pang-o-lin/src/fat12.c

#include "fat12.h"
#include "fat12-internals.h"
#include "io.h"

#include <stdio.h>

struct fat12_partition {
    int fd;

    // Number of bytes in a sector (512)
    uint32_t sector_size;
    uint8_t sector_buffer[512];

    // These units are "sectors"
    uint32_t fat_offset;
    uint32_t fat_size;
    uint32_t root_offset;
    uint32_t first_offset;
    uint32_t cluster_size;

    // These are in single-unit quantities
    uint32_t root_entries;
    uint32_t cluster_count;
    uint32_t cluster_bytes;
    uint32_t sector_count;

    // Used for traversing directories
    uint32_t current_cluster;
};

void fat12_write_u8(void *ptr, uint8_t val) {
    ((uint8_t *)ptr)[0] = (val >> 0) & 0xff;
}

uint8_t fat12_read_u8(void *ptr) {
    uint16_t val = 0;
    val |= (((uint8_t *)ptr)[0] << 0) & 0xff;
    return val;
}

void fat12_write_u16(void *ptr, uint16_t val) {
    ((uint8_t *)ptr)[0] = (val >> 0) & 0xff;
    ((uint8_t *)ptr)[1] = (val >> 8) & 0xff;
}

uint16_t fat12_read_u16(void *ptr) {
    uint16_t val = 0;
    val |= (((uint8_t *)ptr)[0] << 0) & 0x00ff;
    val |= (((uint8_t *)ptr)[1] << 8) & 0xff00;
    return val;
}

void fat12_set_cluster(void *fat, uint32_t cluster, uint32_t value) {
    uint32_t offset = (cluster * 3) / 2;
    if (cluster&1) {
        ((uint8_t *)fat)[offset] = (((uint8_t *)fat)[offset] & 0x0f) | ((value << 4) & 0xf0);
        ((uint8_t *)fat)[offset + 1] = value >> 4;
    }
    else {
        ((uint8_t *)fat)[offset] = value;
        ((uint8_t *)fat)[offset + 1] = (((uint8_t *)fat)[offset] & 0xf0) | ((value >> 8) & 0x0f);
    }
}

uint32_t fat12_get_cluster(void *fat, uint32_t cluster) {
    uint32_t offset = (cluster * 3) / 2;
    uint32_t value = 0;

    if (cluster&1) {
        value |= (((uint8_t *)fat)[offset] >> 4) & 0x00f;
        value |= (((uint8_t *)fat)[offset + 1] << 4) & 0xff0;
    }
    else {
        value |= ((uint8_t *)fat)[offset];
        value |= (((uint8_t *)fat)[offset + 1] << 8) & 0xf00;
    }

    return value;
}

struct fat12_partition *fat12_alloc(void) {
    struct fat12_partition *part = malloc(sizeof(struct fat12_partition));
    memset(part, 0, sizeof(*part));
    return part;
}

int fat12_open(struct fat12_partition *part, const char *filename) {

    if (!part)
        return -1;

    if (part->fd > 0)
        return -1;

    part->fd = pang_open(filename, O_RDWR);
    if (part->fd == -1) {
        part->fd = 0;
        return -1;
    }

    if (pang_read(part->fd, part->sector_buffer, sizeof(part->sector_buffer)) != sizeof(part->sector_buffer)) {
        return -1;
    }

    part->sector_size = fat12_read_u16(part->sector_buffer + 0x0b);

    // These are in single-unit quantities
    part->root_entries = fat12_read_u16(part->sector_buffer + 0x11);
    part->sector_count = fat12_read_u16(part->sector_buffer + 0x13);

    // These units are "sectors"
    part->fat_offset = fat12_read_u16(part->sector_buffer + 0x0e);
    part->fat_size = fat12_read_u16(part->sector_buffer + 0x16);
    part->root_offset = part->fat_offset + part->fat_size;
    part->first_offset = part->root_offset + (part->root_entries * sizeof(struct fat_directory_entry)) / part->sector_size;
    part->cluster_size = fat12_read_u8(part->sector_buffer + 0x0d);

    uint32_t bytes = (part->sector_count - part->first_offset) * part->sector_size;
    part->cluster_count = bytes / part->sector_size / part->cluster_size;
    part->cluster_bytes = (part->cluster_count * 3) / 2;

///
    fprintf(stderr, "part->sector_size: %d\n", part->sector_size);

    // These are in single-unit quantities
    fprintf(stderr, "part->root_entries: %d\n", part->root_entries);
    fprintf(stderr, "part->sector_count: %d\n", part->sector_count);

    // These units are "sectors"
    fprintf(stderr, "part->fat_offset: %d\n", part->fat_offset);
    fprintf(stderr, "part->fat_size: %d\n", part->fat_size);
    fprintf(stderr, "part->root_offset: %d\n", part->root_offset);
    fprintf(stderr, "part->first_offset: %d\n", part->first_offset);
    fprintf(stderr, "part->cluster_size: %d\n", part->cluster_size);

    fprintf(stderr, "part->cluster_count: %d\n", part->cluster_count);
    fprintf(stderr, "part->cluster_bytes: %d\n", part->cluster_bytes);
    fprintf(stderr, "data_bytes: %d\n", bytes);
///

    return 0;
}

int fat12_close(struct fat12_partition *part) {
    if (!part)
        return -1;

    if (part->fd <= 0)
        return -1;

    if (-1 == pang_close(part->fd)) {
        return -1;
    }

    part->fd = 0;
    return 0;
}

void fat12_free(struct fat12_partition **part) {
    if (!part)
        return;

    if (!*part)
        return;

    free(*part);
    *part = NULL;
}