Re: [libvirt] [PATCH 01/23] qemu: driver: Don't call qemuDomainDetermineDiskChain on block jobs

On Wed, Mar 22, 2017 at 14:21:29 -0500, Eric Blake wrote: > On 03/15/2017 11:37 AM, Peter Krempa wrote: >> Our code calls it when starting or re-starting the domain or when >> hotplugging the disk so there's nothing to be detected. >> --- >> src/qemu/qemu_driver.c | 5 ----- >> 1 file changed, 5 deletions(-) >> > > I think I added it here because block jobs have the tendency to rewrite > the backing chain (think active commit, for example, which reduces the > backing chain). Forcing a redetermination is therefore a way to ensure > no stale data associated with the pre-job chain is left in memory. > > So I'm not sure this is correct. We re-detect the backing chain when the VM is started, when we reconnect to it and when we get any of the blockjob-related events.

Additionally if the backing chain is rewritten the code would not be run since the argument that would rewrite any previously detected data is false.