path: root/kernel/fs/fat.c

#include <stdint.h>
#include <stdbool.h>

#include <string.h>
#include <comus/fs.h>

// Attribution: Large amounts of code here were are taken (either as is or modified)
// from strawberryhacker at strawberryhacker/flat32/blob/master
// various errors with fat32
enum
{
    FAT_ERR_NONE  = 0,
    FAT_ERR_NOFAT = -1,
    FAT_ERR_BROKEN  = -2,
    FAT_ERR_IO    = -3,
    FAT_ERR_PARAM = -4,
    FAT_ERR_PATH   = -5,
    // also can tell if files don't exist.
    FAT_ERR_EOF   = -6,
    //
    FAT_ERR_DENIED = -7,
    FAT_ERR_FULL   = -8,
};

enum
{
  FAT_ATTR_NONE     = 0x00,
  FAT_ATTR_RO       = 0x01,
  FAT_ATTR_HIDDEN   = 0x02,
  FAT_ATTR_SYS      = 0x04,
  FAT_ATTR_LABEL    = 0x08,
  FAT_ATTR_DIR      = 0x10,
  FAT_ATTR_ARCHIVE  = 0x20,
  FAT_ATTR_LFN      = 0x0f,
};

enum
{
  FAT_WRITE      = 0x01, // Open file for writing
  FAT_READ       = 0x02, // Open file for reading
  FAT_APPEND     = 0x04, // Set file offset to the end of the file
  FAT_TRUNC      = 0x08, // Truncate the file after opening
  FAT_CREATE     = 0x10, // Create the file if it do not exist

  FAT_ACCESSED   = 0x20, // do not use (internal)
  FAT_MODIFIED   = 0x40, // do not use (internal)
  FAT_FILE_DIRTY = 0x80, // do not use (internal)
};

enum
{
  FAT_SEEK_START,
  FAT_SEEK_CURR,
  FAT_SEEK_END,
};

#define LIMIT(a, b) ((a) < (b) ? (a) : (b))

#define FSINFO_HEAD_SIG    0x41615252
#define FSINFO_STRUCT_SIG  0x61417272
#define FSINFO_TAIL_SIG    0xaa550000

#define MBR_PART_OFF  446

#define EXT_FLAG_MIRROR  (1 << 7)
#define EXT_FLAG_ACT     0x000f
#define EXT_FLAG_SECOND  0x0001

#define LFN_HEAD_MSK  0x40
#define LFN_SEQ_MSK   0x1f

#define SFN_FREE  0xe5
#define SFN_LAST  0x00
#define SFN_PAD   0x20

//------------------------------------------------------------------------------
enum
{
  FAT_BUF_DIRTY  = 0x01,
  FAT_INFO_DIRTY = 0x02,
};

enum
{
  CLUST_FREE = 0x01,
  CLUST_USED = 0x02,
  CLUST_LAST = 0x04,
  CLUST_BAD  = 0x08,
};

typedef struct
{
  bool (*read)(uint8_t* buf, uint32_t sect);
  bool (*write)(const uint8_t* buf, uint32_t sect);
} DiskOps;

// time checker if I can be bothered to implement it.
typedef struct
{
  uint8_t hour;
  uint8_t min;
  uint8_t sec;
  uint8_t day;
  uint8_t month;
  uint16_t year;
} Timestamp;

typedef struct Fat
{
  struct Fat* next;
  DiskOps ops;
  uint32_t clust_msk;
  uint32_t clust_cnt;
  uint32_t info_sect;
  uint32_t fat_sect[2];
  uint32_t data_sect;  
  uint32_t root_clust;
  uint32_t last_used;
  uint32_t free_cnt;
  uint32_t sect;
  uint8_t buf[512];
  uint8_t flags;
  uint8_t clust_shift;
  uint8_t name_len;
  char name[32];
} Fat;

typedef struct
{
  //Timestamp created;
  //Timestamp modified;
  uint32_t size;
  uint8_t attr;
  char name[255];
  uint8_t name_len;
} DirInfo;

typedef struct
{
  Fat* fat;
  uint32_t sclust;
  uint32_t clust;
  uint32_t sect;
  uint16_t idx;
} Dir;

// file structure
typedef struct
{
  Fat* fat;
  uint32_t dir_sect;
  uint32_t sclust;
  uint32_t clust;
  uint32_t sect;
  uint32_t size;
  uint32_t offset;
  uint16_t dir_idx;
  uint8_t attr;
  uint8_t flags;
  uint8_t buf[512];
} File;


typedef struct __attribute__((packed))
{
  uint8_t jump[3];
  char name[8];
  uint16_t bytes_per_sect;
  uint8_t sect_per_clust;
  uint16_t res_sect_cnt;
  uint8_t fat_cnt;
  uint16_t root_ent_cnt;
  uint16_t sect_cnt_16;
  uint8_t media;
  uint16_t sect_per_fat_16;
  uint16_t sect_per_track;
  uint16_t head_cnt;
  uint32_t hidden_sect_cnt;
  uint32_t sect_cnt_32;
  uint32_t sect_per_fat_32;
  uint16_t ext_flags;
  uint8_t minor;
  uint8_t major;
  uint32_t root_cluster;
  uint16_t info_sect;
  uint16_t copy_bpb_sector;
  uint8_t reserved_0[12];
  uint8_t drive_num;
  uint8_t reserved_1;
  uint8_t boot_sig;
  uint32_t volume_id;
  char volume_label[11];
  char fs_type[8];
  uint8_t reserved_2[420];
  uint8_t sign[2];
} Bpb;

typedef struct __attribute__((packed))
{
  uint32_t head_sig;
  uint8_t reserved_0[480];
  uint32_t struct_sig;
  uint32_t free_cnt;
  uint32_t next_free;
  uint8_t reserved_1[12];
  uint32_t tail_sig;
} FsInfo;

typedef struct __attribute__((packed))
{
  uint8_t name[11];
  uint8_t attr;
  uint8_t reserved;
  uint8_t tenth;
  uint16_t cre_time;
  uint16_t cre_date;
  uint16_t acc_date;
  uint16_t clust_hi;
  uint16_t mod_time;
  uint16_t mod_date;
  uint16_t clust_lo;
  uint32_t size;
} Sfn;

typedef union __attribute__((packed))
{
  uint8_t raw[32];
  struct
  {
    uint8_t seq;
    uint8_t name0[10];
    uint8_t attr;
    uint8_t type;
    uint8_t crc;
    uint8_t name1[12];
    uint16_t clust;
    uint8_t name2[4];
  };
} Lfn;

typedef struct
{
  uint32_t sect;
  uint16_t idx;
} Loc;


static Fat* g_fat_list;
static uint8_t g_lfn_indices[13] = {1, 3, 5, 7, 9, 14, 16, 18, 20, 22, 24, 28, 30};
static uint8_t g_buf[512];
static uint16_t g_len;
static uint8_t g_crc;

static Fat* find_fat_volume(const char* name, int len)
{
    for(Fat* it = g_fat_list; it; it = it->next)
    {
        if(len == it->name_len && !memcmp(name, it->name, len)) {
            return it;
        }
    }
    return NULL;
}

static int sync_buf(Fat* fat) {
    // checks whether the flag is active. If not, we 
    if(fat->flags & 0x01) {
        // if write fails for whatever reason
        if(!fat->ops.write(fat->buf, fat->sect)) {
            return FAT_ERR_IO;
        }
    }
}
static int update_buf(Fat* fat, uint32_t sect) {
    // if fat->sect already is sect, we are good
    if(fat->sect != sect) {

    }
}
// attempts to sync the filesystem to fat32. Returns error code assuming one happens.
static int sync_fs(Fat* fat)
{
    int error = sync_buf(fat);
    if (error) {
        return error;
    }
    if(fat->flags & 0x02) {
        error = update_buf(fat, fat->info_sect);
        if(error) {
            return error;
        }
        FsInfo* info = (FsInfo*)fat->buf;
        fat->flags |= 0x01;
        info->next_free = fat->last_used;
        info->free_cnt = fat->free_cnt;

        error = sync_buf(fat);
        if(error) {
            return error;
        }
        fat->flags &= ~0x01;
    }
    return FAT_ERR_NONE;
}

static int get_fat(Fat* fat, uint32_t clust, uint32_t* out_val, uint8_t* out_flags) {

}
/// @brief 
/// @param ops (the operation that is being done)
/// @param partition use 0 for the entire disk
/// @param fat um
/// @param name no clue lol 
/// @return 
int fat_mount(DiskOps* ops, int partition, Fat* fat, const char* name) {
    uint32_t lba;
    int err = probe(ops, partition, &lba);
    if(err) {
        return err;
    }
    Bpb* bpb = (Bpb*)g_buf;
    bool mirror = (bpb->ext_flags & EXT_FLAG_MIRROR) != 0;
    bool use_first = (bpb->ext_flags & EXT_FLAG_SECOND) == 0;

    uint32_t fat_0 = lba + bpb->res_sect_cnt;
    uint32_t fat_1 = lba + bpb->res_sect_cnt + bpb->sect_per_fat_32;
    fat->clust_shift = __builtin_ctz(bpb->sect_per_clust);
    fat->clust_msk = bpb->sect_per_clust - 1;
    fat->clust_cnt = bpb->sect_per_fat_32 * 128;
    fat->root_clust = bpb->root_cluster;
    fat->fat_sect[0] = use_first ? fat_0 : fat_1;
    fat->fat_sect[1] = mirror ? (use_first ? fat_1 : fat_0) : 0;
    fat->info_sect = lba + bpb->info_sect;
    fat->data_sect = lba + bpb->res_sect_cnt + bpb->fat_cnt * bpb->sect_per_fat_32;
    if(!ops->read(g_buf, fat->info_sect)) {
        return FAT_ERR_IO;
    }
    FsInfo* info = (FsInfo*)g_buf;
    if (info->tail_sig != FSINFO_TAIL_SIG || 
        info->head_sig != FSINFO_HEAD_SIG ||
        info->struct_sig != FSINFO_STRUCT_SIG ||
        info->next_free == 0xffffffff || 
        info->free_cnt == 0xffffffff) {
            return FAT_ERR_NOFAT;
        }
  
    fat->last_used = info->next_free;
    fat->free_cnt  = info->free_cnt;

    int name_len = strlen(name);
    if (name_len > sizeof(fat->name)) {
        return FAT_ERR_PARAM;
    }
    memcpy(fat->name, name, name_len);
    fat->name_len = name_len;

    fat->ops = *ops;
    fat->sect = 0;   // Causes buffering on first call

    fat->next = g_fat_list;
    g_fat_list = fat;

    return FAT_ERR_NONE;
}

int fat_unmount(Fat* fat) {
    Fat** it = &g_fat_list;
    while(*it && *it != fat) {
        it = &(*it)->next;
    }
    if(*it == NULL) {
        return FAT_ERR_PARAM;
    }
    *it = fat->next;
    return sync_fs(fat);
}

int fat_sync(Fat* fat)
{
    return sync_fs(fat);
}

int fat_file_open(File* file, const char* path, uint8_t flags) {
    Dir dir;
    dir.fat = 0;

    int err = follow_path(&dir, &path, NULL);
    // if there is an error that isn't EOF
    if(err && err != FAT_ERR_EOF) {
        return err;
    }
    // if the error is EOF, which in this case checks if the file doesn't exist
    if(err == FAT_ERR_EOF) {
        if(0 == (flags & FAT_CREATE)) {
            return FAT_ERR_DENIED;
        }
    }

}