We need basic support for UEFI - many newer servers don't support
BIOS compatibility mode anymore.
However, this patch only implements non-atomic because UEFI is FAT, and
we can't do the previous design for OSTree of atomic swap of
/boot/loader.
The Fedora/RHEL UEFI layout has the kernels on a "real" /boot
partition, and /boot/efi/EFI/$vendor just holds the grub2 UEFI binary
and grub.cfg.
Following this, /boot/loader is still on the OS boot partition, and we
still atomically swap it. This potentially paves the way to atomic
upgrades in the future.
https://bugzilla.gnome.org/show_bug.cgi?id=724246
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.
Giuseppe Scrivano
Colin Walters