Project Description

Standard UNIX and Linux systems come with a few special files like /dev/zero, which returns nothing but zeros when it is read, and /dev/random, which returns random bytes. In this project, you will write a device driver to create a new device, /dev/cards which returns a randomly selected playing card. This will simulate a real deck, with each card being drawn only once until all 52 are selected. It will then restart with a fresh deck.

How It Will Work

For this project we will need to create three parts: the device driver, the special file /dev/cards, and a test program to convince ourselves it works

The test program will be an implementation of the game of blackjack.

Driver Implementation

Our device driver will be a character device that will implement a read function (which is the implementation of the read() syscall) and returns appropriate playing cards (each, a 1 byte value from 0 to 51). As we discussed in class, the kernel does not have the full C Standard library available to it and so we need to use a different function to get random numbers. By including <linux/random.h> we can use the function get_random_bytes(), which you can turn into a helper function to get a single byte:

unsigned char get_random_byte(int max) {

         unsigned char c;

         get_random_bytes(&c, 1);

         return c%max;

}

Your device driver needs to keep the deck state as to avoid dealing a card twice before the deck is exhausted. Use an array to track this information. “Shuffle” the cards using random indices obtained from calls to get_random_byte().

Blackjack Implementation

Blackjack (also known as 21) is a multiplayer card game, with fairly simple rules. For this assignment, you will be implementing a simplified version where a user can play against the computer who acts as dealer.

Two cards are dealt to each player. The dealer shows one card face up, and the other is face down.  The player gets to see both of his or her cards and the total of them is added. Face cards (Kings, Queens, and Jacks) are worth 10 points, Aces are worth 1 or 11 points, and all other cards are worth their face value. The goal of the game is to get as close to 21 (“blackjack”) without going over (called “busting”).

The human player goes first, making his or her decisions based on the single dealer card showing. The player has two choices: Hit or Stand. Hit means to take another card. Stand means that the player wishes no more cards, and ends the turn, allowing for the dealer to play.

The dealer must hit if their card total is less than 17, and must stand if it is 17 or higher.

Whichever player gets closest to 21 without exceeding it, wins.

For this assignment you need to do the following:

·         Write a program that plays Blackjack

·         Have the program intelligently determine if an Ace should be interpreted as a 1 or an 11.

·         Gets cards to display by reading bytes from the /dev/cards file.

Installation and Example

1. On thoth.cs.pitt.edu, login and cd to your /u/SysLab/USERNAME directory.
2. tar xvfz ../shared/hello_dev.tar.gz
3. cd hello_dev
4. Open the Makefile with the editor of your choice. (E.g., pico Makefile)
5. We need to setup the path to compile against the proper version of the kernel. To do this, change the line:

KDIR  := /lib/modules/$(shell uname -r)/build

to

KDIR  := /u/SysLab/shared/linux-2.6.23.1

6. Build the kernel object. The ARCH=i386 is important because we are building a 32-bit kernel on a 64-bit machine.

7. Download and launch QEMU. For Windows users, you can just double click the qemu-win.bat that is supplied in the zipfile available on my website. Mac users should download and install Q.app and use the tty.qcow2 disk image provided in the main zipfile. Linux users are left to install qemu as appropriate and also use the tty.qcow2 disk image provided in the main zipfile.
8. When Linux boots under QEMU login using the root/root account (username/password).
9. We now need to download the kernel module you just built into the kernel using scp:

10. Load the driver using insmod:

11. We now need to make the device file in /dev. First, we need to find the MAJOR and MINOR numbers that identify the new device:

12. The output should be a number like 10:63. The 10 is the MAJOR and the 63 is the MINOR.
13. We use mknod to make a special file. The name will be hello and it is a character device. The 10 and the 63 correspond to the MAJOR and MINOR numbers we discovered above (if different, use the ones you saw.)

14. We can now read the data out of /dev/hello with a simple call to cat:

15. You should see “Hello, world!” which came from the driver. We can clean up by removing the device and unloading the module:

What to Do Next

The code for the example we went through comes from:

http://www.linuxdevcenter.com/pub/a/linux/2007/07/05/devhelloworld-a-simple-introduction-to-device-drivers-under-linux.html?page=2

Read that while going through the source to get an idea of what the Module is doing. Start with the third section entitled “Hello, World! Using /dev/hello_world” and read up until the author starts describing udev rules; we are not using udev under QEMU.

When you have an idea of what is going on, make a new directory under your /u/SysLab/USERNAME directory called card_driver:

Copy and rename the hello_dev.c from the example, and copy over the Makefile. Edit the Makefile to build your new file. Change all the references of “hello” to “card_driver”.

Building the Driver

To build any changes you have made, on thoth in your card_driver directory, simply:

If you want to force a rebuild of everything you may want to remove the object files first:

Copying the Files to QEMU

From QEMU, you will need to download the driver that you just built.  Use scp to download the driver to a home directory (/root/ if root):

Loading the Driver into the Kernel in QEMU

As root (either by logging in or via su):

Making the /dev/cards Device

Like in the example, we’ll need to determine the MAJOR and MINOR numbers for this particular driver.

and use those numbers to make the /dev/cards file:

Unloading the Driver from the Kernel in QEMU

As root (either by logging in or via su):

Then you can remove the /dev/cards file:

Implementing and Building the blackjack Program

Since thoth is a 64-bit machine and QEMU emulates a 32-bit machine, we should build with the -m32 flag:

Running blackjack

We cannot run our blackjack program on thoth.cs.pitt.edu because its kernel does not have the device driver loaded. However, we can test the program under QEMU once we have installed the new driver. We first need to download blackjack using scp as we did for the driver. However, we can just run it from our home directory without any installation necessary.

File Backups

One of the major contributions the university provides for the AFS filesystem is nightly backups. However, the /u/SysLab/ partition is not part of AFS space. Thus, any files you modify under your personal directory in /u/SysLab/ are not backed up. If there is a catastrophic disk failure, all of your work will be irrecoverably lost. As such, it is my recommendation that you:

Backup all the files you change under /u/SysLab to your ~/private/ directory frequently!

Loss of work not backed up is not grounds for an extension. You have been warned.

Hints and Notes

• printk() is the version of printf() you can use for debugging messages from the kernel.
• In the driver, you can use some standard C functions, but not all. They must be part of the kernel to work.
• In the blackjack program, you may use any of the C standard library functions.
• As root, typing poweroff in QEMU will shut it down cleanly.
• If the module crashes, it may become impossible to delete the file you created with mkdev in /dev. If that happens, just grab a new disk image and start over. It’s why we’re developing in a virtual machine as opposed to a real one.

Requirements and Submission

You need to submit:

• Your card_driver.c file and the Makefile
• Your well-commented blackjack program’s source

Make a tar.gz file named USERNAME-project4.tar.gz

Copy it to ~jrmst106/submit/449 by the deadline for credit.