NAME
Funifs - FUSE read-only Union Filesystem
OBJECTIVE
Funifs implements a limited set of unionfs filesystem features (a
read-only union of read-only branches) sufficient for staging web site
testing and development.
The primary motivation for funifs comes from the KISS principle: make
something easy, stable and extensionsable.
HOSTED ON
https://funifs.googlecode.com/hg/
http://search.cpan.org/~vova/Funifs/
INSTALLATION
After downloading and unpacking the tarball, run this in the 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 you who are as paranoid as me, before installing to your
system directories, make sure:
./Build.PL --install_base=/var/tmp/Funifs ; ./Build ; ./Build test ;
./Build install
If running it as a regular user fails, add "user_allow_other" to
/etc/fuse.conf. That should make the Build test happy. Or, just run it
as root.
USAGE CONCEPT
Let's say we have a production website configured like this:
ServerName www.site.com
DocumentRoot /srv/site.com/www/root
And a staging website configured like this:
ServerName w.u.site.com
DocumentRoot /srv/site.com/u/w/root
To mount the staging directory tree (w.u) on top of the production
directory tree (www), configure /etc/fstab like this:
/u/w /srv/site.com/u/w fuse.funifs dirs=/delta/site.com/u/w:/srv/site.com/www 0 0
Your staging website's DocumentRoot now consists of the production tree
overlain with any differences from the staging 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] 2006-2011
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/
