40ignition-ostree: add coreos-inject-rootmap.service

This implements the rootmap functionality that figures out all the
dependencies required to find `/sysroot`, and injects them into the BLS
config. For more information, see:

coreos/fedora-coreos-tracker#94 (comment)

The `rdcore` code supports RAID and LUKS devices, though the latter
needs a new Clevis release with the following patches to be fully
supported:

latchset/clevis#211
latchset/clevis#217

This also implements the `root=UUID=$uuid` inject patch proposed in
coreos/fedora-coreos-tracker#465.

On its own, this unlocks reprovisioning FCOS with root on a RAID device,
or e.g. in-place reprovisioning of root on btrfs.

Closes: coreos/fedora-coreos-tracker#465
Closes: coreos/fedora-coreos-tracker#94

overlay.d/05core/usr/lib/dracut/modules.d/40ignition-ostree/coreos-inject-rootmap.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=CoreOS Inject Rootmap
+# If root is specified, assume rootmap is already configured
+ConditionKernelCommandLine=!root
+OnFailure=emergency.target
+OnFailureJobMode=isolate
+
+After=ignition-files.service
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/rdcore rootmap /sysroot --boot-device /dev/disk/by-label/boot
+RemainAfterExit=yes
+MountFlags=slave

overlay.d/05core/usr/lib/dracut/modules.d/40ignition-ostree/module-setup.sh

@@ -3,7 +3,7 @@
 # ex: ts=8 sw=4 sts=4 et filetype=sh
 
 depends() {
-    echo ignition
+    echo ignition rdcore
 }
 
 install_ignition_unit() {
@@ -90,4 +90,6 @@ install() {
     inst_script "$moddir/coreos-growpart" /usr/libexec/coreos-growpart
 
     inst_script "$moddir/coreos-relabel" /usr/bin/coreos-relabel
+
+    install_ignition_unit coreos-inject-rootmap.service diskful
 }