.. SPDX-License-Identifier: CC-BY-SA-4.0
.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR)
Filesystem Configuration
========================
This section describes configuration options related to filesytems.
By default, the In-Memory Filesystem (IMFS) is used as the base filesystem (also
known as root filesystem). In order to save some memory for your application,
you can disable the filesystem support with the
:ref:`CONFIGURE_APPLICATION_DISABLE_FILESYSTEM` configuration option.
Alternatively, you can strip down the features of the base filesystem with the
:ref:`CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM` and
:ref:`CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM` configuration options. These
three configuration options are mutually exclusive. They are intended for an
advanced application configuration.
Features of the IMFS can be disabled and enabled with the following
configuration options:
* :ref:`CONFIGURE_IMFS_DISABLE_CHMOD`
* :ref:`CONFIGURE_IMFS_DISABLE_CHOWN`
* :ref:`CONFIGURE_IMFS_DISABLE_LINK`
* :ref:`CONFIGURE_IMFS_DISABLE_MKNOD`
* :ref:`CONFIGURE_IMFS_DISABLE_MKNOD_FILE`
* :ref:`CONFIGURE_IMFS_DISABLE_MOUNT`
* :ref:`CONFIGURE_IMFS_DISABLE_READDIR`
* :ref:`CONFIGURE_IMFS_DISABLE_READLINK`
* :ref:`CONFIGURE_IMFS_DISABLE_RENAME`
* :ref:`CONFIGURE_IMFS_DISABLE_RMNOD`
* :ref:`CONFIGURE_IMFS_DISABLE_SYMLINK`
* :ref:`CONFIGURE_IMFS_DISABLE_UNMOUNT`
* :ref:`CONFIGURE_IMFS_DISABLE_UTIME`
* :ref:`CONFIGURE_IMFS_ENABLE_MKFIFO`
.. index:: CONFIGURE_APPLICATION_DISABLE_FILESYSTEM
.. _CONFIGURE_APPLICATION_DISABLE_FILESYSTEM:
CONFIGURE_APPLICATION_DISABLE_FILESYSTEM
----------------------------------------
CONSTANT:
``CONFIGURE_APPLICATION_DISABLE_FILESYSTEM``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then a base filesystem and the
configured filesystems are initialized during system initialization.
DESCRIPTION:
In case this configuration option is defined, then **no** base filesystem is
initialized during system initialization and **no** filesystems are
configured.
NOTES:
Filesystems must be initialized to support file descriptor based device
drivers and basic input/output functions such as :c:func:`printf`.
Filesystems can be disabled to reduce the memory footprint of an application.
.. index:: CONFIGURE_IMFS_DISABLE_CHMOD
.. _CONFIGURE_IMFS_DISABLE_CHMOD:
CONFIGURE_IMFS_DISABLE_CHMOD
----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_CHMOD``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
changing the mode of files.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support changing the mode of files (no support for :c:func:`chmod`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_CHOWN
.. _CONFIGURE_IMFS_DISABLE_CHOWN:
CONFIGURE_IMFS_DISABLE_CHOWN
----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_CHOWN``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
changing the ownership of files.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support changing the ownership of files (no support for :c:func:`chown`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_LINK
.. _CONFIGURE_IMFS_DISABLE_LINK:
CONFIGURE_IMFS_DISABLE_LINK
---------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_LINK``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports hard
links.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support hard links (no support for :c:func:`link`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_MKNOD
.. _CONFIGURE_IMFS_DISABLE_MKNOD:
CONFIGURE_IMFS_DISABLE_MKNOD
----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_MKNOD``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports making
files.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support making files (no support for :c:func:`mknod`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_MKNOD_FILE
.. _CONFIGURE_IMFS_DISABLE_MKNOD_FILE:
CONFIGURE_IMFS_DISABLE_MKNOD_FILE
---------------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_MKNOD_FILE``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports making
regular files.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support making regular files.
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_MOUNT
.. _CONFIGURE_IMFS_DISABLE_MOUNT:
CONFIGURE_IMFS_DISABLE_MOUNT
----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_MOUNT``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
mounting other filesystems.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support mounting other filesystems (no support for :c:func:`mount`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_READDIR
.. _CONFIGURE_IMFS_DISABLE_READDIR:
CONFIGURE_IMFS_DISABLE_READDIR
------------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_READDIR``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
reading directories.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support reading directories (no support for :c:func:`readdir`). It is still
possible to open files in a directory.
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_READLINK
.. _CONFIGURE_IMFS_DISABLE_READLINK:
CONFIGURE_IMFS_DISABLE_READLINK
-------------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_READLINK``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
reading symbolic links.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support reading symbolic links (no support for :c:func:`readlink`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_RENAME
.. _CONFIGURE_IMFS_DISABLE_RENAME:
CONFIGURE_IMFS_DISABLE_RENAME
-----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_RENAME``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
renaming files.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support renaming files (no support for :c:func:`rename`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_RMNOD
.. _CONFIGURE_IMFS_DISABLE_RMNOD:
CONFIGURE_IMFS_DISABLE_RMNOD
----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_RMNOD``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
removing files.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support removing files (no support for :c:func:`rmnod`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_SYMLINK
.. _CONFIGURE_IMFS_DISABLE_SYMLINK:
CONFIGURE_IMFS_DISABLE_SYMLINK
------------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_SYMLINK``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
creating symbolic links.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support creating symbolic links (no support for :c:func:`symlink`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_UNMOUNT
.. _CONFIGURE_IMFS_DISABLE_UNMOUNT:
CONFIGURE_IMFS_DISABLE_UNMOUNT
------------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_UNMOUNT``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
unmounting other filesystems.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support unmounting other filesystems (no support for :c:func:`unmount`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_DISABLE_UTIME
.. _CONFIGURE_IMFS_DISABLE_UTIME:
CONFIGURE_IMFS_DISABLE_UTIME
----------------------------
CONSTANT:
``CONFIGURE_IMFS_DISABLE_UTIME``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS supports
changing file times.
DESCRIPTION:
In case this configuration option is defined, then the root IMFS does not
support changing file times (no support for :c:func:`utime`).
NOTES:
None.
.. index:: CONFIGURE_IMFS_ENABLE_MKFIFO
.. _CONFIGURE_IMFS_ENABLE_MKFIFO:
CONFIGURE_IMFS_ENABLE_MKFIFO
----------------------------
CONSTANT:
``CONFIGURE_IMFS_ENABLE_MKFIFO``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the root IMFS does not
support making FIFOs (no support for :c:func:`mkfifo`).
DESCRIPTION:
In case this configuration option is defined, then the root IMFS supports
making FIFOs.
NOTES:
None.
.. index:: CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK
.. _CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK:
CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK
--------------------------------------
CONSTANT:
``CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK``
DATA TYPE:
Boolean feature macro.
RANGE:
Valid values for this configuration parameter are a power of two (2)
between 16 and 512 inclusive. In other words, valid values are 16, 32, 64,
128, 256,and 512.
DEFAULT VALUE:
The default IMFS block size is 128 bytes.
DESCRIPTION:
This configuration parameter specifies the block size for in-memory files
managed by the IMFS. The configured block size has two impacts. The first
is the average amount of unused memory in the last block of each file. For
example, when the block size is 512, on average one-half of the last block
of each file will remain unused and the memory is wasted. In contrast, when
the block size is 16, the average unused memory per file is only 8
bytes. However, it requires more allocations for the same size file and
thus more overhead per block for the dynamic memory management.
Second, the block size has an impact on the maximum size file that can be
stored in the IMFS. With smaller block size, the maximum file size is
correspondingly smaller. The following shows the maximum file size possible
based on the configured block size:
- when the block size is 16 bytes, the maximum file size is 1,328 bytes.
- when the block size is 32 bytes, the maximum file size is 18,656 bytes.
- when the block size is 64 bytes, the maximum file size is 279,488 bytes.
- when the block size is 128 bytes, the maximum file size is 4,329,344 bytes.
- when the block size is 256 bytes, the maximum file size is 68,173,568 bytes.
- when the block size is 512 bytes, the maximum file size is 1,082,195,456
bytes.
NOTES:
None.
.. index:: CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM
.. _CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM:
CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM
--------------------------------------
CONSTANT:
``CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the described feature is not
enabled.
DESCRIPTION:
In case this configuration option is defined, then an IMFS with a reduced
feature set will be the base filesystem (also known as root filesystem).
NOTES:
In case this configuration option is defined, then the following
configuration options will be defined as well
- :ref:`CONFIGURE_IMFS_DISABLE_CHMOD`,
- :ref:`CONFIGURE_IMFS_DISABLE_CHOWN`,
- :ref:`CONFIGURE_IMFS_DISABLE_LINK`,
- :ref:`CONFIGURE_IMFS_DISABLE_MKNOD_FILE`,
- :ref:`CONFIGURE_IMFS_DISABLE_MOUNT`,
- :ref:`CONFIGURE_IMFS_DISABLE_READDIR`,
- :ref:`CONFIGURE_IMFS_DISABLE_READLINK`,
- :ref:`CONFIGURE_IMFS_DISABLE_RENAME`,
- :ref:`CONFIGURE_IMFS_DISABLE_RMNOD`,
- :ref:`CONFIGURE_IMFS_DISABLE_SYMLINK`,
- :ref:`CONFIGURE_IMFS_DISABLE_UTIME`, and
- :ref:`CONFIGURE_IMFS_DISABLE_UNMOUNT`.
In addition, a simplified path evaluation is enabled. It allows only a look
up of absolute paths.
This configuration of the IMFS is basically a device-only filesystem. It is
comparable in functionality to the pseudo-filesystem name space provided
before RTEMS release 4.5.0.
.. index:: CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM
.. _CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM:
CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM
-----------------------------------------
CONSTANT:
``CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM``
OPTION TYPE:
This configuration option is a boolean feature define.
DEFAULT CONFIGURATION:
If this configuration option is undefined, then the described feature is not
enabled.
DESCRIPTION:
In case this configuration option is defined, then an IMFS with a reduced
feature set will be the base filesystem (also known as root filesystem).
NOTES:
In case this configuration option is defined, then the following
configuration options will be defined as well
- :ref:`CONFIGURE_IMFS_DISABLE_CHMOD`,
- :ref:`CONFIGURE_IMFS_DISABLE_CHOWN`,
- :ref:`CONFIGURE_IMFS_DISABLE_LINK`,
- :ref:`CONFIGURE_IMFS_DISABLE_READLINK`,
- :ref:`CONFIGURE_IMFS_DISABLE_RENAME`,
- :ref:`CONFIGURE_IMFS_DISABLE_SYMLINK`,
- :ref:`CONFIGURE_IMFS_DISABLE_UTIME`, and
- :ref:`CONFIGURE_IMFS_DISABLE_UNMOUNT`.
