dev(file-system): establish VFS and Read-only FAT32 File System

1 files changed, 111 insertions, 0 deletions

diff --git a/include/fs/fat32.h b/include/fs/fat32.h
new file mode 100644
index 0000000..c794bd7
--- /dev/null
+++ b/include/fs/fat32.h
@@ -0,0 +1,111 @@
+#pragma once
+#include "fs/fs.h"
+#include "kernel/buf.h"
+
+// Disk Layout Structures (On-Disk)
+
+// FAT32 Boot Sector (BPB)
+struct FAT32_BPB
+{
+    uint8 jmpBoot[3];
+    char oemName[8];
+    uint16 bytesPerSector;
+    uint8 secPerClus;
+    uint16 reservedSecCnt;
+    uint8 numFATs;
+    uint16 rootEntCnt;
+    uint16 totSec16;
+    uint8 media;
+    uint16 FATSz16;
+    uint16 secPerTrk;
+    uint16 numHeads;
+    uint32 hiddSec;
+    uint32 totSec32;
+    uint32 FATSz32;
+    uint16 extFlags;
+    uint16 FSVer;
+    uint32 rootClus;
+    uint16 FSInfo;
+    uint16 bkBootSec;
+    uint8 reserved[12];
+    uint8 drvNum;
+    uint8 reserved1;
+    uint8 bootSig;
+    uint32 volID;
+    char volLab[11];
+    char filSysType[8];
+} __attribute__((packed));
+
+// FAT32 Directory Entry (32 bytes)
+struct FAT32_DirEnt
+{
+    char name[11]; // 8.3 filename
+    uint8 attr;    // File attributes
+    uint8 ntRes;
+    uint8 crtTimeTenth;
+    uint16 crtTime;
+    uint16 crtDate;
+    uint16 lstAccDate;
+    uint16 fstClusHI; // High 16 bits of first cluster
+    uint16 wrtTime;
+    uint16 wrtDate;
+    uint16 fstClusLO; // Low 16 bits of first cluster
+    uint32 fileSize;
+} __attribute__((packed));
+
+#define ATTR_READ_ONLY 0x01
+#define ATTR_HIDDEN 0x02
+#define ATTR_SYSTEM 0x04
+#define ATTR_VOLUME_ID 0x08
+#define ATTR_DIRECTORY 0x10
+#define ATTR_ARCHIVE 0x20
+#define ATTR_LONG_NAME 0x0F
+
+// In-Memory Classes
+
+class FAT32FileSystem;
+
+class FAT32Inode : public Inode
+{
+public:
+    FAT32FileSystem *fs;
+
+    // FAT32 Private Data
+    uint32 first_clus;  // The starting cluster number of the file
+    uint32 parent_clus; // Starting cluster number of the parent directory
+    uint32 dir_offset;  // The byte offset of this directory entry in the parent directory
+
+    FAT32Inode() : fs(nullptr), first_clus(0) {}
+    // Implement VFS Interface
+    void update() override;
+    int read(char *dst, uint32 off, uint32 n, int isUser) override;
+    int write(const char *src, uint32 off, uint32 n, int isUser) override;
+    Inode *lookup(const char *name) override;
+    Inode *create(const char *name, short type, short major, short minor) override;
+    void truncate() override;
+};
+
+class FAT32FileSystem : public FileSystem
+{
+public:
+    uint32 fat_start_sector;
+    uint32 data_start_sector;
+    uint32 root_cluster;
+    uint32 sectors_per_cluster;
+    uint32 bytes_per_cluster;
+
+    void init() override;
+    Inode* root() override;
+
+    // Helper functions
+    uint32 next_cluster(uint32 cluster); // Check the FAT table for the next cluster
+    uint32 alloc_cluster();              // Assign a new cluster
+    uint32 cluster_to_sector(uint32 cluster);
+
+    // directory entry parsing
+    void read_dir_ent(struct FAT32_DirEnt *de, char *filename);
+};
+
+extern FAT32FileSystem fat32_fs;
+
+void fat32_test();
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