var/log/kern.log 

Verify that you see the banner from the scull driver. Now remove the module from the kernel and verify that it's gone:

$ sudo rmmod scull
$ lsmod |  grep scull 

Turn In

When you're done save the bottom lines of your kernel log to a file called lab11.txt like this:

$ tail /var/log/kern.log > lab7.txt 

Submit your lab11.txt on Canvas. 

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