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96 lines
4.1 KiB
ReStructuredText
96 lines
4.1 KiB
ReStructuredText
.. comment SPDX-License-Identifier: CC-BY-SA-4.0
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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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Pathname Evaluation
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*******************
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This chapter describes the pathname evaluation process for the RTEMS Filesystem
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Infrastructure.
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.. code-block:: shell
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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() is called
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to find, verify privlages on and return information on a node that exists. The
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handler ``evalformake()`` is called to find, verify permissions, and return
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information on a node that is to become a parent. Additionally, evalformake()
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returns a pointer to the start of the name of the new node to be created.
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Pathname evaluation is specific to a filesystem. Each filesystem is required
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to provide both a ``patheval()`` and an ``evalformake()`` routine. Both of
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these routines gets a name to evaluate and a node indicating where to start the
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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 must handle
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crossing the mountpoint. The evaluate routine should evaluate the name upto
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the first directory node where the new filesystem is mounted. The filesystem
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may process terminator characters prior to calling the evaluate routine for the
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new filesystem. A pointer to the portion of the name which has not been
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evaluated along with the root node of the new file system (gotten from the
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mount table entry) is passed to the correct mounted filesystem evaluate
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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
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the ``rtems_filesystem_current``. Both are initially defined to be the root
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node of the base filesystem. Once the chdir command is correctly used the
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``rtems_filesystem_current`` 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,
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the``rtems_filesystem_root`` is used as the node to start the evaluation with.
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Otherwise, the ``rtems_filesystem_current`` node is used as the node to start
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evaluating with. Therefore, a valid rtems_filesystem_location_info_t is given
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to the evaluate routine to start evaluation with. The evaluate routines are
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then responsible for making any changes necessary to this structure to
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correspond to the name being parsed.
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.. code-block:: 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 any
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information necessary to identify a node at this location. This element is
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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 fill
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this in, and it should remain valid until the instance of the filesystem is
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unmounted.
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*handlers*
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This element is defined as a set of routines that may change within a given
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filesystem based upon node type. For example a directory and a memory file
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may have to completely different read routines. This element is set to an
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initialization state defined by the mount table, and may be set to the
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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 to
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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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