fat16.c

AVR读取SD卡里FAT格式内容的源程序

 * \param[in] whence Affects the way \c offset is interpreted, see above.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat16_seek_file(struct fat16_file_struct* fd, int32_t* offset, uint8_t whence)
{
    if(!fd || !offset)
        return 0;

    uint32_t new_pos = fd->pos;
    switch(whence)
    {
        case FAT16_SEEK_SET:
            new_pos = *offset;
            break;
        case FAT16_SEEK_CUR:
            new_pos += *offset;
            break;
        case FAT16_SEEK_END:
            new_pos = fd->dir_entry.file_size + *offset;
            break;
        default:
            return 0;
    }

    if(new_pos > fd->dir_entry.file_size && !fat16_resize_file(fd, new_pos))
        return 0;

    fd->pos = new_pos;
    fd->pos_cluster = 0;

    *offset = new_pos;
    return 1;
}

/**
 * \ingroup fat16_file
 * Resizes a file to have a specific size.
 *
 * Enlarges or shrinks the file pointed to by the file descriptor to have
 * exactly the specified size.
 *
 * If the file is truncated, all bytes having an equal or larger offset
 * than the given size are lost. If the file is expanded, the additional
 * bytes are allocated.
 *
 * \note Please be aware that this function just allocates or deallocates disk
 * space, it does not explicitely clear it. To avoid data leakage, this
 * must be done manually.
 *
 * \param[in] fd The file decriptor of the file which to resize.
 * \param[in] size The new size of the file.
 * \returns 0 on failure, 1 on success.
 */
uint8_t fat16_resize_file(struct fat16_file_struct* fd, uint32_t size)
{
#if FAT16_WRITE_SUPPORT
    if(!fd)
        return 0;

    uint16_t cluster_num = fd->dir_entry.cluster;
    uint16_t cluster_size = fd->fs->header.cluster_size;
    uint32_t size_new = size;

    do
    {
        if(cluster_num == 0 && size_new == 0)
            /* the file stays empty */
            break;

        /* seek to the next cluster as long as we need the space */
        while(size_new > cluster_size)
        {
            /* get next cluster of file */
            uint16_t cluster_num_next = fat16_get_next_cluster(fd->fs, cluster_num);
            if(cluster_num_next)
            {
                cluster_num = cluster_num_next;
                size_new -= cluster_size;
            }
            else
            {
                break;
            }
        }

        if(size_new > cluster_size || cluster_num == 0)
        {
            /* Allocate new cluster chain and append
             * it to the existing one, if available.
             */
            uint16_t cluster_count = size_new / cluster_size;
            if((uint32_t) cluster_count * cluster_size < size_new)
                ++cluster_count;
            uint16_t cluster_new_chain = fat16_append_clusters(fd->fs, cluster_num, cluster_count);
            if(!cluster_new_chain)
                return 0;

            if(!cluster_num)
            {
                cluster_num = cluster_new_chain;
                fd->dir_entry.cluster = cluster_num;
            }
        }

        /* write new directory entry */
        fd->dir_entry.file_size = size;
        if(size == 0)
            fd->dir_entry.cluster = 0;
        if(!fat16_write_dir_entry(fd->fs, &fd->dir_entry))
            return 0;

        if(size == 0)
        {
            /* free all clusters of file */
            fat16_free_clusters(fd->fs, cluster_num);
        }
        else if(size_new <= cluster_size)
        {
            /* free all clusters no longer needed */
            fat16_terminate_clusters(fd->fs, cluster_num);
        }

    } while(0);

    /* correct file position */
    if(size < fd->pos)
    {
        fd->pos = size;
        fd->pos_cluster = 0;
    }

    return 1;
#else
    return 0;
#endif
}

/**
 * \ingroup fat16_dir
 * Opens a directory.
 *
 * \param[in] fs The filesystem on which the directory to open resides.
 * \param[in] dir_entry The directory entry which stands for the directory to open.
 * \returns An opaque directory descriptor on success, 0 on failure.
 * \see fat16_close_dir
 */
struct fat16_dir_struct* fat16_open_dir(struct fat16_fs_struct* fs, const struct fat16_dir_entry_struct* dir_entry)
{
    if(!fs || !dir_entry || !(dir_entry->attributes & FAT16_ATTRIB_DIR))
        return 0;

#if USE_DYNAMIC_MEMORY
    struct fat16_dir_struct* dd = malloc(sizeof(*dd));
    if(!dd)
        return 0;
#else
    struct fat16_dir_struct* dd = fat16_dir_handlers;
    uint8_t i;
    for(i = 0; i < FAT16_DIR_COUNT; ++i)
    {
        if(!dd->fs)
            break;

        ++dd;
    }
    if(i >= FAT16_DIR_COUNT)
        return 0;
#endif
    
    memcpy(&dd->dir_entry, dir_entry, sizeof(*dir_entry));
    dd->fs = fs;
    dd->entry_next = 0;

    return dd;
}

/**
 * \ingroup fat16_dir
 * Closes a directory descriptor.
 *
 * This function destroys a directory descriptor which was
 * previously obtained by calling fat16_open_dir(). When this
 * function returns, the given descriptor will be invalid.
 *
 * \param[in] dd The directory descriptor to close.
 * \see fat16_open_dir
 */
void fat16_close_dir(struct fat16_dir_struct* dd)
{
    if(dd)
#if USE_DYNAMIC_MEMORY
        free(dd);
#else
        dd->fs = 0;
#endif
}

/**
 * \ingroup fat16_dir
 * Reads the next directory entry contained within a parent directory.
 *
 * \param[in] dd The descriptor of the parent directory from which to read the entry.
 * \param[out] dir_entry Pointer to a buffer into which to write the directory entry information.
 * \returns 0 on failure, 1 on success.
 * \see fat16_reset_dir
 */
uint8_t fat16_read_dir(struct fat16_dir_struct* dd, struct fat16_dir_entry_struct* dir_entry)
{
    if(!dd || !dir_entry)
        return 0;

    if(dd->dir_entry.cluster == 0)
    {
        /* read entry from root directory */
        if(fat16_read_root_dir_entry(dd->fs, dd->entry_next, dir_entry))
        {
            ++dd->entry_next;
            return 1;
        }
    }
    else
    {
        /* read entry from a subdirectory */
        if(fat16_read_sub_dir_entry(dd->fs, dd->entry_next, &dd->dir_entry, dir_entry))
        {
            ++dd->entry_next;
            return 1;
        }
    }

    /* restart reading */
    dd->entry_next = 0;

    return 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_next = 0;
    return 1;
}

/**
 * \ingroup fat16_fs
 * Searches for space where to store a directory entry.
 *
 * \param[in] fs The filesystem on which to operate.
 * \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 = fs->header.cluster_zero_offset +
                     (uint32_t) (cluster_num - 2) * fs->header.cluster_size;
            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.
         *