/ 
Funifs-1.2
River stage zero No dependents
/ Funifs

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/