[PATCH 1/3] qemu: implementation of transient option for qcow2 file
pkrempa at redhat.com
Sat Jul 18 06:06:00 UTC 2020
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.
> 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
> 6) Run qemu
And instead of this the VM cpus will be started.
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.
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