This uses our new GRUB2 features to handle GPT priority partition
selection, terminal selection, OEM tweaks, etc. The old SYSLINUX and
PV-GRUB configs are now unused except for maintaining compatibility
with older installs. Of the old configs only the ones that
coreos-postinst copies are needed. The new setup supports using GRUB2
under Xen, giving us automatic fallback support on all of our platforms
for the very first time!
Since grub.cfg is copied into place instead of generated, build_image's
--boot_args option is no longer supported. It could be re-added later
with some sed goo but for now it is easy enough to just edit grub.cfg.
The new grub install script must be called after the image is unmounted
and the old bootloaders script doesn't need to touch grub at all. For
now we will continue to use the existing syslinux configs but
interpreted by grub. Beyond the grub menu flashing by during boot
everything should still be functionally equivalent.
Not currently used, this configuration which sets up grub to re-use the
syslinux configuration only works with recent git versions, not any
releases. Compatibility is also limited because the serial configuration
in syslinux must be duplicated in the grub config.
This should make it less difficult for people to add kernel options for
debugging. Without a prompt/timeout the user must be holding down space
or some other key while syslinux loads but it may not be possible for
the user to do so provide input quite that fast. Only a half second to
avoid needlessly increasing boot times in the common case.
Now with SYSLINUX 6 we can use the same bootloader on EFI and BIOS
systems. This replaces our previous reliance on building default kernel
options into the kernel image itself.
