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Update README files

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Gregory Nutt 2015-06-07 07:28:09 -06:00
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fs/unionfs/README.txt
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fs/unionfs/README.txt
=====================
Overview
--------
This directory contains the NuttX Union File System. The Union file
system is provides a mechanism to overlay two different, mounted file
systems so that they appear as one. In general this works like this:
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The Union File Sysem is enabled by selecting the CONFIG_FS_UNIONFS option
in the NuttX configruation file.
Uses of the Unioin File System
------------------------------
The original motivation for this file was for the use of the built-in
function file system (BINFS) with a web server. In that case, the built
in functions provide CGI programs. But the BINFS file system cannot hold
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on-board FLASH. Later, you overlay that ROMFS file system with additional
files from an SD card by using the Union File System to overlay, and
perhaps replace, the ROMFS files.
Another use case might be to overlay a read-only file system like ROMFS
with a writable file system (like a RAM disk). This should then give
to a readable/write-able file system with some fixed content.
Example Configurations
----------------------
o configs/sim/unionfs - This is a simulator configuration that uses the
Union File System test at apps/examples/unionfs. That test overlays two
small ROMFS file systems with many conflicts in directories and file
names. This is a good platform for testing the Union file System and
apps/examples/unionfs is a good example of how to configure the Union
File System.
o configs/lincoln60/thttpd-binfs - This is an example using the THTTPD
web server. It server up content from a Union File System with fixed
content provided by a ROMFS file system and CGI content provided by a
BINFS file system.
You can see how the Union File System content directory is configured
by logic in apps/example/thttpd/.
o configs/olimex-lpc1766stk/thttpd-binfs - This is essentially the same
as the lincoln60 configuration. It does not work, however, because the
LPC1766 has insufficient RAM to support the THTTPD application in this
configuration.