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Command and Variable Index
##########################
There are currently no Command and Variable Index entries.
.. COMMENT: @printindex fn

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.. include:: filesystem.rst .. COMMENT: %**end of header
.. COMMENT: COPYRIGHT (c) 1989-2013.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. COMMENT: Master file for the Filesystem Design Guide
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. COMMENT: The following determines which set of the tables and figures we will use.
.. COMMENT: We default to ASCII but if available TeX or HTML versions will
.. COMMENT: be used instead.
.. COMMENT: @clear use-html
.. COMMENT: @clear use-tex
.. COMMENT: The following variable says to use texinfo or html for the two column
.. COMMENT: texinfo tables. For somethings the format does not look good in html.
.. COMMENT: With our adjustment to the left column in TeX, it nearly always looks
.. COMMENT: good printed.
.. COMMENT: Custom whitespace adjustments. We could fiddle a bit more.
.. COMMENT: Title Page Stuff
.. COMMENT: I don't really like having a short title page. -joel
.. COMMENT: @shorttitlepage RTEMS Filesystem Design Guide
=============================
RTEMS Filesystem Design Guide
=============================
.. COMMENT: COPYRIGHT (c) 1988-2015.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.
.. COMMENT: The following puts a space somewhere on an otherwise empty page so we
.. COMMENT: can force the copyright description onto a left hand page.
COPYRIGHT © 1988 - 2015.
On-Line Applications Research Corporation (OAR).
The authors have used their best efforts in preparing
this material. These efforts include the development, research,
and testing of the theories and programs to determine their
effectiveness. No warranty of any kind, expressed or implied,
with regard to the software or the material contained in this
document is provided. No liability arising out of the
application or use of any product described in this document is
assumed. The authors reserve the right to revise this material
and to make changes from time to time in the content hereof
without obligation to notify anyone of such revision or changes.
The RTEMS Project is hosted at http://www.rtems.org. Any
inquiries concerning RTEMS, its related support components, or its
documentation should be directed to the Community Project hosted athttp://www.rtems.org.
Any inquiries for commercial services including training, support, custom
development, application development assistance should be directed tohttp://www.rtems.com.
.. COMMENT: This prevents a black box from being printed on "overflow" lines.
.. COMMENT: The alternative is to rework a sentence to avoid this problem.
Table of Contents
-----------------
.. toctree::
:maxdepth: 3
:numbered:
preface
pathname_eval
system_init
mounting_and_unmounting
call_development
fileystem_implmentation
in-memory
minature_in-memory
trivial_ftp
command_and_variable

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Miniature In-Memory Filesystem
##############################
This chapter describes the Miniature In-Memory FileSystem (miniIMFS).
The miniIMFS is a reduced feature version of the IMFS designed to
provide minimal functionality and have a low memory footprint.
This chapter should be written after the IMFS chapter is completed
and describe the implementation of the mini-IMFS.
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

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Mounting and Unmounting Filesystems
###################################
Mount Points
============
The following is the list of the characteristics of a mount point:
- The mount point must be a directory. It may have files and other
directories under it. These files and directories will be hidden when the
filesystem is mounted.
- The task must have read/write/execute permissions to the mount point
or the mount attempt will be rejected.
- Only one filesystem can be mounted to a single mount point.
- The Root of the mountable filesystem will be referenced by the name
of the mount point after the mount is complete.
Mount Table Chain
=================
The mount table chain is a dynamic list of structures that describe
mounted filesystems a specific points in the filesystem hierarchy. It is
initialized to an empty state during the base filesystem initialization.
The mount operation will add entries to the mount table chain. The
un-mount operation will remove entries from the mount table chain.
Each entry in the mount table chain is of the following type:
.. code:: c
struct rtems_filesystem_mount_table_entry_tt
{
Chain_Node Node;
rtems_filesystem_location_info_t mt_point_node;
rtems_filesystem_location_info_t mt_fs_root;
int options;
void \*fs_info;
rtems_filesystem_limits_and_options_t pathconf_limits_and_options;
/*
* When someone adds a mounted filesystem on a real device,
* this will need to be used.
*
* The best option long term for this is probably an
* open file descriptor.
\*/
char \*dev;
};
*Node*
The Node is used to produce a linked list of mount table entry nodes.
*mt_point_node*
The mt_point_node contains all information necessary to access the
directory where a filesystem is mounted onto. This element may contain
memory that is allocated during a path evaluation of the filesystem
containing the mountpoint directory. The generic code allows this
memory to be returned by unmount when the filesystem identified by
mt_fs_root is unmounted.
*mt_fs_root*
The mt_fs_root contains all information necessary to identify the root
of the mounted filesystem. The user is never allowed access to this
node by the generic code, but it is used to identify to the mounted
filesystem where to start evaluation of pathnames at.
*options*
XXX
*fs_info*
The fs_info element is a location available for use by the mounted file
system to identify unique things applicable to this instance of the file
system. For example the IMFS uses this space to provide node
identification that is unique for each instance (mounting) of the filesystem.
*pathconf_limits_and_options*
XXX
*dev*
This character string represents the device where the filesystem will reside.
Adding entries to the chain during mount
========================================
When a filesystem is mounted, its presence and location in the file
system hierarchy is recorded in a dynamic list structure known as a chain.
A unique rtems_filesystem_mount_table_entry_tt structure is logged for
each filesystem that is mounted. This includes the base filesystem.
Removing entries from the chain during unmount
==============================================
When a filesystem is dismounted its entry in the mount table chain is
extracted and the memory for this entry is freed.
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

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Pathname Evaluation
###################
This chapter describes the pathname evaluation process for the
RTEMS Filesystem Infrastructure.
.. code:: c
XXX Include graphic of the path evaluation process
Pathname Evaluation Handlers
============================
There are two pathname evaluation routines. The handler patheval()
is called to find, verify privlages on and return information on a node
that exists. The handler evalformake() is called to find, verify
permissions, and return information on a node that is to become a parent.
Additionally, evalformake() returns a pointer to the start of the name of
the new node to be created.
Pathname evaluation is specific to a filesystem.
Each filesystem is required to provide both a patheval() and an evalformake()
routine. Both of these routines gets a name to evaluate and a node indicating
where to start the evaluation.
Crossing a Mount Point During Path Evaluation
=============================================
If the filesystem supports the mount command, the evaluate routines
must handle crossing the mountpoint. The evaluate routine should evaluate
the name upto the first directory node where the new filesystem is mounted.
The filesystem may process terminator characters prior to calling the
evaluate routine for the new filesystem. A pointer to the portion of the
name which has not been evaluated along with the root node of the new
file system ( gotten from the mount table entry ) is passed to the correct
mounted filesystem evaluate routine.
The rtems_filesystem_location_info_t Structure
==============================================
The ``rtems_filesystem_location_info_t`` structure contains all information
necessary for identification of a node.
The generic rtems filesystem code defines two global
rtems_filesystem_location_info_t structures, the``rtems_filesystem_root`` and the ``rtems_filesystem_current``.
Both are initially defined to be the root node of the base filesystem.
Once the chdir command is correctly used the ``rtems_filesystem_current``
is set to the location specified by the command.
The filesystem generic code peeks at the first character in the name to be
evaluated. If this character is a valid seperator, the``rtems_filesystem_root`` is used as the node to start the evaluation
with. Otherwise, the ``rtems_filesystem_current`` node is used as the
node to start evaluating with. Therefore, a valid
rtems_filesystem_location_info_t is given to the evaluate routine to start
evaluation with. The evaluate routines are then responsible for making
any changes necessary to this structure to correspond to the name being
parsed.
.. code:: c
struct rtems_filesystem_location_info_tt {
void \*node_access;
rtems_filesystem_file_handlers_r \*handlers;
rtems_filesystem_operations_table \*ops;
rtems_filesystem_mount_table_entry_t \*mt_entry;
};
*node_access*
This element is filesystem specific. A filesystem can define and store
any information necessary to identify a node at this location. This element
is normally filled in by the filesystem’s evaluate routine. For the
filesystem’s root node, the filesystem’s initilization routine should
fill this in, and it should remain valid until the instance of the
filesystem is unmounted.
*handlers*
This element is defined as a set of routines that may change within a
given filesystem based upon node type. For example a directory and a
memory file may have to completely different read routines. This element
is set to an initialization state defined by the mount table, and may
be set to the desired state by the evaluation routines.
*ops*
This element is defined as a set of routines that remain static for the
filesystem. This element identifies entry points into the filesystem
to the generic code.
*mt_entry*
This element identifies the mount table entry for this instance of the
filesystem.
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

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Preface
#######
This document describes the implementation of the RTEMS filesystem
infrastructure. This infrastructure supports the following
capabilities:
- Mountable file systems
- Hierarchical file system directory structure
- POSIX compliant set of routines for the manipulation of files and directories
- Individual file and directory support for the following:
# Permissions for read, write and execute
# User ID
# Group ID
# Access time
# Modification time
# Creation time
- Hard links to files and directories
- Symbolic links to files and directories
This has been implemented to provide the framework for a UNIX-like
file system support. POSIX file and directory functions have been
implemented that allow a standard method of accessing file, device and
directory information within file systems. The file system concept that
has been implemented allows for expansion and adaptation of the file
system to a variety of existing and future data storage devices. To this
end, file system mount and unmount capabilities have been included in this
RTEMS framework.
This framework slightly alters the manner in which devices are handled
under RTEMS from that of public release 4.0.0 and earlier. Devices that
are defined under a given RTEMS configuration will now be registered as
files in a mounted file system. Access to these device drivers and their
associated devices may now be performed through the traditional file system
open(), read(), write(), lseek(), fstat() and ioctl() functions in addition
to the interface provided by the IO Manager in the RTEMS Classic API.
An In-Memory File System (IMFS) is included which provides full POSIX
filesystem functionality yet is RAM based. The IMFS maintains a
node structure for each file, device, and directory in each mounted
instantiation of its file system. The node structure is used to
manage ownership, access rights, access time, modification time,
and creation time. A union of structures within the IMFS nodal
structure provide for manipulation of file data, device selection,
or directory content as required by the nodal type. Manipulation of
these properties is accomplished through the POSIX set of file and
directory functions. In addition to being useful in its own right,
the IMFS serves as a full featured example filesystem.
The intended audience for this document is those persons implementing
their own filesystem. Users of the filesystem may find information
on the implementation useful. But the user interface to the filesystem
is through the ISO/ANSI C Library and POSIX 1003.1b file and directory
APIs.
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

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System Initialization
#####################
After the RTEMS initialization is performed, the application’s
initialization will be performed. Part of initialization is a call to
rtems_filesystem_initialize(). This routine will mount the ‘In Memory File
System’ as the base filesystem. Mounting the base filesystem consists
of the following:
- Initialization of mount table chain control structure
- Allocation of a ``jnode`` structure that will server as the root node
of the ‘In Memory Filesystem’
- Initialization of the allocated ``jnode`` with the appropriate OPS,
directory handlers and pathconf limits and options.
- Allocation of a memory region for filesystem specific global
management variables
- Creation of first mount table entry for the base filesystem
- Initialization of the first mount table chain entry to indicate that
the mount point is NULL and the mounted filesystem is the base file
system
After the base filesystem has been mounted, the following operations are
performed under its directory structure:
- Creation of the /dev directory
- Registration of devices under /dev directory
Base Filesystem
===============
RTEMS initially mounts a RAM based file system known as the base file system.
The root directory of this file system tree serves as the logical root of the
directory hierarchy (Figure 3). Under the root directory a ‘/dev’ directory
is created under which all I/O device directories and files are registered as
part of the file system hierarchy.
.. code:: c
Figure of the tree structure goes here.
A RAM based file system draws its management resources from memory. File and
directory nodes are simply allocated blocks of memory. Data associated with
regular files is stored in collections of memory blocks. When the system is
turned off or restarted all memory-based components of the file system are
lost.
The base file system serves as a starting point for the mounting of file
systems that are resident on semi-permanent storage media. Examples of such
media include non- volatile memory, flash memory and IDE hard disk drives
(Figure 3). File systems of other types will be mounted onto mount points
within the base file system or other file systems that are subordinate to the
base file system. The framework set up under the base file system will allow
for these new file system types and the unique data and functionality that is
required to manage the future file systems.
Base Filesystem Mounting
------------------------
At present, the first file system to be mounted is the ‘In Memory File
System’. It is mounted using a standard MOUNT() command in which the mount
point is NULL. This flags the mount as the first file system to be
registered under the operating system and appropriate initialization of file
system management information is performed (See figures 4 and 5). If a
different file system type is desired as the base file system, alterations
must be made to base_fs.c. This routine handles the mount of the base file
system.
.. code:: c
Figure of the mount table chain goes here.
Once the root of the base file system has been established and it has been
recorded as the mount point of the base file system, devices are integrated
into the base file system. For every device that is configured into the
system (See ioman.c) a device registration process is performed. Device
registration produces a unique dev_t handle that consists of a major and
minor device number. In addition, the configuration information for each
device contains a text string that represents the fully qualified pathname to
that device’s place in the base file system’s hierarchy. A file system node
is created for the device along the specified registration path.
.. code:: c
Figure of the Mount Table Processing goes here.
Note: Other file systems can be mounted but they are mounted onto points
(directory mount points) in the base file system.
.. COMMENT: COPYRIGHT (c) 1988-2002.
.. COMMENT: On-Line Applications Research Corporation (OAR).
.. COMMENT: All rights reserved.

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Trivial FTP Client Filesystem
#############################
This chapter describes the Trivial FTP (TFTP) Client Filesystem.
This chapter should be written after the IMFS chapter is completed
and describe the implementation of the TFTP.