docs: formatdomain: Document the temporary file for transient disks

Mention that hypervisors may need a temporary file and document the qemu
template for creating them.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index e6f09a728f0ffec0495563eb165d3d39659f780b..3253a28e5a21034ed7b33e3cc1febb2dfa47f399 100644 (file)
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -3479,6 +3479,13 @@ paravirtualized driver is specified via the ``disk`` element.
    ``shareBacking`` attribute should be set to ``yes``. Note that hypervisor
    drivers may need to hotplug such disk and thus it works only with
    configurations supporting hotplug. :since:`Since 7.4.0`
+
+   Hypervisors may need to store a temporary file containing the data written
+   by the domain while running, which may be stored in the same location
+   as the original source of the disk (The ``qemu`` driver stores the temporary
+   files as ``$(origsource).TRANSIENT-$(vmname)``, where ``$(origsource)`` is
+   the full original path of the disk source and ``$(vmname)`` is the name of the
+   domain).
 ``serial``
    If present, this specify serial number of virtual hard drive. For example, it
    may look like ``<serial>WD-WMAP9A966149</serial>``. Not supported for