add 'btrfs' role, move vars to host_vars

roles/btrfs/files/btrfs-scrub@.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=Btrfs scrub on %f
+ConditionPathIsMountPoint=%f
+RequiresMountsFor=%f
+
+[Service]
+Nice=19
+IOSchedulingClass=idle
+KillSignal=SIGINT
+ExecStart=/usr/bin/btrfs scrub start -B %f

roles/btrfs/files/btrfs-scrub@.timer

@@ -0,0 +1,11 @@
+[Unit]
+Description=Monthly Btrfs scrub on %f
+
+[Timer]
+OnCalendar=monthly
+AccuracySec=1d
+RandomizedDelaySec=1w
+Persistent=true
+
+[Install]
+WantedBy=timers.target

roles/btrfs/handlers/main.yml

@@ -0,0 +1,5 @@
+- name: Reload systemd
+  ansible.builtin.systemd:
+    daemon_reload: true
+  become: true
+  listen: daemon_reload

roles/btrfs/tasks/main.yml

@@ -0,0 +1,32 @@
+- name: Setup scrub units
+  ansible.builtin.copy:
+    src: "{{ item }}"
+    dest: /etc/systemd/system/
+    mode: "0644"
+    owner: root
+    group: root
+  with_items:
+    - 'btrfs-scrub@.service'
+    - 'btrfs-scrub@.timer'
+  notify: daemon_reload
+  become: true
+
+- name: Run pending handlers
+  ansible.builtin.meta: flush_handlers
+
+- name: Determine btrfs mounts
+  ansible.builtin.set_fact:
+    btrfs_mounts: "{{ ansible_facts['mounts'] | selectattr('fstype', 'equalto', 'btrfs') | map(attribute='mount') | list }}"
+
+- name: Determine systemd-friendly refs for BTRFS mount points
+  ansible.builtin.command: "systemd-escape -p -- {{ item }}"
+  register: sanitized_mounts
+  loop: "{{ btrfs_mounts }}"
+  changed_when: false
+
+- name: Ensure the scrub timer is enabled for discovered BTRFS filesystems
+  ansible.builtin.systemd:
+    name: "btrfs-scrub@{{ item.stdout }}.timer"
+    enabled: true
+  with_items: "{{ sanitized_mounts.results }}"
+  become: true