This series is a larger rework of the block migration support qemu
recently gained. Besides lots of code refactorings the major changes
are:
- Faster restore due to larger block sizes (even if the target disk is
unallocated)
- Off-by-one fixes in the block dirty tracking code
- Allow for multiple migrations (after cancellation or if migrating
into a backup image)
- Proper error handling
- Progress reporting fixes: report to monitor instead of stdout, report
sum of multiple disks
- Report disk migration progress via 'info migrate'
- Progress report during restore
One patch is directly taken from Pierre Riteau queue [1] who happend to
work on the some topic the last days, two more are derived from his
commits.
These patches make block migration usable for us. Still, there are two
more major improvements on my wish/todo list:
- Respect specified maximum migration downtime (will require tracking
of the number of dirty blocks + some coordination with ram migration)
- Do not transfere unallocated disk space (also for raw images, ie. add
bdrv_is_allocated support for the latter)
In an off-list chat, Liran additionally brought up the topic that RAM
migration should not start too early so that we avoid re-transmitting
dirty pages over and over again while the disk image is slowly beamed
over.
I hope we can join our efforts to resolve the open topics quickly, the
critical ones ideally before the merge window closes.