FAT12

Preface

1. Why FAT12?
2. Who This Book Is For
3. What You Will Build
4. What You Will Learn
5. A Note on Style
6. How to Read This Book
7. About the Author
8. Feedback

Prerequisites

1. Operating System
2. C Compiler and Dependencies
3. Editor and Hex Editor
4. Getting the Code (Optional)

Part I: Reading

Chapter 1: Hello, Disk!

1. What Is FAT12?
2. Creating a Virtual Disk
3. Sectors and LBA
4. A Tale of Four Regions
5. Project Layout
6. A Portable Foundation: The BlockDevice
7. Reading Sector 0
8. Tracing the Translation
9. Production Notes
10. What Is Next

Chapter 2: The Blueprint (BPB)

1. Boot Sector Structure
2. Mapping Bytes to Structs
3. The FAT12 Library
4. The Info Command
5. Debugging
6. Production Notes
7. What Is Next

Chapter 3: The Root Directory

1. What Is the Root Directory?
2. Loading the Root Directory
3. Formatting an 8.3 Name
4. Decoding Timestamps
5. The ls Command
6. Updating the Header
7. Building
8. Verification: Create Real Files
9. Debugging with a Hexdump
10. Production Notes
11. What Is Next

Chapter 4: Reading Files

1. What the FAT Actually Is
2. Where the FAT Lives
3. Data Region Geometry
4. Reading a FAT Entry
5. Loading the FAT
6. Reading a Cluster Chain
7. File API
8. The cat Command
9. Updating the Header
10. Building
11. Verification: Create a Real File
12. Hexdump Verification
13. Multi-Cluster File
14. Production Notes
15. FAT Family: FAT16 and FAT32
16. What Is Next

Part II: Writing

Chapter 5: Full Path Walking

1. Subdirectories in FAT12
2. Reading a Subdirectory from a Cluster Chain
3. Splitting a Path into Tokens
4. Finding an Entry by Name
5. The Centerpiece: fat12_resolve_path
6. Wiring into fat12_opendir
7. Wiring into fat12_open
8. Updating the CLI Commands
9. Verification: Nested Directories
10. Production Notes
11. The FAT Family: FAT32 Root Cluster
12. What Is Next

Chapter 6: Writing Files

1. The Write Path
2. Writing FAT Entries
3. Finding Free Clusters
4. Allocating a Chain
5. Writing Data Clusters
6. Syncing the FAT
7. Loading the Parent Directory
8. Finding a Free Slot
9. Formatting 8.3 Names
10. Creating a Directory Entry
11. Updating the File Struct
12. Splitting a Path into Parent and Name
13. Adding Write Mode to fat12_open
14. Adding fat12_write
15. Updating fat12_close
16. Updating the Header
17. The Write CLI Command
18. Verification
19. Production Notes
20. Append Mode
21. FAT Family: Writing Across FAT Variants
22. What Is Next

Chapter 7: Creating Directories

1. What We Need to Do
2. What Are . and ..?
3. The fat12_mkdir Function
4. Helper: Creating Directory Contents
5. Updating the Header
6. The mkdir CLI Command
7. Verification
8. Production Notes
9. FAT Family: Directories Across FAT Variants
10. What Is Next

Chapter 8: Deleting

1. Production Notes
2. FAT Family: Deleting Across FAT Variants
3. What Is Next

Chapter 9: Renaming and Moving

1. The Two Cases
2. The fat12_move Function
3. The update_dotdot Helper
4. Updating the Header
5. The mv CLI Command
6. Verification
7. Production Notes
8. FAT Family: Rename and Move Across FAT Variants
9. What Is Next

Part III: Advanced

Chapter 10: Formatting

1. What We Are Building
2. What We Need to Do
3. compute_sectors_per_fat
4. format_boot_sector
5. format_fats
6. format_root_dir
7. Updating the Header
8. The format CLI Command
9. Verification
10. Production Notes
11. FAT Family: Formatting Across FAT Variants
12. What Is Next

Chapter 11: Into the Kernel

1. What Changes, What Does Not
2. The Freestanding Environment
3. lib.c — Heap, Memory, and String Functions
4. ATA PIO Block Device
5. The Kernel Entry Point
6. Linking at 1 MB
7. kernel_main — Boot-Time Operations
8. Building
9. Running in QEMU
10. Debugging Tips
11. Production Notes
12. FAT Family: Multiplatform Payoff
13. What Is Next

Conclusion

1. The Architecture
2. What Is Next
3. Thank You