Re: [Qemu-devel] [PATCH V9 00/11] Quorum block driver

[Max Reitz <mreitz@redhat.com>]

Am 29.10.2013 08:59, schrieb Benoît Canet:
> Le Friday 04 Oct 2013 à 16:31:56 (+0200), Max Reitz a écrit :
>> On 2013-10-02 14:39, Benoît Canet wrote:
>>> It must be applied on top of "block: Add BlockDriver.bdrv_check_ext_snapshot."
>>>
>>> This patchset create a block driver implementing a quorum using total qemu disk
>>> images. Writes are mirrored on the $total files.
>>> For the reading part the $total files are read at the same time and a vote is
>>> done to determine if a qiov version is present $threshold or more times. It then
>>> return this majority version to the upper layers.
>>> When i < $threshold versions of the data are returned by the lower layer the
>>> quorum is broken and the read return -EIO.
>>>
>>> The goal of this patchset is to be turned in a QEMU block filter living just
>>> above raw-*.c and below qcow2/qed when the required infrastructure will be done.
>>>
>>> Main use of this feature will be people using NFS appliances which can be
>>> subjected to bitflip errors.
>>>
>>> This patchset can be used to replace blkverify and the out of tree blkmirror.
>>>
>>> v9: integrate latests comments from kevin
>>>
>>> Benoît Canet (11):
>>>   quorum: Create quorum.c, add QuorumSingleAIOCB and QuorumAIOCB.
>>>   quorum: Create BDRVQuorumState and BlkDriver and do init.
>>>   quorum: Add quorum_aio_writev and its dependencies.
>>>   blkverify: Extract qemu_iovec_clone() and qemu_iovec_compare() from
>>>     blkverify.
>>>   quorum: Add quorum_aio_readv.
>>>   quorum: Add quorum mechanism.
>>>   quorum: Add quorum_getlength().
>>>   quorum: Add quorum_invalidate_cache().
>>>   quorum: Add quorum_co_get_block_status.
>>>   quorum: Add quorum_co_flush().
>>>   quorum: Add quorum_open() and quorum_close().
>>>
>>>  block/Makefile.objs       |    1 +
>>>  block/blkverify.c         |  108 +----
>>>  block/quorum.c            | 1035 +++++++++++++++++++++++++++++++++++++++++++++
>>>  configure                 |   36 ++
>>>  include/monitor/monitor.h |    2 +
>>>  include/qemu-common.h     |    2 +
>>>  monitor.c                 |    2 +
>>>  util/iov.c                |  103 +++++
>>>  8 files changed, 1183 insertions(+), 106 deletions(-)
>>>  create mode 100644 block/quorum.c
>>>
>> Could you add a qemu-iotest if possible?
> I don't see how to specify quorum to qemu-io for bytes checking.
>
> Best regards
>
> Benoît

As of commit b543c5cd, you can pass options to the block driver through
qemu-io -c open. The problem for quorum is that it cannot handle the
filename option (which qemu-io will always set). I've attached a diff to
change this behavior (which makes the path parameter for open optional
and passes NULL to bdrv_open if it is not given). You're free to make
use of it. ;-)

If this diff is applied, you can invoke qemu-io with quorum for example
as following:
qemu-io -c 'open -o
file.driver=quorum,file.children.0.file.filename=[Image
1],file.children.1.file.filename=[Image 2],file.vote_threshold=[x]'

Max