As rpm-ostree evolves, it keeps driving API additions to libostree.
This creates a relatively tight coupling.
However, if delivering via e.g. RPM, unless one manually remembers to
increment the `Requires:` in the spec file, it's possible for the two
to become desynchronized.
RPM handles versioned symbols and will ensure a dependency if the
application starts using a newer version.
To implement this, switch to `-fvisibility=hidden`, along with an
annotation in the header, and finally add a `.sym` file.
This matches what other projects like systemd and libvirt do.
Although rather than attempting to retroactively version symbols, glom
them all onto the current one.
Right now though, almost all of the details of deltas are private, so
we can't do the "honest thing" and have the command line just use the
shared library.
Eventually some of this should appear in the API, but for now add
command line which is useful for debugging.
In this approach, we drop a /etc/grub.d/15_ostree file which is a
hybrid of shell/C that picks up bits from the GRUB2 library (e.g. the
block device script generation), and then calls into libostree's
GRUB2 code which knows about the BLS entries.
This is admittedly ugly. There exists another approach for GRUB2 to
learn the BLS specification. However, the spec has a few issues:
https://www.redhat.com/archives/anaconda-devel-list/2014-July/msg00002.html
This approach also gives a bit more control to the admin via the
naming of the 15_ostree symlink; they can easily disable it:
Or reorder the ostree entries ahead of 10_linux:
Also, this approach doesn't require patches for grub2, which is an
issue with the pressure to backport (rpm-)OSTree to EL7.
Colin Walters
Giuseppe Scrivano