[libvirt] [PATCH 4/5]: Make dumpXML more idempotent with defineXML

Currently, you can define a logical storage pool with something like the following: <pool type='logical'> <source> <name>MyVG</name> <device name='/dev/sdb'/> ... However, dumping out the XML for this same storage pool (with, say, virsh pool-dumpxml), gives: <pool type='logical'> <source> <name>MyVG</name> <device name='/dev/sdb'> </device> To make this more idempotent, do the <device name='/dev/sdb'/> form by default, and only do the <device>...</device> form if .nfreeExtent is defined for the storage pool. Signed-off-by: Chris Lalancette <clalance(a)redhat.com&gt;