source: rtems/doc/new_chapters/confspace.t @ 08142b48

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

@chapter Configuration Space Manager

@section Introduction

The configuration space manager provides a portable
interface for manipulating configuration data.
The capabilities in this manager were defined in the POSIX
1003.1h/D3 proposed standard titled @b{Services for Reliable,
Available, and Serviceable Systems}.

The directives provided by the configuration space manager are:

@itemize @bullet
@item @code{cfg_mount} - Mount a Configuration Space
@item @code{cfg_unmount} - Unmount a Configuration Space
@item @code{cfg_mknod} - Create a Configuration Node
@item @code{cfg_get} - Get Configuration Node Value
@item @code{cfg_set} - Set Configuration Node Value
@item @code{cfg_link} - Create a Configuration Link
@item @code{cfg_unlink} - Remove a Configuration Link
@item @code{cfg_open} - Open a Configuration Space
@item @code{cfg_read} - Read a Configuration Space
@item @code{cfg_children} - Get Node Entries
@item @code{cfg_mark} - Set Configuration Space Option
@item @code{readdir} - Reads a directory
@item @code{umask} - Sets a file creation mask
@item @code{link} - Creates a link to a file
@item @code{unlink} - Removes a directory entry
@item @code{mkdir} - Makes a directory
@item @code{open} - Opens a file
@item @code{chmod} - Changes file mode
@item @code{chown} - Changes the owner and/or group of a file
@end itemize

@section Background

@subsection Configuration Nodes

@subsection Configuration Space

@subsection Format of a Configuration Space File

@section Operations

@subsection Mount and Unmounting

@subsection Creating a Configuration Node

@subsection Removing a Configuration Node

@subsection Manipulating a Configuration Node

@subsection Traversing a Configuration Space

@section Directives

This section details the configuration space manager's directives.
A subsection is dedicated to each of this manager's directives
and describes the calling sequence, related constants, usage,
and status codes.

@page
@subsection cfg_mount - Mount a Configuration Space

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_mount(
  const char     *file,
  const char     *cfgpath,
  log_facility_t  notification,
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EPERM
The caller does not have the appropriate privilege.

@item EACCES
Search permission is denied for a component of the path prefix.

@item EEXIST
The file specified by the file argument does not exist

@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters while
@code{_POSIX_NO_TRUNC} is in effect.

@item ENOENT
A component of cfgpath does not exist.

@item ENOTDIR
A component of the file path prefix is not a directory.

@item EBUSY
The configuration space defined by file is already mounted.

@item EINVAL
The notification argument specifies an invalid log facility.

@end table

@subheading DESCRIPTION:

The @code{cfg_mount} function maps a configuration space defined
by the file identified by the the @code{file} argument.  The 
distinguished node of the mapped configuration space shall be
mounted in the active space at the point identified by the
@code{cfgpath} configuration pathname.

The @code{notification} argument specifies how changes to the
mapped configuration space shall be communicated to the application.
If the @code{notification} argument is NULL, no notification shall
be performed for the mapped configuration space.  If the Event
Logging option is defined, the notification argument defines the
facility to which changes in the mapped configuration space shall
be logged.  Otherwise, the @code{notification} argument shall
specify an implementation defined method of notifying the application
of changes to the mapped configuration space.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_unmount - Unmount a Configuration Space

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_unmount(
  const char     *cfgpath
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EPERM
The caller does not have the appropriate privileges.

@item EACCES
Search permission is denied for a component of the path prefix.

@item ENOENT
A component of cfgpath does not exist.

@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters while
@code{_POSIX_NO_TRUNC} is in effect.

@item EINVAL
The requested node is not the distinguished node of a mounted
configuration space.

@item EBUSY
One or more processes has an open configuration traversal
stream for the configuration space whose distinguished node is
referenced by the cfgpath argument.

@item ELOOP
A node appears more than once in the path specified by the 
cfg_path argument

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument

@end table

@subheading DESCRIPTION:

The @code{cfg_umount} function unmaps the configuration space whose 
distinguished node is mapped in the active space at the location defined
by @code{cfgpath} configuration pathname.  All system resources 
allocated for this configuration space should be deallocated.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_mknod - Create a Configuration Node

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_mknod(
  const char   *cfgpath,
  mode_t        mode,
  cfg_type_t    type         
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters while
@code{_POSIX_NO_TRUNC} is in effect.

@item ENOENT
A component of the path prefix does not exist.

@item EACCES
Search permission is denied for a component of the path prefix.

@item ELOOP
Too many symbolic links were encountered in translating the 
pathname.

@item EPERM
The calling process does not have the appropriate privilege.

@item EEXIST
The named node exists.

@item EINVAL
The value of mode is invalid.

@item EINVAL
The value of type is invalid.

@item ELOOP
A node appears more than once in the path specified by the 
cfg_path argument

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument.

@item EROFS
The named node resides on a read-only configuration space.

@end table

@subheading DESCRIPTION:

The @code{cfg_mknod} function creates a new node in the configuration
space which contains the pathname prefix of @code{cfgpath}.  T he node
name shall be defined by the pathname suffix of @code{cfgpath}.  The
node name shall be defined by the pathname suffix of @code{cfgpath}. 
The node permissions shall be specified by the value of @code{mode}.
The node type shall be specified by the value of @code{type}.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_get - Get Configuration Node Value

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_get(
  const char  *cfgpath
  cfg_value_t *value
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters while
@code{_POSIX_NO_TRUNC} is in effect.

@item ENOENT
A component of cfgpath does not exist.

@item EACCES
Search permission is denied for a component of the path prefix.

@item EPERM
The calling process does not have the appropriate privileges.

@item ELOOP
A node appears more than once in the path specified by the 
cfg_path argument

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument.

@end table

@subheading DESCRIPTION:

The @code{cfg_get} function stores the value attribute of the
configuration node identified by @code{cfgpath}, into the buffer
described by the @code{value} pointer.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_set - Set Configuration Node Value

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_set(
  const char  *cfgpath
  cfg_value_t *value
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters while
@code{_POSIX_NO_TRUNC} is in effect.

@item ENOENT
A component of cfgpath does not exist

@item EACCES
Search permission is denied for a component of the path prefix.

@item EPERM
The calling process does not have the appropriate privilege.

@item ELOOP
A node appears more than once in the path specified by the
cfg-path argument.

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument.

@end table

@subheading DESCRIPTION:

The @code{cfg_set} function stores the value specified by the
@code{value} argument in the configuration node defined by the 
@code{cfgpath} argument.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_link - Create a Configuration Link

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_link(
  const char *src
  const char *dest
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters while
@code{_POSIX_NO_TRUNC} is in effect.

@item ENOENT
A component of either path prefix does not exist.

@item EACCES
A component of either path prefix denies search permission.

@item EACCES
The requested link requires writing in a node with a mode that
denies write permission.

@item ENOENT
The node named by src does not exist.

@item EEXIST
The node named by dest does exist.

@item EPERM
The calling process does not have the appropriate privilege to
modify the node indicated by the src argument.

@item EXDEV
The link named by dest and the node named by src are from different
configuration spaces.

@item ENOSPC
The node in which the entry for the new link is being placed
cannot be extended because there is no space left on the 
configuration space containing the node.

@item EIO
An I/O error occurred while reading from or writing to the 
configuration space to make the link entry.

@item EROFS
The requested link requires writing in a node on a read-only
configuration space.

@item ELOOP
A node appears more than once in the path specified by the
cfg-path argument.

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument.

@end table

@subheading DESCRIPTION:

The @code{src} and @code{dest}arguments point to pathnames which 
name existing nodes.  The @code{cfg_link} function shall atomically 
create a link between specified nodes, and increment by one the link 
count of the node specified by the @code{src} argument. 

If the @code{cfg_link} function fails, no link shall be created, and
the link count of the node shall remain unchanged by this function
call.

This implementation may require that the calling process has permission 
to access the specified nodes.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_unlink - Remove a Configuration Link

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_unlink(
  const char    *cfgpath
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item ENAMETOOLONG
A component of a pathname exceeded @code{NAME_MAX} characters,
or an entire path name exceed @code{PATH_MAX} characters.

@item ENOENT
The named  node does not exist.

@item EACCES
Search permission is denied on the node containing the link to
be removed.

@item EACCES
Write permission is denied on the node containing the link to 
be removed.

@item ENOENT
A component of cfgpath does not exist.

@item EPERM
The calling process does not have the appropriate privilege to 
modify the node indicated by the path prefix of the cfgpath
argument.

@item EBUSY
The node to be unlinked is the distinguished node of a mounted
configuration space.

@item EIO
An I/O error occurred while deleting the link entry or deallocating
the node.

@item EROFS
The named node resides in a read-only configuration space.

@item ELOOP
A node appears more than once in the path specified by the
cfg-path argument.

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument.

@end table

@subheading DESCRIPTION:

The @code{cfg_unlink} function removes the link between the node
specified by the @code{cfgpath} path prefix and the parent node 
specified by @code{cfgpath}, and shall decrement the link count 
of the @code{cfgpath} node.

When the link count of the node becomes zero, the space occupied
by the node shall be freed and the node shall no longer be accessible.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_open - Open a Configuration Space

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_open(
  const char     *pathnames[],
  int             options,
  int           (*compar)(const CFGENT **f1, const CFGENT **f2),
  CFG           **cfgstream
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for any component of a pathname.

@item ELOOP
A loop exists in symbolic links encountered during resolution 
of a pathname.

@item ENAMETOOLONG
The length of a pathname exceeds @code{PATH_MAX}, or a pathname
component is longer than @code{NAME_MAX} while @code{_POSIX_NO_TRUNC}

@item ENOENT
The pathname argument is an empty string or the named node
does not exist.

@item EINVAL
Either both or neither of CFG_LOGICAL and CFG_PHYSICAL are
specified by the options argument ???????????

@item ENOMEM
Not enough memory is available to create the necessary structures.

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the pathnames argument.

@item ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the
pathname specified by the pathnames argument, the length of
the substituted pathname string exceeded @code{PATH_MAX}.

@end table

@subheading DESCRIPTION:

The @code{cfg_open} function shall open a configuration traversal stream
rooted in the configuration nodes name by the @code{pathnames} argument.
It shall store a pointer to a CFG object that represents that stream at 
the location identified the @code{cfgstream} pointer.  The @code{pathnames}
argument is an array of character pointers to NULL-terminated strings. 
The last member of this array shall be a NULL pointer.

The value of @code{options} is the bitwise inclusive OR of values from the 
following lists.  Applications shall supply exactly one of the first two 
values below in @code{options}.

@table @b

@item CFG_LOGICAL
When symbolic links referencing existing nodes are 
encountered during the traversal, the @code{cfg_info}
field of the returned CFGENT structure shall describe
the target node pointed to by the link instead of the 
link itself, unless the target node does not exist. 
If the target node has children, the pre-order return,
followed by the return of structures referencing all of
its descendants, followed by a post-order return, shall
be done.
                    
@item CFG_PHYSICAL
When symbolic links are encountered during the traversal,
the @code{cfg_info} field shall describe the symbolic 
link.

@end table
                    

Any combination of the remaining flags can be specified in the value of 
@code{options}

@table @b

@item CFG_COMFOLLOW
When symbolic links referencing existing nodes are
specified in the @code{pathnames} argument, the 
@code{cfg_info} field of the returned CFGENT structure
shall describe the target node pointed to by the link
instead of the link itself, unless the target node does
not exist.  If the target node has children, the 
pre-order return, followed by the return of structures
referencing all its descendants, followed by a post-order
return, shall be done.

@item CFG_XDEV
The configuration space functions shall not return a
CFGENT structure for any node in a different configuration
space than the configuration space of the nodes identified 
by the CFGENT structures for the @code{pathnames} argument.

@end table

The @code{cfg_open} argument @code{compar} shall either be NULL or point
to a function that shall be called with two pointers to pointers to CFGENT 
structures that shall return less than, equal to , or greater than zero if 
the node referenced by the first argument is considered to be respectively
less than, equal to, or greater than the node referenced by the second.
The CFGENT structure fields provided to the comparison routine shall be as 
described with the exception that the contents of the @code{cfg_path} and
@code{cfg_pathlen} fields are unspecified.

This comparison routine is used to determine the order in which nodes in
directories encountered during the traversal are returned, and the order
of traversal when more than one node is specified in the @code{pathnames}
argument to @code{cfg_open}.  If a comparison routine is specified, the
order of traversal shall be from the least to the greatest.  If the 
@code{compar} argument is NULL, the order of traversal shall be as listed
in the @code{pathnames} argument. 

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_read - Read a Configuration Space

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_read(  
  CFG           *cfgp,
  CFGENT       **node
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for any component of a pathname.

@item EBADF
The cfgp argument does not refer to an open configuration
space.

@item ELOOP
A loop exists in symbolic links encountered during resolution
of a pathname.

@item ENOENT
A named node does not exist.

@item ENOMEM
Not enough memory is available to create the necessary structures.

@item ELOOP
More than @code{SYMLOOP_MAX} symbolic links were encountered during
resolution of the cfgpath argument.

@item ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the
pathname specified by the pathnames argument, the length of the
substituted pathname string exceeded @code{PATH_MATH}.

@end table

@subheading DESCRIPTION:

The @code{cfg_read} function returns a pointer to a CFGENT structure
representing a node in the configuration space to which @code{cfgp}
refers.  The returned pointer shall be stored at the location 
indicated by the @code{node} argument.

The child nodes of each node in the configuration tree is returned
by @code{cfg_read}.  If a comparison routine is specified to the
@code{cfg_open} function, the order of return of the child nodes shall
be as specified by the routine, from least to greatest.  Otherwise
the order of return is unspecified.

Structures referencing nodes with children shall be returned by the 
function @code{cfg_read} at least twice [unless the application
specifies otherwise with @code{cfg_mark}]-once immediately before
the structures representing their descendants, are returned 
(pre-order), and once immediately after structures representing all
of their descendants, if any, are returned (post-order).  The 
CFGENT structure returned in post-order (with the exception of the 
@code{cfg_info} field) shall be identical to that returned in pre-order.
Structures referencing nodes of other types shall be returned at least
once.

The fields of the CFGENT structure shall contain the following 
information:

@table @b

@item cfg_parent
A pointer to the structure returned by the 
@code{cfg_read} function for the node that contains
the entry for the current node.  A @code{cfg_parent}
structure shall be provided for the node(s) specified
by the @code{pathnames} argument to the @code{cfg_open}
function, but the contents of other than its 
@code{cfg_number}, @code{cfg_pointer}, @code{cfg_parent},
and @code{cfg_parent}, and @code{cfg_level} fields are
unspecified.  Its @code{cfg_link} field is unspecified.

@item cfg_link
Upon return from the @code{cfg_children} function, the
@code{cfg_link} field points to the next CFGENT structure 
in a NULL-terminated linked list of CFGENT structures.  
Otherwise, the content of the @code{cfg_link} field is 
unspecified.

@item cfg_cycle
If the structure being returned by @code{cfg_read} 
represents a node that appears in the @code{cfg_parent}
linked list tree, the @code{cfg_cycle} field shall point 
to the structure representing that entry from the 
@code{cfg_parent} linked list.  Otherwise the content of
the @code{cfg_cycle} field is unspecified.

@item cfg_number
The @code{cfg_number} field is provided for use by the 
application program.  It shall be initialized to zero for 
each new node returned by the @code{cfg_read} function, 
but shall not be further modified the configuration space
routines.

@item cfg_pointer
The @code{cfg_pointer} field is provided for use by the
application program.  It shall be initialized to NULL for
each new node returned by the @code{cfg_read} function, 
but shall not be further modified by the configuration 
space routines.

@item cfg_path
A pathname for the node including and relative to the 
argument supplied to the @code{cfg_open} routine for this
configuration space.  This pathname may be longer than
@code{PATH_MAX} bytes.  This pathname shall be NULL-terminated.

@item cfg_name
The nodename of the node.

@item cfg_pathlen
The length of the string pointed at by the @code{cfg_path}
field when returned by @code{cfg_read}.

@item cfg_namelen
The length of the string pointed at by the @code{cfg_name}
field.

@item cfg_level
The depth of the current entry in the configuration space.
The @code{cfg_level} field of the @code{cfg_parent} 
structure for each of the node(s) specified in the 
@code{pathnames} argument to the @code{cfg_open} function
shall be set to 0, and this number shall be incremented for
for each node level descendant.

@item cfg_info
This field shall contain one of the values listed below.  If
an object can have more than one info value, the first 
appropriate value listed below shall be returned. 

@table @b

@item CFG_D
The structure represents a node with children in
pre-order.

@item CFG_DC
The structure represents a node that is a parent
of the node most recently returned by @code{cfg_read}.
The @code{cfg_cycle} field shall reference the 
structure previously returned by @code{cfg_read} that
is the same as the returned structure.

@item CFG_DEFAULT
The structure represents a node that is not 
represented by one of the other node types

@item CFG_DNR
The structure represents a node, not of type symlink,
that is unreadable.  The variable @code{cfg_errno}
shall be set to the appropriate value.

@item CFG_DP
The structure represents a node with children in
post-order.  This value shall occur only if CFG_D 
has previously been returned for this entry.

@item CFG_ERR
The structure represents a node for which an error has 
occurred.  The variable @code{cfg_errno} shall be set
to the appropriate value.

@item CFG_F
The structure represents a node without children.

@item CFG_SL
The structure represents a node of type symbolic link.

@item CFG_SLNONET
The structure represents a node of type symbolic link
with a target node for which node characteristic
information cannot be obtained.

@end table

@end table

Structures returned by @code{cfg_read} with a @code{cfg_info} field equal
to CFG_D shall be accessible until a subsequent call, on the same
configuration traversal stream, to @code{cfg_close}, or to @code{cfg_read}
after they have been returned by the @code{cfg_read} function in
post-order.  Structures returned by @code{cfg_read} with an
@code{cfg_info} field not equal to CFG_D shall be accessible until a
subsequent call, on the same configuration traversal stream, to
@code{cfg_close} or @code{cfg_read}. 

The content of the @code{cfg_path} field is specified only for the
structure most recently returned by @code{cfg_read}. 

The specified fields in structures in the list representing nodes for
which structures have previously been returned by @code{cfg_children},
shall be identical to those returned by @code{cfg_children}, except that
the contents of the @code{cfg_path} and @code{cfg_pathlen} fields are
unspecified. 
         
@subheading NOTES: 

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_children - Get Node Entries

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_children(
  CFG           *cfgp,
  int            options,
  CFGENT       **children
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for any component of a pathname

@item EBADF
The cfgp argument does not refer to an open configuration space.

@item ELOOP
A loop exists in symbolic links encountered during resolution of 
a pathname.

@item ENAMETOOLONG
The length of a pathname exceeds @code{PATH_MAX}, or a pathname
component is longer than @code{NAME_MAX} while @code{_POSIX_NO_TRUNC} is
in effect.

@item EINVAL
The specified value of the options argument is invalid.

@item ENOENT
The named node does not exist.

@item ENOMEM
Not enough memory is available to create the necessary structures.

@end table

@subheading DESCRIPTION:

The first @code{cfg_children} call after a @code{cfg_read} shall 
return information about the first node without children under the
node returned by @code{cfg_read}.  Subsequent calls to 
@code{cfg_children} without the intervening @code{cfg_read} shall
return information about the remaining nodes without children under
that same node.

If @code{cfg_read} has not yet been called for the configuration
traversal stream represented by @code{cfgp}, @code{cfg_children}
shall return a pointer to the first entry in a list of the nodes 
represented by the @code{pathnames} argument to @code{cfg_open}.

In either case, the list shall be NULL-terminated, ordered by the 
user-specified comparison function, if any, and linked through the
cfg_link field.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_mark - Set Configuration Space Options

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_mark(
  CFG           *cfgp,
  CFGENT        *f,
  int            options
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EINVAL
The specified combination of the cfgp and f arguments is not 
supported by the implementation.

@item EINVAL
The specified value of the options argument is invalid.

@end table

@subheading DESCRIPTION:

The @code{cfg_mark} function modifies the subsequent behavior of
the cfg functions with regard to the node referenced by the structure
pointed to by the argument @code{f} or the configuration space referenced 
by the structure pointed to by the argument @code{cfgp}.

Exactly one of the @code{f} argument and the @code{cfgp} argument shall
be NULL.

The value of the @code{options} argument shall be exactly one of the
flags specified in the following list: 

@table @b

@item CFG_AGAIN
If the @code{cfgp} argument is non-NULL, or the @code{f}
argument is NULL, or the structure referenced by @code{f}
is not the one most recently returned by @code{cfg_read},
@code{cfg_mark} shall return an error.  Otherwise, the next 
call to the @code{cfg_read} function shall return the 
structure referenced by @code{f} with the @code{cfg_info}
field reinitialized.  Subsequent behavior of the @code{cfg}
functions shall be based on the reinitialized value of 
@code{cfg_info}.

@item CFG_SKIP
If the @code{cfgp} argument is non-NULL, or the @code{f}
argument is NULL, or the structure referenced by @code{f}
is not one of those specified as accessible, or the structure
referenced by @code{f} is not for a node of type pre-order 
node, @code{cfg_mark} shall return an error.  Otherwise, no 
more structures for the node referenced by @code{f} or its 
descendants shall be returned by the @code{cfg_read} function.

@item CFG_FOLLOW
If the @code{cfgp} argument is non-NULL, or the @code{f} 
argument is NULL, or the structure referenced by @code{f}
is not one of those specified as accessible, or the structure
referenced by @code{f} is not for a node of type symbolic link,
@code{cfg_mark} shall return an error.  Otherwise, the next
call to the @code{cfg_read} function shall return the structure
referenced by @code{f} with the @code{cfg_info} field reset
to reflect the target of the symbolic link instead of the 
symbolic link itself.  If the target of the link is node with
children, the pre-order return, followed by the return of 
structures referencing all of its descendants, followed by a 
post-order return, shall be done.

@end table

If the target of the symbolic link does not exist, the fields
of the structure by @code{cfg_read} shall be unmodified, except
that the @code{cfg_info} field shall be reset to @code{CFG_SLNONE}.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection cfg_close - Close a Configuration Space

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <cfg.h>

int cfg_close(
  CFG           *cfgp
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EBADF
The cfgp argument does not refer to an open configuration space
traversal stream.

@end table

@subheading DESCRIPTION:

The @code{cfg_close} function closes a configuration space transversal
stream represented by the CFG structure pointed at by the @code{cfgp}
argument.  All system resources allocated for this configuration space
traversal stream should be deallocated.  Upon return, the value of 
@code{cfgp} need not point to an accessible object of type CFG.

@subheading NOTES:

The @code{_POSIX_CFG} feature flag is defined to indicate
this service is available.

@page
@subsection readdir - Reads a directory

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <sys/types.h>
#include <dirent.h>

struct dirent *readdir(
  DIR   *dirp
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EBADF
Invalid file descriptor

@end table

@subheading DESCRIPTION:

The @code{readdir} function returns a pointer to a structure @code{dirent}
representing the next directory entry from the directory stream pointed to
by @code{dirp}.  On end-of-file, NULL is returned.

The @code{readdir} function may (or may not) return entries for . or .. Your
program should tolerate reading dot and dot-dot but not require them.

The data pointed to be @code{readdir} may be overwritten by another call to
@code{readdir} for the same directory stream.  It will not be overwritten by 
a call for another directory.

@subheading NOTES:

If ptr is not a pointer returned by @code{malloc}, @code{calloc}, or 
@code{realloc} or has been deallocated with @code{free} or @code{realloc}, 
the results are not portable and are probably disastrous.

@page
@subsection open - Opens a file

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int open(
   const char *path,
   int         oflag,
   mode_t      mode
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for a directory in a file's path prefix
@item EEXIST
The named file already exists.
@item EINTR
Function was interrupted by a signal.
@item EISDIR
Attempt to open a directory for writing or to rename a file to be a
directory.
@item EMFILE
Too many file descriptors are in use by this process.
@item ENAMETOOLONG
Length of a filename string exceeds PATH_MAX and _POSIX_NO_TRUNC is in
effect.
@item ENFILE
Too many files are currently open in the system.
@item ENOENT
A file or directory does not exist.
@item ENOSPC
No space left on disk.
@item ENOTDIR
A component of the specified pathname was not a directory when a directory
was expected.
@item ENXIO
No such device.  This error may also occur when a device is not ready, for 
example, a tape drive is off-line.
@item EROFS
Read-only file system.
@end table

@subheading DESCRIPTION:

The @code{open} function establishes a connection between a file and a file 
descriptor.  The file descriptor is a small integer that is used by I/O 
functions to reference the file.  The @code{path} argument points to the 
pathname for the file.

The @code{oflag} argument is the bitwise inclusive OR of the values of 
symbolic constants.  The programmer must specify exactly one of the following
three symbols:

@table @b
@item O_RDONLY
Open for reading only.

@item O_WRONLY
Open for writing only.

@item O_RDWR
Open for reading and writing.

@end table

Any combination of the following symbols may also be used.

@table @b
@item O_APPEND
Set the file offset to the end-of-file prior to each write.

@item O_CREAT
If the file does not exist, allow it to be created.  This flag indicates
that the @code{mode} argument is present in the call to @code{open}.

@item O_EXCL
This flag may be used only if O_CREAT is also set.  It causes the call
to @code{open} to fail if the file already exists.

@item O_NOCTTY
If @code{path} identifies a terminal, this flag prevents that teminal from
becoming the controlling terminal for thi9s process.  See Chapter 8 for a
description of terminal I/O.

@item O_NONBLOCK
Do no wait for the device or file to be ready or available.  After the file
is open, the @code{read} and @code{write} calls return immediately.  If the 
process would be delayed in the read or write opermation, -1 is returned and 
@code{errno} is set to @code{EAGAIN} instead of blocking the caller.

@item O_TRUNC
This flag should be used only on ordinary files opened for writing.  It 
causes the file to be tuncated to zero length..

@end table

Upon successful completion, @code{open} returns a non-negative file 
descriptor.

@subheading NOTES:

@page
@subsection umask - Sets a file creation mask.

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <sys/types.h>
#include <sys/stat.h>

mode_t umask(
  mode_t cmask
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@subheading DESCRIPTION:

The @code{umask} function sets the process file creation mask to @code{cmask}.
The file creation mask is used during @code{open}, @code{creat}, @code{mkdir},
@code{mkfifo} calls to turn off permission bits in the @code{mode} argument.
Bit positions that are set in @code{cmask} are cleared in the mode of the
created file.

The file creation mask is inherited across @code{fork} and @code{exec} calls.
This makes it possible to alter the default permission bits of created files.

@subheading NOTES:

The @code{cmask} argument should have only permission bits set.  All other 
bits should be zero.

@page
@subsection link - Creates a link to a file

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <unistd.h>

int link(
  const char *existing,
  const char *new
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for a directory in a file's path prefix
@item EEXIST
The named file already exists.
@item EMLINK
The number of links would exceed @code{LINK_MAX}.
@item ENAMETOOLONG
Length of a filename string exceeds PATH_MAX and _POSIX_NO_TRUNC is in
effect.
@item ENOENT
A file or directory does not exist.
@item ENOSPC
No space left on disk.
@item ENOTDIR
A component of the specified pathname was not a directory when a directory
was expected.
@item EPERM
Operation is not permitted.  Process does not have the appropriate priviledges
or permissions to perform the requested operations.
@item EROFS
Read-only file system.
@item EXDEV
Attempt to link a file to another file system.

@end table

@subheading DESCRIPTION:

The @code{link} function atomically creates a new link for an existing file
and increments the link count for the file.

If the @code{link} function fails, no directories are modified.

The @code{existing} argument should not be a directory.

The callder may (or may not) need permission to access the existing file.

@subheading NOTES:

@page
@subsection unlink - Removes a directory entry

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <unistd.h>

int unlink(
  const char path
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for a directory in a file's path prefix
@item EBUSY
The directory is in use.
@item ENAMETOOLONG
Length of a filename string exceeds PATH_MAX and _POSIX_NO_TRUNC is in
effect.
@item ENOENT
A file or directory does not exist.
@item ENOTDIR
A component of the specified pathname was not a directory when a directory
was expected.
@item EPERM
Operation is not permitted.  Process does not have the appropriate priviledges
or permissions to perform the requested operations.
@item EROFS
Read-only file system.

@end table

@subheading DESCRIPTION:

The @code{unlink} function removes the link named by @{code} and decrements the
link count of the file referenced by the link.  When the link count goes to zero
and no process has the file open, the space occupied by the file is freed and the
file is no longer accessible. 

@subheading NOTES:

@page
@subsection mkdir - Makes a directory

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <sys/types.h>
#include <sys/stat.h>

int mkdir(
  const char *path,
  mode_t      mode
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for a directory in a file's path prefix
@item EEXIST
The name file already exist.  
@item EMLINK
The number of links would exceed LINK_MAX
@item ENAMETOOLONG
Length of a filename string exceeds PATH_MAX and _POSIX_NO_TRUNC is in
effect.
@item ENOENT
A file or directory does not exist.
@item ENOSPC
No space left on disk.
@item ENOTDIR
A component of the specified pathname was not a directory when a directory
was expected.
@item EROFS
Read-only file system.

@end table

@subheading DESCRIPTION:

The @code{mkdir} function creates a new diectory named @code{path}.  The 
permission bits (modified by the file creation mask) are set from @code{mode}.
The owner and group IDs for the directory are set from the effective user ID
and group ID.

The new directory may (or may not) contain entries for. and .. but is otherwise
empty.

@subheading NOTES:

@page
@subsection chmod - Changes file mode.

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <sys/types.h>
#include <sys/stat.h>

int chmod(
  const char *path,
  mode_t      mode
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for a directory in a file's path prefix
@item ENAMETOOLONG
Length of a filename string exceeds PATH_MAX and _POSIX_NO_TRUNC is in
effect.
@item ENOENT
A file or directory does not exist.
@item ENOTDIR
A component of the specified pathname was not a directory when a directory
was expected.
@item EPERM
Operation is not permitted.  Process does not have the appropriate priviledges
or permissions to perform the requested operations.
@item EROFS
Read-only file system.

@end table

@subheading DESCRIPTION:

Set the file permission bits, the set user ID bit, and the set group ID bit 
for the file named by @code{path} to @code{mode}.  If the effective user ID 
does not match the owner of the file and the calling process does not have 
the appropriate privileges, @code{chmod} returns -1 and sets @code{errno} to
@code{EPERM}.

@subheading NOTES:

@page
@subsection chown - Changes the owner and/or group of a file.

@subheading CALLING SEQUENCE:

@ifset is-C
@example
#include <sys/types.h>
#include <unistd.h>

int chown(
  const char *path,
  uid_t       owner,
  gid_t       group
);
@end example
@end ifset

@ifset is-Ada
@end ifset

@subheading STATUS CODES:

@table @b
@item EACCES
Search permission is denied for a directory in a file's path prefix
@item EINVAL
Invalid argument
@item ENAMETOOLONG
Length of a filename string exceeds PATH_MAX and _POSIX_NO_TRUNC is in
effect.
@item ENOENT
A file or directory does not exist.
@item ENOTDIR
A component of the specified pathname was not a directory when a directory
was expected.
@item EPERM
Operation is not permitted.  Process does not have the appropriate priviledges
or permissions to perform the requested operations.
@item EROFS
Read-only file system.

@end table

@subheading DESCRIPTION:

The user ID and group ID of the file named by @code{path} are set to 
@cdoe{owner} and @code{path}, respectively.

For regular files, the set group ID (S_ISGID) and set user ID (S_ISUID)
bits are cleared.

Some systems consider it a security violation to allow the owner of a file to
be changed,  If users are billed for disk space usage, loaning a file to 
another user could result in incorrect billing.  The @code{chown} function
may be restricted to privileged users for some or all files.  The group ID can
still be changed to one of the supplementary group IDs.

@subheading NOTES:

This function may be restricted for some file.  The @code{pathconf} function
can be used to test the _PC_CHOWN_RESTRICTED flag.