kexec-parse-boot don't parse grub.cfg functions nor variables

[tlaurion]

Example debian-11.6.0-ppc64el-netinst.iso (Talos II debian image) contains unexpected grub.cfg content, resulting in usb-init failing to parse ISO boot options and simply failing, saying that no boot options were found.

user@talos-tests:/media$ cat /media/boot/grub/grub.cfg 
set default=2
set timeout=-1

insmod echo
insmod gzio
insmod minicmd
insmod normal

menuentry "Debian GNU/Linux installer boot menu" {
	true
}

menuentry "" {
	true
}

function boot_one {
	echo "Loading ..."
	linux	/install/vmlinux $options --- quiet
	initrd	/install/initrd.gz
}

menuentry "Default install" {
        boot_one
}

menuentry "Automated install" {
	set options="auto=true priority=critical"
	boot_one
}

menuentry "Expert install" {
	set options="priority=low"
	boot_one
}

menuentry "Rescue mode" {
	set options="rescue/enable=true"
	boot_one
}

kexec-parse-boot only parses grub menuentry and tries to find initrd kernel and xen entries. It has no knowledge of function nor anything else exposed in previous grub.cfg.

---

Workaround is to construct kexec load line manually (-l) and then execute (-e).... After attempting to boot from usb is to do from command line:

kexec -l /media/install/vmlinux --initrd=/media/install/initrd.gz
kexec -e