Secret XML format
Secret XML
      Secrets stored by libvirt may have attributes associated with them, using
      the secret element.  The secret element has two
      optional attributes, each with values 'yes' and
      'no', and defaulting to 'no':
    
- ephemeral
- This secret must only be kept in memory, never stored persistently.
- private
- The value of the secret must not be revealed to any caller of libvirt, nor to any other node.
      The top-level secret element may contain the following
      elements:
    
- uuid
- An unique identifier for this secret (not necessarily in the UUID format). If omitted when defining a new secret, a random UUID is generated.
- description
- A human-readable description of the purpose of the secret.
- usage
- 
        Specifies what this secret is used for.  A mandatory
        typeattribute specifies the usage category, currently onlyvolumeandcephare defined. Specific usage categories are described below.
Usage type "volume"
      This secret is associated with a volume, and it is safe to delete the
      secret after the volume is deleted.  The <usage
      type='volume'> element must contain a
      single volume element that specifies the key of the volume
      this secret is associated with.
    
Usage type "ceph"
      This secret is associated with a Ceph RBD (rados block device).
      The <usage type='ceph'> element must contain
      a single name element that specifies a usage name
      for the secret.  The Ceph secret can then be used by UUID or by
      this usage name via the <auth> element of
      a disk
      device. Since 0.9.7.
    
Example
      <secret ephemeral='no' private='yes'>
         <description>LUKS passphrase for the main hard drive of our mail server</description>
         <usage type='volume'>
            <volume>/var/lib/libvirt/images/mail.img</volume>
         </usage>
      </secret>
      