On Sat, Jul 18, 2020 at 08:06:00AM +0200, Peter Krempa wrote: > On Thu, Jul 16, 2020 at 20:55:29 -0400, Masayoshi Mizuma wrote: > > Thank you for your review. > > > > On Tue, Jul 07, 2020 at 06:36:23AM -0500, Eric Blake wrote: > > > On 7/7/20 2:12 AM, Peter Krempa wrote: > > > > > > > You can install a qcow2 overlay on top of a raw file too. IMO the > > > > implications of using <transient/> allow that. > > > > > > > > As said above I'd strongly prefer if the overlay is created in qemu > > > > using the blockdev-create blockjob (there is already infrastructure in > > > > libvirt to achieve that). > > > > > > Agreed. At this point, any time we call out to qemu-img as a separate > > > process, we are probably doing it wrong. > > > > Got it. I'm thinking about the procedure such as followings. > > Does that make sense? > > > > 1) Open the monitor with qemuProcessQMPNew()/qemuProcessQMPStart(), > > and connect it. > > Starting a new qemu process just to format an image is extreme overkill > and definitely not what we want to do. I see, thanks. > > > 2) Setup the transient disk with qemuDomainPrepareStorageSourceBlockdev(), > > qemuBlockStorageSourceAttachApplyStorage(), qemuBlockStorageSourceCreateGetFormatProps() > > and something... > > > > 3) Run blockdev-create command with qemuMonitorBlockdevCreate(), then > > close the monitor. > > These two steps should be exectued in the qemu process which already > will run the VM prior to starting the guest CPUs. > > > 4) Switch the original disk to the transient disk. > > > > 5) Build the blockdev argument for qemu. > > And instead of this step, you use the external snapshot infrastructure > to install the overlays via 'blockdev-snapshot' QMP command OK. I suppose qemuDomainSnapshotDiskPrepare() and qemuDomainSnapshotDiskUpdateSource() maybe helpful to implement the setup steps of transient disk. > > > > > 6) Run qemu > > And instead of this the VM cpus will be started. Got it, I think the appropriate place is after virCommandRun() at qemuProcessLaunch(), and before qemuProcessFinishStartup(). > > > The above steps require factoring out snapshot code a bit. I have a few > patches in that direction so I'll try posting them next week hopefully. Great, thanks! - Masa
