Reading the book "Linux Device Driver [Third Edition]" I will publish examples on the chapters that I am reading, to put into practice the concepts explained.
file --> 1_alloc_major_number
In this example we can see how to dynamically get major and minor numbers for 4 character devices driver.
(Like scull example)
[Linux device driver]: https://www.xml.com/ldd/chapter/book/ch03.html
Open Terminal (press ctrl-t)
Get the repository:
gitclone https://github.com/Scott31393/linux_device_driver_examples.git
cd /1_alloc_major-number
make
Dynamically linking the module to the kernel:
sudo insmod main.ko
Visualize messages contained by the kernel buffer on the stardard output of the OS :
dmesg
Remove kernel module:
sudo rmmod main.ko
file --> 2_proc_write_read
In this example we create the new proc filesystem /proc/my_proc to write and read data to/from kernel space.
As a user if we want to look into what the kernel is up to, we would need our application to read the data in kernel space. But applications running in the user space can not access the data in the kernel space, in such situations the proc file system comes to rescue. The proc file system is an interface between the kernel and the userspace. Every entry in the proc file system provides some information from the kernel. The proc file system is also very useful when we want to debug a kernel module. While debugging we might want to know the values of various variables in the module or may be the data that module is handling. In such situations we can create a proc entry for our selves and dump what ever data we want to look into in the entry. The proc entry can also be used to pass data to the kernel by writing into the kernel, so there can be two kinds of proc entries An entry that only reads data from the kernel space. An entry that reads as well as writes data into and from kernel space.
From "Linux Device driver", "Linux world blogspot".
Open Terminal:
(press ctrl-t)
Get the files from the repository:
gitclone https://github.com/Scott31393/linux_device_driver_examples.git
cd /2_proc_write_read
make
Dynamically linking the module to the kernel:
sudo insmod main.ko
Visualize messages contained by the kernel buffer on the stardard output of the OS :
dmesg
We the Kern alert log: "Entry module".
Now we can play with our new /proc/my_proc. First we make the file readable, writable and executable by everyone using chmod 777:
sudo chmod 777 /proc/my_proc
Now we can write data string to the file, like "hello", using echo in Terminal:
echo "hello" > /proc/my_proc
And we can read that string using cat:
cat /proc/my_proc
After that "hello" strings appear in the Terminal console. To remove the loadable kernel module (LKM) press:
sudo rmmod main.ko
"Cleanup module" log appear on the dmesg log.
file --> 3_simply_chdvdriver
In this example (play_with_simply_chdvdriver) we create a new character device driver, in the next example we how to write into the device and we see also how to read from this device
Open Terminal:
(press ctrl-t)
Get the files from the repository:
gitclone https://github.com/Scott31393/linux_device_driver_examples.git
cd /3_simply_chdvdriver
make
Dynamically linking the module to the kernel:
sudo insmod main.ko
Visualize messages contained by the kernel buffer on the stardard output of the OS :
dmesg
We the Kern alert log: "DEVICE --> scottdevice,[ Major = 239 ], [ minor = 0 ]".
We make the character device file readable, writable and executable by everyone using chmod 777:
sudo chmod 777 /dev/scottdevice
In the next example (4) we see how to play with this character device.
To remove the loadable kernel module (LKM) press:
sudo rmmod main.ko
"Unload module" log appear on the dmesg log.
4) Create a User space App [play] That Can Write/Read From/To The Simple Character Device Driver [/dev/scottdevice]
file--> 4_play_with_simply_chdvdriver
In this example we create a simple user application that can write or read data to/from the device created in the previous example: "/dev/scottdevice".
Open Terminal:
(press ctrl-t)
Get the files from the repository:
gitclone https://github.com/Scott31393/linux_device_driver_examples.git
cd /4_play_with_simply_chdvdriver
make
Now just execute it using:
./play
Terminal ask you if you want write to the character device that we have created, just press:
w
or if you want read from the character device that we have created, just press press:
r
file --> 5_load_remove_module_shell
Instead of the use of the following Terminal's commands:
insmod
chmod
rmmod
mknod
etc..
We can simply create a shell script, that does everything with a single command. In particular you can try my shell scripts to load and remove module from the Linux kernel.
Open Terminal:
(press ctrl-t)
Get the files from the repository:
gitclone https://github.com/Scott31393/linux_device_driver_examples.git
cd /5_load_remove_module_shell
Then after we build the "module".ko, we can link/remove that to the kernel using these scripts after we have positioned that in the same folder of the module.
First we make these scipts readable, writable and executable by everyone using chmod 777.
sudo chmod 777 load_module
sudo chmod 777 remove_module
Now to Load the "scottdevice" belonging to the "main".ko module just execute the load script:
./load_module
To remove the module just press:
./remove_module
To check if these scripts do the right, we can visualize the messages in the kernel buffer in the standard output using:
dmesg
file --> 6_POSIX_semaphore_example
In this pic we can this the use of (Posix) semaphore to archived the mutual exclusion.
- 1 -> Semaphore is initialized to 1 (using sem_init() function).
- 2 -> Process/Thread P_1 see the value of semaphore (set to 1) then can access to resource.
- 3 -> During the execution of the Process/Thread P_1, semaphore's value is flipped to 0 (using sem_wait() function).
- 4 -> When the Process/Thread P_1 finished semaphore's value is flipped again to 1 (using sem_post() function). In this way next Process/Thread can access to resources.
we can see more in the specification in the following example:
Open Terminal:
(press ctrl-t)
Get the files from the repository:
gitclone https://github.com/Scott31393/linux_device_driver_examples.git
cd /6_POSIX_semaphore_example
make
Now just execute it using:
./main