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46a0737e13
Currently the qemuDomainGetBlockInfo will return allocation == physical for most backing stores. For a qcow2 block backed device it's possible to return the highest lv extent allocated from qemu for an active guest. That is a value where allocation != physical and one would hope be less. However, if the guest is not running, then the code falls back to returning allocation == physical. This turns out to be problematic for rhev which monitors the size of the backing store. During a migration, before the VM has been started on the target and while it is deemed inactive on the source, there's a small window of time where the allocation is returned as physical triggering the code to extend the file unnecessarily. Since rhev uses transient domains and this is edge condition for a transient domain, rather than returning good status and allocation == physical when this "window of opportunity" exists, this patch will check for a transient (or non persistent) domain and return a failure to the caller rather than returning the defaults. For a persistent domain, the defaults will be returned. The description for the virDomainGetBlockInfo has been updated to describe the phenomena.
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>