fat16.c

采用fat格式对sd卡进行操作

            /* we reached the cluster border and switch to the next cluster */
            cluster_offset = 0;

            /* get number of next cluster */
            if(!(cluster_num = fat16_get_next_cluster(dd->fs, cluster_num)))
            {
                /* directory entry not found, reset directory handle */
                cluster_num = dd->dir_entry.cluster;
                break;
            }
        }
    }

    dd->entry_cluster = cluster_num;
    dd->entry_offset = cluster_offset;

    return dir_entry->long_name[0] != '\0' ? 1 : 0;
}

/**
 * \ingroup fat16_dir
 * Resets a directory handle.
 *
 * Resets the directory handle such that reading restarts
 * with the first directory entry.
 *
 * \param[in] dd The directory handle to reset.
 * \returns 0 on failure, 1 on success.
 * \see fat16_read_dir
 */
uint8_t fat16_reset_dir(struct fat16_dir_struct* dd)
{
    if(!dd)
        return 0;

    dd->entry_cluster = dd->dir_entry.cluster;
    dd->entry_offset = 0;
    return 1;
}

/**
 * \ingroup fat16_fs
 * Callback function for reading a directory entry.
 */
uint8_t fat16_dir_entry_read_callback(uint8_t* buffer, uint32_t offset, void* p)
{
    struct fat16_read_dir_callback_arg* arg = p;
    struct fat16_dir_entry_struct* dir_entry = arg->dir_entry;

    arg->bytes_read += 32;

    /* skip deleted or empty entries */
    if(buffer[0] == FAT16_DIRENTRY_DELETED || !buffer[0])
        return 1;

    if(!dir_entry->entry_offset)
        dir_entry->entry_offset = offset;
    
    switch(fat16_interpret_dir_entry(dir_entry, buffer))
    {
        case 0: /* failure */
        {
            return 0;
        }
        case 1: /* buffer successfully parsed, continue */
        {
            return 1;
        }
        case 2: /* directory entry complete, finish */
        {
            arg->finished = 1;
            return 0;
        }
    }

    return 0;
}

/**
 * \ingroup fat16_fs
 * Interprets a raw directory entry and puts the contained
 * information into the directory entry.
 * 
 * For a single file there may exist multiple directory
 * entries. All except the last one are lfn entries, which
 * contain parts of the long filename. The last directory
 * entry is a traditional 8.3 style one. It contains all
 * other information like size, cluster, date and time.
 * 
 * \param[in,out] dir_entry The directory entry to fill.
 * \param[in] raw_entry A pointer to 32 bytes of raw data.
 * \returns 0 on failure, 1 on success and 2 if the
 *          directory entry is complete.
 */
uint8_t fat16_interpret_dir_entry(struct fat16_dir_entry_struct* dir_entry, const uint8_t* raw_entry)
{
    if(!dir_entry || !raw_entry || !raw_entry[0])
        return 0;

    char* long_name = dir_entry->long_name;
    if(raw_entry[11] == 0x0f)
    {
        /* Lfn supports unicode, but we do not, for now.
         * So we assume pure ascii and read only every
         * second byte.
         */
        uint16_t char_offset = ((raw_entry[0] & 0x3f) - 1) * 13;
        const uint8_t char_mapping[] = { 1, 3, 5, 7, 9, 14, 16, 18, 20, 22, 24, 28, 30 };
        for(uint8_t i = 0; i <= 12 && char_offset + i < sizeof(dir_entry->long_name) - 1; ++i)
            long_name[char_offset + i] = raw_entry[char_mapping[i]];

        return 1;
    }
    else
    {
        /* if we do not have a long name, take the short one */
        if(long_name[0] == '\0')
        {
            uint8_t i;
            for(i = 0; i < 8; ++i)
            {
                if(raw_entry[i] == ' ')
                    break;
                long_name[i] = raw_entry[i];
            }
            if(long_name[0] == 0x05)
                long_name[0] = (char) FAT16_DIRENTRY_DELETED;

            if(raw_entry[8] != ' ')
            {
                long_name[i++] = '.';

                uint8_t j = 8;
                for(; j < 11; ++j)
                {
                    if(raw_entry[j] != ' ')
                    {
                        long_name[i++] = raw_entry[j];
                    }
                    else
                    {
                        break;
                    }
                }
            } 

            long_name[i] = '\0';
        }
        
        /* extract properties of file and store them within the structure */
        dir_entry->attributes = raw_entry[11];
        dir_entry->cluster = ((uint16_t) raw_entry[26]) |
                             ((uint16_t) raw_entry[27] << 8);
        dir_entry->file_size = ((uint32_t) raw_entry[28]) |
                               ((uint32_t) raw_entry[29] << 8) |
                               ((uint32_t) raw_entry[30] << 16) |
                               ((uint32_t) raw_entry[31] << 24);

#if FAT16_DATETIME_SUPPORT
        dir_entry->modification_time = ((uint16_t) raw_entry[22]) |
                                       ((uint16_t) raw_entry[23] << 8);
        dir_entry->modification_date = ((uint16_t) raw_entry[24]) |
                                       ((uint16_t) raw_entry[25] << 8);
#endif

        return 2;
    }
}

/**
 * \ingroup fat16_fs
 * Searches for space where to store a directory entry.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] parent The directory in which to search.
 * \param[in] dir_entry The directory entry for which to search space.
 * \returns 0 on failure, a device offset on success.
 */
uint32_t fat16_find_offset_for_dir_entry(const struct fat16_fs_struct* fs, const struct fat16_dir_struct* parent, const struct fat16_dir_entry_struct* dir_entry)
{
#if FAT16_WRITE_SUPPORT
    if(!fs || !dir_entry)
        return 0;

    /* search for a place where to write the directory entry to disk */
    uint8_t free_dir_entries_needed = (strlen(dir_entry->long_name) + 12) / 13 + 1;
    uint8_t free_dir_entries_found = 0;
    uint16_t cluster_num = parent->dir_entry.cluster;
    uint32_t dir_entry_offset = 0;
    uint32_t offset = 0;
    uint32_t offset_to = 0;

    if(cluster_num == 0)
    {
        /* we read/write from the root directory entry */
        offset = fs->header.root_dir_offset;
        offset_to = fs->header.cluster_zero_offset;
        dir_entry_offset = offset;
    }
    
    while(1)
    {
        if(offset == offset_to)
        {
            if(cluster_num == 0)
                /* We iterated through the whole root directory entry
                 * and could not find enough space for the directory entry.
                 */
                return 0;

            if(offset)
            {
                /* We reached a cluster boundary and have to
                 * switch to the next cluster.
                 */

                uint16_t cluster_next = fat16_get_next_cluster(fs, cluster_num);
                if(!cluster_next)
                {
                    cluster_next = fat16_append_clusters(fs, cluster_num, 1);
                    if(!cluster_next)
                        return 0;

                    /* we appended a new cluster and know it is free */
                    dir_entry_offset = fs->header.cluster_zero_offset +
                                       (uint32_t) (cluster_next - 2) * fs->header.cluster_size;

                    /* clear cluster to avoid garbage directory entries */
                    fat16_clear_cluster(fs, cluster_next);

                    break;
                }
                cluster_num = cluster_next;
            }

            offset = fat16_cluster_offset(fs, cluster_num);
            offset_to = offset + fs->header.cluster_size;
            dir_entry_offset = offset;
            free_dir_entries_found = 0;
        }
        
        /* read next lfn or 8.3 entry */
        uint8_t first_char;
        if(!fs->partition->device_read(offset, &first_char, sizeof(first_char)))
            return 0;

        /* check if we found a free directory entry */
        if(first_char == FAT16_DIRENTRY_DELETED || !first_char)
        {
            /* check if we have the needed number of available entries */
            ++free_dir_entries_found;
            if(free_dir_entries_found >= free_dir_entries_needed)
                break;

            offset += 32;
        }
        else
        {
            offset += 32;
            dir_entry_offset = offset;
            free_dir_entries_found = 0;
        }
    }

    return dir_entry_offset;

#else
    return 0;
#endif
}

/**
 * \ingroup fat16_fs
 * Writes a directory entry to disk.
 *
 * \note The file name is not checked for invalid characters.
 *
 * \note The generation of the short 8.3 file name is quite
 * simple. The first eight characters are used for the filename.
 * The extension, if any, is made up of the first three characters
 * following the last dot within the long filename. If the
 * filename (without the extension) is longer than eight characters,
 * the lower byte of the cluster number replaces the last two
 * characters to avoid name clashes. In any other case, it is your
 * responsibility to avoid name clashes.
 *
 * \param[in] fs The filesystem on which to operate.
 * \param[in] dir_entry The directory entry to write.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat16_write_dir_entry(const struct fat16_fs_struct* fs, struct fat16_dir_entry_struct* dir_entry)
{
#if FAT16_WRITE_SUPPORT
    if(!fs || !dir_entry)
        return 0;
    
#if FAT16_DATETIME_SUPPORT
    {
        uint16_t year;
        uint8_t month;
        uint8_t day;
        uint8_t hour;
        uint8_t min;
        uint8_t sec;

        fat16_get_datetime(&year, &month, &day, &hour, &min, &sec);
        fat16_set_file_modification_date(dir_entry, year, month, day);
        fat16_set_file_modification_time(dir_entry, hour, min, sec);
    }
#endif

    device_write_t device_write = fs->partition->device_write;
    uint32_t offset = dir_entry->entry_offset;
    const char* name = dir_entry->long_name;
    uint8_t name_len = strlen(name);
    uint8_t lfn_entry_count = (name_len + 12) / 13;
    uint8_t buffer[32];

    /* write 8.3 entry */

    /* generate 8.3 file name */
    memset(&buffer[0], ' ', 11);
    char* name_ext = strrchr(name, '.');
    if(name_ext && *++name_ext)
    {
        uint8_t name_ext_len = strlen(name_ext);
        name_len -= name_ext_len + 1;

        if(name_ext_len > 3)
            name_ext_len = 3;
        
        memcpy(&buffer[8], name_ext, name_ext_len);
    }
    
    if(name_len <= 8)
    {
        memcpy(buffer, name, name_len);

        /* For now, we create lfn entries for all files,
         * except the "." and ".." directory references.
         * This is to avoid difficulties with capitalization,
         * as 8.3 filenames allow uppercase letters only.
         *
         * Theoretically it would be possible to leave
         * the 8.3 entry alone if the basename and the
         * extension have no mixed capitalization.
         */
        if(name[0] == '.' &&
           ((name[1] == '.' && name[2] == '\0') ||
            name[1] == '\0')
          )
            lfn_entry_count = 0;
    }
    else
    {
        memcpy(buffer, name, 8);

        /* Minimize 8.3 name clashes by appending
         * the lower byte of the cluster number.
         */
        uint8_t num = dir_entry->cluster & 0xff;

        buffer[6] = (num < 0xa0) ? ('0' + (num >> 4)) : ('a' + (num >> 4));
        num &= 0x0f;
        buffer[7] = (num < 0x0a) ? ('0' + num) : ('a' + num);
    }
    if(buffer[0] == FAT16_DIRENTRY_DELETED)
        buffer[0] = 0x05;

    /* fill directory entry buffer */
    memset(&buffer[11], 0, sizeof(buffer) - 11);
    buffer[0x0b] = dir_entry->attributes;
#if FAT16_DATETIME_SUPPORT
    buffer[0x16] = (dir_entry->modification_time >> 0) & 0xff;
    buffer[0x17] = (dir_entry->modification_time >> 8) & 0xff;
    buffer[0x18] = (dir_entry->modification_date >> 0) & 0xff;
    buffer[0x19] = (dir_entry->modification_date >> 8) & 0xff;
#endif
    buffer[0x1a] = (dir_entry->cluster >> 0) & 0xff;
    buffer[0x1b] = (dir_entry->cluster >> 8) & 0xff;
    buffer[0x1c] = (dir_entry->file_size >> 0) & 0xff;
    buffer[0x1d] = (dir_entry->file_size >> 8) & 0xff;
    buffer[0x1e] = (dir_entry->file_size >> 16) & 0xff;
    buffer[0x1f] = (dir_entry->file_size >> 24) & 0xff;

    /* write to disk */
    if(!device_write(offset + (uint32_t) lfn_entry_count * 32, buffer, sizeof(buffer)))
        return 0;
    
    /* calculate checksum of 8.3 name */
    uint8_t checksum = buffer[0];
    for(uint8_t i = 1; i < 11; ++i)
        checksum = ((checksum >> 1) | (checksum << 7)) + buffer[i];
    
    /* write lfn entries */
    for(uint8_t lfn_entry = lfn_entry_count; lfn_entry > 0; --lfn_entry)
    {
        memset(buffer, 0xff, sizeof(buffer));
        
        /* set file name */
        const char* long_name_curr = name + (lfn_entry - 1) * 13;
        uint8_t i = 1;
        while(i < 0x1f)
        {
            buffer[i++] = *long_name_curr;
            buffer[i++] = 0;

            switch(i)
            {
                case 0x0b:
                    i = 0x0e;
                    break;
                case 0x1a:
                    i = 0x1c;
                    break;
            }

            if(!*long_name_curr++)
                break;
        }
        
        /* set index of lfn entry */
        buffer[0x00] = lfn_entry;
        if(lfn_entry == lfn_entry_count)
            buffer[0x00] |= FAT16_DIRENTRY_LFNLAST;

        /* mark as lfn entry */
        buffer[0x0b] = 0x0f;

        /* set 8.3 checksum */