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Joel Sherrill
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doc/filesystem/basefs.t
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@@ -9,112 +9,121 @@
@chapter Base File System
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.
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.
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.
@example
Figure of the tree structure goes here.
@end example
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.
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.
@section Base File System 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
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.
@example
Figure 4
Figure of the mount table chain goes here.
@end example
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.
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.
@example
Figure 5
Figure of the Mount Table Processing goes here.
@end example
Note: Other file systems can be mounted but they are mounted onto points (directory
mount points) in the base file system.
Note: Other file systems can be mounted but they are mounted onto points
(directory mount points) in the base file system.
@subsection Base File System Node Structure and Function
Each regular file, device, hard link, and directory is represented by a data
structure called a @code{jnode}. The -jnode- is formally represented by the 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 */
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;
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 file system.
The key elements of this structure are listed below together with a brief
explanation of their role in the file system.
@table @b
@item node
This element exists simply to allow the entire @code{jnode} structure to be
@item Node
This element exists simply to allow the entire @code{jnode} structure to be
included in a chain.
@item parent
A pointer to another @code{jnode} structure that is the logical parent of the
node in which it appears. There are circumstances that will produce a null parent
pointer within a @code{jnode}. This can occur when a hard link is created to a file and
the file is then removed without removing the hard link.
@item Parent
A pointer to another @code{jnode} structure that is the logical parent of the
node in which it appears. There are circumstances that will produce a null
parent pointer within a @code{jnode}. This can occur when a hard link is
created to a file and the file is then removed without removing the hard
link.
@item name
The name of this node within the file system hierarchical tree. Example:
If the fully qualified pathname to the @code{jnode} was /a/b/c, the -jnode- name field
would contain the null terminated string "c"
The name of this node within the file system hierarchical tree. Example: If
the fully qualified pathname to the @code{jnode} was /a/b/c, the @code{jnode} name
field would contain the null terminated string "c"
@item st_mode
The standard Unix access permissions for the file or directory.
@item st_nlink
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.
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
A unique node identification number
@@ -147,41 +156,45 @@ The indication of node type must be one of the following states:
@item info
This contains a structure that is unique to file type(See IMFS_typs_union in
imfs.h )
This contains a structure that is unique to file type (See IMFS_typs_union
in imfs.h).
@itemize @bullet
@item IMFS_DIRECTORY
An in memory file system directory contains a
dynamic chain structure that records all files and directories that are
subordinate to the directory node.
An in memory file system 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 file system 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.
These memory-tracking techniques are graphically depicted in figures XXX
and XXX of appendix A.
Under the in memory file system 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. These
memory-tracking techniques are graphically depicted in figures XXX and XXX of
appendix A.
@item IMFS_HARD_LINK
The IMFS file system supports the concept of hard
links to other nodes in the IMFS file system. These hard links are actual
pointers to the memory associated with other nodes in the file system. This
type of link cannot cross-file system boundaries.
The IMFS file system supports the concept of hard links to other nodes in the
IMFS file system. These hard links are actual pointers to the memory
associated with other nodes in the file system. This type of link cannot
cross-file system boundaries.
@item IMFS_SYM_LINK
The IMFS file system supports the concept of symbolic
links to other nodes in any file system. 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-file system boundaries.
The IMFS file system supports the concept of symbolic links to other nodes in
any file system. 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-file system boundaries.
@item IMFS_DEVICE
All RTEMS devices now appear as files under the in
memory file system. On system initialization, all devices are registered as
nodes under the file system.
All RTEMS devices now appear as files under the in memory file system. On
system initialization, all devices are registered as nodes under the file
system.
@end itemize
@@ -193,6 +206,7 @@ nodes under the file system.
@itemize @bullet
@item If a node is a directory with children it cannot be removed.
@item The root node of the base file system or the mounted file system
cannot be removed.
@@ -208,13 +222,13 @@ link count must be less than one to allow for removal of the node.
@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 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.
@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
@@ -224,6 +238,7 @@ IMFS_memfile_remove() function.
@subsection OPS Table Functions for the In Memory File System (IMFS)
@example
OPS Table Functions File Routine Name
Evalpath Imfs_eval.c IMFS_eval_path()