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96 lines
4.1 KiB
ReStructuredText
96 lines
4.1 KiB
ReStructuredText
Pathname Evaluation
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###################
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This chapter describes the pathname evaluation process for the
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RTEMS Filesystem Infrastructure.
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.. code:: c
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XXX Include graphic of the path evaluation process
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Pathname Evaluation Handlers
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============================
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There are two pathname evaluation routines. The handler patheval()
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is called to find, verify privlages on and return information on a node
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that exists. The handler evalformake() is called to find, verify
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permissions, and return information on a node that is to become a parent.
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Additionally, evalformake() returns a pointer to the start of the name of
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the new node to be created.
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Pathname evaluation is specific to a filesystem.
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Each filesystem is required to provide both a patheval() and an evalformake()
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routine. Both of these routines gets a name to evaluate and a node indicating
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where to start the evaluation.
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Crossing a Mount Point During Path Evaluation
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=============================================
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If the filesystem supports the mount command, the evaluate routines
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must handle crossing the mountpoint. The evaluate routine should evaluate
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the name upto the first directory node where the new filesystem is mounted.
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The filesystem may process terminator characters prior to calling the
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evaluate routine for the new filesystem. A pointer to the portion of the
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name which has not been evaluated along with the root node of the new
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file system ( gotten from the mount table entry ) is passed to the correct
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mounted filesystem evaluate routine.
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The rtems_filesystem_location_info_t Structure
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==============================================
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The ``rtems_filesystem_location_info_t`` structure contains all information
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necessary for identification of a node.
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The generic rtems filesystem code defines two global
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rtems_filesystem_location_info_t structures, the``rtems_filesystem_root`` and the ``rtems_filesystem_current``.
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Both are initially defined to be the root node of the base filesystem.
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Once the chdir command is correctly used the ``rtems_filesystem_current``
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is set to the location specified by the command.
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The filesystem generic code peeks at the first character in the name to be
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evaluated. If this character is a valid seperator, the``rtems_filesystem_root`` is used as the node to start the evaluation
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with. Otherwise, the ``rtems_filesystem_current`` node is used as the
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node to start evaluating with. Therefore, a valid
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rtems_filesystem_location_info_t is given to the evaluate routine to start
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evaluation with. The evaluate routines are then responsible for making
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any changes necessary to this structure to correspond to the name being
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parsed.
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.. code:: c
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struct rtems_filesystem_location_info_tt {
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void \*node_access;
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rtems_filesystem_file_handlers_r \*handlers;
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rtems_filesystem_operations_table \*ops;
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rtems_filesystem_mount_table_entry_t \*mt_entry;
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};
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*node_access*
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This element is filesystem specific. A filesystem can define and store
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any information necessary to identify a node at this location. This element
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is normally filled in by the filesystem’s evaluate routine. For the
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filesystem’s root node, the filesystem’s initilization routine should
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fill this in, and it should remain valid until the instance of the
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filesystem is unmounted.
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*handlers*
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This element is defined as a set of routines that may change within a
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given filesystem based upon node type. For example a directory and a
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memory file may have to completely different read routines. This element
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is set to an initialization state defined by the mount table, and may
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be set to the desired state by the evaluation routines.
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*ops*
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This element is defined as a set of routines that remain static for the
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filesystem. This element identifies entry points into the filesystem
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to the generic code.
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*mt_entry*
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This element identifies the mount table entry for this instance of the
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filesystem.
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.. COMMENT: COPYRIGHT (c) 1988-2002.
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.. COMMENT: On-Line Applications Research Corporation (OAR).
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.. COMMENT: All rights reserved.
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