PoC RFC Add iPXE files to install-amd64-minimal upload on demeter

Extracts and generates needed files to perform iPXE boot from gentoo mirrors
Provided as PoC of what is needed for this to be vaild
If merged this would resolve NiKiZe/Gentoo-iPXE#2
Will be providing PoC for doing most of this in catalyst instead as well
Really want to have this in the same target as minimal livecd

To test result with qemu localy after build (replace your variables):
qemu-system-x86_64 -enable-kvm -M q35 -m 1024 -cpu host -nic user,model=virtio,\
tftp="${BUILD_SRCDIR_BASE}"/builds/default,\
bootfile=install-amd64-minimal-${TIMESTAMP}.ipxe \
-watchdog i6300esb -watchdog-action reset -boot menu=on -usb

Signed-off-by: Christian Nilsson <nikize@gmail.com>

tools/catalyst-auto-amd64-demeter.conf

@@ -88,7 +88,39 @@ post_build() {
 		upload stage3-amd64-systemd-${TIMESTAMP}.tar.xz*
 		;;
 	installcd-stage2-minimal.spec)
-		upload install-amd64-minimal-${TIMESTAMP}.iso*
+		dstname=install-amd64-minimal-${TIMESTAMP}
+		isoname=${dstname}.iso
+
+		# This PXE extraction and pack part is to use the same files as livecd
+		# and also to not clober the support scripts and spec files
+		echo "Extract files from ${isoname} for PXE boot"
+		isoinfo -R -i ${isoname} -X -find -path /boot/gentoo && mv boot/gentoo ${dstname}.lkrn
+		isoinfo -R -i ${isoname} -X -find -path /image.squashfs
+		# combine original initrd with squashfs
+		# different variants can be used, compression
+		# the selected combination here gives most responsive boot (avoids several seconds of black screen)
+		(isoinfo -R -i ${isoname} -x /boot/gentoo.igz; (echo image.squashfs | cpio -H newc -o)) > ${dstname}.igz
+		# remove temp file, needed as file to create cpio header
+		rm image.squashfs
+		# grab the main kernel cmdline from boot config
+		grubkernel=$(isoinfo -R -i ${isoname} -x /grub/grub.cfg | grep "gentoo.* root=" | grep -v docache)
+		# remove grub command and kernel name to get only cmdline
+		grubkernel=${grubkernel#*/boot/gentoo }
+		ipxename=${dstname}.ipxe
+		echo "Generating iPXE script ${ipxename}"
+		echo '#!ipxe' > ${ipxename}
+		echo '# allow for external keymap setting' >> ${ipxename}
+		echo 'isset ${keymap} || set keymap dokeymap' >> ${ipxename}
+		echo '# allow for external cmdline options' >> ${ipxename}
+		echo 'isset ${cmdline} || set cmdline vga=791' >> ${ipxename}
+		# initrd= on cmdline is needed for efi
+		echo "kernel ${dstname}.lkrn ${grubkernel/dokeymap/\$\{keymap\}} initrd=${dstname}.igz \${cmdline}" >> ${ipxename}
+		echo "initrd ${dstname}.igz" >> ${ipxename}
+		echo 'imgstat' >> ${ipxename}
+		echo 'boot' >> ${ipxename}
+
+		# TODO create latest links (*-latest.ipxe) to ${ipxename}
+		upload ${dstname}*
 		;;
 	nomultilib/stage3-openrc.spec)
 		upload stage3-amd64-nomultilib-openrc-${TIMESTAMP}.tar.xz*