fat16.c

MMC/SD操作

        }
    }
    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
 * 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(struct fat16_fs_struct* fs, const struct fat16_dir_entry_struct* dir_entry)
{
#if FAT16_WRITE_SUPPORT
    if(!fs || !dir_entry)
        return 0;
    
    device_write_t device_write = fs->partition->device_write;
    uint32_t offset = dir_entry->entry_offset;
    uint8_t name_len = strlen(dir_entry->long_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(dir_entry->long_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, dir_entry->long_name, name_len);
    }
    else
    {
        memcpy(buffer, dir_entry->long_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);
    }

    /* fill directory entry buffer */
    memset(&buffer[11], 0, sizeof(buffer) - 11);
    buffer[0x0b] = dir_entry->attributes;
    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, 0, sizeof(buffer));
        memset(&buffer[0x01], 0xff, 10);
        memset(&buffer[0x0e], 0xff, 12);
        memset(&buffer[0x1c], 0xff, 4);
        
        buffer[0x00] = lfn_entry;
        if(lfn_entry == lfn_entry_count)
            buffer[0x00] |= FAT16_DIRENTRY_LFNLAST;

        /* set file name */
        const char* long_name_curr = dir_entry->long_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;
        }
        
        /* mark as lfn entry */
        buffer[0x0b] = 0x0f;

        /* set checksum */
        buffer[0x0d] = checksum;

        /* write entry */
        device_write(offset, buffer, sizeof(buffer));
    
        offset += sizeof(buffer);
    }
    
    return 1;

#else
    return 0;
#endif
}

/**
 * \ingroup fat16_file
 * Creates a file.
 *
 * Creates a file and obtains the directory entry of the
 * new file. If the file to create already exists, the
 * directory entry of the existing file will be returned
 * within the dir_entry parameter.
 *
 * \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] parent The handle of the directory in which to create the file.
 * \param[in] file The name of the file to create.
 * \param[out] dir_entry The directory entry to fill for the new file.
 * \returns 0 on failure, 1 on success.
 * \see fat16_delete_file
 */
uint8_t fat16_create_file(struct fat16_dir_struct* parent, const char* file, struct fat16_dir_entry_struct* dir_entry)
{
#if FAT16_WRITE_SUPPORT
    if(!parent || !file || !file[0])
        return 0;

    /* check if the file already exists */
    while(1)
    {
        if(!fat16_read_dir(parent, dir_entry))
            break;

        if(strcmp(file, dir_entry->long_name) == 0)
        {
            fat16_reset_dir(parent);
            return 1;
        }
    }

    memset(dir_entry, 0, sizeof(*dir_entry));
    
    strncpy(dir_entry->long_name, file, sizeof(dir_entry->long_name));
    dir_entry->long_name[sizeof(dir_entry->long_name)] = '\0';

    /* search for a place where to write the directory entry to disk */
    uint8_t free_dir_entries_needed = strlen(file) / 13 + 1 + 1;
    uint8_t free_dir_entries_found = 0;
    struct fat16_fs_struct* fs = parent->fs;
    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_cluster(fs, cluster_num);
                    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;
                    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)
        {
            if(!first_char)
            {
                /* Mark the directory entries as deleted.
                 * This is needed if our new directory entry is
                 * too large to fit into the current cluster.
                 */
                first_char = FAT16_DIRENTRY_DELETED;
                if(!fs->partition->device_write(offset, &first_char, sizeof(first_char)))
                    return 0;
            }

            /* 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;
        }
    }
    
    /* write directory entry to disk */
    dir_entry->entry_offset = dir_entry_offset;
    if(!fat16_write_dir_entry(fs, dir_entry))
        return 0;
    
    return 1;
    
#else
    return 0;
#endif
}

/**
 * \ingroup fat16_file
 * Deletes a file or directory.
 *
 * It is not checked if the file to delete is a directory.
 * If a directory is deleted without first deleting its
 * subdirectories and files, disk space occupied by these
 * files will get wasted as there is no chance to release
 * it and mark it as free.
 * 
 * \param[in] fs The filesystem on which to operate.
 * \param[in] dir_entry The directory entry of the file to delete.
 * \returns 0 on failure, 1 on success.
 * \see fat16_create_file
 */
uint8_t fat16_delete_file(struct fat16_fs_struct* fs, struct fat16_dir_entry_struct* dir_entry)
{
#if FAT16_WRITE_SUPPORT
    if(!fs || !dir_entry)
        return 0;

    /* get offset of the file's directory entry */
    uint32_t dir_entry_offset = dir_entry->entry_offset;
    if(!dir_entry_offset)
        return 0;

    uint8_t buffer[12];
    while(1)
    {
        /* read directory entry */
        if(!fs->partition->device_read(dir_entry_offset, buffer, sizeof(buffer)))
            return 0;
        
        /* mark the directory entry as deleted */
        buffer[0] = FAT16_DIRENTRY_DELETED;
        
        /* write back entry */
        if(!fs->partition->device_write(dir_entry_offset, buffer, sizeof(buffer)))
            return 0;

        /* check if we deleted the whole entry */
        if(buffer[11] != 0x0f)
            break;

        dir_entry_offset += 32;
    }

    /* We deleted the directory entry. The next thing to do is
     * marking all occupied clusters as free.
     */
    uint16_t cluster_num = dir_entry->cluster;
    uint16_t cluster_num_next;
    while(cluster_num)
    {
        /* get next cluster before freeing the previous one */
        cluster_num_next = fat16_get_next_cluster(fs, cluster_num);

        /* free cluster */
        fat16_free_cluster(fs, cluster_num);
        
        cluster_num = cluster_num_next;
    }
    
    return 1;
#else
    return 0;
#endif
}