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1Preface
2#######
3
4This document describes the implementation of the RTEMS filesystem
5infrastructure.  This infrastructure supports the following
6capabilities:
7
8- Mountable file systems
9
10- Hierarchical file system directory structure
11
12- POSIX compliant set of routines for the manipulation of files and directories
13
14- Individual file and directory support for the following:
15  # Permissions for read, write and execute
16  # User ID
17  # Group ID
18  # Access time
19  # Modification time
20  # Creation time
21
22- Hard links to files and directories
23
24- Symbolic links to files and directories
25
26This has been implemented to provide the framework for a UNIX-like
27file system support. POSIX file and directory functions have been
28implemented that allow a standard method of accessing file, device and
29directory information within file systems. The file system concept that
30has been implemented allows for expansion and adaptation of the file
31system to a variety of existing and future data storage devices. To this
32end, file system mount and unmount capabilities have been included in this
33RTEMS framework.
34
35This framework slightly alters the manner in which devices are handled
36under RTEMS from that of public release 4.0.0 and earlier.  Devices that
37are defined under a given RTEMS configuration will now be registered as
38files in a mounted file system.  Access to these device drivers and their
39associated devices may now be performed through the traditional file system
40open(), read(), write(), lseek(), fstat() and ioctl() functions in addition
41to the interface provided by the IO Manager in the RTEMS Classic API.
42
43An In-Memory File System (IMFS) is included which provides full POSIX
44filesystem functionality yet is RAM based.  The IMFS maintains a
45node structure for each file, device, and directory in each mounted
46instantiation of its file system. The node structure is used to
47manage ownership, access rights, access time, modification time,
48and creation time.  A union of structures within the IMFS nodal
49structure provide for manipulation of file data, device selection,
50or directory content as required by the nodal type. Manipulation of
51these properties is accomplished through the POSIX set of file and
52directory functions.  In addition to being useful in its own right,
53the IMFS serves as a full featured example filesystem.
54
55The intended audience for this document is those persons implementing
56their own filesystem.  Users of the filesystem may find information
57on the implementation useful.  But the user interface to the filesystem
58is through the ISO/ANSI C Library and POSIX 1003.1b file and directory
59APIs.
60
61.. COMMENT: COPYRIGHT (c) 1988-2002.
62
63.. COMMENT: On-Line Applications Research Corporation (OAR).
64
65.. COMMENT: All rights reserved.
66
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