40ignition-ostree: add autosave-xfs transposefs unit

Add a new transposefs unit: `autosave-xfs`. This unit runs after
`ignition-disks` and `ignition-ostree-growfs,` but before the `restore`
transposefs unit.

If the XFS root was grown, it checks if the allocation group count
(agcount) is within a reasonable amount (128 is chosen here). If
it isn't, it saves the rootfs and reformats the filesystem. The
`restore` unit will then restore it as usual. In the case of in-place
reprovisioning like LUKS (i.e. where the partition table isn't modified
by the Ignition config), the rootfs is still saved only once.

Ideally, instead of adding a new transposefs unit, we would make it
part of the initial `save` unit. But at that point, there's no way to
tell whether we should autosave without gazing even more deeply into the
Ignition config. We also don't want to unconditionally save the rootfs
when we may not need it.

Closes: coreos/fedora-coreos-tracker#1183

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

@@ -145,5 +145,6 @@ case "${ROOTFS_TYPE}" in
     btrfs) btrfs filesystem resize max ${path} ;;
 esac
 
-# this is useful for tests
+# The ignition-ostree-transposefs-xfsauto.service unit needs to know if we
+# actually run. This is also useful for tests.
 touch /run/ignition-ostree-growfs.stamp

overlay.d/05core/usr/lib/dracut/modules.d/40ignition-ostree/ignition-ostree-transposefs-autosave-xfs.service

@@ -0,0 +1,19 @@
+[Unit]
+Description=Ignition OSTree: Autosave XFS Rootfs Partition
+DefaultDependencies=false
+After=ignition-disks.service
+# Avoid racing with UUID regeneration
+After=ignition-ostree-uuid-root.service
+After=ignition-ostree-growfs.service
+Before=ignition-ostree-transposefs-restore.service
+OnFailure=emergency.target
+OnFailureJobMode=isolate
+
+ConditionKernelCommandLine=ostree
+# only run if ignition-ostree-growfs ran since that's when pathological cases occur
+ConditionPathExists=/run/ignition-ostree-growfs.stamp
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/libexec/ignition-ostree-transposefs autosave-xfs

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

@@ -127,6 +127,27 @@ mount_and_save_filesystem_by_label() {
     fi
 }
 
+# This implements https://github.com/coreos/fedora-coreos-tracker/issues/1183.
+should_autosave_rootfs() {
+    local fstype
+    fstype=$(lsblk -no FSTYPE "${root_part}")
+    if [ "$fstype" != xfs ]; then
+        echo "Filesystem is not XFS (found $fstype); skipping"
+        return 1
+    fi
+    local agcount
+    eval $(xfs_info "${root_part}" | grep -o 'agcount=[0-9]*')
+    # Semi-arbitrarily chosen: this is roughly ~64G currently (based on initial
+    # ag sizing at build time) which seems like a good rootfs size at which to
+    # discriminate between "throwaway/short-lived systems" and "long-running
+    # workload systems". It's not like XFS performance is way worse at 128.
+    if [ "$agcount" -lt 128 ]; then
+        echo "Filesystem agcount is $agcount; skipping"
+        return 1
+    fi
+    return 0
+}
+
 ensure_zram_dev() {
     if test -d "${saved_data}"; then
         return 0
@@ -219,6 +240,22 @@ case "${1:-}" in
             mkdir "${saved_prep}"
         fi
         ;;
+    autosave-xfs)
+        if should_autosave_rootfs; then
+            wipes_root=1
+            ensure_zram_dev
+            # in the in-place reprovisioning case, the rootfs was already saved
+            if [ ! -d "${saved_root}" ]; then
+                mkdir "${saved_root}"
+                echo "Moving rootfs to RAM..."
+                mount_and_save_filesystem_by_label root "${saved_root}"
+                print_zram_mm_stat
+            fi
+            mkfs.xfs "${root_part}" -L root -f
+            # for tests
+            touch /run/ignition-ostree-autosaved-xfs.stamp
+        fi
+        ;;
     save)
         # Mounts happen in a private mount namespace since we're not "offically" mounting
         if [ -d "${saved_root}" ]; then

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

@@ -28,6 +28,8 @@ install() {
         systemd-sysusers \
         systemd-tmpfiles \
         sort \
+        xfs_info \
+        xfs_spaceman \
         uniq
 
     if [[ $(uname -m) = s390x ]]; then
@@ -81,7 +83,7 @@ install() {
 
     inst_multiple jq chattr
     inst_script "$moddir/ignition-ostree-transposefs.sh" "/usr/libexec/ignition-ostree-transposefs"
-    for x in detect save restore; do
+    for x in detect save autosave-xfs restore; do
         install_ignition_unit ignition-ostree-transposefs-${x}.service
     done