Re: [Qemu-devel] [RFC V3 0/9] Quorum disk image corruption resiliency

[Stefan Hajnoczi]

On Tue, Aug 14, 2012 at 3:14 PM, Benoît Canet <address@hidden> wrote:
> This patchset create a block driver implementing a quorum using m qemu disk
> images. Writes are mirrored on the m files.
> For the reading part the m files are read at the same time and a vote is
> done to determine if a qiov version is present n or more times. It then return
> this majority version to the upper layers.
> When i < n 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.
>
> usage: -drive file=quorum:n/m:image_1.raw:...:image_m.raw,if=virtio,cache=none
>
> in v2:
>
> eblake: fix typos
>         squash two first commits
>
> afärber: Modify the Makefile on first commit
>
> bcanet: move function prototype of quorum.c one patch down
>
> in v3:
>
> Blue Swirl: change char * to uint8_t * in QuorumSingleAIOCB
>
> Eric Blake: Add escaping of the : separator
>             Allow to specify the n/m ratio parameters of the Quorum
>
> Stefan Hajnoczi: Squash quorum_close and quorum_open patch to avoid leak
>                  Add missing bdrv_delete() in quorum_close
>                  simpler quorum_getlength
>                  make the quorum_check_ret threshold a user setting (bind it 
> to n)
>                  move blkverify_iovec_clone() and blkverify_iovec_compare() 
> to cutils.c
>                  free unconditionally qemu_blockalign() with qemu_vfree()
>                  turn assignement into assert in quorum_copy_qiov()
>
> Benoît Canet (9):
>   quorum: Create quorum.c, add QuorumSingleAIOCB and QuorumAIOCB.
>   quorum: Create BDRVQuorumState and BlkDriver and do init.
>   quorum: Add quorum_open() and quorum_close().
>   quorum: Add quorum_getlength().
>   quorum: Add quorum_aio_writev and its dependencies.
>   blkverify: Extract qemu_iovec_clone() and qemu_iovec_compare() from
>     blkverify.
>   quorum: Add quorum_co_flush().
>   quorum: Add quorum_aio_readv.
>   quorum: Add quorum mechanism.
>
>  block/Makefile.objs |    1 +
>  block/blkverify.c   |  108 +---------
>  block/quorum.c      |  559 
> +++++++++++++++++++++++++++++++++++++++++++++++++++
>  cutils.c            |  103 ++++++++++
>  qemu-common.h       |    2 +
>  5 files changed, 667 insertions(+), 106 deletions(-)
>  create mode 100644 block/quorum.c

BTW once this feature is merged we could drop blkverify since quorum
is more generic and provides blkverify behavior in the n=2/m=2
configuration.

Stefan