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Experimentation showed that if virNetworkCreateXML() was called for a network that was already defined, and then the network was subsequently shutdown, the network would continue to be persistent after the shutdown (expected/desired), but the original config would be lost in favor of the transient config sent in with virNetworkCreateXML() (which would then be the new persistent config) (obviously unexpected/not desired). To fix this, virNetworkObjAssignDef() has been changed to 1) properly save/free network->def and network->newDef for all the various combinations of live/active/persistent, including some combinations that were previously considered to be an error but didn't need to be (e.g. setting a "live" config for a network that isn't yet active but soon will be - that was previously considered an error, even though in practice it can be very useful). 2) automatically set the persistent flag whenever a new non-live config is assigned to the network (and clear it when the non-live config is set to NULL). the libvirt network driver no longer directly manipulates network->persistent, but instead relies entirely on virNetworkObjAssignDef() to do the right thing automatically. After this patch, the following sequence will behave as expected: virNetworkDefineXML(X) virNetworkCreateXML(X') (same name but some config different) virNetworkDestroy(X) At the end of these calls, the network config will remain as it was after the initial virNetworkDefine(), whereas previously it would take on the changes given during virNetworkCreateXML(). Another effect of this tighter coupling between a) setting a !live def and b) setting/clearing the "persistent" flag, is that future patches which change the details of network lifecycle management (e.g. upcoming patches to fix detection of "active" networks when libvirtd is restarted) will find it much more difficult to break persistence functionality.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>