On 03/16/2012 04:05 PM, Eric Blake wrote:
Taking an external snapshot of just one disk is atomic, without having to pause and resume the VM. This also paves the way for later patches to interact with the new qemu 'transaction' monitor command.
The various scenarios when requesting atomic are: online, 1 disk, old qemu - safe, allowed by this patch online, more than 1 disk, old qemu - failure, this patch offline snapshot - safe, once a future patch implements offline disk snapshot online, 1 or more disks, new qemu - safe, once future patch uses transaction
This is incomplete:
@@ -10069,7 +10081,8 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain, VIR_DOMAIN_SNAPSHOT_CREATE_HALT | VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY | VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT | - VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE, NULL); + VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE | + VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC, NULL);
By accepting the new 'atomic' flag, we now have to ensure it works for all modes. As written, v1 covered the disk-snapshot mode. The live system checkpoint mode is already atomic ('savevm' is a single monitor command; if it can fail partway through, that's a bug in qemu). But for offline internal snapshots, we were making iterative calls to 'qemu-img snapshot -c', and not cleaning up after partial failure. I'm sending a v2 to fix that. -- Eric Blake eblake@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org