overlay.d/05core: add coreos-rootflags back to diskful sysroot.mount

In 45396d8 we started creating a static sysroot.mount to appease
systemd 254+ (see [1]), but it missed the `coreos-rootflags` handling
that was present in ignition-ostree-mount-sysroot.sh.

This PR adds back in the dynamic rootflags by using an EnvironmentFile
generated by a coreos-rootflags.service to get the same behavior.

[1] coreos/fedora-coreos-tracker#1527 (comment)

overlay.d/05core/usr/lib/dracut/modules.d/35coreos-ignition/coreos-diskful-generator

@@ -41,6 +41,21 @@ add_requires() {
     ln -sf "../${name}" "${requires_dir}/${name}"
 }
 
+# Generate a sysroot.mount unit. We can't do this later by dynamically
+# doing the mount like we used to because systemd 254+ will drop units that
+# require sysroot.mount from the transaction:
+# https://github.com/coreos/fedora-coreos-tracker/issues/1527#issuecomment-1656786452
+#
+# We'll dynamically pick up what mount options to use from the OPTIONS
+# environment variable in /run/coreos-rootflags (generated by
+# coreos-rootflags.service).
+#
+# Note that for new machines this is *only* useful on first boot because
+# coreos-boot-edit.service will add the root= and rootflags= kargs to the
+# kernel command line for subsequent boots. However we haven't migrated
+# all old machines so there are still some that could exist that don't
+# have root= and rootflags= kargs. For that reason we run this bit of
+# code on EVERY diskful boot.
 if ! is-live-image; then
     mkdir -p ${UNIT_DIR}
     # We want to generate sysroot.mount on ostree systems, but we don't want
@@ -50,9 +65,12 @@ if ! is-live-image; then
         cat >${UNIT_DIR}/sysroot.mount << 'EOF'
 [Unit]
 Before=initrd-root-fs.target
+After=coreos-rootflags.service
 [Mount]
+EnvironmentFile=/run/coreos-rootflags
 What=/dev/disk/by-label/root
 Where=/sysroot
+Options=${OPTIONS}
 EOF
         add_requires sysroot.mount initrd-root-fs.target
     fi

overlay.d/05core/usr/lib/dracut/modules.d/35coreos-ignition/coreos-rootflags.service

@@ -0,0 +1,27 @@
+[Unit]
+Description=Determine root FS mount option flags
+DefaultDependencies=false
+ConditionKernelCommandLine=!root
+ConditionPathExists=!/run/ostree-live
+# Just in case. We shouldn't run twice.
+ConditionPathExists=!/run/coreos-rootflags
+# Since the sysroot.mount depends on the options generated by us
+# we must run before sysroot.mount
+Before=sysroot.mount
+# In case the disk was manipulated by Ignition and we need to pick
+# up mount options from Ignition config.
+After=ignition-disks.service
+# The script checks if the rootfs was reprovisioned so let's wait
+# until after that has completed if it was requested.
+After=ignition-ostree-transposefs-restore.service
+# Requires the root device to exist
+Requires=dev-disk-by\x2dlabel-root.device
+After=dev-disk-by\x2dlabel-root.device
+
+[Service]
+Type=oneshot
+StandardError=journal
+StandardOutput=append:/run/coreos-rootflags
+ExecStartPre=echo -n 'OPTIONS='
+ExecStart=/usr/sbin/coreos-rootflags
+RemainAfterExit=yes

overlay.d/05core/usr/lib/dracut/modules.d/35coreos-ignition/module-setup.sh

@@ -90,4 +90,5 @@ install() {
     inst_multiple jq blkid
     inst_script "$moddir/coreos-rootflags.sh" \
         "/usr/sbin/coreos-rootflags"
+    install_ignition_unit coreos-rootflags.service initrd-root-fs.target
 }