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rtems-docs/filesystem/in-memory.rst
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.. SPDX-License-Identifier: CC-BY-SA-4.0
.. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR)
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-block:: 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
==============================
TBD
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`.
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-block:: 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
IMFS_evalformake()
^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
IMFS_link()
^^^^^^^^^^^
Corresponding Structure Element:
``link``
Arguments:
.. code-block:: 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.
IMFS_unlink()
^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
IMFS_node_type()
^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_node_type()``
Arguments:
.. code-block:: 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-block:: 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).
IMFS_rmnod()
^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
IMFS_chown()
^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_chown()``
Arguments:
.. code-block:: 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.
IMFS_freenod()
^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_freenod()``
Arguments:
.. code-block:: 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.
IMFS_freenodinfo()
^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_freenodinfo()``
Arguments:
.. code-block:: 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.
IMFS_mount()
^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_mount()``
Arguments:
.. code-block:: 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.
IMFS_fsmount_me()
^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_initialize()``
Arguments:
.. code-block:: 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:
.. code-block:: c
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.
.. code-block:: c
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.
.. code-block:: c
rtems_filesystem_options_t options,
Read only or read/write access
.. code-block:: c
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.
.. code-block:: c
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.
.. code-block:: c
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.
IMFS_unmount()
^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_unmount()``
Arguments:
.. code-block:: 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.
IMFS_fsunmount()
^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``imfs_fsunmount()``
Arguments:
.. code-block:: 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.
IMFS_utime()
^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
IMFS_eval_link()
^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
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-block:: 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
};
memfile_open() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``memfile_open()``
Arguments:
.. code-block:: 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.
memfile_close() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``memfile_close()``
Arguments:
.. code-block:: 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.
memfile_read() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``memfile_read()``
Arguments:
.. code-block:: 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
memfile_write() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
memfile_ioctl() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
.. code-block:: 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.
memfile_lseek() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``Memfile_lseek()``
Arguments:
.. code-block:: 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.
IMFS_stat() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_stat()``
Arguments:
.. code-block:: 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
IMFS_fchmod() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_fchmod()``
Arguments:
.. code-block:: 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.
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
No fsync() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
IMFS_fdatasync() for Regular Files
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
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
};
IMFS_dir_open() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``imfs_dir_open()``
Arguments:
.. code-block:: 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.
IMFS_dir_close() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``imfs_dir_close()``
Arguments:
.. code-block:: 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.
IMFS_dir_read() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``imfs_dir_read``
Arguments:
.. code-block:: 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.
No write() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
No ioctl() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``ioctl``
Arguments:
Not supported
File:
Not supported
Description:
XXX
IMFS_dir_lseek() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``imfs_dir_lseek()``
Arguments:
.. code-block:: 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.
IMFS_dir_fstat() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``imfs_dir_fstat()``
Arguments:
.. code-block:: 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.
IMFS_fchmod() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_fchmod()``
Arguments:
.. code-block:: 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.
No ftruncate() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
No fpathconf() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``fpathconf``
Arguments:
Not Implemented
File:
Not Implemented
Description:
Not Implemented
No fsync() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
IMFS_fdatasync() for Directories
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
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-block:: 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;
device_open() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``device_open()``
Arguments:
.. code-block:: 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.
device_close() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``device_close()``
Arguments:
.. code-block:: 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.
device_read() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``device_read()``
Arguments:
.. code-block:: 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.
device_write() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
device_ioctl() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``ioctl``
Arguments:
.. code-block:: 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.
device_lseek() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``device_lseek()``
Arguments:
.. code-block:: 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.
IMFS_stat() for Devices
^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_stat()``
Arguments:
.. code-block:: 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
IMFS_fchmod() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``IMFS_fchmod()``
Arguments:
.. code-block:: 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.
No ftruncate() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
No fpathconf() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
``fpathconf``
Arguments:
Not Implemented
File:
Not Implemented
Description:
Not Implemented
No fsync() for Devices
^^^^^^^^^^^^^^^^^^^^^^
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
No fdatasync() for Devices
^^^^^^^^^^^^^^^^^^^^^^^^^^
Not Implemented
Corresponding Structure Element:
XXX
Arguments:
XXX
File:
XXX
Description:
XXX
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