Re: [Qemu-devel] [RFC PATCH COLO v2 00/13] Block replication for continuous checkpoints

[Michael R. Hines]

On 03/25/2015 04:36 AM, Wen Congyang wrote:
> Block replication is a very important feature which is used for
> continuous checkpoints(for example: COLO).
>
> Usage:
> Please refer to docs/block-replication.txt
>
> You can get the patch here:
> https://github.com/wencongyang/qemu-colo/commits/block-replication-v2
>
> Changs Log:
> V2:
> 1. Redesign the secondary qemu(use image-fleecing)
> 2. Use Error objects to return error message
> 3. Address the comments from Max Reitz and Eric Blake
>
> Wen Congyang (13):
>    docs: block replication's description
>    quorum: allow ignoring child errors
>    NBD client: connect to nbd server later
>    Add new block driver interfaces to control block replication
>    quorum: implement block driver interfaces for block replication
>    NBD client: implement block driver interfaces for block replication
>    allow writing to the backing file
>    Allow creating backup jobs when opening BDS
>    block: Parse "backing_reference" option to reference existing BDS
>    Backup: clear all bitmap when doing block checkpoint
>    qcow2: support colo
>    skip nbd_target when starting block replication
>    Don't allow a disk use backing reference target
>
>   block.c                    | 242 +++++++++++++++++++++++-
>   block/Makefile.objs        |   2 +-
>   block/backup.c             |  12 ++
>   block/nbd.c                | 171 +++++++++++++++--
>   block/qcow2.c              | 447 ++++++++++++++++++++++++++++++++++++++++++++-
>   block/qcow2.h              |   6 +
>   block/quorum.c             | 143 ++++++++++++++-
>   docs/block-replication.txt | 147 +++++++++++++++
>   include/block/block.h      |   5 +
>   include/block/block_int.h  |  13 ++
>   include/qemu/hbitmap.h     |   8 +
>   qapi/block.json            |  16 ++
>   tests/qemu-iotests/051     |  13 ++
>   tests/qemu-iotests/051.out |  13 ++
>   util/hbitmap.c             |  19 ++
>   15 files changed, 1230 insertions(+), 27 deletions(-)
>   create mode 100644 docs/block-replication.txt

When I try this patch with the MicroCheckpointing codebase, I'm having 
trouble starting up the secondary/backup VM
using the branch "block-replication-v7"

$ qemu-system-x86_64 -drive 
if=none,driver=raw,file=file.raw,id=nbd_target1 -drive 
if=virtio,driver=replication,mode=secondary,export=foo,file.file.filename=active_disk.qcow2,file.driver=qcow2,file.backing_reference.drive_id=nbd_target1,file.backing_reference.hidden-disk.file.filename=hidden_disk.qcow2,file.backing_reference.hidden-disk.driver=qcow2,file.backing_reference.hidden-disk.allow-write-backing-file=on

Block format 'qcow2' used by device '' doesn't support the option 
'backing_reference.hidden-disk.allow-write-backing-file'

What am I doing wrong here?

- Michael