From 0d60bdeb7fa50e68aa0576c6bd37f858562ab10f Mon Sep 17 00:00:00 2001
From: Mathieu Maret <mathieu.maret@gmail.com>
Date: Sat, 3 Aug 2024 11:19:28 +0200
Subject: [PATCH] wip fat16/32

---
 core/fs.h       | 17 ++++++++--
 drivers/fat16.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+), 2 deletions(-)
 create mode 100644 drivers/fat16.c

diff --git a/core/fs.h b/core/fs.h
index dbf3fbd..712bcfe 100644
--- a/core/fs.h
+++ b/core/fs.h
@@ -1,4 +1,5 @@
 #pragma once
+#include "ata.h"
 #include "fsEntry.h"
 #include "process.h"
 #include "stdint.h"
@@ -88,6 +89,8 @@ struct file_system_instance {
     struct file_system_instance *prev, *next;
 };
 
+typedef enum { SEEK_SET, SEEK_CUR, SEEK_END } seek_mode_t;
+
 struct file_system {
     char name[FS_NAME_MAXLEN];
     struct file_system_instance *instances;
@@ -98,11 +101,21 @@ struct file_system {
 
     int (*umount)(struct file_system *this, struct file_system_instance *mountedFs);
 
+
+    //tmp function to implement fs in kernel only as a firts step
+    void *(*open)(struct ata_device *disk, struct ata_partition *path, uint32_t mode);
+    int (*read)(struct ata_device *disk, void *private, uint32_t size, uint32_t nmemb,
+                char *out);
+    int (*resolve)(struct ata_device *disk);
+
+    int (*close)(void *private);
+
+    int (*seek)(void *private, uint32_t offset, seek_mode_t seek_mode);
+    // end tmp
+
     struct file_system *prev, *next;
 };
 
-typedef enum { SEEK_SET, SEEK_CUR, SEEK_END } seek_mode_t;
-
 struct file_operations {
     loff_t (*llseek)(struct file *this, loff_t offset, seek_mode_t whence);
     ssize_t (*read)(struct file *this, char *buf, size_t size, loff_t *offset);
diff --git a/drivers/fat16.c b/drivers/fat16.c
new file mode 100644
index 0000000..4127ccb
--- /dev/null
+++ b/drivers/fat16.c
@@ -0,0 +1,83 @@
+#include <stdint.h>
+
+/**
+ * media organization:
+ * * boot record (1 sector, so could be called boot sector): BPB + Extended Boot Record
+ * * File Allocation Table (FAT)
+ * * data area
+ */
+
+
+struct ebr_fat16 { // Extended Boot Record for FAT16
+    uint8_t drive_number;
+    uint8_t flags;
+    uint8_t signature; // Must be 0x29 for FAT16
+    uint8_t vol_id[4];
+    uint8_t vol_label[11];
+    uint8_t sys_id[8]; // Do not trust this!
+    uint8_t bootcode[448];
+    uint16_t bootable_signature; // 0xAA55
+} __attribute__((packed));
+
+struct ebr_fat32 { // Extended Boot Record for FAT32
+    uint32_t fat_size;
+    uint16_t flags;
+    uint16_t fat_version_number;
+    uint32_t root_cluster_nb;
+    uint8_t reserved[12];
+    uint8_t drive_number;
+    uint8_t flags_nt;
+    uint8_t signature;
+    uint8_t vol_id[4];
+    uint8_t vol_label[11];
+    uint8_t sys_id[8]; // Should be always "FAT32"
+    uint8_t bootcode[420];
+    uint16_t bootable_signature; // 0xAA55
+} __attribute__((packed));
+
+struct bpb { // Bios Param Block
+    uint8_t jump_ins[3];
+    uint8_t oem_id[3];
+    uint16_t bytes_per_sector;
+    uint8_t sector_per_cluster;
+    uint16_t reserved_sectors; // boot sectors included
+    uint8_t nb_fat;
+    uint16_t nb_root_dirs;
+    uint16_t nb_sectors;
+    uint8_t media_description_type;
+    uint16_t sectors_per_fat;
+    uint16_t sectors_per_track;
+    uint16_t number_of_heads;
+    uint32_t hidden_sectors;
+    uint32_t nb_large_sectors;
+    union {
+        struct ebr_fat32 fat32;
+        struct ebr_fat16 fat16;
+    };
+} __attribute__((packed));
+
+typedef enum {
+    READ_ONLY = 0x01,
+    HIDDEN    = 0x02,
+    SYSTEM    = 0x04,
+    VOLUME_ID = 0x08,
+    DIRECTORY = 0x10,
+    ARCHIVE   = 0x20,
+    LFN       = READ_ONLY | HIDDEN | SYSTEM | VOLUME_ID,
+} __attribute__((__packed__)) directory_entry_type_t;
+
+struct directory_entry {
+    uint8_t filename[11];
+    directory_entry_type_t type;
+    uint8_t reserved;
+    uint8_t creation_time_hundredths_sec;
+    uint16_t creation_time;    // hour[5] min[6] sec[5]
+    uint16_t creation_date;    // year[7] month[4] day[5]
+    uint16_t last_access_date; // year[7] month[4] day[5]
+    uint16_t cluster_nb_high;
+    uint16_t modification_time; // hour[5] min[6] sec[5]
+    uint16_t modification_date; // year[7] month[4] day[5]
+    uint16_t cluster_nb_low;
+    uint32_t size; // in bytes
+} __attribute__((packed));
+