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28 lines
2.2 KiB
Markdown
28 lines
2.2 KiB
Markdown
# Filesystem Architecture
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BoredOS implements a rudimentary but functional filesystem layer designed to support reading system assets and user applications during runtime.
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## Virtual File System (VFS)
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The Virtual File System acts as an abstraction layer across different underlying storage mechanisms (even if, currently, only one type is fully utilized). System calls targeting files (`SYS_FS`) route through the VFS rather than interacting with the disk directly.
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Key VFS functionalities include:
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- **File Descriptors**: Mapping integer IDs to internal file structures for userland processes.
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- **Standard Operations**: Standardizing `open()`, `read()`, `write()`, `close()`, `seek()`, and directory listings.
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- **Path Parsing**: Resolving absolute and relative paths.
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## FAT32 Implementation
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The primary filesystem logic in `fat32.c` has a dual nature, supporting both an in-memory RAM filesystem for booting and standard block devices for external storage.
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### Booting and the RAMFS
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Since BoredOS boots from a CD-ROM ISO image generated by `xorriso`, it does not read directly off the CD to execute applications.
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1. **ISO Booting**: During boot, Limine loads necessary files (such as userland `.elf` binaries, fonts, and wallpapers) into memory as standard boot modules.
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2. **RAM Simulation**: The FAT32 filesystem code parses these loaded memory modules and automatically constructs a synthetic FAT32 directory tree inside RAM.
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3. **Root Filesystem**: All active execution of built-in GUI and CLI apps occurs off this read-only, in-memory FAT32 simulation.
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### ATA Disk Support
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Beyond the core RAMFS used for booting, the FAT32 implementation natively supports interacting with permanent storage:
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1. **ATA Block Driver**: The kernel features an ATA block device driver capable of communicating with physical hard disks (or raw disk images attached via QEMU).
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2. **Partition Compatibility**: The driver can recognize and natively mount external ATA disks formatted as single FAT32 filesystems or structured with a Master Boot Record (MBR) partition table.
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3. **VFS Integration**: When external storage is mounted, the VFS delegates operations down directly to the FAT32 driver, which will read native sectors across the ATA interface.
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