embpart/fs/fat32/fat32.c

//
// Created by epagris on 2023.09.28..
//

#include <memory.h>
#include <stdbool.h>
#include "fat32.h"
#include "../../MassStorage.h"

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

#define SECTOR_SIZE (512)
static uint8_t buffer[2 * SECTOR_SIZE]; // TODO access to this variable should be protected!

static inline void fat32_copy_second_to_first_buffer() {
    memcpy(buffer, buffer + SECTOR_SIZE, SECTOR_SIZE);
}

static inline uint32_t fat32_get_first_sector_of_cluster(const Fat32_CtrlBlock *ctrl, uint32_t cluster) {
    return (cluster - 2) * ctrl->sectors_per_cluster + ctrl->data_s;
}

int fat32_load(Fat32_CtrlBlock *ctrl, uint32_t bpb_s, const MassStorage *mstg) {
    ctrl->mstg = mstg;

    ctrl->bpb_s = bpb_s;

    // load Boot Parameter Block
    mstg->read_sector(mstg, bpb_s, buffer);
    const Bpb_Fat32 *bpb_obj = (Bpb_Fat32 *) buffer;

    ctrl->bytes_per_sector = bpb_obj->bytes_per_sector;
    ctrl->sectors_per_cluster = bpb_obj->sectors_per_cluster;
    ctrl->sectors_per_fat = bpb_obj->n_sectors_per_fat;
    memcpy(ctrl->volume_label, bpb_obj->volume_label, 11);
    ctrl->serial_number = bpb_obj->volume_serial_number;
    ctrl->fat_copies = bpb_obj->n_fats;
    ctrl->fat_entries_per_sector = ctrl->bytes_per_sector / sizeof(Fat32_FatTableEntry);

    ctrl->fat_s = ctrl->bpb_s + bpb_obj->n_reserved_sectors; // FATs are stored on the hidden area right after the reserved sectors
    ctrl->data_s = ctrl->fat_s + ctrl->fat_copies * ctrl->sectors_per_fat; // data region begins right after the FAT copies
    ctrl->root_s = fat32_get_first_sector_of_cluster(ctrl, bpb_obj->root_first_cluster); // first sector of root directory is determined using the cluster number as an offset

    return 0;
}

#define FETCH_MSTG const MassStorage * mstg = ctrl->mstg
#define READ_MSTG_TO_FIRST_BUFFER(idx) MSTG_READ(mstg, (idx), buffer)
#define READ_MSTG_TO_SECOND_BUFFER(idx) MSTG_READ(mstg, (idx), buffer + SECTOR_SIZE)

// TODO some dirty function to chop the high byte from the unicode charcode...
static inline uint8_t fat32_unicode_to_utf8(uint16_t unicode) {
    return unicode & 0x00FF;
}

uint32_t fat32_trim_str_right(char *str) {
    uint32_t len = 0;
    while (*str > ' ') {
        str++;
        len++;
    }
    *str = '\0';
    return len;
}

// TODO loop unroll!
uint16_t fat32_extract_lfn_text(const Fat32_LongFileNameEntry *lfnEntry, char *str) {
    uint16_t idx = 0;
    for (uint8_t i = 0; i < 5; i++) { // first block
        str[idx++] = (char) fat32_unicode_to_utf8(((uint8_t *) lfnEntry->ustr04)[2 * i]);
    }
    for (uint8_t i = 0; i < 6; i++) { // second block
        str[idx++] = (char) fat32_unicode_to_utf8(((uint8_t *) lfnEntry->ustr5A)[2 * i]);
    }
    for (uint8_t i = 0; i < 2; i++) { // third block
        str[idx++] = (char) fat32_unicode_to_utf8(((uint8_t *) lfnEntry->ustrBC)[2 * i]);
    }
    return idx;
}

#define LONG_FILE_NAME_ATTRIB_TEST(a) ((a) & (1 << 3)) && ((a) & (1 << 2)) && ((a) & (1 << 1)) && ((a) & (1))
#define LINELENGTH (32)

uint16_t fat32_get_file_entry(Fat32_FileEntry **const entry, char *entry_name) {
    //static char entry_name[261];
    bool done = false;
    bool reading_lfn = false;
    uint8_t rewind = 0;
    uint8_t attribs;

    // look for the first non-LFN entry and count the LFNs
    while (!done) {
        attribs = (*entry)->attributes;
        if (LONG_FILE_NAME_ATTRIB_TEST(attribs)) { // if this is an LFN-entry
            rewind++;
            reading_lfn = true;
            (*entry)++; // advance in the table
        } else { // if this is NOT an LFN-entry
            done = true;
        }
    }

    Fat32_FileEntry *const finalEntry = *(entry); // final, non-LFN entry
    attribs = finalEntry->attributes;
    uint16_t name_len = 0;

    // print the name of the entry
    if (reading_lfn) { // if the entry has a long name
        const Fat32_LongFileNameEntry *lfnEntry = (const Fat32_LongFileNameEntry *) (finalEntry - 1); // by order first (by address last) LFN entry

        // fetch long name
        for (uint8_t i = 0; i < rewind; i++) {
            name_len += fat32_extract_lfn_text(lfnEntry, entry_name + name_len);
            lfnEntry--; // retreat entry
        }
        entry_name[name_len] = '\0'; // terminate string
        name_len = fat32_trim_str_right(entry_name); // trim residual whitespaces
    } else { // if the entry has only a short name
        memcpy(entry_name, finalEntry->short_fname, 8); // copy basename
        name_len = fat32_trim_str_right(entry_name); // trim whitespaces
        if (!((attribs & FAT32_FATT_VOLUME) || (attribs & FAT32_FATT_DIRECTORY))) { // omit dot if volume label or directory
            entry_name[name_len++] = '.'; // insert dot
        }
        memcpy(entry_name + name_len, finalEntry->extension, 3); // copy extension
        name_len = fat32_trim_str_right(entry_name); // trim whitespaces
        if (entry_name[name_len - 1] == '.') { // chop dot if no extension
            name_len--;
        }
        entry_name[name_len] = '\0'; // terminate string
    }

    return name_len;
}

int fat32_print_file_entry(Fat32_FileEntry **const entry) {
    static char entry_name[261];
    uint16_t name_len = fat32_get_file_entry(entry, entry_name);
    uint8_t attribs = (*entry)->attributes;

    // print entry type
    char entry_type[5] = {'F', ' ', ' ', ' ', '\0'}; // file, by default
    if (attribs & FAT32_FATT_DIRECTORY) {
        entry_type[0] = 'D';
    } else if (attribs & FAT32_FATT_VOLUME) {
        entry_type[0] = 'V';
    } else if (attribs & FAT32_FATT_HIDDEN) {
        entry_type[1] = 'H';
    } else if (attribs & FAT32_FATT_READ_ONLY) {
        entry_type[2] = 'R';
    } else if (attribs & FAT32_FATT_SYSTEM) {
        entry_type[3] = 'S';
    }

    uint16_t padding = 1;
    if (name_len < LINELENGTH) {
        padding = LINELENGTH - name_len;
    }

    MSG("%s%*c%s %u\n", entry_name, padding, ' ', entry_type, (*entry)->size);

    return 0;
}

#define FAT32_UNUSED_FILE_ENTRY (0xE5)
#define FAT32_DIRECTORY_SEPARATOR ('/')
#define FAT32_MAX_BASENAME_LENGTH (47)

static inline uint16_t fat32_extract_next_basename_length(const char *path) {
    uint16_t i;
    for (i = 0; (path[i] != FAT32_DIRECTORY_SEPARATOR) && (path[i] != '\0'); i++) {}
    return i;
}

const Fat32_FileEntry *fat32_locate_file(const Fat32_CtrlBlock *ctrl, const char *path) {
    FETCH_MSTG;

    // start search in the root directory
    uint32_t sector = ctrl->root_s;
    READ_MSTG_TO_FIRST_BUFFER(sector);
    READ_MSTG_TO_SECOND_BUFFER(sector + 1);

    bool file_found = false; // file is not found in the beginning
    bool no_such_file = false; // assume that there is such a file
    const char *path_iter = path; // path is being fetched from its beginning
    char basename[FAT32_MAX_BASENAME_LENGTH + 1]; // basename
    basename[FAT32_MAX_BASENAME_LENGTH] = '\0'; // NULL-termination
    char entry_name[FAT32_MAX_BASENAME_LENGTH + 1]; // entry name
    Fat32_FileEntry *entry = NULL; // entry iterator

    while ((!file_found) && (!no_such_file)) {
        // extract first basename
        uint16_t basename_len = fat32_extract_next_basename_length(path_iter); // get basename length
        uint16_t copy_len = MIN(basename_len, FAT32_MAX_BASENAME_LENGTH);
        memcpy(basename, path_iter, copy_len); // extract basename
        basename[copy_len] = '\0'; // NULL-termination
        path_iter += basename_len; // advance basename

        // search for basename in the current directory
        // acquire pointer to the beginning of the file entry table
        entry = (Fat32_FileEntry *) buffer;
        bool basename_entry_found = false;
        while ((entry->short_fname[0] != 0x00) && (!basename_entry_found)) {
            if (entry->short_fname[0] != FAT32_UNUSED_FILE_ENTRY) {
                fat32_get_file_entry(&entry, entry_name);

                // compare entry name
                if (!strncmp(entry_name, basename, basename_len)) { // if matches...
                    basename_entry_found = true; // ...then the entry is found
                    continue;
                }
            }

            entry++;

            // if we crossed the first buffer - second buffer border, then
            // copy the second buffer to the first one and load the next sector
            // to the second buffer
            if ((void *) entry > (void *) (buffer + SECTOR_SIZE)) {
                // copy the second buffer to the first one
                fat32_copy_second_to_first_buffer();
                sector++;
                READ_MSTG_TO_SECOND_BUFFER(sector + 1);

                // modify the entry pointer, since it's been moved
                entry = (Fat32_FileEntry *) (((uint8_t *) (entry)) - SECTOR_SIZE);
            }
        }

        // if the basename entry is found...
        if (basename_entry_found) {
            if (path_iter[0] == '\0') { // ...and it's the end of the path
                file_found = true; // ...then the file is found
            } else { // ...if it's not the end of the path, then load the cluster corresponding to the entry
                // determine sector number
                uint32_t next_cluster = (entry->first_cluster_high << 16) | (entry->first_cluster_low);
                uint32_t next_sector = fat32_get_first_sector_of_cluster(ctrl, next_cluster);

                // load sectors
                READ_MSTG_TO_FIRST_BUFFER(next_sector);
                READ_MSTG_TO_SECOND_BUFFER(next_sector + 1);
            }
        } else { // if not found...
            no_such_file = true; // ...then the file could not be located
        }
    }

    // return with appropriate value
    if (!no_such_file) {
        return entry;
    } else {
        return NULL;
    }
}

int fat32_list_dir(const Fat32_CtrlBlock *ctrl, const char *dir) {
    // TODO find directory

    // read root directory
    FETCH_MSTG;
    uint32_t sector = ctrl->root_s;
    READ_MSTG_TO_FIRST_BUFFER(sector);
    READ_MSTG_TO_SECOND_BUFFER(sector + 1);

    // acquire pointer to the beginning of the file entry table
    Fat32_FileEntry *entry = (Fat32_FileEntry *) buffer;
    while (entry->short_fname[0] != 0x00) {
        if (entry->short_fname[0] != FAT32_UNUSED_FILE_ENTRY) {
            fat32_print_file_entry(&entry);
        }
        entry++;

        // if we crossed the first buffer - second buffer border, then
        // copy the second buffer to the first one and load the next sector
        // to the second buffer
        if ((void *) entry > (void *) (buffer + SECTOR_SIZE)) {
            // copy the second buffer to the first one
            fat32_copy_second_to_first_buffer();
            sector++;
            READ_MSTG_TO_SECOND_BUFFER(sector + 1);

            // modify the entry pointer, since it's been moved
            entry = (Fat32_FileEntry *) (((uint8_t *) (entry)) - SECTOR_SIZE);
        }
    }

    return 0;
}

static inline uint32_t fat32_get_fat_entry_sector_by_cluster_index(const Fat32_CtrlBlock *ctrl, uint32_t cluster) {
    return cluster * sizeof(Fat32_FatTableEntry) / ctrl->bytes_per_sector + ctrl->fat_s;
}

static inline uint32_t fat32_get_cluster_from_pos(const Fat32_CtrlBlock * ctrl, uint32_t first_cluster, uint32_t pos) {
    FETCH_MSTG;
    uint32_t cluster_link_number = pos / (ctrl->sectors_per_cluster * ctrl->bytes_per_sector); // calculate the sequence number of the FAT entry containing the reference to the desired data cluster
    uint32_t fat_iter_sector = 0;
    uint32_t cluster = first_cluster; // linked cluster
    Fat32_FatTableEntry * fat_iter = NULL; // iterator on FAT table

    for (uint32_t hop = 0; hop < cluster_link_number; hop++) {
        uint32_t new_fat_iter_sector = fat32_get_fat_entry_sector_by_cluster_index(ctrl, cluster); // get the FAT sector containing the referred entry
        if (new_fat_iter_sector != fat_iter_sector) {
            READ_MSTG_TO_FIRST_BUFFER(new_fat_iter_sector); // read FAT sector containing the specific entry to the buffer
            fat_iter_sector = new_fat_iter_sector;
        }
        fat_iter = ((Fat32_FatTableEntry *) buffer) + (cluster % ctrl->fat_entries_per_sector); // get FAT iter
        uint32_t next_cluster = (*fat_iter) & ~(0xF << 28);
        if (next_cluster >= 2 && next_cluster <= 0xFFFFFEF) {
            cluster = next_cluster;
        }
    }
    return cluster;
}

int fat32_read_file(const Fat32_CtrlBlock * ctrl, const Fat32_FileEntry * entry, uint32_t pos, uint32_t len, uint8_t * p) {
    FETCH_MSTG;
    uint32_t first_cluster = (entry->first_cluster_high << 16) | (entry->first_cluster_low);
    uint32_t cluster = fat32_get_cluster_from_pos(ctrl, first_cluster, pos);
    uint32_t sector = fat32_get_first_sector_of_cluster(ctrl, cluster);
    READ_MSTG_TO_FIRST_BUFFER(sector);
    uint32_t pos_in_sector = pos % ctrl->bytes_per_sector;
    memcpy(p, buffer + pos_in_sector, len);
    return len; // TODO
}