Fileset {
  Name = "Gipervizors-backup"
  Include {
    File = "/var/lib/libvirt/images"
    Options {
      Compression = "Gzip"
      Signature = "Md5"
      Plugin = "\\|/usr/local/sbin/kvm_bpipe.sh"
    }
  }
}

root@node3:/usr/local/sbin# ls -la
total 16
drwxr-xr-x  2 root     root     4096 Jul  6 19:48 .
drwxr-xr-x 10 root     root     4096 Jul 31  2020 ..
-rwxrwxrwx  1 www-data www-data  648 Jul  6 19:48 kvm_bpipe.sh
-rwxrwxrwx  1 www-data www-data  398 Jul  6 19:48 kvm_commit.sh

root@node3:/usr/local/sbin# cat kvm_bpipe.sh 
#!/bin/bash
DOMAIN=`virsh list --all | tail -n -2 | head -n -1 | awk '{print $2}'`
for d in $DOMAIN; do
  TARGETS=`virsh domblklist "$DOMAIN" --details | grep ^file | grep -v cdrom | awk '{print $3}'`
  IMAGES=`virsh domblklist "$DOMAIN" --details | grep ^file | awk '{print $4}'`
  for t in $TARGETS; do
    virsh snapshot-create-as --domain $DOMAIN --name backup --no-metadata -atomic --disk-only --diskspec $t,snapshot=external >/dev/null
  done
  for t in $IMAGES; do
    NAME=`basename "$t"`
    echo "bpipe:/mnt/$NAME.bkp:cat $t:dd of=/tmp/$NAME.bkp"
    echo "bpipe:/mnt/$NAME.xml.bkp:virsh dumpxml $DOMAIN:dd/tmp/$NAME.xml.bkp"
  done
done

1.  Plugin = "\\|/usr/local/sbin/kvm_bpipe.sh"
2.  Plugin = "\|/usr/local/sbin/kvm_bpipe.sh"
3.  Plugin = "/usr/local/sbin/kvm_bpipe.sh"