Disable CoW on the systemd journal directory

journald's append-heavy writes fragment badly under btrfs
copy-on-write. Pre-create the journal directory with NODATACOW while
it is still empty so the journal files written on first boot inherit
it.

Author: Yury-MonZon

debian-rk3576-img.yaml

@@ -98,6 +98,17 @@ actions:
       UUID=$FSUUID  /var/cache   btrfs  {{ $btrfsopts }},subvol=@var-cache  0  0
       EOF
 
+  # journald's append-heavy writes fragment badly under btrfs copy-on-write. Pre-create
+  # the journal dir with NODATACOW (chattr +C) while it's still empty, so the journal
+  # files written on first boot inherit it. (+C also implies no compression.)
+  - action: run
+    description: Disable CoW on the systemd journal directory
+    chroot: false
+    command: |
+      set -eu
+      mkdir -p "$IMAGEMNTDIR/var/log/journal"
+      chattr +C "$IMAGEMNTDIR/var/log/journal"
+
   - action: overlay
     description: Copy Linux kernel packages into the target
     source: {{ $kerneldir }}