Re: [libvirt] [PATCH v2] Block info query: Add check for transient domain

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.

@@ -10300,6 +10310,15 @@ cleanup: VIR_FREE(alias); virStorageFileFreeMetadata(meta); VIR_FORCE_CLOSE(fd); + + /* If we failed to get data from a domain because it's inactive and + * it's not a persisent domain, then force failure.