While I was still studying in unviersity, I found myself a passion for taking operating system courses. Before, the operating was just a mystical black box. I was simply intrigued by solving the unique challenges of programming an operating system and the opportunity to explore one of humanity's most complex inventions.
Since graduating, I haven't worked on many projects that require low-level interaction with the operating systems, and my knowledge in this area has faded. Additionally, I ran across problems in my work that required a deep understanding of OS concepts to solve. So I decided to take this course to refresh my memory and hopefully get back a hang of how things work at a low level.
If you want to complete this assignment on Debian, the dependencies required to run the QEMU simulators need to be installed:
sudo apt-get install git build-essential gdb-multiarch qemu-system-misc gcc-riscv64-linux-gnu binutils-riscv64-linux-gnu
| Labs | Accomplishments |
|---|---|
| Lab 1 - UTIL | - Created a user program named sleep that invokes system call and pause the shell for a certain period - Created a user program named pingpong that exchanges a byte using a pipe - Created a user program named primes that implements a concurrent pipe-based prime sieve, according to this paper - Created a user program named find that recursively searches for files with specific names - Created a user program named xargs that converts outputs from stdout to program arguments |
| Lab 2 - SYSCALL | - Created a syscall trace that prints the invocations of syscalls and return values - Created a syscall sysinfo that prints number of active processes and bytes of free memory |
| Lab 3 - PGTBL | - Created a demo program ugetpid for quick data sharing between user and kernel. Kernel installs a mapping from USYSCALL to the kernel page that has the data. User can access this memory directly, avoiding copyout from a kernel page to a user page.- Created a kernel helper function vmprint to print all PTEs in a page table - Created a syscall pgaccess to print all pages that are accessed since the last syscall |
| Lab 4 - TRAPS | - Create a kernel helper function backtrace to print all return addresses in the call stacks when kernel panics. - Create syscalls sigalarm and sigreturn that registers a handler to be called when ticks have passed by, and the handler calls sigreturn to resume the instruction before the interruption. This example show how callback for an async call can be designed in kernel. sigalarm must save the trapframe before interruption and sets epc to alarm handler address to make usertrap return to alarm handler. sigreturn restores the trapframe before interruption. |
| Lab 5 - COW | - Modified fork syscall to use copy-on-write mechanism. fork makes parent and child processes share pages which are made write-protected. When either user process tries to write data to the pages, the hardware triggers an exception which calls the trap handler, which allocates a new page for the faulting process.- Modified copyout kernel function to allocate a new page if the dest user page is copy-on-write protected.- Tracked reference count to COW pages, which are added to the freelist when no processs are using it. |
| Lab 6 - THREAD | - Created a program that implements threads with software-level context switching enabled. The thread yields voluntarily to another thread. - Designed a program barrier with mutex and cv that blocks a thread from executing until enough threads have arrived.- Added mutex per hashtable cell to make a hashtable concurrency-safe |
| LAB 7 - NET | - Added e1000_transmit and e1000_recv that interacts with a UDP server on host computer |
| Lab 8 - LOCK | - Reduce lock contention by updating the kernel memory allocator to use per-core kernel memory - Reduce lock contention by updating the bcache layer to use hashtable and per-bucket lock |
| Lab 9 - FS | - Supported doubly linked list inode - Added symlink syscall to create soft link for a file |
| Lab 10 - MMAP | - Supported mmap and munmap that maps a file to a user-controlled virtual memory address. Supported permission control for that virtual memory segment. Also supported writing modifications back to the file with MAP_SHARED. |