NAME Funifs - FUSE read-only Union Filesystem OBJECTIVE Funifs implements limited set of unionfs filesystem features (read-only union of read-only branches), sufficient for staging web site testing and development. Primary motivations of funifs comes from KISS principle: make something easy and stable whilst open for extensions. HOSTED ON https://funifs.googlecode.com/hg/ http://search.cpan.org/~vova/Funifs/ INSTALLATION After download and unpack tarball, run this in directory with Build.PL: ./Build.PL ; ./Build ; ./Build test ; ./Build install PACKAGE FILES funifs - /usr/sbin/funifs - funifs userspace FUSE driver rcfunifs - /etc/init.d/funifs - service script to mount/unmount at system boot fstab (in /usr/share/doc/packages/funifs/) - examples of /etc/fstab lines. DRY RUN For those of us who are that paranoid as I am, before installation to system directories, make sure: ./Build.PL --install_base=/var/tmp/Funifs ; ./Build ; ./Build test ; ./Build install It may fail, if you run it with regular user rights. If so, adding "user_allow_other" to /etc/fuse.conf should make Build test happy. Or, just run it as root superuser. USAGE CONCEPT Let's say we have production web site configured as: ServerName www.site.com DocumentRoot /srv/site.com/www/root Then, staging site is configured in httpd.conf as: ServerName w.u.site.com DocumentRoot /srv/site.com/u/w/root Mounting of staging (w.u) site delta tree on the top of the production (www) site directory tree can be configured in /etc/fstab as: funifs#/u/w /srv/site.com/u/w fuse dirs=/delta/site.com/u/w:/srv/site.com/www 0 0 That way we get in staging DocumentRoot the read-only union of production site DocumentRoot and delta tree. Delta branches sandwich can have multiple layers, not just one. PREREQUISITES Funifs relies on FUSE library, fuse.ko kernel module, and perl modules: * Fuse * Filesys::Statvfs * Unix::Syslog * Module::Build Perl module Fuse.pm works flawless starting version Fuse-0.08. Multi-threaded use has buggy history on RHEL/Centos 5. AVOID INDEXING It's recommended to disable filesystem crawling for "fuse" type filesystems. You may want to update system configuration files, such as /etc/sysconfig/locate /etc/cron.daily/slocate.cron /etc/updatedb.conf /usr/share/msec/security.sh KNOWN ISSUES Funifs is not a comprehensive driver, it has limited features due to specific demands and stacking nature. The most visible are: Lack of whiteouts support "Whiteout" is the way to "remove" file from the union, when it physically exists in one of branches. That is, if program code relies on a file presence test -f $path ... and file exists in bottom branch of union, funifs has no way to emulate removal by manipulating the delta branches content. Application code should not rely on a file presence. For a templates (where empty file equivalent to missing file) the lack of whiteout-s is not an issue: zero-size file in top layer has the same effect as the whiteout. Lack of persistent i-nodes support Unionfs semantics by it's nature is inaccurate about files i-nodes, thus any attempt to compare two files i-nodes most likely will return false, even for identical files on underlying filesystem branches. Application code should not rely on i-node values. Copy file to "itself" bug Attempt to copy file to delta branch from another branch using the union as the source tends to produce empty file of non-zero length. Fix for this issue is not known: funifs driver is unable to control this. Application code should refer to bottom branch content explicitly, rather then use result of union-ing. LICENSE AND COPYRIGHT Copyright (C) Vladimir V. Kolpakov [aka double-you] 2006-2010 This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License. See http://dev.perl.org/licenses/ for more information. THANKS To Stephane Saux and Ben Schein at SFGate for inspiration and insistency, to Mark Glines and Dobrica Pavlinusic for the bridge FUSE--Perl, to Denis Cirulis at opensource for the bugs hunting. FEEDBACKS I would really appreciate it if you could publish your ideas, bug reports, or feature request on http://groups.google.com/group/funifs/topics or even submit fixes on funifs.googlecode.com. Releasing new version on googlecode, don't forget also upload tarball to CPAN, that is result of the ./Build dist SEE ALSO Funion - somewhat similar to funifs, but seems unfinished http://code.google.com/p/funion/ Unionfs-fuse - read/write FUSE union http://podgorny.cz/moin/UnionFsFuse Perl wrapper for FUSE http://search.cpan.org/~dpavlin/Fuse/