Re: Storing collection ref (collection ID + ref) in the commit metadata

[Colin Walters <walters verbum org>]

On Fri, Jun 23, 2017, at 10:12 AM, Krzesimir Nowak wrote:
> > Storing it in commit metadata means that the collection ref is signed
> > as a part of the commit, so we can trust it from the start. But it
> > also means that we need to specify the collection ref from the
> > beginning and it can never change (that would change the commit's
> > checksum) - that makes the --orphan flag a whole lot less useful. Also
> > it is not fine when ostree refs have discontinuous history (ref
> > pointed to commit 1, then later it points to commit 2 which is not a
> > child of commit 1, so commit 1 is not a part of ref's history).

I've been advocating for doing content and not commit promotion,
like https://github.com/cgwalters/ostree-releng-scripts/blob/master/do-release-tags

It does mean commit checksums become a bit less meaningful in general,
but I think there's a big difference between "production" repos and transient
commits in a testing pipeline that humans may never run.

So think storing it in the commit metadata itself is best to so we don't
need yet another signature mechanism. 

> 1. Do we want to store not one collection ref, but many of them in the
> commit metadata? I wasn't sure whether we should allow for many
> collection refs there or rather for one collection id and many refs.
> Philip argued for the former.

Supporting multiple may make sense...though it feels like the use
case would overlap a lot with the endoflife rebase?

> 2. As a part of the metadata we store the timestamp, which tells when
> this particular piece of metadata was modified. I guess that the only
> useful check we can perform with it is to compare it with the
> timestamp from the older detached metadata of the commit (if we had it
> before). Anything else comes to your mind?

This and below aren't necessary if the metadata is inline, right?

> 3. I wasn't sure if we want to bail out when the detached metadata is
> invalid or just skip this commit. Bailing out is easier, so this is
> what I went with for now.
> 4. If we set the collection ref for a commit, should we also set it
> for all its parent commits too?