Re: [Qemu-devel] [PATCH v13 00/10] Block replication for continuous checkpoints

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

Hi,
  I've got a block error if I kill the secondary.

Start both primary & secondary
kill -9 secondary qemu
x_colo_lost_heartbeat on primary

The guest sees a block error and the ext4 root switches to read-only.

I gdb'd the primary with a breakpoint on quorum_report_bad; see
backtrace below.
(This is based on colo-v2.4-periodic-mode of the framework
code with the block and network proxy merged in; so it could be my
merging but I don't think so ?)


(gdb) where
#0  quorum_report_bad (node_name=0x7f2946a0892c "node0", ret=-5, acb=0x7f2946cb3910, acb=0x7f2946cb3910)
    at /root/colo/jan-2016/qemu/block/quorum.c:222
#1  0x00007f2943b23058 in quorum_aio_cb (opaque=<optimized out>, ret=<optimized out>)
    at /root/colo/jan-2016/qemu/block/quorum.c:315
#2  0x00007f2943b311be in bdrv_co_complete (acb=0x7f2946cb3f60) at /root/colo/jan-2016/qemu/block/io.c:2122
#3  0x00007f2943ae777d in aio_bh_call (bh=<optimized out>) at /root/colo/jan-2016/qemu/async.c:64
#4  aio_bh_poll (ctx=ctx@entry=0x7f2945b771d0) at /root/colo/jan-2016/qemu/async.c:92
#5  0x00007f2943af5090 in aio_dispatch (ctx=0x7f2945b771d0) at /root/colo/jan-2016/qemu/aio-posix.c:305
#6  0x00007f2943ae756e in aio_ctx_dispatch (source=<optimized out>, callback=<optimized out>, 
    user_data=<optimized out>) at /root/colo/jan-2016/qemu/async.c:231
#7  0x00007f293b84a79a in g_main_context_dispatch () from /lib64/libglib-2.0.so.0
#8  0x00007f2943af3a00 in glib_pollfds_poll () at /root/colo/jan-2016/qemu/main-loop.c:211
#9  os_host_main_loop_wait (timeout=<optimized out>) at /root/colo/jan-2016/qemu/main-loop.c:256
#10 main_loop_wait (nonblocking=<optimized out>) at /root/colo/jan-2016/qemu/main-loop.c:504
#11 0x00007f29438529ee in main_loop () at /root/colo/jan-2016/qemu/vl.c:1945
#12 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at /root/colo/jan-2016/qemu/vl.c:4707

(gdb) p s->num_children
$1 = 2
(gdb) p acb->success_count
$2 = 0
(gdb) p acb->is_read
$5 = false

(qemu) info block
colo-disk0 (#block080): json:{"children": [{"driver": "raw", "file": {"driver": "file", "filename": "/root/colo/bugzilla.raw"}}, {"driver": "replication", "mode": "primary", "file": {"port": "8889", "host": "ibpair", "driver": "nbd", "export": "colo-disk0"}}], "driver": "quorum", "blkverify": false, "rewrite-corrupted": false, "vote-threshold": 1} (quorum)
    Cache mode:       writeback, direct

Dave

* Changlong Xie (xiecl.fnst@cn.fujitsu.com) wrote:
> Block replication is a very important feature which is used for
> continuous checkpoints(for example: COLO).
> 
> You can get the detailed information about block replication from here:
> http://wiki.qemu.org/Features/BlockReplication
> 
> Usage:
> Please refer to docs/block-replication.txt
> 
> This patch series is based on the following patch series:
> 1. http://lists.nongnu.org/archive/html/qemu-devel/2015-12/msg04570.html
> 
> You can get the patch here:
> https://github.com/Pating/qemu/tree/changlox/block-replication-v13
> 
> You can get the patch with framework here:
> https://github.com/Pating/qemu/tree/changlox/colo_framework_v12
> 
> TODO:
> 1. Continuous block replication. It will be started after basic functions
>    are accepted.
> 
> Changs Log:
> V13:
> 1. Rebase to the newest codes
> 2. Remove redundant marcos and semicolon in replication.c 
> 3. Fix typos in block-replication.txt
> V12:
> 1. Rebase to the newest codes
> 2. Use backing reference to replcace 'allow-write-backing-file'
> V11:
> 1. Reopen the backing file when starting blcok replication if it is not
>    opened in R/W mode
> 2. Unblock BLOCK_OP_TYPE_BACKUP_SOURCE and BLOCK_OP_TYPE_BACKUP_TARGET
>    when opening backing file
> 3. Block the top BDS so there is only one block job for the top BDS and
>    its backing chain.
> V10:
> 1. Use blockdev-remove-medium and blockdev-insert-medium to replace backing
>    reference.
> 2. Address the comments from Eric Blake
> V9:
> 1. Update the error messages
> 2. Rebase to the newest qemu
> 3. Split child add/delete support. These patches are sent in another patchset.
> V8:
> 1. Address Alberto Garcia's comments
> V7:
> 1. Implement adding/removing quorum child. Remove the option non-connect.
> 2. Simplify the backing refrence option according to Stefan Hajnoczi's suggestion
> V6:
> 1. Rebase to the newest qemu.
> V5:
> 1. Address the comments from Gong Lei
> 2. Speed the failover up. The secondary vm can take over very quickly even
>    if there are too many I/O requests.
> V4:
> 1. Introduce a new driver replication to avoid touch nbd and qcow2.
> V3:
> 1: use error_setg() instead of error_set()
> 2. Add a new block job API
> 3. Active disk, hidden disk and nbd target uses the same AioContext
> 4. Add a testcase to test new hbitmap API
> 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 (10):
>   unblock backup operations in backing file
>   Store parent BDS in BdrvChild
>   Backup: clear all bitmap when doing block checkpoint
>   Allow creating backup jobs when opening BDS
>   docs: block replication's description
>   Add new block driver interfaces to control block replication
>   quorum: implement block driver interfaces for block replication
>   Implement new driver for block replication
>   support replication driver in blockdev-add
>   Add a new API to start/stop replication, do checkpoint to all BDSes
> 
>  block.c                    | 145 ++++++++++++
>  block/Makefile.objs        |   3 +-
>  block/backup.c             |  14 ++
>  block/quorum.c             |  78 +++++++
>  block/replication.c        | 545 +++++++++++++++++++++++++++++++++++++++++++++
>  blockjob.c                 |  11 +
>  docs/block-replication.txt | 227 +++++++++++++++++++
>  include/block/block.h      |   9 +
>  include/block/block_int.h  |  15 ++
>  include/block/blockjob.h   |  12 +
>  qapi/block-core.json       |  33 ++-
>  11 files changed, 1089 insertions(+), 3 deletions(-)
>  create mode 100644 block/replication.c
>  create mode 100644 docs/block-replication.txt
> 
> -- 
> 1.9.3
> 
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK