[Qemu-devel] [PATCH RFC 0/7] COLO block replication supports shared disk case

[zhanghailiang]

COLO block replication doesn't support the shared disk case,
Here we try to implement it.

Just as the scenario of non-shared disk block replication,
we are going to implement block replication from many basic
blocks that are already in QEMU.
The architecture is:

         virtio-blk                     ||                               
.----------
             /                          ||                               | 
Secondary
            /                           ||                               
'----------
           /                            ||                                 
virtio-blk
          /                             ||                                      
|
          |                             ||                               
replication(5)
          |                    NBD  -------->   NBD   (2)                       
|
          |                  client     ||    server ---> hidden disk <-- 
active disk(4)
          |                     ^       ||                      |
          |              replication(1) ||                      |
          |                     |       ||                      |
          |   +-----------------'       ||                      |
         (3)  |drive-backup sync=none   ||                      |
--------. |   +-----------------+       ||                      |
Primary | |                     |       ||           backing    |
--------' |                     |       ||                      |
          V                     |                               |
       +-------------------------------------------+            |
       |               shared disk                 | <----------+
       +-------------------------------------------+
1) Primary writes will read original data and forward it to Secondary
   QEMU.
2) The hidden-disk will buffers the original content that is modified
   by the primary VM. It should also be an empty disk, and
   the driver supports bdrv_make_empty() and backing file.
3) Primary write requests will be written to Shared disk.
4) Secondary write requests will be buffered in the active disk and it
   will overwrite the existing sector content in the buffe

For more details, please refer to patch 1.

The complete codes can be found from the link:
https://github.com/coloft/qemu/tree/colo-v5.1-developing-COLO-frame-v21-with-shared-disk

Test steps:
1. Secondary:
# x86_64-softmmu/qemu-system-x86_64 -boot c -m 2048 -smp 2 -qmp stdio -vnc :9 
-name secondary -enable-kvm -cpu qemu64,+kvmclock -device piix3-usb-uhci -drive 
if=none,driver=qcow2,file.filename=/mnt/ramfs/hidden_disk.img,id=hidden_disk0,backing.driver=raw,backing.file.filename=/work/kvm/suse11_sp3_64
  -drive 
if=virtio,id=active-disk0,driver=replication,mode=secondary,file.driver=qcow2,top-id=active-disk0,file.file.filename=/mnt/ramfs/active_disk.img,file.backing=hidden_disk0,shared-disk=on
 -incoming tcp:0:9999

Issue qmp commands:
{'execute':'qmp_capabilities'}
{'execute': 'nbd-server-start', 'arguments': {'addr': {'type': 'inet', 'data': 
{'host': '0', 'port': '9998'} } } }
{'execute': 'nbd-server-add', 'arguments': {'device': 'hidden_disk0', 
'writable': true } }

2.Primary:
# x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 2048 -smp 2 -qmp stdio -vnc 
:9 -name primary -cpu qemu64,+kvmclock -device piix3-usb-uhci -drive 
if=virtio,id=primary_disk0,file.filename=/work/kvm/suse11_sp3_64,driver=raw -S

Issue qmp commands:
{'execute':'qmp_capabilities'}
{'execute': 'human-monitor-command', 'arguments': {'command-line': 'drive_add 
-n buddy 
driver=replication,mode=primary,file.driver=nbd,file.host=9.42.3.17,file.port=9998,file.export=hidden_disk0,shared-disk-id=primary_disk0,shared-disk=on,node-name=rep'}}
{'execute': 'migrate-set-capabilities', 'arguments': {'capabilities': [ 
{'capability': 'x-colo', 'state': true } ] } }
{'execute': 'migrate', 'arguments': {'uri': 'tcp:9.42.3.17:9999' } }

3. Failover
Secondary side:
Issue qmp commands:
{ 'execute': 'nbd-server-stop' }
{ "execute": "x-colo-lost-heartbeat" }

Please review and any commits are welcomed.

Cc: Juan Quintela <address@hidden>
Cc: Amit Shah <address@hidden> 
Cc: Dr. David Alan Gilbert (git) <address@hidden>

zhanghailiang (7):
  docs/block-replication: Add description for shared-disk case
  block-backend: Introduce blk_root() helper
  replication: add shared-disk and shared-disk-id options
  replication: Split out backup_do_checkpoint() from
    secondary_do_checkpoint()
  replication: fix code logic with the new shared_disk option
  replication: Implement block replication for shared disk case
  nbd/replication: implement .bdrv_get_info() for nbd and replication
    driver

 block/block-backend.c          |   5 ++
 block/nbd.c                    |  12 ++++
 block/replication.c            | 146 +++++++++++++++++++++++++++++++----------
 docs/block-replication.txt     | 131 ++++++++++++++++++++++++++++++++++--
 include/sysemu/block-backend.h |   1 +
 5 files changed, 258 insertions(+), 37 deletions(-)

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1.8.3.1