[Qemu-devel] [RFC V4 0/9] Quorum disk image corruption resiliency

[Benoît Canet]

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.

usage: -drive 
file=quorum:threshold/total:image_1.raw:...:image_total.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()

in v4:

Eric Blake: verbose commit message for "Add quorum_open() and quorum_close()"
            use of a bool for the escape variable in the same commit
            simplify a if to a one liner in the same commit
            replace "+= 1" by ++ in a number of places
            make quorum_getlength return a quorum vote.

Blue Swirl: replace n and m by threshold and total
            ignore flush errors in quorum_co_flush

Stefan Hajnoczi: removal of a macro in "Add quorum mechanism"
                 call qemu_iovec_destroy in the bh

Benoît Canet: Now use QuorumVoteItem and QuorumVoteVersion as names for the
              voting structs 
              refactor and rename function to quorum_count_vote.

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_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.
  quorum: Add quorum_getlength().

 block/Makefile.objs |    1 +
 block/blkverify.c   |  108 +---------
 block/quorum.c      |  577 +++++++++++++++++++++++++++++++++++++++++++++++++++
 cutils.c            |  103 +++++++++
 qemu-common.h       |    2 +
 5 files changed, 685 insertions(+), 106 deletions(-)
 create mode 100644 block/quorum.c

-- 
1.7.9.5