upload: organized projects of PD511

Project2-Process-Scheduler/pstat.h

@@ -0,0 +1,14 @@
+#ifndef _PSTAT_H_
+#define _PSTAT_H_
+
+#include "param.h"
+
+struct pstat {
+    int inuse[NPROC]; // whether this slot of the process process table is in use (1 or 0)
+    int pid[NPROC];   // the PID of each process
+    int hticks[NPROC]; // the number of ticks each process has accumulated at priority 2
+    int lticks[NPROC]; // the number of ticks each process has accumulated at priority 1
+};
+
+
+#endif // _PSTAT_H_

Project4-Filesystem-Optimization/fspatch.patch

@@ -0,0 +1,69 @@
+--- ./kernel/fs.c
++++ ./kernel/fs.c
+@@ -53,15 +53,22 @@
+ static uint
+ balloc(uint dev)
+ {
+-  int b, bi, m;
++  int b, bi, m, bound;
+   struct buf *bp;
+   struct superblock sb;
+-
++
+   bp = 0;
+   readsb(dev, &sb);
+   for(b = 0; b < sb.size; b += BPB){
+     bp = bread(dev, BBLOCK(b, sb.ninodes));
+-    for(bi = 0; bi < BPB; bi++){
++
++    if(b+BPB > sb.size){ //last bitmap block
++      bound = sb.size % BPB;
++    } else {
++      bound = BPB;
++    }
++
++    for(bi = 0; bi < bound; bi++){
+       m = 1 << (bi % 8);
+       if((bp->data[bi/8] & m) == 0){  // Is block free?
+         bp->data[bi/8] |= m;  // Mark block in use on disk.
+@@ -72,7 +79,9 @@
+     }
+     brelse(bp);
+   }
+-  panic("balloc: out of blocks");
++
++  //panic("balloc: out of blocks");
++  return 0;
+ }
+
+ // Free a disk block.
+@@ -409,7 +418,12 @@
+     n = ip->size - off;
+
+   for(tot=0; tot<n; tot+=m, off+=m, dst+=m){
+-    bp = bread(ip->dev, bmap(ip, off/BSIZE));
++    uint sector_number = bmap(ip, off/BSIZE);
++    if(sector_number == 0){ //failed to find block
++      panic("readi: trying to read a block that was never allocated");
++    }
++
++    bp = bread(ip->dev, sector_number);
+     m = min(n - tot, BSIZE - off%BSIZE);
+     memmove(dst, bp->data + off%BSIZE, m);
+     brelse(bp);
+@@ -436,7 +450,13 @@
+     n = MAXFILE*BSIZE - off;
+
+   for(tot=0; tot<n; tot+=m, off+=m, src+=m){
+-    bp = bread(ip->dev, bmap(ip, off/BSIZE));
++    uint sector_number = bmap(ip, off/BSIZE);
++    if(sector_number == 0){ //failed to find block
++      n = tot; //return number of bytes written so far
++      break;
++    }
++
++    bp = bread(ip->dev, sector_number);
+     m = min(n - tot, BSIZE - off%BSIZE);
+     memmove(bp->data + off%BSIZE, src, m);
+     bwrite(bp);
+

README.md

@@ -0,0 +1,72 @@
+# Operating Systems and System Programming: A Deep Dive into xv6
+
+## Overview
+
+This repository showcases a series of projects developed as part of an Operating Systems course at KAIST, using the xv6 teaching operating system. Each project focuses on enhancing or extending various components of xv6, providing hands-on experience with operating system concepts.
+
+## Projects
+
+### 00. [Introduction to xv6](./Project0-Adding-System-Calls)
+![Introduction to xv6](assets/images/system-call.png)
+
+*Image sourced from [Guru99](https://www.guru99.com/system-call-operating-system.html)*
+
+Refer to the [project instructions](Project0-Adding-System-Calls/Project0.pdf) to view the list of tasks to be completed.
+<details>
+  <summary>Project Description</summary>
+  This initial project introduces xv6, a teaching operating system used in the MIT Operating Systems course. The project involved gaining familiarity with the xv6 architecture and adding basic system calls to extend its functionality.
+</details>
+
+### 01. [Kernel Threading](./Project1-Kernel-Threading)
+![Kernel Threading](assets/images/OS-Kernel-Threading.png)
+
+*Image sourced from [Scaler](https://www.scaler.com/topics/user-level-threads-and-kernel-level-threads/)*
+
+Refer to the [project instructions](Project1-Kernel-Threading/Project1.pdf) to view the list of tasks to be completed.
+<details>
+  <summary>Project Description</summary>
+  Implemented kernel threading in xv6 by creating kernel threads using `clone()` and `join()` system calls. Additionally, a user-level thread library was developed with functions such as `thread_create()`, `lock_acquire()`, and `lock_release()`.
+</details>
+
+### 02. [Process Scheduler](./Project2-Process-Scheduler)
+![Process Scheduler](assets/images/OS-Process-Scheduler.png)
+
+*Image sourced from [Scaler](https://www.scaler.com/topics/operating-system/cpu-scheduling/)*
+
+Refer to the [project instructions](Project2-Process-Scheduler/Project2.pdf) to view the list of tasks to be completed.
+<details>
+  <summary>Project Description</summary>
+  Developed a priority-based process scheduler for xv6. This scheduler assigns different priority levels to processes, ensuring higher-priority processes receive more CPU time compared to those with lower priority.
+</details>
+
+### 03. [Null Pointer Dereferences and Shared Memory](./Project3-NullPtr-Dereferences-and-Shared-Memory)
+![Nullptr Dereferences and Shared Memory](assets/images/OS-Nullptr-Dereferences-Shared-Memory.png)
+
+*Image sourced from [MITRE CWE](https://cwe.mitre.org/data/definitions/476.html)*
+
+Refer to the [project instructions](Project3-NullPtr-Dereferences-and-Shared-Memory/Project3.pdf) to view the list of tasks to be completed.
+<details>
+  <summary>Project Description</summary>
+  Enhanced xv6 by adding mechanisms to handle null pointer dereferences, ensuring that any process attempting to dereference a null pointer is terminated immediately. Also implemented shared memory functionality, complete with system calls for managing and tracking shared memory usage across processes.
+</details>
+
+### 04. [Filesystem Optimization](./Project4-Filesystem-Optimization)
+![Filesystem Optimization](assets/images/OS-Filesystem-Optimization.png)
+
+*Image sourced from [UNIX v6/xv6 Book](https://pekopeko11.sakura.ne.jp/unix_v6/xv6-book/en/File_system.html)*
+
+Refer to the [project instructions](Project4-Filesystem-Optimization/Project4.pdf) to view the list of tasks to be completed.
+<details>
+  <summary>Project Description</summary>
+  Optimized the xv6 filesystem to enhance performance when handling small files. This project involved modifying the filesystem's data structures and algorithms to reduce overhead and improve efficiency for operations involving small files.
+</details>
+
+## Resources
+
+- [Book of xv6 (PDF)](assets/xv6book.pdf)
+- [Operating System Lecture Slides - KAIST (Merged PDF)](assets/EE415_Operating_Systems_Slides_merged.pdf)
+- [Course Syllabus](./assets/Syllabus.pdf)
+
+### Note
+
+This project was organized with the aim of demonstrating my past experience with operating systems and their low-level operations, both as a reference for myself and to showcase my skills to potential future employers. Although I uploaded this after graduation, ***the work reflects projects I completed during my master's studies.*** I believe it's important to maintain a well-documented digital footprint, especially since a recruiter once inquired about my experience with low-level concepts.