On Tue, Jun 21, 2011 at 07:36:23 -0600, Eric Blake wrote:
On 06/21/2011 07:14 AM, Stefan Hajnoczi wrote:
This new virDomainBlockCopy API is different. It can be used when you have a disk image (no matter what kind) stored somewhere and you need to copy it somewhere else. It takes two different and independent images, one currently assigned to a virtual block device and a new unassigned one, copies all data from the old one to the new one and reconfigures the block device to use the new image. Neither of the image formats has to be even capable of backing images.
Right.
This sounds related to my thread on snapshot capabilities, where if the disk is not in a format where qemu can do a live snapshot, then libvirt needs a command to pause guest I/O, libvirt snapshots the disk, then libvirt informs qemu that the block device has a new image.
It's all connected in some way, which is also why qemu will probably utilize common code to provide these functions. However, since BlockCopy is not a snapshot, it's about copying all data from one image to another qemu can do it all internally with a single monitor command to minimize the impact on running guest. Jirka