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96 lines
4.0 KiB
ReStructuredText
96 lines
4.0 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR)
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System Initialization
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*********************
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After the RTEMS initialization is performed, the application's initialization
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will be performed. Part of initialization is a call to
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``rtems_filesystem_initialize()``. This routine will mount the 'In Memory File
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System' as the base filesystem. Mounting the base filesystem consists of the
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following:
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- Initialization of mount table chain control structure
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- Allocation of a ``jnode`` structure that will server as the root node of the
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'In Memory Filesystem'
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- Initialization of the allocated ``jnode`` with the appropriate OPS, directory
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handlers and pathconf limits and options.
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- Allocation of a memory region for filesystem specific global management
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variables
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- Creation of first mount table entry for the base filesystem
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- Initialization of the first mount table chain entry to indicate that the
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mount point is NULL and the mounted filesystem is the base file system
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After the base filesystem has been mounted, the following operations are
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performed under its directory structure:
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- Creation of the /dev directory
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- Registration of devices under /dev directory
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Base Filesystem
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===============
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RTEMS initially mounts a RAM based file system known as the base file system.
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The root directory of this file system tree serves as the logical root of the
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directory hierarchy (Figure 3). Under the root directory a '/dev' directory is
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created under which all I/O device directories and files are registered as part
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of the file system hierarchy.
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.. code-block:: shell
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Figure of the tree structure goes here.
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A RAM based file system draws its management resources from memory. File and
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directory nodes are simply allocated blocks of memory. Data associated with
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regular files is stored in collections of memory blocks. When the system is
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turned off or restarted all memory-based components of the file system are
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lost.
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The base file system serves as a starting point for the mounting of file
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systems that are resident on semi-permanent storage media. Examples of such
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media include non- volatile memory, flash memory and IDE hard disk drives
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(Figure 3). File systems of other types will be mounted onto mount points
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within the base file system or other file systems that are subordinate to the
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base file system. The framework set up under the base file system will allow
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for these new file system types and the unique data and functionality that is
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required to manage the future file systems.
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Base Filesystem Mounting
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------------------------
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At present, the first file system to be mounted is the 'In Memory File
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System'. It is mounted using a standard MOUNT() command in which the mount
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point is NULL. This flags the mount as the first file system to be registered
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under the operating system and appropriate initialization of file system
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management information is performed (See figures 4 and 5). If a different file
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system type is desired as the base file system, alterations must be made to
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base_fs.c. This routine handles the mount of the base file system.
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.. code-block:: shell
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Figure of the mount table chain goes here.
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Once the root of the base file system has been established and it has been
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recorded as the mount point of the base file system, devices are integrated
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into the base file system. For every device that is configured into the system
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(See ioman.c) a device registration process is performed. Device registration
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produces a unique dev_t handle that consists of a major and minor device
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number. In addition, the configuration information for each device contains a
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text string that represents the fully qualified pathname to that device's place
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in the base file system's hierarchy. A file system node is created for the
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device along the specified registration path.
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.. code-block:: shell
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Figure of the Mount Table Processing goes here.
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Note: Other file systems can be mounted but they are mounted onto points
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(directory mount points) in the base file system.
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