Description

CS614: Linux Kernel Programming
In this assignment, you have to implement character device drivers (one driver for each part). Name of the char device must be cs614 device (i.e. its absolute path will be /dev /cs614_device). Your driver should also create sysfs directory named cs614 sysfs within /sys/kernel directory (i.e. /sys/kernel/cs614 sysfs) and a file named cs614 value within this cs614 sysfs directory (i.e. /sys/kernel/cs614_sysfs/cs614_value).
User programs will communicate with your driver in following manner:
• User program will write some operation number (Example: 0, 1, 2 etc., also referred to as “command” in this document) to the sysfs file /sys/kernel/cs614_sysfs/cs614_value • Your driver should do the specified operation mentioned below (under different parts of the assignment).
• User program will read the result through device file /dev/cs614_device using the read system call.
Example: If the user process writes ‘6’ to the sysfs file /sys/kernel/cs614_sysfs/cs614_value to know the number of files opened by the process, the module will store this command. When the user program does read() operation on device file /dev/cs614_device, it should fill up the buffer argument of the read system call with th e number of files opened by the calling process. Note: The process setting the command through the sysfs file will read the result.
Assumptions
• The command set by the sysfs write is applied only at the time of handling the read on the chardev.
• In the testing, we will only user open(), write(), close() functionalities on the sysfs file /sys/kernel/cs614_sysfs/cs614_value
• No operation except open(), read(), close() will be used during testing for the device file /dev/cs614_device
• sysfs file /sys/kernel/cs614_sysfs/cs614_value will be created with 0660 permissions
• For values beyond ‘7’, write for the sysfs file /sys/kernel/cs614_sysfs/cs614_value must return -EINVAL.
• Read operation on /dev/cs614_device will be done only after a write operation has happened on /sys/kernel/cs614_sysfs/cs614_value
Part1: Single Process Access [20 Marks]
In this question, you can assume that there will be only a single process that will use the character driver at any time. You have to implement support for following functionality in the character driver:
1. Pid (command = 0): Whenever value ‘0’ is written to /sys/kernel/cs614_sysfs/ cs614_value by a user process and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process, then, value of pid (process id) of the user process should be filled in the buf passed as argument to read() system call. Your read() system call should return the number of bytes read.
2. Static priority (command = 1): Whenever value ’1’ is written to /sys/kernel/cs61 4_sysfs/cs614_value by a user process and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process, then, value of static priority of the user process should be filled in the buf passed as argument to read() system call. Your read() system call should return the number of bytes read.
3. Command Name (command = 2): Whenever value ‘2’ is written to /sys/kernel/ cs614_sysfs/cs614_value by a user process and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process, then, name of the of the user process should be filled in the buf passed as argument to the read() system call. Your read() system call should return value ‘n’ (where ‘n’ is the number of characters in the command name excluding the null terminator) in this case.
4. Ppid (command = 3): Whenever value ‘3’ is written to /sys/kernel/cs614_sysfs/cs 614_value by a user process and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process, then, value of the real parent’s process id of the user process should be filled in the buf passed as argument to read() system call. Your read() system call should return the number of bytes read.
5. Number of voluntary context switches (command = 4): Whenever value ‘4’ is written to /sys/kernel/cs614_sysfs/cs614_value by a user process and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process, then, value of number of voluntary context switches) of the user process should be filled in the buf passed as argument to read() system call. Your read() system call should return value the number of bytes read.
Part2: Multiprocess Access [30 Marks]
In this part, you have to modify your kernel module (to implement an extended module) written in Part 1 to add the ability such that multiple processes can use your module simultaneously. For example: Consider that there are two processes P1 and P2 using the character driver. Inter-leavings like the following should give correct results:
P1 performs write on the sysfs file command = 0
P2 performs write on the sysfs file command = 3
P1 reads the chardev with a buf argument. Should return the PID of P1
P2 reads the chardev with a buf argument. Should return the PPID of P2
Note: Your implementation should not impose any limits on # of processes using the sysfs file and chardev.
Part3: Multithreaded Access [50 Marks]
In this part, you have to modify your kernel module written in part2 to support following functionalities. Note that, any thread in the process can use the following commands and any other thread in the process can read the result values using the chardev.
1. Number of Threads (command = 5): Whenever value ‘5’ is written to /sys/kerne l/cs614_sysfs/cs614_value by a user process and read(fd, buf, size) system call
is made on the device file /dev/cs614_device by the user process/threads, then, value of number of threads created by the user process using pthread create() + 1 (main/process thread itself) should be filled in the buf passed as argument to read() system call. Your read() system call should return the number of bytes read.
2. Number of Open Files (command = 6): Whenever value ‘6’ is written to /sys/k ernel/cs614_sysfs/cs614_value by a user process/thread and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process, then, value of number of files opened by the process/user thread should be filled in the buf passed as argument to read() system call. Your read() system call should return the number of bytes read.
3. Max Stack Usage PID (command = 7): Whenever value ‘7’ is written to /sys/k ernel/cs614_sysfs/cs614_value by a user process and read(fd, buf, size) system call is made on the device file /dev/cs614_device by that user process or any of its threads, then pid of the thread that consumes maximum amount of user stack among all threads including the main process should be filled in the buf passed as argument to read() system call. Your read() system call should return the number of bytes read.
Organization and Testing
A1_release| |-CS614_Assignment1_2023.pdf
|-examples
| |-chdev
| |-kernth
| |-traphook-sysfs
|-Part1
| |-driver.c
| |-Makefile
| |-user_progs
|-Part2
| |-driver.c
| |-Makefile
| |-user_progs
|-Part3
| |-driver.c
| |-Makefile
| |-user_progs
The examples directory contains modules used in the class. Please refer to the class Piazza page. Part1 to Part3 contain a template file for your implementation along with the user test programs. To test your implementation, follow the steps mentioned below,
• Please refer to the readme file in each user progs directory to know how to compile,run and use the test cases.
Submission
You have to submit a single zip file named your roll number.zip. For example if your roll no is 1211405, you should create the zip file named 1211405.zip containing only the following files in specified folder format. Note that, the zip file should expand into a directory named as your roll number.
RollNo|
|-Part1
| |-driver.c
| |-Makefile
|-Part2
| |-driver.c
| |-Makefile
|-Part3
| |-driver.c
| |-Makefile