cookbook/container: example of building+running docker containers.

This got... long... and complicated.  But I think it's a really good
demonstration of getting redo to do complicated things elegantly.  At
least, I hope it is.

docs/cookbook/container/default.runkvm.do

@@ -0,0 +1,34 @@
+exec >&2
+./need.sh python kvm busybox
+
+redo-ifchange "$2.initrd" memcalc.py
+rm -f "$3.out" "$3.code"
+
+# Linux only allows an initrd of size < 50% of RAM,
+# so set a RAM amount based on the initrd size.
+mem=$(./memcalc.py "$2.initrd")
+echo "$2: kvm memory required: $mem"
+
+kvm \
+	-m "$mem" \
+	-kernel /boot/vmlinuz-$(uname -r) \
+	-initrd "$2.initrd" \
+	-append 'rdinit=/rdinit panic=1 console=ttyS0 loglevel=4' \
+	-no-reboot \
+	-display none \
+	-chardev stdio,mux=on,id=char0 \
+	-chardev file,id=char1,path="$3.out" \
+	-chardev file,id=char2,path="$3.code" \
+	-serial chardev:char0 \
+	-serial chardev:char1 \
+	-serial chardev:char2
+read rv <$3.code || true
+[ -z "$rv" ] && exit 99
+if [ "$rv" -eq 0 ]; then
+	sed -e 's/\r//g' "$3.out" >$3
+	echo "ok." >&2
+else
+	echo "kvm program returned error: $rv" >&2
+fi
+rm -f "$3.out" "$3.code"
+exit "$rv"