Add general ignition-ostree module with rootfs replacement

Previously the `40coreos-var` module was "special /var
handling for Ignition + OSTree".

This new module takes over that, renaming it to `ignition-ostree`,
and extends it with support for replacing the root filesystem.

overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/ignition-ostree-dracut-rootfs.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+set -euo pipefail
+
+rootmnt=/sysroot
+tmproot=/run/ignition-ostree-rootfs
+
+case "${1:-}" in
+    detect)
+        # This is obviously crude; perhaps in the future we could change ignition's `fetch`
+        # stage to write out a file if the rootfs is being replaced or so.  But eh, it
+        # works for now.
+        has_rootfs=$(jq '.storage?.filesystems? // [] | map(select(.label == "root")) | length' < /run/ignition.json)
+        if [ "${has_rootfs}" = "0" ]; then
+            exit 0
+        fi
+        echo "Detected rootfs replacement in fetched Ignition config: /run/ignition.json"
+        mkdir "${tmproot}"
+        ;;
+    save)
+        # This one is in a private mount namespace since we're not "offically" mounting
+        mount /dev/disk/by-label/root $rootmnt
+        echo "Moving rootfs to RAM..."
+        # OSTree added the immutable bit on the deployment root, and
+        # cosa's create_disk added it to the rootfs
+        chattr -i ${rootmnt} ${rootmnt}/ostree/deploy/*/deploy/*.0
+        for x in boot ostree; do
+            # TODO; copy instead of mv to avoid writes, since we're just
+            # about to blow away the whole FS anyways?
+            mv -Tn ${rootmnt}/${x} ${tmproot}/${x}
+        done
+        umount ${rootmnt}
+        echo "Moved rootfs to RAM, pending redeployment: ${tmproot}"
+        ;;
+    restore)
+        # This one is in a private mount namespace since we're not "offically" mounting
+        mount /dev/disk/by-label/root $rootmnt
+        if [ -d "${rootmnt}/boot" ] || [ -d "${rootmnt}/ostree" ]; then
+            echo "ERROR: Detected Ignition rootfs replacement, but filesystem is not empty" 1>&2
+            exit 1
+        fi
+        echo "Restoring rootfs from RAM..."
+        for x in boot ostree; do
+            mv -Tn ${tmproot}/${x} ${rootmnt}/${x}
+        done
+        # And restore the immutable bits
+        chattr +i ${rootmnt}/ostree/deploy/*/deploy/*.0 ${rootmnt}
+        echo "...done"
+        umount $rootmnt
+        ;;
+    *)
+        echo "Unsupported operation: ${1:-}"
+        ;;
+esac

overlay.d/05core/usr/lib/dracut/modules.d/40coreos-var/coreos-mount-var.service → overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/ignition-ostree-mount-var.service

@@ -1,6 +1,7 @@
 [Unit]
-Description=Mount OSTree /var
+Description=Ignition OSTree: Mount /var
 DefaultDependencies=false
+ConditionKernelCommandLine=ostree
 ConditionPathExists=!/run/ostree-live
 
 # Make sure ExecStop= runs before we switch root
@@ -21,5 +22,5 @@ Before=ignition-mount.service
 [Service]
 Type=oneshot
 RemainAfterExit=yes
-ExecStart=/usr/sbin/coreos-mount-var mount
-ExecStop=/usr/sbin/coreos-mount-var umount
+ExecStart=/usr/sbin/ignition-ostree-mount-var mount
+ExecStop=/usr/sbin/ignition-ostree-mount-var umount

overlay.d/05core/usr/lib/dracut/modules.d/40coreos-var/coreos-populate-var.service → overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/ignition-ostree-populate-var.service

@@ -1,5 +1,6 @@
 [Unit]
-Description=Populate OSTree /var
+Description=Ignition OSTree: Populate /var
+ConditionKernelCommandLine=ostree
 DefaultDependencies=false
 
 # Need to do this with all mount points active
@@ -11,4 +12,4 @@ Before=ignition-files.service
 [Service]
 Type=oneshot
 RemainAfterExit=yes
-ExecStart=/usr/sbin/coreos-populate-var
+ExecStart=/usr/sbin/ignition-ostree-populate-var

overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/ignition-ostree-rootfs-detect.service

@@ -0,0 +1,18 @@
+[Unit]
+Description=Ignition OSTree: detect rootfs replacement
+DefaultDependencies=false
+After=ignition-fetch.service
+Before=ignition-disks.service
+Before=initrd-root-fs.target
+Before=sysroot.mount
+ConditionKernelCommandLine=ostree
+
+# This stage requires udevd to detect disks
+Requires=systemd-udevd.service
+After=systemd-udevd.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+EnvironmentFile=/run/ignition.env
+ExecStart=/usr/libexec/ignition-ostree-dracut-rootfs detect

overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/ignition-ostree-rootfs-restore.service

@@ -0,0 +1,16 @@
+[Unit]
+Description=Ignition OSTree: restore rootfs
+DefaultDependencies=false
+After=ignition-disks.service
+Before=sysroot.mount
+
+ConditionKernelCommandLine=ostree
+ConditionPathIsDirectory=/run/ignition-ostree-rootfs
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+EnvironmentFile=/run/ignition.env
+# So we can transiently mount sysroot
+MountFlags=slave
+ExecStart=/usr/libexec/ignition-ostree-dracut-rootfs restore

overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/ignition-ostree-rootfs-save.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=Ignition OSTree: save rootfs
+DefaultDependencies=false
+After=ignition-ostree-rootfs-detect.service
+Before=ignition-disks.service
+ConditionKernelCommandLine=ostree
+ConditionPathIsDirectory=/run/ignition-ostree-rootfs
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+EnvironmentFile=/run/ignition.env
+# So we can transiently mount sysroot
+MountFlags=slave
+ExecStart=/usr/libexec/ignition-ostree-dracut-rootfs save

overlay.d/05core/usr/lib/dracut/modules.d/31ignition-ostree/module-setup.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# -*- mode: shell-script; indent-tabs-mode: nil; sh-basic-offset: 4; -*-
+# ex: ts=8 sw=4 sts=4 et filetype=sh
+
+depends() {
+    echo ignition ostree
+}
+
+install_ignition_unit() {
+    unit=$1; shift
+    inst_simple "$moddir/$unit" "$systemdsystemunitdir/$unit"
+    ln_r "../$unit" "$systemdsystemunitdir/ignition-complete.target.requires/$unit"
+}
+
+install() {
+    inst_multiple \
+        systemd-sysusers \
+        systemd-tmpfiles \
+        ostree tar chattr \
+        jq
+
+    mkdir -p "$initdir/$systemdsystemunitdir/ignition-complete.target.requires"
+
+    install_ignition_unit ignition-ostree-mount-var.service
+    inst_script "$moddir/ignition-ostree-mount-var.sh" \
+        "/usr/sbin/ignition-ostree-mount-var"
+
+    install_ignition_unit ignition-ostree-populate-var.service
+    inst_script "$moddir/ignition-ostree-populate-var.sh" \
+        "/usr/sbin/ignition-ostree-populate-var"
+    inst_script "$moddir/ignition-ostree-dracut-rootfs.sh" \
+        "/usr/libexec/ignition-ostree-dracut-rootfs"
+    install_ignition_unit ignition-ostree-rootfs-detect.service
+    install_ignition_unit ignition-ostree-rootfs-save.service
+    install_ignition_unit ignition-ostree-rootfs-restore.service
+}