= How to update AUFS2 =

This document covers the process for updating aufs2 within the Ubuntu
drivers directory.  

== Background ==

Upstream aufs2 is maintained in a git tree as below (which is _not_ used
when updating Ubuntu).  This represents the primary upstream source tree:

    http://git.c3sl.ufpr.br/pub/scm/aufs/aufs2-2.6.git

However this is on an http: transport and incredibly slow.  It is advisable
to also add the gitorius mirror to your tree, fetching that before origin
to reduce the objects you need from the main tree:

    git://gitorious.org/aufs2/aufs2.git

Ubuntu updates are actually taken from the aufs2-standalone tree, somewhat
similar to the compat-wireless tree.  The version in this tree is based on
the mainline tree above but is modularisable, a key requirement for Ubuntu.
This tree is found at the git tree below (check the BOM for the definative
location):

    http://git.c3sl.ufpr.br/pub/scm/aufs/aufs2-standalone.git

This tree contains a set of branches, one per upstream release.  The
aufs2.1 branch represents the mainline tracking branch, with aufs-2.1-38
representing the delta to mainline 2.6.38.  Each branch contains a set
of patches which affect the core enabling the application of aufs2, plus
an open tree for the fs/aufs tree.  The core patches tend to be static
from early in the line of an upstream release, and thus generally do not
need updating as often.

== Updating the core patches ==

Ubuntu uses two of the core enablement patches, which are applied in the
order below.  The remaining changes required to enable aufs are Ubuntu
specific and static:

    aufs2-base.patch
    aufs2-standalone.patch

In order to update these patches it is simplest to simply revert the
existing pair and apply these as two commit.  This allows us to more
easily drop aufs in the future should that be required.

As these core enablement patches are very slow in changing we normally
do not need to update these more than once per upstream mainline release
though sometimes changes do affect these.

== Updating aufs2 ==

Once the enablement patches are updated we can simply use the aufs-update
script in the ubuntu/ directory to update the existing source.  There are
regular updates to the aufs2 upstream and it is likely we will see updates
there more than once a month.

Firstly checkout the upstream standalone tree (see the BOM for the
location) and checkout an appropriate branch for the release you are
updating.  Then simply run the aufs-update command from within the ubuntu/
drivers directory, supplying the location of the local aufs2-standalone tree
on the command line:

	cd ubuntu
	sh aufs-update ../../aufs2-standalone

This will result in an update commit containing the updated code and
also updating the BOM.  Note that any local modifications are now lost.
Where those exist they should be cherry-picked and then squashed into
the update commit to ensure we retain them.

== Ubuntu modifications ==

We carry a very small delta to the upstream aufs2 source.  Any such changes
need to be cherry-picked from the history and squashed into any update
commit in order to prevent regression.  Any current patches are listed below:

Lucid/Maverick/Natty/Oneiric:
    UBUNTU: ubuntu: AUFS -- suppress benign plink warning messages