From afd7ef15dde1717ea46d559728b66f40a9692173 Mon Sep 17 00:00:00 2001 From: Gregory Nutt Date: Sun, 7 Jun 2015 07:28:09 -0600 Subject: [PATCH] Update README files --- fs/unionfs/README.txt | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/fs/unionfs/README.txt b/fs/unionfs/README.txt index 9369531320..fb2d4530b0 100755 --- a/fs/unionfs/README.txt +++ b/fs/unionfs/README.txt @@ -1,6 +1,8 @@ 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: @@ -22,6 +24,8 @@ fs/unionfs/README.txt 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 @@ -37,3 +41,30 @@ fs/unionfs/README.txt 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.