source: rtems/doc/filesystem/imfs.t @ 7441fe2c

@c  COPYRIGHT (c) 1988-1998.
@c  On-Line Applications Research Corporation (OAR).
@c  All rights reserved.
@c
@c  $Id$
@c

@chapter 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.

@section IMFS Per Node Data Structure

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

@example
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;
@};
@end example

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

@table @b

@item Node
exists to allow the entire @code{jnode} structure to be included in a chain.

@item Parent
is a pointer to another @code{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.

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

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

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

@item st_ino
is a unique node identification number

@item st_uid
is the user ID of the file's owner

@item st_gid
is the group ID of the file's owner

@item st_atime
is the time of the last access to this file

@item st_mtime
is the time of the last modification of this file

@item st_ctime
is the time of the last status change to the file

@item type
is the indication of node type must be one of the following states:

@itemize @bullet
@item IMFS_DIRECTORY 
@item IMFS_MEMORY_FILE 
@item IMFS_HARD_LINK
@item IMFS_SYM_LINK
@item IMFS_DEVICE 
@end itemize


@item info
is this contains a structure that is unique to file type (See IMFS_typs_union
in imfs.h).

@itemize @bullet

@item IMFS_DIRECTORY

An IMFS directory contains a dynamic chain structure that
records all files and directories that are subordinate to the directory node.

@item 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.

@item 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.

@item 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.

@item 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.

@end itemize

@end table

@section Miscellaneous IMFS Information

@section 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.

@subsection Node removal constraints for the IMFS

The IMFS conforms to the general filesystem requirements for node
removal.  See @ref{File and Directory Removal Constraints}.

@subsection IMFS General Housekeeping Notes

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

@itemize @bullet 

@item 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.

@item 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.

@end itemize

@section IMFS Operation Tables

@subsection 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.

@example
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
@};
@end example

@c
@c
@c
@page

@subsubsection IMFS_evalpath()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection IMFS_evalformake()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection IMFS_link()

@subheading Corresponding Structure Element:

link

@subheading Arguments:


@example
rtems_filesystem_location_info_t    *to_loc,      /* IN */
rtems_filesystem_location_info_t    *parent_loc,  /* IN */
const char                          *token        /* IN */
@end example

@subheading File:

imfs_link.c

@subheading 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:

@itemize @bullet

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

@item Type will be set to IMFS_HARD_LINK

@item name will be set to the normalized name

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

@end itemize

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.


@c
@c
@c
@page

@subsubsection IMFS_unlink()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection IMFS_node_type()

@subheading Corresponding Structure Element:

IMFS_node_type()

@subheading Arguments:

@example
rtems_filesystem_location_info_t    *pathloc        /* IN */
@end example

@subheading File:

imfs_ntype.c

@subheading 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:

@itemize @bullet

@item RTEMS_FILESYSTEM_DIRECTORY

@item RTEMS_FILESYSTEM_DEVICE

@item RTEMS_FILESYSTEM_HARD_LINK

@item RTEMS_FILESYSTEM_MEMORY_FILE

@end itemize

@c
@c
@c
@page

@subsubsection IMFS_mknod()

@subheading Corresponding Structure Element:

IMFS_mknod()

@subheading Arguments:

@example
const char                          *token,        /* IN */
mode_t                               mode,         /* IN */
dev_t                                dev,          /* IN */
rtems_filesystem_location_info_t    *pathloc       /* IN/OUT */
@end example

@subheading File:

imfs_mknod.c

@subheading 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 @code{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 @code{jnode} (ENOMEN).


@c
@c
@c
@page

@subsubsection IMFS_rmnod()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection IMFS_chown()

@subheading Corresponding Structure Element:

IMFS_chown()

@subheading Arguments:

@example
rtems_filesystem_location_info_t    *pathloc        /* IN */
uid_t                                owner          /* IN */
gid_t                                group          /* IN */
@end example

@subheading File:

imfs_chown.c

@subheading 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.



@c
@c
@c
@page

@subsubsection IMFS_freenod()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX 


@c
@c
@c
@page

@subsubsection IMFS_mount()

@subheading Corresponding Structure Element:

IMFS_mount()

@subheading Arguments:

@example
rtems_filesystem_mount_table_entry_t   *mt_entry
@end example

@subheading File:

imfs_mount.c

@subheading 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.


@c
@c
@c
@page

@subsubsection IMFS_fsmount_me()

@subheading Corresponding Structure Element:

IMFS_initialize()

@subheading Arguments:

@example
rtems_filesystem_mount_table_entry_t   *mt_entry    
@end example

@subheading File:

imfs_init.c

@subheading 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:

@itemize @bullet

@item link_max

@item max_canon

@item max_input

@item name_max

@item path_max

@item pipe_buf

@item posix_async_io

@item posix_chown_restrictions

@item posix_no_trunc

@item posix_prio_io

@item posix_sync_io

@item posix_vdisable

@end itemize

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:

@itemize @bullet

@item pointer to the allocated root node of the filesystem

@item directory handlers for a directory node under the IMFS filesystem

@item OPS table functions for the IMFS

@end itemize

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


@c
@c
@c
@page

@subsubsection IMFS_unmount()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX 


@c
@c
@c
@page

@subsubsection IMFS_fsunmount_me()

@subheading Corresponding Structure Element:

imfs_fsunmount_me()

@subheading Arguments:

@example
rtems_filesystem_mount_table_entry_t   *mt_entry    
@end example

@subheading File:

imfs_fsunmount_me.c

@subheading Description:

XXX 


@c
@c
@c
@page

@subsubsection IMFS_utime()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX 


@c
@c
@c
@page

@subsubsection IMFS_eval_link()

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page
@subsection 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.

@example
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
@};
@end example


@c
@c
@c
@page

@subsubsection memfile_open() for Regular Files

@subheading Corresponding Structure Element:

memfile_open()

@subheading Arguments:

@example
rtems_libio_t   *iop,
const char      *pathname,
unsigned32       flag,
unsigned32       mode
@end example

@subheading File:

memfile.c

@subheading Description:

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

@c
@c
@c
@page

@subsubsection memfile_close() for Regular Files

@subheading Corresponding Structure Element:

memfile_close()

@subheading Arguments:

@example
rtems_libio_t     *iop
@end example

@subheading File:

memfile.c

@subheading 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.


@c
@c
@c
@page

@subsubsection memfile_read() for Regular Files

@subheading Corresponding Structure Element:

memfile_read()

@subheading Arguments:

@example
rtems_libio_t     *iop,
void              *buffer,
unsigned32         count
@end example

@subheading File:

memfile.c

@subheading Description:

This routine will determine the @code{jnode} that is associated with this file.

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

IMFS_memfile_read() will do the following:

@itemize @bullet

@item Verify that the @code{jnode} is associated with a memory file

@item Verify that the destination of the read is valid

@item Adjust the length of the read if it is too long

@item Acquire data from the memory blocks associated with the file

@item Update the access time for the data in the file

@end itemize

@c
@c
@c
@page

@subsubsection memfile_write() for Regular Files

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page

@subsubsection memfile_ioctl() for Regular Files

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

@example
rtems_libio_t     *iop,
unsigned32       command,
void              *buffer
@end example

@subheading File:

memfile.c

@subheading Description:

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

@c
@c
@c
@page

@subsubsection memfile_lseek() for Regular Files

@subheading Corresponding Structure Element:

Memfile_lseek()

@subheading Arguments:

@example
rtems_libio_t     *iop,
off_t              offset,
int                whence
@end example

@subheading File:

memfile.c

@subheading 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.

@c
@c
@c
@page

@subsubsection IMFS_stat() for Regular Files

@subheading Corresponding Structure Element:

IMFS_stat()

@subheading Arguments:

@example
rtems_filesystem_location_info_t   *loc,
struct stat                        *buf
@end example

@subheading File:

imfs_stat.c

@subheading 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:

@itemize @bullet

@item st_mode

@item st_nlink

@item st_ino

@item st_uid

@item st_gid

@item st_atime

@item st_mtime

@item st_ctime

@end itemize

@c
@c
@c
@page

@subsubsection IMFS_fchmod() for Regular Files

@subheading Corresponding Structure Element:

IMFS_fchmod()

@subheading Arguments:

@example
rtems_libio_t     *iop
mode_t              mode
@end example

@subheading File:

imfs_fchmod.c

@subheading 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.

@c
@c
@c
@page

@subsubsection memfile_ftruncate() for Regular Files

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX


@subsubsection No pathconf() for Regular Files

@subheading Corresponding Structure Element:

NULL

@subheading Arguments:

Not Implemented

@subheading File:

Not Implemented

@subheading Description:

Not Implemented


@c
@c
@c
@page

@subsubsection No fsync() for Regular Files

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection IMFS_fdatasync() for Regular Files

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page
@subsection 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.

@example
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
@};
@end example


@c
@c
@c
@page
@subsubsection IMFS_dir_open() for Directories

@subheading Corresponding Structure Element:

imfs_dir_open()

@subheading Arguments:

@example
rtems_libio_t  *iop,
const char     *pathname,
unsigned32      flag,
unsigned32      mode
@end example

@subheading File:

imfs_directory.c

@subheading Description:

This routine will look into the file control block to find the @code{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.

@c
@c
@c
@page

@subsubsection IMFS_dir_close() for Directories

@subheading Corresponding Structure Element:

imfs_dir_close()

@subheading Arguments:

@example
rtems_libio_t     *iop
@end example

@subheading File:

imfs_directory.c

@subheading Description:

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

@c
@c
@c
@page

@subsubsection IMFS_dir_read() for Directories

@subheading Corresponding Structure Element:

imfs_dir_read

@subheading Arguments:

@example
rtems_libio_t  *iop,
void           *buffer,
unsigned32      count
@end example

@subheading File:

imfs_directory.c

@subheading 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.


@c
@c
@c
@page

@subsubsection No write() for Directories

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page

@subsubsection No ioctl() for Directories

@subheading Corresponding Structure Element:

ioctl

@subheading Arguments:


@subheading File:

Not supported

@subheading Description:

XXX

@c
@c
@c
@page

@subsubsection IMFS_dir_lseek() for Directories

@subheading Corresponding Structure Element:

imfs_dir_lseek()

@subheading Arguments:

@example
rtems_libio_t      *iop,
off_t               offset,
int                 whence
@end example

@subheading File:

imfs_directory.c

@subheading 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.

@c
@c
@c
@page

@subsubsection IMFS_dir_fstat() for Directories

@subheading Corresponding Structure Element:

imfs_dir_fstat()

@subheading Arguments:


@example
rtems_filesystem_location_info_t   *loc,
struct stat                        *buf
@end example

@subheading File:

imfs_directory.c

@subheading 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:

@itemize @bullet
@item st_ino
@item st_mode
@item st_nlink
@item st_uid
@item st_gid
@item st_atime
@item st_mtime
@item st_ctime
@end itemize

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.

@c
@c
@c
@page

@subsubsection IMFS_fchmod() for Directories

@subheading Corresponding Structure Element:

IMFS_fchmod()

@subheading Arguments:

@example
rtems_libio_t     *iop
mode_t             mode
@end example

@subheading File:

imfs_fchmod.c

@subheading 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.

@c
@c
@c
@page

@subsubsection No ftruncate() for Directories

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page

@subsubsection No fpathconf() for Directories

@subheading Corresponding Structure Element:

fpathconf

@subheading Arguments:

Not Implemented

@subheading File:

Not Implemented

@subheading Description:

Not Implemented


@c
@c
@c
@page

@subsubsection No fsync() for Directories

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection IMFS_fdatasync() for Directories

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page
@subsection 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.

@example
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;
@end example

@c
@c
@c
@page

@subsubsection device_open() for Devices

@subheading Corresponding Structure Element:

device_open()

@subheading Arguments:

@example
rtems_libio_t     *iop,
const char        *pathname,
unsigned32         flag,
unsigned32         mode
@end example

@subheading File:

deviceio.c

@subheading 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 @code{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.

@c
@c
@c
@page

@subsubsection device_close() for Devices

@subheading Corresponding Structure Element:

device_close()

@subheading Arguments:

@example
rtems_libio_t     *iop
@end example

@subheading File:

deviceio.c

@subheading 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.


@c
@c
@c
@page

@subsubsection device_read() for Devices

@subheading Corresponding Structure Element:

device_read()

@subheading Arguments:

@example
rtems_libio_t     *iop,
void              *buffer,
unsigned32         count
@end example

@subheading File:

deviceio.c

@subheading 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:

@itemize @bullet
@item file control block

@item file position index

@item buffer pointer where the data read is to be placed

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

@item flags from the file control block

@end itemize

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


@c
@c
@c
@page

@subsubsection device_write() for Devices

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page

@subsubsection device_ioctl() for Devices

@subheading Corresponding Structure Element:

ioctl

@subheading Arguments:

@example
rtems_libio_t     *iop,
unsigned32         command,
void              *buffer
@end example

@subheading File:

deviceio.c

@subheading 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.

@c
@c
@c
@page

@subsubsection device_lseek() for Devices

@subheading Corresponding Structure Element:

device_lseek()

@subheading Arguments:

@example
rtems_libio_t     *iop,
off_t              offset,
int                whence
@end example

@subheading File:

deviceio.c

@subheading Description:

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

@c
@c
@c
@page

@subsubsection IMFS_stat() for Devices

@subheading Corresponding Structure Element:

IMFS_stat()

@subheading Arguments:

@example
rtems_filesystem_location_info_t   *loc,
struct stat                        *buf
@end example

@subheading File:

imfs_stat.c

@subheading 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:

@itemize @bullet

@item st_mode

@item st_nlink

@item st_ino

@item st_uid

@item st_gid

@item st_atime

@item st_mtime

@item st_ctime

@end itemize



@c
@c
@c
@page

@subsubsection IMFS_fchmod() for Devices

@subheading Corresponding Structure Element:

IMFS_fchmod()

@subheading Arguments:

@example
rtems_libio_t     *iop
mode_t             mode
@end example

@subheading File:

imfs_fchmod.c

@subheading 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.


@c
@c
@c
@page

@subsubsection No ftruncate() for Devices

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX
@subheading File:

XXX

@subheading Description:

XXX

@c
@c
@c
@page

@subsubsection No fpathconf() for Devices

@subheading Corresponding Structure Element:

fpathconf

@subheading Arguments:

Not Implemented

@subheading File:

Not Implemented

@subheading Description:

Not Implemented


@c
@c
@c
@page

@subsubsection No fsync() for Devices

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX


@c
@c
@c
@page

@subsubsection No fdatasync() for Devices

Not Implemented

@subheading Corresponding Structure Element:

XXX

@subheading Arguments:

XXX

@subheading File:

XXX

@subheading Description:

XXX