Add new build target 'minikernel':

./rootfs minikernel

will download external helper script,
which compiles a kernel and starts qemu
(if possible in kvm mode) together with
the already generated initital ramdisk.

all tempfiles are in already provided tmpfs
and lost at the very end during unmount and exit.

also add a logfile for all targets, which
can be used to better spot errors.

rootfs.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 set -ex
 
-QEMU_CMD="${1:-qemu-system-x86_64}"	# or 'chroot'
+QEMU_CMD="${1:-qemu-system-x86_64}"	# or 'chroot' or 'minikernel'
 QEMU_RAM="${2:-8G}"
 
 pushd sysa
@@ -12,6 +12,8 @@ pushd sysa
 mkdir -p tmp/
 sudo mount -t tmpfs -o size=8G tmpfs tmp
 
+LOGFILE="$PWD/tmp/bootstrap.log"
+
 # base: mescc-tools-seed
 # copy in all the mescc-tools-seed stuff
 cp -r mescc-tools-seed/src/mescc-tools-seed/x86/* tmp
@@ -125,17 +127,33 @@ cd tmp
 find . | cpio -H newc -o | gzip > initramfs.igz
 
 # Run
-if [ "${QEMU_CMD}" = 'chroot' ]; then
-	sudo PATH="/after/bin:${PATH}" chroot . /init
-else
-	${QEMU_CMD} -enable-kvm \
-	    -m "${QEMU_RAM}" \
-	    -nographic \
-	    -no-reboot \
-	    -kernel ../../kernel -initrd initramfs.igz -append console=ttyS0
-fi
+case "${QEMU_CMD}" in
+	chroot)
+		sudo PATH="/after/bin:${PATH}" chroot . /init | tee "$LOGFILE"
+	;;
+	minikernel)
+		git clone --depth 1 --branch v0.4 https://github.com/bittorf/kritis-linux.git
+
+		kritis-linux/ci_helper.sh \
+			--arch x86_64 \
+			--ramsize 4G \
+			--kernel 5.10.8 \
+			--initrd initramfs.igz \
+			--log "$LOGFILE"
+	;;
+	*)
+		${QEMU_CMD} -enable-kvm \
+		    -m "${QEMU_RAM:-8G}" \
+		    -nographic \
+		    -no-reboot \
+		    -kernel ../../kernel -initrd initramfs.igz -append console=ttyS0 | tee "$LOGFILE"
+	;;
+esac
 
 cd ../..
 
+# eventually keep logfile before unmount:
+echo "see logfile: $LOGFILE"
+
 # Cleanup
 sudo umount sysa/tmp