Make default prepare scripts skip /lib/{modules,firmware} on xen VMs

Now that we use pygrub, these dirs are populated by quite a lot of files
that we don't want to back up but are dynamically built by the kernel/related
packages so do not make it into the the prepared "excludes" file

ROOT/DEBIAN/control

@@ -3,6 +3,6 @@ Priority: optional
 Section: otherosfs
 Maintainer: Chemistry COs <support@ch.cam.ac.uk>
 Architecture: all
-Version: 0.9-ch92
+Version: 0.9-ch93
 Depends: zfs-dkms, postgresql-13 | postgresql-9.5 | postgresql-9.4 , liblockfile-simple-perl, libdbi-perl, libjson-perl, libzfs-perl-chem, libnet-openssh-perl, libdbd-pg-perl, mbuffer, rsync, nfs-kernel-server, pv, libwww-curl-perl
 Description: a backup system using ZFS (repository 'backup-scheduler')

ROOT/etc/chem-zfs-backup-server/zfs-rsync.d/prepare

@@ -42,6 +42,19 @@ if [ ! -f $CONFDIR/$SERVER/exclude ] ; then
  $SCP -q root@$SERVER:/var/adm/backup/package-files $CONFDIR/$SERVER/exclude
 fi
 
+# If we can identify this as a xen VM, add some extra dirs to the exclude list
+# because they include some files built by the kernel package but are not
+# provided by it.
+# systemd-detect-virt is present on all our Ubuntu VMs so is hopefully a 
+# reliable method to use
+VIRT_TYPE=$(ssh root@$SERVER systemd-detect-virt 2>/dev/null)
+if [ "$VIRT_TYPE" == "xen" ] ; then
+cat<<EOF >> $CONFDIR/$SERVER/exclude
+/lib/modules
+/lib/firmware
+EOF
+fi
+
 if $SSH root@$SERVER id postgres >/dev/null 2>&1 ; then
   PGVER=$($SSH root@$SERVER pg_lsclusters| awk -F '[. ]+' '/online/ { print $1 }')
   if [[ -n "$PGVER" ]]; then

ROOT/etc/chem-zfs-backup-server/zfs-rsync.d/prepare-ignore-mysql

@@ -48,6 +48,19 @@ if [ ! -f $CONFDIR/$SERVER/exclude ] ; then
  $SCP -q root@$SERVER:/var/adm/backup/package-files $CONFDIR/$SERVER/exclude
 fi
 
+# If we can identify this as a xen VM, add some extra dirs to the exclude list
+# because they include some files built by the kernel package but are not
+# provided by it.
+# systemd-detect-virt is present on all our Ubuntu VMs so is hopefully a
+# reliable method to use
+VIRT_TYPE=$(ssh root@$SERVER systemd-detect-virt 2>/dev/null)
+if [ "$VIRT_TYPE" == "xen" ] ; then
+cat<<EOF >> $CONFDIR/$SERVER/exclude
+/lib/modules
+/lib/firmware
+EOF
+fi
+
 $SSH root@$SERVER "
 # Ensure that things are not readable where they ought not to be
 umask 077

ROOT/etc/chem-zfs-backup-server/zfs-rsync.d/prepare-ignore-mysql-and-postgres

@@ -48,6 +48,19 @@ if [ ! -f $CONFDIR/$SERVER/exclude ] ; then
  $SCP -q root@$SERVER:/var/adm/backup/package-files $CONFDIR/$SERVER/exclude
 fi
 
+# If we can identify this as a xen VM, add some extra dirs to the exclude list
+# because they include some files built by the kernel package but are not
+# provided by it.
+# systemd-detect-virt is present on all our Ubuntu VMs so is hopefully a
+# reliable method to use
+VIRT_TYPE=$(ssh root@$SERVER systemd-detect-virt 2>/dev/null)
+if [ "$VIRT_TYPE" == "xen" ] ; then
+cat<<EOF >> $CONFDIR/$SERVER/exclude
+/lib/modules
+/lib/firmware
+EOF
+fi
+
 $SSH root@$SERVER "
 # Ensure that things are not readable where they ought not to be
 umask 077