File Systems Overview

Purpose

Provides file system implementations —file server fsy plug-ins — for devices that are reasonably expected to be used on a Symbian platform device. The file systems implement a storage and access format most appropriate to the media. Please see a file system's guide for its specific purpose.

Architecture

The File Systems collection provides several kinds of file system implementations. File system binaries are built as FSY plugins that are loaded (added and mounted) by the file server; either at startup or as required such as when a device is physically attached to the phone (inserting a memory card into the card slot).

The file server uses these implementations to access data on different media.

Description

The File Systems collection consists of a series of file server plugins, one for each file system. The various systems are loaded into a file server instance. Different devices use different file systems based on the characteristics of the storage medium.

The following table lists several file systems and the different media that use them.

The ROM file system is implemented as part of the file server component. The other files systems are implemented as separate file server plugins, which may be loaded using ESTART or as part of a mounting operation.

All file system plugins files have .fsy extensions.

File System Summary

The following file system plug-ins are provided:

• Composite File System (ecomp.fsy): The Composite File System for NAND flash devices presents a single drive Z: to the File Server that layers thinly over both the core ROM and the ROFS file systems. It redirects File Server requests to the core ROM or ROFS as required. See Flash Translation Layer Technology for more information on why this is required.

  This unifies the file systems for flash devices (ROM, ROFS and FAT file systems) into a common file system that is used with drive Z:. The file server will direct requests to the required file system as required.

• FAT File System (efat.fsy or elocal.fsy when built for an emulator target.) : The FAT File System implements a file system that supports the VFAT standard. This is used for user data storage on NAND Flash, internal RAM drives, and removable media.

  This is the file system that was originally used by IBM PCs and is an industry standard for file systems. It is supported by all operating systems that execute on PCs. Symbian platform FAT only supports FAT12 and FAT16 types.

• FAT32 File System (efat32.fsy): The FAT32 File System implements the enhanced version of the FAT file system standard that includes FAT32 support.

  The FAT32 file system is an update of the industry standard FAT file system. The Symbian platform FAT32 file system supports the FAT12, FAT16 and FAT32 file systems.

• ISO9660 File System (iso9660.fsy): The ISO9660 File System implements a ISO9660 file system, that reads CDROM and DVD-ROM. This is only for the internal X86 port.

  The ISO9660 is an internationally agreed standard for the file system used by CD-ROM and DVD-ROM media.

  Note: ISO9660 is for Symbian internal use only.

• LFFS File System (elffs.fsy): The LFFS File System provides data storage on NOR type flash memory, and is portable to a wide range of Flash devices.

  LFFS is designed specifically to be used with NOR flash and has the ability to protect itself against power loss.

• NTFS File System (ntfs.fsy): The NTFS File System provides read-only support for the NTFS file system standards. This is only for the internal X86 port.

  This is the file system for Windows NT, Windows 2000, Windows-XP, Windows Server 2003, Windows Server 2008 and Windows Vista.

  Note: NTFS is for Symbian internal use only.

• ROFS File System (erofs.fsy): The Read-only File System (ROFS) supports a ROM-structured local file system that can be located on NAND flash, or other media, where executables are not executed in place (non-XIP).

  ROFS stands for Read Only File System and is used for accessing code storage on media that cannot be executed in that media (otherwise known as non-XIP storage), for example NAND flash.

• ROM File System (No FSY, ROM is the default file system build defined by f32.iby): The ROM file system is used to access the "core ROM image": this contains files that are copied from NAND Flash storage into RAM on boot.

  This is the file system that is used when the phone boots up.

• USB Mass Storage File System (msfs.fsy and possibly msfs_db.fsy, depending on configuration): The USB Mass Storage File System is provided to support a licensee-provided USB mass storage application, which allows a desktop host computer access to a FAT-formatted drive on the phone.

  The USB Mass Storage Server is used when a USB memory device is connected directly to the device executing Symbian platform.

  The USB Mass Storage File System is used when the media on the device is accessed by an external device i.e. a PC when it is in "USB mass storage" mode.

Using File System Plug-ins

The file systems are used to allow kernel access to data on a media storage device such as Flash, MMC cards, SD cards, etc. A file systems FSY plug-in must be added to the file server and mounted before the kernel is granted access.

Accessing a file system specific device requires:

• Adding a file system to the file server using RFs::AddFileSystem()

• Mounting the file system using RFs::MountFileSystem()

The file server handles all requests to access a mounted file system.