source: rtems-docs/filesystem/filesystem.rst @ 9e27b86

:orphan:



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.. COMMENT: Master file for the Filesystem Design Guide

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.. COMMENT: @shorttitlepage RTEMS Filesystem Design Guide

=============================
RTEMS Filesystem Design Guide
=============================

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.. COMMENT: On-Line Applications Research Corporation (OAR).

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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.

RTEMS Filesystem Design Guide
#############################

.. COMMENT: COPYRIGHT (c) 1989-2011.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

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.

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.

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.

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.

System Call Development Notes
#############################

This set of routines represents the application’s interface to files and directories
under the RTEMS filesystem. All routines are compliant with POSIX standards if a
specific interface has been established. The list below represents the routines that have
been included as part of the application’s interface.

# access()

# chdir()

# chmod()

# chown()

# close()

# closedir()

# dup()

# dup2()

# fchmod()

# fcntl()

# fdatasync()

# fpathconf()

# fstat()

# ioctl()

# link()

# lseek()

# mkdir()

# mkfifo()

# mknod()

# mount()

# open()

# opendir()

# pathconf()

# read()

# readdir()

# unmount()

The sections that follow provide developmental information concerning each
of these functions.

.. COMMENT: @page

access
======

**File:**

access.c

**Processing:**

This routine is layered on the stat() function. It acquires the current
status information for the specified file and then determines if the
caller has the ability to access the file for read, write or execute
according to the mode argument to this function.

**Development Comments:**

This routine is layered on top of the stat() function. As long as the
st_mode element in the returned structure follow the standard UNIX
conventions, this function should support other filesystems without
alteration.

.. COMMENT: @page

chdir
=====

**File:**

chdir.c

**Processing:**

This routine will determine if the pathname that we are attempting to make
that current directory exists and is in fact a directory. If these
conditions are met the global indication of the current directory
(rtems_filesystem_current) is set to the rtems_filesystem_location_info_t
structure that is returned by the rtems_filesystem_evaluate_path()
routine.

**Development Comments:**

This routine is layered on the rtems_filesystem_evaluate_path() routine
and the filesystem specific OP table function node_type().

The routine node_type() must be a routine provided for each filesystem
since it must access the filesystems node information to determine which
of the following types the node is:

- RTEMS_FILESYSTEM_DIRECTORY

- RTEMS_FILESYSTEM_DEVICE

- RTEMS_FILESYSTEM_HARD_LINK

- RTEMS_FILESYSTEM_MEMORY_FILE

This acknowledges that the form of the node management information can
vary from one filesystem implementation to another.

RTEMS has a special global structure that maintains the current directory
location. This global variable is of type rtems_filesystem_location_info_t
and is called rtems_filesystem_current. This structure is not always
valid. In order to determine if the structure is valid, you must first
test the node_access element of this structure. If the pointer is NULL,
then the structure does not contain a valid indication of what the current
directory is.

.. COMMENT: @page

chmod
=====

**File:**

chmod.c

**Processing:**

This routine is layered on the open(), fchmod() and close() functions. As
long as the standard interpretation of the mode_t value is maintained,
this routine should not need modification to support other filesystems.

**Development Comments:**

The routine first determines if the selected file can be open with
read/write access.  This is required to allow modification of the mode
associated with the selected path.

The fchmod() function is used to actually change the mode of the path
using the integer file descriptor returned by the open() function.

After mode modification, the open file descriptor is closed.

.. COMMENT: @page

chown
=====

**File:**

chown.c

**Processing:**

This routine is layered on the rtems_filesystem_evaluate_path() and the
file system specific chown() routine that is specified in the OPS table
for the file system.

**Development Comments:**

rtems_filesystem_evaluate_path() is used to determine if the path
specified actually exists. If it does a rtems_filesystem_location_info_t
structure will be obtained that allows the shell function to locate the
OPS table that is to be used for this filesystem.

It is possible that the chown() function that should be in the OPS table
is not defined. A test for a non-NULL OPS table chown() entry is performed
before the function is called.

If the chown() function is defined in the indicated OPS table, the
function is called with the rtems_filesystem_location_info_t structure
returned from the path evaluation routine, the desired owner, and group
information.

.. COMMENT: @page

close
=====

**File:**

close.c

**Processing:**

This routine will allow for the closing of both network connections and
file system devices. If the file descriptor is associated with a network
device, the appropriate network function handler will be selected from a
table of previously registered network functions (rtems_libio_handlers)
and that function will be invoked.

If the file descriptor refers to an entry in the filesystem, the
appropriate handler will be selected using information that has been
placed in the file control block for the device (rtems_libio_t structure).

**Development Comments:**

rtems_file_descriptor_type examines some of the upper bits of the file
descriptor index. If it finds that the upper bits are set in the file
descriptor index, the device referenced is a network device.

Network device handlers are obtained from a special registration table
(rtems_libio_handlers) that is set up during network initialization. The
network handler invoked and the status of the network handler will be
returned to the calling process.

If none of the upper bits are set in the file descriptor index, the file
descriptor refers to an element of the RTEMS filesystem.

The following sequence will be performed for any filesystem file
descriptor:

# Use the rtems_libio_iop() function to obtain the rtems_libio_t
  structure for the file descriptor

# Range check the file descriptor using rtems_libio_check_fd()

# Determine if there is actually a function in the selected handler
  table that processes the close() operation for the filesystem and node
  type selected.  This is generally done to avoid execution attempts on
  functions that have not been implemented.

# If the function has been defined it is invoked with the file control
  block pointer as its argument.

# The file control block that was associated with the open file
  descriptor is marked as free using rtems_libio_free().

# The return code from the close handler is then passed back to the
  calling program.

.. COMMENT: @page

closedir
========

**File:**

closedir.c

**Processing:**

The code was obtained from the BSD group. This routine must clean up the
memory resources that are required to track an open directory. The code is
layered on the close() function and standard memory free() functions. It
should not require alterations to support other filesystems.

**Development Comments:**

The routine alters the file descriptor and the index into the DIR
structure to make it an invalid file descriptor. Apparently the memory
that is about to be freed may still be referenced before it is
reallocated.

The dd_buf structure’s memory is reallocated before the control structure
that contains the pointer to the dd_buf region.

DIR control memory is reallocated.

The close() function is used to free the file descriptor index.

.. COMMENT: @page

dup()      Unimplemented
========================

**File:**

dup.c

**Processing:**

**Development Comments:**

.. COMMENT: @page

dup2()      Unimplemented
=========================

**File:**

dup2.c

**Processing:**

**Development Comments:**

.. COMMENT: @page

fchmod
======

**File:**

fchmod.c

**Processing:**

This routine will alter the permissions of a node in a filesystem. It is
layered on the following functions and macros:

- rtems_file_descriptor_type()

- rtems_libio_iop()

- rtems_libio_check_fd()

- rtems_libio_check_permissions()

- fchmod() function that is referenced by the handler table in the
  file control block associated with this file descriptor

**Development Comments:**

The routine will test to see if the file descriptor index is associated
with a network connection. If it is, an error is returned from this
routine.

The file descriptor index is used to obtain the associated file control
block.

The file descriptor value is range checked.

The file control block is examined to determine if it has write
permissions to allow us to alter the mode of the file.

A test is made to determine if the handler table that is referenced in the
file control block contains an entry for the fchmod() handler function. If
it does not, an error is returned to the calling routine.

If the fchmod() handler function exists, it is called with the file
control block and the desired mode as parameters.

.. COMMENT: @page

fcntl()
=======

**File:**

fcntl.c

**Processing:**

This routine currently only interacts with the file control block. If the
structure of the file control block and the associated meanings do not
change, the partial implementation of fcntl() should remain unaltered for
other filesystem implementations.

**Development Comments:**

The only commands that have been implemented are the F_GETFD and F_SETFD.
The commands manipulate the LIBIO_FLAGS_CLOSE_ON_EXEC bit in the``flags`` element of the file control block associated with the file
descriptor index.

The current implementation of the function performs the sequence of
operations below:

# Test to see if we are trying to operate on a file descriptor
  associated with a network connection

# Obtain the file control block that is associated with the file
  descriptor index

# Perform a range check on the file descriptor index.

.. COMMENT: @page

fdatasync
=========

**File:**

fdatasync.c

**Processing:**

This routine is a template in the in memory filesystem that will route us to the
appropriate handler function to carry out the fdatasync() processing. In the in
memory filesystem this function is not necessary. Its function in a disk based file
system that employs a memory cache is to flush all memory based data buffers to
disk. It is layered on the following functions and macros:

- rtems_file_descriptor_type()

- rtems_libio_iop()

- rtems_libio_check_fd()

- rtems_libio_check_permissions()

- fdatasync() function that is referenced by the handler table in the
  file control block associated with this file descriptor

**Development Comments:**

The routine will test to see if the file descriptor index is associated
with a network connection. If it is, an error is returned from this
routine.

The file descriptor index is used to obtain the associated file control
block.

The file descriptor value is range checked.

The file control block is examined to determine if it has write
permissions to the file.

A test is made to determine if the handler table that is referenced in the
file control block contains an entry for the fdatasync() handler function.
If it does not an error is returned to the calling routine.

If the fdatasync() handler function exists, it is called with the file
control block as its parameter.

.. COMMENT: @page

fpathconf
=========

**File:**

fpathconf.c

**Processing:**

This routine is layered on the following functions and macros:

- rtems_file_descriptor_type()

- rtems_libio_iop()

- rtems_libio_check_fd()

- rtems_libio_check_permissions()

When a filesystem is mounted, a set of constants is specified for the
filesystem.  These constants are stored with the mount table entry for the
filesystem. These constants appear in the POSIX standard and are listed
below.

- PCLINKMAX

- PCMAXCANON

- PCMAXINPUT

- PCNAMEMAX

- PCPATHMAX

- PCPIPEBUF

- PCCHOWNRESTRICTED

- PCNOTRUNC

- PCVDISABLE

- PCASYNCIO

- PCPRIOIO

- PCSYNCIO

This routine will find the mount table information associated the file
control block for the specified file descriptor parameter. The mount table
entry structure contains a set of filesystem specific constants that can
be accessed by individual identifiers.

**Development Comments:**

The routine will test to see if the file descriptor index is associated
with a network connection. If it is, an error is returned from this
routine.

The file descriptor index is used to obtain the associated file control
block.

The file descriptor value is range checked.

The file control block is examined to determine if it has read permissions
to the file.

Pathinfo in the file control block is used to locate the mount table entry
for the filesystem associated with the file descriptor.

The mount table entry contains the pathconf_limits_and_options element.
This element is a table of constants that is associated with the
filesystem.

The name argument is used to reference the desired constant from the
pathconf_limits_and_options table.

.. COMMENT: @page

fstat
=====

**File:**

fstat.c

**Processing:**

This routine will return information concerning a file or network
connection. If the file descriptor is associated with a network
connection, the current implementation of ``fstat()`` will return a
mode set to ``S_IFSOCK``. In a later version, this routine will map the
status of a network connection to an external handler routine.

If the file descriptor is associated with a node under a filesystem, the
fstat()  routine will map to the fstat() function taken from the node
handler table.

**Development Comments:**

This routine validates that the struct stat pointer is not NULL so that
the return location is valid.

The struct stat is then initialized to all zeros.

rtems_file_descriptor_type() is then used to determine if the file
descriptor is associated with a network connection. If it is, network
status processing is performed. In the current implementation, the file
descriptor type processing needs to be improved. It currently just drops
into the normal processing for file system nodes.

If the file descriptor is associated with a node under a filesystem, the
following steps are performed:

# Obtain the file control block that is associated with the file descriptor
  index.

# Range check the file descriptor index.

# Test to see if there is a non-NULL function pointer in the handler
  table for the fstat() function. If there is, invoke the function with the
  file control block and the pointer to the stat structure.

.. COMMENT: @page

ioctl
=====

**File:**

ioctl.c

**Processing:**

Not defined in the POSIX 1003.1b standard but commonly supported in most
UNIX and POSIX system. Ioctl() is a catchall for I/O operations. Routine
is layered on external network handlers and filesystem specific handlers.
The development of new filesystems should not alter the basic processing
performed by this routine.

**Development Comments:**

The file descriptor is examined to determine if it is associated with a
network device. If it is processing is mapped to an external network
handler. The value returned by this handler is then returned to the
calling program.

File descriptors that are associated with a filesystem undergo the
following processing:

# The file descriptor index is used to obtain the associated file
  control block.

# The file descriptor value is range checked.

# A test is made to determine if the handler table that is referenced
  in the file control block contains an entry for the ioctl() handler
  function. If it does not, an error is returned to the calling routine.

# If the ioctl() handler function exists, it is called with the file
  control block, the command and buffer as its parameters.

# The return code from this function is then sent to the calling
  routine.

.. COMMENT: @page

link
====

**File:**

link.c

**Processing:**

This routine will establish a hard link to a file, directory or a device.
The target of the hard link must be in the same filesystem as the new link
being created. A link to an existing link is also permitted but the
existing link is evaluated before the new link is made. This implies that
links to links are reduced to links to files, directories or devices
before they are made.

**Development Comments:**

Calling parameters:
const char   \*existing
const char   \*new

link() will determine if the target of the link actually exists using
rtems_filesystem_evaluate_path()

rtems_filesystem_get_start_loc() is used to determine where to start the
path evaluation of the new name. This macro examines the first characters
of the name to see if the name of the new link starts with a
rtems_filesystem_is_separator. If it does the search starts from the root
of the RTEMS filesystem; otherwise the search will start from the current
directory.

The OPS table evalformake() function for the parent’s filesystem is used
to locate the node that will be the parent of the new link. It will also
locate the start of the new path’s name. This name will be used to define
a child under the parent directory.

If the parent is found, the routine will determine if the hard link that
we are trying to create will cross a filesystem boundary. This is not
permitted for hard-links.

If the hard-link does not cross a filesystem boundary, a check is
performed to determine if the OPS table contains an entry for the link()
function.

If a link() function is defined, the OPS table link() function will be
called to establish the actual link within the filesystem.

The return code from the OPS table link() function is returned to the
calling program.

.. COMMENT: @page

lseek
=====

**File:**

lseek.c

**Processing:**

This routine is layered on both external handlers and filesystem / node
type specific handlers. This routine should allow for the support of new
filesystems without modification.

**Development Comments:**

This routine will determine if the file descriptor is associated with a
network device. If it is lseek will map to an external network handler.
The handler will be called with the file descriptor, offset and whence as
its calling parameters. The return code from the external handler will be
returned to the calling routine.

If the file descriptor is not associated with a network connection, it is
associated with a node in a filesystem. The following steps will be
performed for filesystem nodes:

# The file descriptor is used to obtain the file control block for the
  node.

# The file descriptor is range checked.

# The offset element of the file control block is altered as indicated
  by the offset and whence calling parameters

# The handler table in the file control block is examined to determine
  if it contains an entry for the lseek() function. If it does not an error
  is returned to the calling program.

# The lseek() function from the designated handler table is called
  with the file control block, offset and whence as calling arguments

# The return code from the lseek() handler function is returned to the
  calling program

.. COMMENT: @page

mkdir
=====

**File:**

mkdir.c

**Processing:**

This routine attempts to create a directory node under the filesystem. The
routine is layered the mknod() function.

**Development Comments:**

See mknod() for developmental comments.

.. COMMENT: @page

mkfifo
======

**File:**

mkfifo.c

**Processing:**

This routine attempts to create a FIFO node under the filesystem. The
routine is layered the mknod() function.

**Development Comments:**

See mknod() for developmental comments

.. COMMENT: @page

mknod
=====

**File:**

mknod.c

**Processing:**

This function will allow for the creation of the following types of nodes
under the filesystem:

- directories

- regular files

- character devices

- block devices

- fifos

At the present time, an attempt to create a FIFO will result in an ENOTSUP
error to the calling function. This routine is layered the filesystem
specific routines evalformake and mknod. The introduction of a new
filesystem must include its own evalformake and mknod function to support
the generic mknod() function.  Under this condition the generic mknod()
function should accommodate other filesystem types without alteration.

**Development Comments:**

Test for nodal types - I thought that this test should look like the
following code:
.. code:: c

    if ( (mode & S_IFDIR) = = S_IFDIR) \||
    (mode & S_IFREG) = = S_IFREG) \||
    (mode & S_IFCHR) = = S_IFCHR) \||
    (mode & S_IFBLK) = = S_IFBLK) \||
    (mode & S_IFIFO) = = S_IFIFO))
    Set_errno_and_return_minus_one (EINVAL);

Where:

- S_IFREG (0100000) - Creation of a regular file

- S_IFCHR (0020000) - Creation of a character device

- S_IFBLK (0060000) - Creation of a block device

- S_IFIFO (0010000) - Creation of a FIFO

Determine if the pathname that we are trying to create starts at the root
directory or is relative to the current directory using the
rtems_filesystem_get_start_loc()  function.

Determine if the pathname leads to a valid directory that can be accessed
for the creation of a node.

If the pathname is a valid location to create a node, verify that a
filesystem specific mknod() function exists.

If the mknod() function exists, call the filesystem specific mknod()
function.  Pass the name, mode, device type and the location information
associated with the directory under which the node will be created.

.. COMMENT: @page

mount
=====

**File:**

mount.c

Arguments (Not a standard POSIX call):

rtems_filesystem_mount_table_entry_t   \**mt_entry,

If the mount operation is successful, this pointer to a pointer will be
set to reference the mount table chain entry that has been allocated for
this file system mount.

rtems_filesystem_operations_table   \*fs_ops,

This is a pointer to a table of functions that are associated with the
file system that we are about to mount. This is the mechanism to selected
file system type without keeping a dynamic database of all possible file
system types that are valid for the mount operation. Using this method, it
is only necessary to configure the filesystems that we wish to use into
the RTEMS build. Unused filesystems types will not be drawn into the
build.

char                      \*fsoptions,

This argument points to a string that selects mounting for read only
access or read/write access. Valid states are "RO" and "RW"

char                      \*device,

This argument is reserved for the name of a device that will be used to
access the filesystem information. Current filesystem implementations are
memory based and do not require a device to access filesystem information.

char                      \*mount_point

This is a pathname to a directory in a currently mounted filesystem that
allows read, write and execute permissions.  If successful, the node found
by evaluating this name, is stored in the mt_entry.

**Processing:**

This routine will handle the mounting of a filesystem on a mount point. If
the operation is successful, a pointer to the mount table chain entry
associated with the mounted filesystem will be returned to the calling
function. The specifics about the processing required at the mount point
and within the filesystem being mounted is isolated in the filesystem
specific mount() and fsmount_me()  functions. This allows the generic
mount() function to remain unaltered even if new filesystem types are
introduced.

**Development Comments:**

This routine will use get_file_system_options() to determine if the mount
options are valid ("RO" or "RW").

It confirms that a filesystem ops-table has been selected.

Space is allocated for a mount table entry and selective elements of the
temporary mount table entry are initialized.

If a mount point is specified: The mount point is examined to determine
that it is a directory and also has the appropriate permissions to allow a
filesystem to be mounted.

The current mount table chain is searched to determine that there is not
another filesystem mounted at the mount point we are trying to mount onto.

If a mount function is defined in the ops table for the filesystem
containing the mount point, it is called at this time.

If no mount point is specified: Processing if performed to set up the
mount table chain entry as the base filesystem.

If the fsmount_me() function is specified for ops-table of the filesystem
being mounted, that function is called to initialize for the new
filesystem.

On successful completion, the temporary mount table entry will be placed
on the mount table chain to record the presence of the mounted filesystem.

.. COMMENT: @page

open
====

**File:**

open.c

**Processing:**

This routine is layered on both RTEMS calls and filesystem specific
implementations of the open() function. These functional interfaces should
not change for new filesystems and therefore this code should be stable as
new file systems are introduced.

**Development Comments:**

This routine will allocate a file control block for the file or device
that we are about to open.

It will then test to see if the pathname exists. If it does a
rtems_filesystem_location_info_t data structure will be filled out. This
structure contains information that associates node information,
filesystem specific functions and mount table chain information with the
pathname.

If the create option has been it will attempt to create a node for a
regular file along the specified path. If a file already exists along this
path, an error will be generated; otherwise, a node will be allocated for
the file under the filesystem that contains the pathname. When a new node
is created, it is also evaluated so that an appropriate
rtems_filesystem_location_info_t data structure can be filled out for the
newly created node.

If the file exists or the new file was created successfully, the file
control block structure will be initialized with handler table
information, node information and the rtems_filesystem_location_info_t
data structure that describes the node and filesystem data in detail.

If an open() function exists in the filesystem specific handlers table for
the node that we are trying to open, it will be called at this time.

If any error is detected in the process, cleanup is performed. It consists
of freeing the file control block structure that was allocated at the
beginning of the generic open() routine.

On a successful open(), the index into the file descriptor table will be
calculated and returned to the calling routine.

.. COMMENT: @page

opendir
=======

**File:**

opendir.c

**Processing:**

This routine will attempt to open a directory for read access. It will
setup a DIR control structure that will be used to access directory
information. This routine is layered on the generic open() routine and
filesystem specific directory processing routines.

**Development Comments:**

The BSD group provided this routine.

.. COMMENT: @page

pathconf
========

**File:**

pathconf.c

**Processing:**

This routine will obtain the value of one of the path configuration
parameters and return it to the calling routine. It is layered on the
generic open() and fpathconf()  functions. These interfaces should not
change with the addition of new filesystem types.

**Development Comments:**

This routine will try to open the file indicated by path.

If successful, the file descriptor will be used to access the pathconf
value specified by ``name`` using the fpathconf() function.

The file that was accessed is then closed.

.. COMMENT: @page

read
====

**File:**

deviceio.c

**Processing:**

This routine is layered on a set of RTEMS calls and filesystem specific
read operations. The functions are layered in such a way as to isolate
them from change as new filesystems are introduced.

**Development Comments:**

This routine will examine the type of file descriptor it is sent.

If the file descriptor is associated with a network device, the read
function will be mapped to a special network handler. The return code from
the network handler will then be sent as the return code from generic
read() function.

For file descriptors that are associated with the filesystem the following
sequence will be performed:

# Obtain the file control block associated with the file descriptor

# Range check the file descriptor

# Determine that the buffer pointer is not invalid

# Check that the count is not zero

# Check the file control block to see if we have permissions to read

# If there is a read function in the handler table, invoke the handler
  table read() function

# Use the return code from the handler table read function(number of
  bytes read) to increment the offset element of the file control block

# Return the number of bytes read to the calling program

.. COMMENT: @page

readdir
=======

**File:**

readdir.c

**Processing:**

This routine was acquired from the BSD group. It has not been altered from
its original form.

**Development Comments:**

The routine calls a customized getdents() function that is provided by the
user.  This routine provides the filesystem specific aspects of reading a
directory.

It is layered on the read() function in the directory handler table. This
function has been mapped to the Imfs_dir_read() function.

.. COMMENT: @page

unmount
=======

**File:**

unmount.c

**Processing:**

This routine will attempt to dismount a mounted filesystem and then free
all resources that were allocated for the management of that filesystem.

**Development Comments:**

- This routine will determine if there are any filesystems currently
  mounted under the filesystem that we are trying to dismount. This would
  prevent the dismount of the filesystem.

- It will test to see if the current directory is in the filesystem
  that we are attempting to dismount. This would prevent the dismount of the
  filesystem.

- It will scan all the currently open file descriptors to determine is
  there is an open file descriptor to a file in the filesystem that we are
  attempting to unmount().

If the above preconditions are met then the following sequence is
performed:

# Call the filesystem specific unmount() function for the filesystem
  that contains the mount point. This routine should indicate that the mount
  point no longer has a filesystem mounted below it.

# Call the filesystem specific fsunmount_me() function for the mounted
  filesystem that we are trying to unmount(). This routine should clean up
  any resources that are no longer needed for the management of the file
  system being un-mounted.

# Extract the mount table entry for the filesystem that was just
  dismounted from the mount table chain.

# Free the memory associated with the extracted mount table entry.

.. COMMENT: @page

eval
====

**File:**

XXX

**Processing:**

XXX

**Development Comments:**

XXX

.. COMMENT: @page

getdentsc
=========

**File:**

XXX

**Processing:**

XXX

**Development Comments:**

XXX

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

Filesystem Implementation Requirements
######################################

This chapter details the behavioral requirements that all filesystem
implementations must adhere to.

General
=======

The RTEMS filesystem framework was intended to be compliant with the
POSIX Files and Directories interface standard. The following filesystem
characteristics resulted in a functional switching layer.
.. code:: c

    Figure of the Filesystem Functional Layering goes here.
    This figure includes networking and disk caching layering.

# Application programs are presented with a standard set of POSIX
  compliant functions that allow them to interface with the files, devices
  and directories in the filesystem. The interfaces to these routines do
  not reflect the type of subordinate filesystem implementation in which
  the file will be found.

# The filesystem framework developed under RTEMS allows for mounting
  filesystem of different types under the base filesystem.

# The mechanics of locating file information may be quite different
  between filesystem types.

# The process of locating a file may require crossing filesystem
  boundaries.

# The transitions between filesystem and the processing required to
  access information in different filesystem is not visible at the level
  of the POSIX function call.

# The POSIX interface standard provides file access by character
  pathname to the file in some functions and through an integer file
  descriptor in other functions.

# The nature of the integer file descriptor and its associated
  processing is operating system and filesystem specific.

# Directory and device information must be processed with some of the
  same routines that apply to files.

# The form and content of directory and device information differs
  greatly from that of a regular file.

# Files, directories and devices represent elements (nodes) of a tree
  hierarchy.

# The rules for processing each of the node types that exist under the
  filesystem are node specific but are still not reflected in the POSIX
  interface routines.

.. code:: c

    Figure of the Filesystem Functional Layering goes here.
    This figure focuses on the Base Filesystem and IMFS.

.. code:: c

    Figure of the IMFS Memfile control blocks

.. _File-and-Directory-Removal-Constraints:

File and Directory Removal Constraints
======================================

The following POSIX constraints must be honored by all filesystems.

- If a node is a directory with children it cannot be removed.

- The root node of any filesystem, whether the base filesystem or a
  mounted filesystem, cannot be removed.

- A node that is a directory that is acting as the mount point of a file
  system cannot be removed.

- On filesystems supporting hard links, a link count is maintained.
  Prior to node removal, the node’s link count is decremented by one.  The
  link count must be less than one to allow for removal of the node.

API Layering
============

Mapping of Generic System Calls to Filesystem Specific Functions
----------------------------------------------------------------

The list of generic system calls includes the routines open(), read(),
write(), close(), etc..

The Files and Directories section of the POSIX Application Programs
Interface specifies a set of functions with calling arguments that are
used to gain access to the information in a filesystem. To the
application program, these functions allow access to information in any
mounted filesystem without explicit knowledge of the filesystem type or
the filesystem mount configuration. The following are functions that are
provided to the application:

# access()

# chdir()

# chmod()

# chown()

# close()

# closedir()

# fchmod()

# fcntl()

# fdatasync()

# fpathconf()

# fstat()

# fsync()

# ftruncate()

# link()

# lseek()

# mkdir()

# mknod()

# mount()

# open()

# opendir()

# pathconf()

# read()

# readdir()

# rewinddir()

# rmdir()

# rmnod()

# scandir()

# seekdir()

# stat()

# telldir()

# umask()

# unlink()

# unmount()

# utime()

# write()

The filesystem’s type as well as the node type within the filesystem
determine the nature of the processing that must be performed for each of
the functions above. The RTEMS filesystem provides a framework that
allows new filesystem to be developed and integrated without alteration
to the basic framework.

To provide the functional switching that is required, each of the POSIX
file and directory functions have been implemented as a shell function.
The shell function adheres to the POSIX interface standard. Within this
functional shell, filesystem and node type information is accessed which
is then used to invoke the appropriate filesystem and node type specific
routine to process the POSIX function call.

File/Device/Directory function access via file control block - rtems_libio_t structure
--------------------------------------------------------------------------------------

The POSIX open() function returns an integer file descriptor that is used
as a reference to file control block information for a specific file. The
file control block contains information that is used to locate node, file
system, mount table and functional handler information. The diagram in
Figure 8 depicts the relationship between and among the following
components.

# File Descriptor Table
  This is an internal RTEMS structure that tracks all currently defined file
  descriptors in the system. The index that is returned by the file open()
  operation references a slot in this table. The slot contains a pointer to
  the file descriptor table entry for this file. The rtems_libio_t structure
  represents the file control block.

# Allocation of entry in the File Descriptor Table
  Access to the file descriptor table is controlled through a semaphore that
  is implemented using the rtems_libio_allocate() function. This routine
  will grab a semaphore and then scan the file control blocks to determine
  which slot is free for use. The first free slot is marked as used and the
  index to this slot is returned as the file descriptor for the open()
  request. After the alterations have been made to the file control block
  table, the semaphore is released to allow further operations on the table.

# Maximum number of entries in the file descriptor table is
  configurable through the src/exec/sapi/headers/confdefs.h file. If the
  CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS constant is defined its value
  will represent the maximum number of file descriptors that are allowed.
  If CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS is not specified a default
  value of 20 will be used as the maximum number of file descriptors
  allowed.

# File control block - rtems_libio_t structure
  .. code:: c
      struct rtems_libio_tt {
      rtems_driver_name_t              \*driver;
      off_t                             size;
      off_t                             offset;
      unsigned32                        flags;
      rtems_filesystem_location_info_t  pathinfo;
      Objects_Id                        sem;
      unsigned32                        data0;
      void                              data1;
      void                              file_info;
      rtems_filesystem_file_handlers_r  handlers;
      };
  A file control block can exist for regular files, devices and directories.
  The following fields are important for regular file and directory access:
  - Size - For a file this represents the number of bytes currently
    stored in a file. For a directory this field is not filled in.
  - Offset - For a file this is the byte file position index relative to
    the start of the file. For a directory this is the byte offset into a
    sequence of dirent structures.
  - Pathinfo - This is a structure that provides a pointer to node
    information, OPS table functions, Handler functions and the mount table
    entry associated with this node.
  - file_info - A pointer to node information that is used by Handler
    functions
  - handlers - A pointer to a table of handler functions that operate on
    a file, device or directory through a file descriptor index

File/Directory function access via rtems_filesystem_location_info_t structure
-----------------------------------------------------------------------------

The rtems_filesystem_location_info_tt structure below provides sufficient
information to process nodes under a mounted filesystem.
.. 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;
    };

It contains a void pointer to filesystem specific nodal structure,
pointers to the OPS table for the filesystem that contains the node, the
node type specific handlers for the node and a reference pointer to the
mount table entry associated with the filesystem containing the node

Operation Tables
================

Filesystem specific operations are invoked indirectly.  The set of
routines that implement the filesystem are configured into two tables.
The Filesystem Handler Table has routines that are specific to a
filesystem but remain constant regardless of the actual file type.
The File Handler Table has routines that are both filesystem and file type
specific.

Filesystem Handler Table Functions
----------------------------------

OPS table functions are defined in a ``rtems_filesystem_operations_table``
structure.  It defines functions that are specific to a given filesystem.
One table exists for each filesystem that is supported in the RTEMS
configuration. The structure definition appears below and is followed by
general developmental information on each of the functions contained in this
function management structure.
.. code:: c

    typedef struct {
    rtems_filesystem_evalpath_t        evalpath;
    rtems_filesystem_evalmake_t        evalformake;
    rtems_filesystem_link_t            link;
    rtems_filesystem_unlink_t          unlink;
    rtems_filesystem_node_type_t       node_type;
    rtems_filesystem_mknod_t           mknod;
    rtems_filesystem_rmnod_t           rmnod;
    rtems_filesystem_chown_t           chown;
    rtems_filesystem_freenode_t        freenod;
    rtems_filesystem_mount_t           mount;
    rtems_filesystem_fsmount_me_t      fsmount_me;
    rtems_filesystem_unmount_t         unmount;
    rtems_filesystem_fsunmount_me_t    fsunmount_me;
    rtems_filesystem_utime_t           utime;
    rtems_filesystem_evaluate_link_t   eval_link;
    rtems_filesystem_symlink_t         symlink;
    } rtems_filesystem_operations_table;

.. COMMENT: @page

evalpath Handler
~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

evalpath

**Arguments:**

.. code:: c

    const char                        \*pathname,      /* IN     \*/
    int                                flags,         /* IN     \*/
    rtems_filesystem_location_info_t  \*pathloc        /* IN/OUT \*/

**Description:**

This routine is responsible for evaluating the pathname passed in
based upon the flags and the valid ``rthems_filesystem_location_info_t``.
Additionally, it must make any changes to pathloc necessary to identify
the pathname node.  This should include calling the evalpath for a mounted
filesystem, if the given filesystem supports the mount command.

This routine returns a 0 if the evaluation was successful.
Otherwise, it returns a -1 and sets errno to the correct error.

This routine is required and should NOT be set to NULL.

.. COMMENT: @page

evalformake Handler
~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

evalformake

**Arguments:**

.. code:: c

    const char                       \*path,       /* IN \*/
    rtems_filesystem_location_info_t \*pathloc,    /* IN/OUT \*/
    const char                      \**name        /* OUT    \*/

**Description:**

This method is given a path to evaluate and a valid start location.  It
is responsible for finding the parent node for a requested make command,
setting pathloc information to identify the parent node, and setting
the name pointer to the first character of the name of the new node.
Additionally, if the filesystem supports the mount command, this method
should call the evalformake routine for the mounted filesystem.

This routine returns a 0 if the evaluation was successful.  Otherwise, it
returns a -1 and sets errno to the correct error.

This routine is required and should NOT be set to NULL.  However, if
the filesystem does not support user creation of a new node, it may
set errno to ENOSYS and return -1.

.. COMMENT: @page

link Handler
~~~~~~~~~~~~

**Corresponding Structure Element:**

link

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t    \*to_loc,      /* IN \*/
    rtems_filesystem_location_info_t    \*parent_loc,  /* IN \*/
    const char                          \*token        /* IN \*/

**Description:**

This routine is used to create a hard-link.

It will first examine the st_nlink count of the node that we are trying to.
If the link count exceeds LINK_MAX an error will be returned.

The name of the link will be normalized to remove extraneous separators from
the end of the name.

This routine is not required and may be set to NULL.

.. COMMENT: @page

unlink Handler
~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

.. COMMENT: @page

node_type Handler
~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

node_type()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t    \*pathloc        /* IN \*/

**Description:**

XXX

.. COMMENT: @page

mknod Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

mknod()

**Arguments:**

.. code:: c

    const char                          \*token,        /* IN \*/
    mode_t                               mode,         /* IN \*/
    dev_t                                dev,          /* IN \*/
    rtems_filesystem_location_info_t    \*pathloc       /* IN/OUT \*/

**Description:**

XXX

.. COMMENT: @page

rmnod Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

.. COMMENT: @page

chown Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

chown()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t    \*pathloc        /* IN \*/
    uid_t                                owner          /* IN \*/
    gid_t                                group          /* IN \*/

**Description:**

XXX

.. COMMENT: @page

freenod Handler
~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

freenod()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t      \*pathloc       /* IN \*/

**Description:**

This routine is used by the generic code to allow memory to be allocated
during the evaluate routines, and set free when the generic code is finished
accessing a node.  If the evaluate routines allocate memory to identify
a node this routine should be utilized to free that memory.

This routine is not required and may be set to NULL.

.. COMMENT: @page

mount Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

mount()

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**Description:**

XXX

.. COMMENT: @page

fsmount_me Handler
~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**Description:**

This function is provided with a filesystem to take care of the internal
filesystem management details associated with mounting that filesystem
under the RTEMS environment.

It is not responsible for the mounting details associated the filesystem
containing the mount point.

The rtems_filesystem_mount_table_entry_t structure contains the key elements
below:

rtems_filesystem_location_info_t         \*mt_point_node,

This structure contains information about the mount point. This
allows us to find the ops-table and the handling functions
associated with the filesystem containing the mount point.

rtems_filesystem_location_info_t         \*fs_root_node,

This structure contains information about the root node in the file
system to be mounted. It allows us to find the ops-table and the
handling functions associated with the filesystem to be mounted.

rtems_filesystem_options_t                 options,

Read only or read/write access

void                                         \*fs_info,

This points to an allocated block of memory the will be used to
hold any filesystem specific information of a global nature. This
allocated region if important because it allows us to mount the
same filesystem type more than once under the RTEMS system.
Each instance of the mounted filesystem has its own set of global
management information that is separate from the global
management information associated with the other instances of the
mounted filesystem type.

rtems_filesystem_limits_and_options_t    pathconf_info,

The table contains the following set of values associated with the
mounted filesystem:

- link_max

- max_canon

- max_input

- name_max

- path_max

- pipe_buf

- posix_async_io

- posix_chown_restrictions

- posix_no_trunc

- posix_prio_io

- posix_sync_io

- posix_vdisable

These values are accessed with the pathconf() and the fpathconf ()
functions.

const char                                   \*dev

The is intended to contain a string that identifies the device that contains
the filesystem information. The filesystems that are currently implemented
are memory based and don’t require a device specification.

If the mt_point_node.node_access is NULL then we are mounting the base file
system.

The routine will create a directory node for the root of the IMFS file
system.

The node will have read, write and execute permissions for owner, group and
others.

The node’s name will be a null string.

A filesystem information structure(fs_info) will be allocated and
initialized for the IMFS filesystem. The fs_info pointer in the mount table
entry will be set to point the filesystem information structure.

The pathconf_info element of the mount table will be set to the appropriate
table of path configuration constants (LIMITS_AND_OPTIONS).

The fs_root_node structure will be filled in with the following:

- pointer to the allocated root node of the filesystem

- directory handlers for a directory node under the IMFS filesystem

- OPS table functions for the IMFS

A 0 will be returned to the calling routine if the process succeeded,
otherwise a 1 will be returned.

.. COMMENT: @page

unmount Handler
~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

.. COMMENT: @page

fsunmount_me Handler
~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_fsunmount_me()

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**Description:**

XXX

.. COMMENT: @page

utime Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

.. COMMENT: @page

eval_link Handler
~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

.. COMMENT: @page

symlink Handler
~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

.. COMMENT: @page

File Handler Table Functions
----------------------------

Handler table functions are defined in a ``rtems_filesystem_file_handlers_r``
structure. It defines functions that are specific to a node type in a given
filesystem. One table exists for each of the filesystem’s node types. The
structure definition appears below. It is followed by general developmental
information on each of the functions associated with regular files contained
in this function management structure.
.. code:: c

    typedef struct {
    rtems_filesystem_open_t           open;
    rtems_filesystem_close_t          close;
    rtems_filesystem_read_t           read;
    rtems_filesystem_write_t          write;
    rtems_filesystem_ioctl_t          ioctl;
    rtems_filesystem_lseek_t          lseek;
    rtems_filesystem_fstat_t          fstat;
    rtems_filesystem_fchmod_t         fchmod;
    rtems_filesystem_ftruncate_t      ftruncate;
    rtems_filesystem_fpathconf_t      fpathconf;
    rtems_filesystem_fsync_t          fsync;
    rtems_filesystem_fdatasync_t      fdatasync;
    rtems_filesystem_fcntl_t          fcntl;
    } rtems_filesystem_file_handlers_r;

.. COMMENT: @page

open Handler
~~~~~~~~~~~~

**Corresponding Structure Element:**

open()

**Arguments:**

.. code:: c

    rtems_libio_t   \*iop,
    const char      \*pathname,
    unsigned32       flag,
    unsigned32       mode

**Description:**

XXX

.. COMMENT: @page

close Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

close()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

read Handler
~~~~~~~~~~~~

**Corresponding Structure Element:**

read()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    void              \*buffer,
    unsigned32         count

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

write Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

ioctl Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    unsigned32       command,
    void              \*buffer

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

lseek Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

lseek()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    off_t              offset,
    int                whence

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

fstat Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

fstat()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t   \*loc,
    struct stat                        \*buf

**Description:**

The following information is extracted from the filesystem
specific node and placed in the ``stat`` structure:

- st_mode

- st_nlink

- st_ino

- st_uid

- st_gid

- st_atime

- st_mtime

- st_ctime

**NOTES:**

Both the ``stat()`` and ``lstat()`` services are
implemented directly using the ``fstat()`` handler.  The
difference in behavior is determined by how the path is evaluated
prior to this handler being called on a particular
file entity.

The ``fstat()`` system call is implemented directly
on top of this filesystem handler.

.. COMMENT: @page

fchmod Handler
~~~~~~~~~~~~~~

**Corresponding Structure Element:**

fchmod()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop
    mode_t              mode

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

ftruncate Handler
~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

**NOTES:**

XXX

fpathconf Handler
~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

fsync Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

fdatasync Handler
~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: @page

fcntl Handler
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**Description:**

XXX

**NOTES:**

XXX

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

In-Memory Filesystem
####################

This chapter describes the In-Memory FileSystem (IMFS).  The IMFS is a
full featured POSIX filesystem that keeps all information in memory.

IMFS Per Node Data Structure
============================

Each regular file, device, hard link, and directory is represented by a data
structure called a ``jnode``. The ``jnode`` is formally represented by the
structure:
.. code:: c

    struct IMFS_jnode_tt {
    Chain_Node          Node;             /* for chaining them together \*/
    IMFS_jnode_t       \*Parent;           /* Parent node \*/
    char                name[NAME_MAX+1]; /* "basename" \*/
    mode_t              st_mode;          /* File mode \*/
    nlink_t             st_nlink;         /* Link count \*/
    ino_t               st_ino;           /* inode \*/
    uid_t               st_uid;           /* User ID of owner \*/
    gid_t               st_gid;           /* Group ID of owner \*/
    time_t              st_atime;         /* Time of last access \*/
    time_t              st_mtime;         /* Time of last modification \*/
    time_t              st_ctime;         /* Time of last status change \*/
    IMFS_jnode_types_t  type;             /* Type of this entry \*/
    IMFS_typs_union     info;
    };

The key elements of this structure are listed below together with a brief
explanation of their role in the filesystem.

*Node*
    exists to allow the entire ``jnode`` structure to be included in a chain.

*Parent*
    is a pointer to another ``jnode`` structure that is the logical parent of the
    node in which it appears.  This field may be NULL if the file associated with
    this node is deleted but there are open file descriptors on this file or
    there are still hard links to this node.

*name*
    is the name of this node within the filesystem hierarchical tree. Example:  If
    the fully qualified pathname to the ``jnode`` was ``/a/b/c``, the``jnode`` name field would contain the null terminated string ``"c"``.

*st_mode*
    is the standard Unix access permissions for the file or directory.

*st_nlink*
    is the number of hard links to this file. When a ``jnode`` is first created
    its link count is set to 1. A ``jnode`` and its associated resources
    cannot be deleted unless its link count is less than 1.

*st_ino*
    is a unique node identification number

*st_uid*
    is the user ID of the file’s owner

*st_gid*
    is the group ID of the file’s owner

*st_atime*
    is the time of the last access to this file

*st_mtime*
    is the time of the last modification of this file

*st_ctime*
    is the time of the last status change to the file

*type*
    is the indication of node type must be one of the following states:
    - IMFS_DIRECTORY
    - IMFS_MEMORY_FILE
    - IMFS_HARD_LINK
    - IMFS_SYM_LINK
    - IMFS_DEVICE

*info*
    is this contains a structure that is unique to file type (See IMFS_typs_union
    in imfs.h).
    - IMFS_DIRECTORY
      An IMFS directory contains a dynamic chain structure that
      records all files and directories that are subordinate to the directory node.
    - IMFS_MEMORY_FILE
      Under the in memory filesystem regular files hold data. Data is dynamically
      allocated to the file in 128 byte chunks of memory.  The individual chunks of
      memory are tracked by arrays of pointers that record the address of the
      allocated chunk of memory. Single, double, and triple indirection pointers
      are used to record the locations of all segments of the file.  The
      memory organization of an IMFS file are discussed elsewhere in this manual.
    - IMFS_HARD_LINK
      The IMFS filesystem supports the concept of hard links to other nodes in the
      IMFS filesystem.  These hard links are actual pointers to other nodes in the
      same filesystem. This type of link cannot cross-filesystem boundaries.
    - IMFS_SYM_LINK
      The IMFS filesystem supports the concept of symbolic links to other nodes in
      any filesystem. A symbolic link consists of a pointer to a character string
      that represents the pathname to the target node. This type of link can
      cross-filesystem boundaries.  Just as with most versions of UNIX supporting
      symbolic links, a symbolic link can point to a non-existent file.
    - IMFS_DEVICE
      All RTEMS devices now appear as files under the in memory filesystem. On
      system initialization, all devices are registered as nodes under the file
      system.

Miscellaneous IMFS Information
==============================

Memory associated with the IMFS
===============================

A memory based filesystem draws its resources for files and directories
from the memory resources of the system. When it is time to un-mount the
filesystem, the memory resources that supported filesystem are set free.
In order to free these resources, a recursive walk of the filesystems
tree structure will be performed. As the leaf nodes under the filesystem
are encountered their resources are freed. When directories are made empty
by this process, their resources are freed.

Node removal constraints for the IMFS
-------------------------------------

The IMFS conforms to the general filesystem requirements for node
removal.  See :ref:`File and Directory Removal Constraints <File-and-Directory-Removal-Constraints>`.

IMFS General Housekeeping Notes
-------------------------------

The following is a list of odd housekeeping notes for the IMFS.

- If the global variable rtems_filesystem_current refers to the node that
  we are trying to remove, the node_access element of this structure must be
  set to NULL to invalidate it.

- If the node was of IMFS_MEMORY_FILE type, free the memory associated
  with the memory file before freeing the node. Use the IMFS_memfile_remove()
  function.

IMFS Operation Tables
=====================

IMFS Filesystem Handler Table Functions
---------------------------------------

OPS table functions are defined in a rtems_filesystem_operations_table
structure.  It defines functions that are specific to a given filesystem.
One table exists for each filesystem that is supported in the RTEMS
configuration. The structure definition appears below and is followed by
general developmental information on each of the functions contained in this
function management structure.
.. code:: c

    rtems_filesystem_operations_table  IMFS_ops = {
    IMFS_eval_path,
    IMFS_evaluate_for_make,
    IMFS_link,
    IMFS_unlink,
    IMFS_node_type,
    IMFS_mknod,
    IMFS_rmnod,
    IMFS_chown,
    IMFS_freenodinfo,
    IMFS_mount,
    IMFS_initialize,
    IMFS_unmount,
    IMFS_fsunmount,
    IMFS_utime,
    IMFS_evaluate_link,
    IMFS_symlink,
    IMFS_readlink
    };

.. COMMENT: @page

IMFS_evalpath()
~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_evalformake()
~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_link()
~~~~~~~~~~~

**Corresponding Structure Element:**

link

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t    \*to_loc,      /* IN \*/
    rtems_filesystem_location_info_t    \*parent_loc,  /* IN \*/
    const char                          \*token        /* IN \*/

**File:**

imfs_link.c

**Description:**

This routine is used in the IMFS filesystem to create a hard-link.

It will first examine the st_nlink count of the node that we are trying to.
If the link count exceeds LINK_MAX an error will be returned.

The name of the link will be normalized to remove extraneous separators from
the end of the name.

IMFS_create_node will be used to create a filesystem node that will have the
following characteristics:

- parent that was determined in the link() function in file link.c

- Type will be set to IMFS_HARD_LINK

- name will be set to the normalized name

- mode of the hard-link will be set to the mode of the target node

If there was trouble allocating memory for the new node an error will be
returned.

The st_nlink count of the target node will be incremented to reflect the new
link.

The time fields of the link will be set to reflect the creation time of the
hard-link.

.. COMMENT: @page

IMFS_unlink()
~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_node_type()
~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_node_type()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t    \*pathloc        /* IN \*/

**File:**

imfs_ntype.c

**Description:**

This routine will locate the IMFS_jnode_t structure that holds ownership
information for the selected node in the filesystem.

This structure is pointed to by pathloc->node_access.

The IMFS_jnode_t type element indicates one of the node types listed below:

- RTEMS_FILESYSTEM_DIRECTORY

- RTEMS_FILESYSTEM_DEVICE

- RTEMS_FILESYSTEM_HARD_LINK

- RTEMS_FILESYSTEM_MEMORY_FILE

.. COMMENT: @page

IMFS_mknod()
~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_mknod()

**Arguments:**

.. code:: c

    const char                          \*token,        /* IN \*/
    mode_t                               mode,         /* IN \*/
    dev_t                                dev,          /* IN \*/
    rtems_filesystem_location_info_t    \*pathloc       /* IN/OUT \*/

**File:**

imfs_mknod.c

**Description:**

This routine will examine the mode argument to determine is we are trying to
create a directory, regular file and a device node. The creation of other
node types is not permitted and will cause an assert.

Memory space will be allocated for a ``jnode`` and the node will be set up
according to the nodal type that was specified. The IMFS_create_node()
function performs the allocation and setup of the node.

The only problem that is currently reported is the lack of memory when we
attempt to allocate space for the ``jnode`` (ENOMEN).

.. COMMENT: @page

IMFS_rmnod()
~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_chown()
~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_chown()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t    \*pathloc        /* IN \*/
    uid_t                                owner          /* IN \*/
    gid_t                                group          /* IN \*/

**File:**

imfs_chown.c

**Description:**

This routine will locate the IMFS_jnode_t structure that holds ownership
information for the selected node in the filesystem.

This structure is pointed to by pathloc->node_access.

The st_uid and st_gid fields of the node are then modified. Since this is a
memory based filesystem, no further action is required to alter the
ownership of the IMFS_jnode_t structure.

.. COMMENT: @page

IMFS_freenod()
~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_freenod()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t      \*pathloc       /* IN \*/

**File:**

imfs_free.c

**Description:**

This method is a private function to the IMFS.  It is called by IMFS routines
to free nodes that have been allocated.  Examples of where this routine
may be called from are unlink and rmnod.

Note:  This routine should not be confused with the filesystem callback
freenod.  The IMFS allocates memory until the node no longer exists.

.. COMMENT: @page

IMFS_freenodinfo()
~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_freenodinfo()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t      \*pathloc       /* IN \*/

**File:**

imfs_free.c

**Description:**

The In-Memory File System does not need to allocate memory during the
evaluate routines. Therefore, this routine simply routines PASS.

.. COMMENT: @page

IMFS_mount()
~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_mount()

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**File:**

imfs_mount.c

**Description:**

This routine provides the filesystem specific processing required to mount a
filesystem for the system that contains the mount point. It will determine
if the point that we are trying to mount onto is a node of IMFS_DIRECTORY
type.

If it is the node’s info element is altered so that the info.directory.mt_fs
element points to the mount table chain entry that is associated with the
mounted filesystem at this point. The info.directory.mt_fs element can be
examined to determine if a filesystem is mounted at a directory. If it is
NULL, the directory does not serve as a mount point. A non-NULL entry
indicates that the directory does serve as a mount point and the value of
info.directory.mt_fs can be used to locate the mount table chain entry that
describes the filesystem mounted at this point.

.. COMMENT: @page

IMFS_fsmount_me()
~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_initialize()

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**File:**

imfs_init.c

**Description:**

This function is provided with a filesystem to take care of the internal
filesystem management details associated with mounting that filesystem
under the RTEMS environment.

It is not responsible for the mounting details associated the filesystem
containing the mount point.

The rtems_filesystem_mount_table_entry_t structure contains the key elements
below:

rtems_filesystem_location_info_t         \*mt_point_node,

This structure contains information about the mount point. This
allows us to find the ops-table and the handling functions
associated with the filesystem containing the mount point.

rtems_filesystem_location_info_t         \*fs_root_node,

This structure contains information about the root node in the file
system to be mounted. It allows us to find the ops-table and the
handling functions associated with the filesystem to be mounted.

rtems_filesystem_options_t                 options,

Read only or read/write access

void                                         \*fs_info,

This points to an allocated block of memory the will be used to
hold any filesystem specific information of a global nature. This
allocated region if important because it allows us to mount the
same filesystem type more than once under the RTEMS system.
Each instance of the mounted filesystem has its own set of global
management information that is separate from the global
management information associated with the other instances of the
mounted filesystem type.

rtems_filesystem_limits_and_options_t    pathconf_info,

The table contains the following set of values associated with the
mounted filesystem:

- link_max

- max_canon

- max_input

- name_max

- path_max

- pipe_buf

- posix_async_io

- posix_chown_restrictions

- posix_no_trunc

- posix_prio_io

- posix_sync_io

- posix_vdisable

These values are accessed with the pathconf() and the fpathconf ()
functions.

const char                                   \*dev

The is intended to contain a string that identifies the device that contains
the filesystem information. The filesystems that are currently implemented
are memory based and don’t require a device specification.

If the mt_point_node.node_access is NULL then we are mounting the base file
system.

The routine will create a directory node for the root of the IMFS file
system.

The node will have read, write and execute permissions for owner, group and
others.

The node’s name will be a null string.

A filesystem information structure(fs_info) will be allocated and
initialized for the IMFS filesystem. The fs_info pointer in the mount table
entry will be set to point the filesystem information structure.

The pathconf_info element of the mount table will be set to the appropriate
table of path configuration constants ( IMFS_LIMITS_AND_OPTIONS ).

The fs_root_node structure will be filled in with the following:

- pointer to the allocated root node of the filesystem

- directory handlers for a directory node under the IMFS filesystem

- OPS table functions for the IMFS

A 0 will be returned to the calling routine if the process succeeded,
otherwise a 1 will be returned.

.. COMMENT: @page

IMFS_unmount()
~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_unmount()

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**File:**

imfs_unmount.c

**Description:**

This routine allows the IMFS to unmount a filesystem that has been
mounted onto a IMFS directory.

The mount entry mount point node access is verified to be a mounted
directory.  It’s mt_fs is set to NULL.  This identifies to future
calles into the IMFS that this directory node is no longer a mount
point.  Additionally, it will allow any directories that were hidden
by the mounted system to again become visible.

.. COMMENT: @page

IMFS_fsunmount()
~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_fsunmount()

**Arguments:**

.. code:: c

    rtems_filesystem_mount_table_entry_t   \*mt_entry

**File:**

imfs_init.c

**Description:**

This method unmounts this instance of the IMFS file system.  It is the
counterpart to the IMFS_initialize routine.  It is called by the generic
code under the fsunmount_me callback.

All method loops finding the first encountered node with no children and
removing the node from the tree, thus returning allocated resources.  This
is done until all allocated nodes are returned.

.. COMMENT: @page

IMFS_utime()
~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_eval_link()
~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

Regular File Handler Table Functions
------------------------------------

Handler table functions are defined in a rtems_filesystem_file_handlers_r
structure. It defines functions that are specific to a node type in a given
filesystem. One table exists for each of the filesystem’s node types. The
structure definition appears below. It is followed by general developmental
information on each of the functions associated with regular files contained
in this function management structure.
.. code:: c

    rtems_filesystem_file_handlers_r IMFS_memfile_handlers = {
    memfile_open,
    memfile_close,
    memfile_read,
    memfile_write,
    memfile_ioctl,
    memfile_lseek,
    IMFS_stat,
    IMFS_fchmod,
    memfile_ftruncate,
    NULL,                /* fpathconf \*/
    NULL,                /* fsync \*/
    IMFS_fdatasync,
    IMFS_fcntl
    };

.. COMMENT: @page

memfile_open() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

memfile_open()

**Arguments:**

.. code:: c

    rtems_libio_t   \*iop,
    const char      \*pathname,
    unsigned32       flag,
    unsigned32       mode

**File:**

memfile.c

**Description:**

Currently this function is a shell. No meaningful processing is performed and
a success code is always returned.

.. COMMENT: @page

memfile_close() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

memfile_close()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop

**File:**

memfile.c

**Description:**

This routine is a dummy for regular files under the base filesystem. It
performs a capture of the IMFS_jnode_t pointer from the file control block
and then immediately returns a success status.

.. COMMENT: @page

memfile_read() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

memfile_read()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    void              \*buffer,
    unsigned32         count

**File:**

memfile.c

**Description:**

This routine will determine the ``jnode`` that is associated with this file.

It will then call IMFS_memfile_read() with the ``jnode``, file position index,
buffer and transfer count as arguments.

IMFS_memfile_read() will do the following:

- Verify that the ``jnode`` is associated with a memory file

- Verify that the destination of the read is valid

- Adjust the length of the read if it is too long

- Acquire data from the memory blocks associated with the file

- Update the access time for the data in the file

.. COMMENT: @page

memfile_write() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

memfile_ioctl() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    unsigned32       command,
    void              \*buffer

**File:**

memfile.c

**Description:**

The current code is a placeholder for future development. The routine returns
a successful completion status.

.. COMMENT: @page

memfile_lseek() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

Memfile_lseek()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    off_t              offset,
    int                whence

**File:**

memfile.c

**Description:**

This routine make sure that the memory based file is sufficiently large to
allow for the new file position index.

The IMFS_memfile_extend() function is used to evaluate the current size of
the memory file and allocate additional memory blocks if required by the new
file position index. A success code is always returned from this routine.

.. COMMENT: @page

IMFS_stat() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_stat()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t   \*loc,
    struct stat                        \*buf

**File:**

imfs_stat.c

**Description:**

This routine actually performs status processing for both devices and regular
files.

The IMFS_jnode_t structure is referenced to determine the type of node under
the filesystem.

If the node is associated with a device, node information is extracted and
transformed to set the st_dev element of the stat structure.

If the node is a regular file, the size of the regular file is extracted from
the node.

This routine rejects other node types.

The following information is extracted from the node and placed in the stat
structure:

- st_mode

- st_nlink

- st_ino

- st_uid

- st_gid

- st_atime

- st_mtime

- st_ctime

.. COMMENT: @page

IMFS_fchmod() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_fchmod()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop
    mode_t              mode

**File:**

imfs_fchmod.c

**Description:**

This routine will obtain the pointer to the IMFS_jnode_t structure from the
information currently in the file control block.

Based on configuration the routine will acquire the user ID from a call to
getuid()  or from the IMFS_jnode_t structure.

It then checks to see if we have the ownership rights to alter the mode of
the file.  If the caller does not, an error code is returned.

An additional test is performed to verify that the caller is not trying to
alter the nature of the node. If the caller is attempting to alter more than
the permissions associated with user group and other, an error is returned.

If all the preconditions are met, the user, group and other fields are set
based on the mode calling parameter.

.. COMMENT: @page

memfile_ftruncate() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

No pathconf() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

NULL

**Arguments:**

Not Implemented

**File:**

Not Implemented

**Description:**

Not Implemented

.. COMMENT: @page

No fsync() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_fdatasync() for Regular Files
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

Directory Handler Table Functions
---------------------------------

Handler table functions are defined in a rtems_filesystem_file_handlers_r
structure. It defines functions that are specific to a node type in a given
filesystem. One table exists for each of the filesystem’s node types. The
structure definition appears below. It is followed by general developmental
information on each of the functions associated with directories contained in
this function management structure.
.. code:: c

    rtems_filesystem_file_handlers_r IMFS_directory_handlers = {
    IMFS_dir_open,
    IMFS_dir_close,
    IMFS_dir_read,
    NULL,             /* write \*/
    NULL,             /* ioctl \*/
    IMFS_dir_lseek,
    IMFS_dir_fstat,
    IMFS_fchmod,
    NULL,             /* ftruncate \*/
    NULL,             /* fpathconf \*/
    NULL,             /* fsync \*/
    IMFS_fdatasync,
    IMFS_fcntl
    };

.. COMMENT: @page

IMFS_dir_open() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_dir_open()

**Arguments:**

.. code:: c

    rtems_libio_t  \*iop,
    const char     \*pathname,
    unsigned32      flag,
    unsigned32      mode

**File:**

imfs_directory.c

**Description:**

This routine will look into the file control block to find the ``jnode`` that
is associated with the directory.

The routine will verify that the node is a directory. If its not a directory
an error code will be returned.

If it is a directory, the offset in the file control block will be set to 0.
This allows us to start reading at the beginning of the directory.

.. COMMENT: @page

IMFS_dir_close() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_dir_close()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop

**File:**

imfs_directory.c

**Description:**

This routine is a dummy for directories under the base filesystem. It
immediately returns a success status.

.. COMMENT: @page

IMFS_dir_read() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_dir_read

**Arguments:**

.. code:: c

    rtems_libio_t  \*iop,
    void           \*buffer,
    unsigned32      count

**File:**

imfs_directory.c

**Description:**

This routine will read a fixed number of directory entries from the current
directory offset. The number of directory bytes read will be returned from
this routine.

.. COMMENT: @page

No write() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

No ioctl() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

ioctl

**Arguments:**

**File:**

Not supported

**Description:**

XXX

.. COMMENT: @page

IMFS_dir_lseek() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_dir_lseek()

**Arguments:**

.. code:: c

    rtems_libio_t      \*iop,
    off_t               offset,
    int                 whence

**File:**

imfs_directory.c

**Description:**

This routine alters the offset in the file control block.

No test is performed on the number of children under the current open
directory.  The imfs_dir_read() function protects against reads beyond the
current size to the directory by returning a 0 bytes transfered to the
calling programs whenever the file position index exceeds the last entry in
the open directory.

.. COMMENT: @page

IMFS_dir_fstat() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

imfs_dir_fstat()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t   \*loc,
    struct stat                        \*buf

**File:**

imfs_directory.c

**Description:**

The node access information in the rtems_filesystem_location_info_t structure
is used to locate the appropriate IMFS_jnode_t structure. The following
information is taken from the IMFS_jnode_t structure and placed in the stat
structure:

- st_ino

- st_mode

- st_nlink

- st_uid

- st_gid

- st_atime

- st_mtime

- st_ctime

The st_size field is obtained by running through the chain of directory
entries and summing the sizes of the dirent structures associated with each
of the children of the directory.

.. COMMENT: @page

IMFS_fchmod() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_fchmod()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop
    mode_t             mode

**File:**

imfs_fchmod.c

**Description:**

This routine will obtain the pointer to the IMFS_jnode_t structure from the
information currently in the file control block.

Based on configuration the routine will acquire the user ID from a call to
getuid()  or from the IMFS_jnode_t structure.

It then checks to see if we have the ownership rights to alter the mode of
the file.  If the caller does not, an error code is returned.

An additional test is performed to verify that the caller is not trying to
alter the nature of the node. If the caller is attempting to alter more than
the permissions associated with user group and other, an error is returned.

If all the preconditions are met, the user, group and other fields are set
based on the mode calling parameter.

.. COMMENT: @page

No ftruncate() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

No fpathconf() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

fpathconf

**Arguments:**

Not Implemented

**File:**

Not Implemented

**Description:**

Not Implemented

.. COMMENT: @page

No fsync() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

IMFS_fdatasync() for Directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

Device Handler Table Functions
------------------------------

Handler table functions are defined in a rtems_filesystem_file_handlers_r
structure. It defines functions that are specific to a node type in a given
filesystem. One table exists for each of the filesystem’s node types. The
structure definition appears below. It is followed by general developmental
information on each of the functions associated with devices contained in
this function management structure.
.. code:: c

    typedef struct {
    rtems_filesystem_open_t           open;
    rtems_filesystem_close_t          close;
    rtems_filesystem_read_t           read;
    rtems_filesystem_write_t          write;
    rtems_filesystem_ioctl_t          ioctl;
    rtems_filesystem_lseek_t          lseek;
    rtems_filesystem_fstat_t          fstat;
    rtems_filesystem_fchmod_t         fchmod;
    rtems_filesystem_ftruncate_t      ftruncate;
    rtems_filesystem_fpathconf_t      fpathconf;
    rtems_filesystem_fsync_t          fsync;
    rtems_filesystem_fdatasync_t      fdatasync;
    } rtems_filesystem_file_handlers_r;

.. COMMENT: @page

device_open() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

device_open()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    const char        \*pathname,
    unsigned32         flag,
    unsigned32         mode

**File:**

deviceio.c

**Description:**

This routine will use the file control block to locate the node structure for
the device.

It will extract the major and minor device numbers from the ``jnode``.

The major and minor device numbers will be used to make a rtems_io_open()
function call to open the device driver. An argument list is sent to the
driver that contains the file control block, flags and mode information.

.. COMMENT: @page

device_close() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

device_close()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop

**File:**

deviceio.c

**Description:**

This routine extracts the major and minor device driver numbers from the
IMFS_jnode_t that is referenced in the file control block.

It also forms an argument list that contains the file control block.

A rtems_io_close() function call is made to close the device specified by the
major and minor device numbers.

.. COMMENT: @page

device_read() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

device_read()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    void              \*buffer,
    unsigned32         count

**File:**

deviceio.c

**Description:**

This routine will extract the major and minor numbers for the device from the -
jnode- associated with the file descriptor.

A rtems_io_read() call will be made to the device driver associated with the file
descriptor. The major and minor device number will be sent as arguments as well
as an argument list consisting of:

- file control block

- file position index

- buffer pointer where the data read is to be placed

- count indicating the number of bytes that the program wishes to read
  from the device

- flags from the file control block

On return from the rtems_io_read() the number of bytes that were actually
read will be returned to the calling program.

.. COMMENT: @page

device_write() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

device_ioctl() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

ioctl

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    unsigned32         command,
    void              \*buffer

**File:**

deviceio.c

**Description:**

This handler will obtain status information about a device.

The form of status is device dependent.

The rtems_io_control() function uses the major and minor number of the device
to obtain the status information.

rtems_io_control() requires an rtems_libio_ioctl_args_t argument list which
contains the file control block, device specific command and a buffer pointer
to return the device status information.

The device specific command should indicate the nature of the information
that is desired from the device.

After the rtems_io_control() is processed, the buffer should contain the
requested device information.

If the device information is not obtained properly a -1 will be returned to
the calling program, otherwise the ioctl_return value is returned.

.. COMMENT: @page

device_lseek() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

device_lseek()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop,
    off_t              offset,
    int                whence

**File:**

deviceio.c

**Description:**

At the present time this is a placeholder function. It always returns a
successful status.

.. COMMENT: @page

IMFS_stat() for Devices
~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_stat()

**Arguments:**

.. code:: c

    rtems_filesystem_location_info_t   \*loc,
    struct stat                        \*buf

**File:**

imfs_stat.c

**Description:**

This routine actually performs status processing for both devices and regular files.

The IMFS_jnode_t structure is referenced to determine the type of node under the
filesystem.

If the node is associated with a device, node information is extracted and
transformed to set the st_dev element of the stat structure.

If the node is a regular file, the size of the regular file is extracted from the node.

This routine rejects other node types.

The following information is extracted from the node and placed in the stat
structure:

- st_mode

- st_nlink

- st_ino

- st_uid

- st_gid

- st_atime

- st_mtime

- st_ctime

.. COMMENT: @page

IMFS_fchmod() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

IMFS_fchmod()

**Arguments:**

.. code:: c

    rtems_libio_t     \*iop
    mode_t             mode

**File:**

imfs_fchmod.c

**Description:**

This routine will obtain the pointer to the IMFS_jnode_t structure from the
information currently in the file control block.

Based on configuration the routine will acquire the user ID from a call to
getuid()  or from the IMFS_jnode_t structure.

It then checks to see if we have the ownership rights to alter the mode of
the file.  If the caller does not, an error code is returned.

An additional test is performed to verify that the caller is not trying to
alter the nature of the node. If the caller is attempting to alter more than
the permissions associated with user group and other, an error is returned.

If all the preconditions are met, the user, group and other fields are set
based on the mode calling parameter.

.. COMMENT: @page

No ftruncate() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

No fpathconf() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

fpathconf

**Arguments:**

Not Implemented

**File:**

Not Implemented

**Description:**

Not Implemented

.. COMMENT: @page

No fsync() for Devices
~~~~~~~~~~~~~~~~~~~~~~

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: @page

No fdatasync() for Devices
~~~~~~~~~~~~~~~~~~~~~~~~~~

Not Implemented

**Corresponding Structure Element:**

XXX

**Arguments:**

XXX

**File:**

XXX

**Description:**

XXX

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.

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.

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.

Command and Variable Index
##########################

There are currently no Command and Variable Index entries.

.. COMMENT: @printindex fn

Concept Index
#############

There are currently no Concept Index entries.

.. COMMENT: @printindex cp