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@c

@c  COPYRIGHT (c) 1988-2002.

@c  On-Line Applications Research Corporation (OAR).

@c  All rights reserved.

@c

@c  syscalls.t,v 1.7 2002/01/17 21:47:45 joel Exp

@c

@chapter 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.

@enumerate

@item access()

@item chdir()

@item chmod()

@item chown()

@item close()

@item closedir()

@item dup()

@item dup2()

@item fchmod()

@item fcntl()

@item fdatasync()

@item fpathconf()

@item fstat()

@item ioctl()

@item link()

@item lseek()

@item mkdir()

@item mkfifo()

@item mknod()

@item mount()

@item open()

@item opendir()

@item pathconf()

@item read()

@item readdir()

@item unmount()

@end enumerate

The sections that follow provide developmental information concerning each

of these functions.

@c @page

@section access

@subheading File:

access.c

@subheading 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.

@subheading 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.

@c @page

@section chdir

@subheading File:

chdir.c

@subheading 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.

@subheading 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:

@itemize @bullet

@item RTEMS_FILESYSTEM_DIRECTORY

@item RTEMS_FILESYSTEM_DEVICE

@item RTEMS_FILESYSTEM_HARD_LINK

@item RTEMS_FILESYSTEM_MEMORY_FILE

@end itemize

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.

@c @page

@section chmod

@subheading File:

chmod.c

@subheading 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.

@subheading 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.

@c @page

@section chown

@subheading File:

chown.c

@subheading 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.

@subheading 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.

@c @page

@section close

@subheading File:

close.c

@subheading 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).

@subheading 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:

@enumerate

@item Use the rtems_libio_iop() function to obtain the rtems_libio_t

structure for the file descriptor

@item Range check the file descriptor using rtems_libio_check_fd()

@item 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.

@item If the function has been defined it is invoked with the file control

block pointer as its argument.

@item The file control block that was associated with the open file

descriptor is marked as free using rtems_libio_free().

@item The return code from the close handler is then passed back to the

calling program.

@end enumerate

@c @page

@section closedir

@subheading File:

closedir.c

@subheading 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.

@subheading 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.

@c @page

@section dup()      Unimplemented

@subheading File:

dup.c

@subheading Processing:

@subheading Development Comments:

@c @page

@section dup2()      Unimplemented

@subheading File:

dup2.c

@subheading Processing:

@subheading Development Comments:

@c @page

@section fchmod

@subheading File:

fchmod.c

@subheading Processing:

This routine will alter the permissions of a node in a filesystem. It is

layered on the following functions and macros:

@itemize @bullet

@item rtems_file_descriptor_type()

@item rtems_libio_iop()

@item rtems_libio_check_fd()

@item rtems_libio_check_permissions()

@item fchmod() function that is referenced by the handler table in the

file control block associated with this file descriptor

@end itemize

@subheading 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.

@c @page

@section fcntl()

@subheading File:

fcntl.c

@subheading 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.

@subheading 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

@code{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:

@enumerate

@item Test to see if we are trying to operate on a file descriptor

associated with a network connection

@item Obtain the file control block that is associated with the file

descriptor index

@item Perform a range check on the file descriptor index.

@end enumerate

@c @page

@section fdatasync

@subheading File:

fdatasync.c

@subheading 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:

@itemize @bullet

@item rtems_file_descriptor_type()

@item rtems_libio_iop()

@item rtems_libio_check_fd()

@item rtems_libio_check_permissions()

@item fdatasync() function that is referenced by the handler table in the

file control block associated with this file descriptor

@end itemize

@subheading 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.

@c @page

@section fpathconf

@subheading File:

fpathconf.c

@subheading Processing:

This routine is layered on the following functions and macros:

@itemize @bullet

@item rtems_file_descriptor_type()

@item rtems_libio_iop()

@item rtems_libio_check_fd()

@item rtems_libio_check_permissions()

@end itemize

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.

@itemize @bullet

@item PCLINKMAX

@item PCMAXCANON

@item PCMAXINPUT

@item PCNAMEMAX

@item PCPATHMAX

@item PCPIPEBUF

@item PCCHOWNRESTRICTED

@item PCNOTRUNC

@item PCVDISABLE

@item PCASYNCIO

@item PCPRIOIO

@item PCSYNCIO

@end itemize

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.

@subheading 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.

@c @page

@section fstat

@subheading File:

fstat.c

@subheading 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 @code{fstat()} will return a

mode set to @code{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.

@subheading 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:

@enumerate

@item Obtain the file control block that is associated with the file descriptor

index.

@item Range check the file descriptor index.

@item 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.

@end enumerate

@c @page

@section ioctl

@subheading File:

ioctl.c

@subheading 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.

@subheading 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:

@enumerate

@item The file descriptor index is used to obtain the associated file

control block.

@item The file descriptor value is range checked.

@item 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.

@item If the ioctl() handler function exists, it is called with the file

control block, the command and buffer as its parameters.

@item The return code from this function is then sent to the calling

routine.

@end enumerate

@c @page

@section link

@subheading File:

link.c

@subheading 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.

@subheading 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.

@c @page

@section lseek

@subheading File:

lseek.c

@subheading 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.

@subheading 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:

@enumerate

@item The file descriptor is used to obtain the file control block for the

node.

@item The file descriptor is range checked.

@item The offset element of the file control block is altered as indicated

by the offset and whence calling parameters

@item 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.

@item The lseek() function from the designated handler table is called

with the file control block, offset and whence as calling arguments

@item The return code from the lseek() handler function is returned to the

calling program

@end enumerate

@c @page

@section mkdir

@subheading File:

mkdir.c

@subheading Processing:

This routine attempts to create a directory node under the filesystem. The

routine is layered the mknod() function.

@subheading Development Comments:

See mknod() for developmental comments.

@c @page

@section mkfifo

@subheading File:

mkfifo.c

@subheading Processing:

This routine attempts to create a FIFO node under the filesystem. The

routine is layered the mknod() function.

@subheading Development Comments:

See mknod() for developmental comments

@c @page

@section mknod

@subheading File:

mknod.c

@subheading Processing:

This function will allow for the creation of the following types of nodes

under the filesystem:

@itemize @bullet

@item directories

@item regular files

@item character devices

@item block devices

@item fifos

@end itemize

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.

@subheading Development Comments:

Test for nodal types - I thought that this test should look like the

following code:

@example

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);

@end example

Where:

@itemize @bullet

@item S_IFREG (0100000) - Creation of a regular file

@item S_IFCHR (0020000) - Creation of a character device

@item S_IFBLK (0060000) - Creation of a block device

@item S_IFIFO (0010000) - Creation of a FIFO

@end itemize

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.

@c @page

@section mount

@subheading 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.

@subheading 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.

@subheading 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.

@c @page

@section open

@subheading File:

open.c

@subheading 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.

@subheading 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.