Re: Moving existing ostree users to a new branch

[Colin Walters <walters verbum org>]

On Fri, Mar 17, 2017, at 11:12 AM, Daniel Drake wrote:

> We now need to implement this automatic migration. I understand there
> have been some previous conversations touching on the possibility of
> having a new commit type which marks a specific branch as end-of-life.
> I now plan to implement such functionality. I will aim for inclusion
> upstream once the initial implementation is ready, so I would
> appreciate any quick design guidance before I get into it.

One option is to include a systemd unit
which executes an idempotent script to change the config as part of an update.
I've thought a few times about writing a general framework for something
like this that has a "versioned" concept of configuration and makes it
easy to drop in snippets, but anyways the crude version is:

systemd unit:
Before=eos-updater.service
ConditionPathExists=!/var/lib/eos/newhotness-origin-transition
ExecStart=/usr/bin/eos-newhotness-transition.sh

shell (usr/bin/eos-newhotness-transition.sh)
origin=$(ostree admin --print-current-dir).origin
if grep -q /oldhardware/ ${origin}; then
  sed -i -e s,oldhardware,newhotness, ${origin}
  touch /var/lib/eos/newhotness-origin-transiction
fi

> My thinking is that this new commit type would also point to a new
> branch that the client should switch to. When doing an ostree update
> that ends up on this type of commit, the client would then update the
> local repo config to point at the new branch. Then it would restart
> the update process using the new branch.

The ugly thing about this is going to be it crosses layers - the "repo pull"
part of libostree (OstreeRepo) is lower level than the "sysroot management"
(OstreeSysroot).  That's not insurmountable obviously...maybe the rebase
target could be provided as part of the status?  A little ugly...

It would make sense to me to have standardized metadata for this though;
a a{sv} entry "ostree.endoflife"  => string:"some reason text here"?
And an optional "ostree.endoflife-rebase" string"exampleos/42/x86_64/newhotness" ?