Re: [Qemu-devel] migrate -b problems

[858585 jemmy <jemmy858585@gmail.com>]

it this bug?
https://bugs.launchpad.net/qemu/+bug/1681688

On Wed, Apr 12, 2017 at 5:18 PM, Kevin Wolf <kwolf@redhat.com> wrote:
> Hi all,
>
> after getting assertion failure reports for block migration in the last
> minute, we just hacked around it by commenting out op blocker assertions
> for the 2.9 release, but now we need to see how to fix things properly.
> Luckily, get_maintainer.pl doesn't report me, but only you. :-)
>
> The main problem I see with the block migration code (on the
> destination) is that it abuses the BlockBackend that belongs to the
> guest device to make its own writes to the image file. If the guest
> isn't allowed to write to the image (which it now isn't during incoming
> migration since it would conflict with the newer style of block
> migration using an NBD server), writing to this BlockBackend doesn't
> work any more.
>
> So what should really happen is that incoming block migration creates
> its own BlockBackend for writing to the image. Now we don't want to do
> this anew for every incoming block, but ideally we'd just create all
> necessary BlockBackends upfront and then keep using them throughout the
> whole migration. Is there a way to get some setup/teardown callbacks
> at the start/end of the migration that could initialise and free such
> global data?
>
> The other problem with block migration is that is uses a BlockBackend
> name to identify which device is migrated. However, there can be images
> that are not attached to any BlockBackend, or if it is, the BlockBackend
> might be anonymous, so this doesn't work. I suppose changing the field
> to "device name if available, node-name otherwise" would solve this.
>
> Kevin
>