Re: Question: How do I discard any changes for the device which is set by blockdev option?

On 5/19/20 12:56 PM, Masayoshi Mizuma wrote: > Hello, > > I would like to discard any changes while the qemu guest OS is done. > I can do that with snapshot and drive option. > However, snapshot option doesn't work for the device which set by > blockdev option like as: > > $QEMU --enable-kvm \ > -m 1024 \ > -nographic \ > -serial mon:stdio \ > -blockdev driver=file,node-name=mydisk,filename=/mnt/fedora.qcow2 \ > -blockdev driver=qcow2,node-name=vda,file=mydisk \ > -device virtio-blk-pci,drive=vda,bootindex=1 \ > -snapshot > > I would like to use blockdev option to set the device because > libvirt uses blockdev option for disk element. > > If there's no way to do so, does that make sense to get available > snapshot option to blockdev as well? If that makes sense, I'll try to > implement that. > > As for qcow2, I think we can do such things to use qemu-img snapshot > command, for example save the original image and restore the image > after the qemu guest OS is shutdowned. However, it may be complecated > for user. I would like the simple way like as snapshot/drive option... > > If I'm missing something, let me know. > Sounds like a repeat of this thread: https://lists.gnu.org/archive/html/qemu-devel/2020-01/msg06144.html where the consensus is yes, -blockdev and -snapshot are incompatible, libvirt has plans to use the <transient/> tag to behave the same as what -snapshot does (but no one has implemented it yet), and in the meantime, it is possible to force libvirt to avoid -blockdev if you still need to supply -snapshot behind libvirt's back.

-- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org