build: Add /.coreos-aleph-version.json to target

It will be very useful in the future to be able to more rigorously
know the state that a given machine *started* from.  For example,
small tweaks like `chattr +i /sysroot` are things that won't
happen for in-place updates.

The term "aleph" here means "start".

If we decide to introduce a mechanism (e.g. systemd
unit) that performs those changes even for old in-place installs,
it could be useful to know exactly what the starting state was.

Note this ends up in the *physical* storage root `/` which
appears as `/sysroot` when booted.

Closes: coreos/fedora-coreos-tracker#170

src/cmd-buildextend-metal

@@ -173,7 +173,7 @@ if [ -z "${use_anaconda}" ]; then
         ref_arg=${commit}
     fi
 
-    runvm -drive "if=virtio,id=target,format=${image_format},file=${path}.tmp" -- /usr/lib/coreos-assembler/create_disk.sh /dev/vda "$ostree_repo" "${ref_arg}" "${ostree_remote}" /usr/lib/coreos-assembler/grub.cfg "$name" "${save_var_subdirs}" "\"$kargs\""
+    runvm -drive "if=virtio,id=target,format=${image_format},file=${path}.tmp" -- /usr/lib/coreos-assembler/create_disk.sh /dev/vda "${build}" "${img}" "$ostree_repo" "${ref_arg}" "${ostree_remote}" /usr/lib/coreos-assembler/grub.cfg "$name" "${save_var_subdirs}" "\"$kargs\""
     mv "${path}.tmp" "$path"
     echo "{}" > tmp/vm-iso-checksum.json
 else

src/create_disk.sh

@@ -10,8 +10,8 @@
 # an issue and we can discuss configuration needs.
 set -euo pipefail
 
-if [ "$#" -ne 8 ]; then
-	echo 'create_disk <device> <ostree-repo> <ostree-ref> <ostree-remote> <grub-script> <os-name> <save-var-subdirs> <space separated kargs>'
+if [ "$#" -ne 10 ]; then
+	echo 'create_disk <device> <buildid> <imageid> <ostree-repo> <ostree-ref> <ostree-remote> <grub-script> <os-name> <save-var-subdirs> <space separated kargs>'
 	exit 1
 fi
 
@@ -20,6 +20,8 @@ export PATH=$PATH:/sbin:/usr/sbin
 arch="$(uname -m)"
 
 disk="$1" && shift
+buildid="$1" && shift
+imgid="$1" && shift
 ostree="$1" && shift
 ref="$1" && shift
 remote_name="$1" && shift
@@ -87,6 +89,22 @@ do
 done
 ostree admin deploy "${deploy_ref}" --sysroot rootfs --os "$os_name" $kargsargs
 
+# This will allow us to track the version that an install
+# originally used; if we later need to understand something
+# like "exactly what mkfs.xfs version was used" we can do
+# that via looking at the upstream build and finding the
+# build logs for it, getting the coreos-assembler version,
+# and getting the `rpm -qa` from that.
+ostree_commit=$(ostree --repo="${ostree}" rev-parse "${ref}")
+cat > rootfs/.coreos-aleph-version.json << EOF
+{
+	"build": "${buildid}",
+	"ref": "${ref}",
+	"ostree-commit": "${ostree_commit}",
+	"imgid": "${imgid}"
+}
+EOF
+
 # See the equivalent code in gf-anaconda-cleanup
 # /var hack: we'd like to remove all of /var, but SELinux issues prevent that.
 # see https://github.com/coreos/ignition-dracut/pull/79#issuecomment-488446949