[Qemu-devel] [PATCH 0/8] add basic recovery logic to quorum driver

[Liu Yuan <namei.unix@gmail.com>]

This patch set mainly add mainly two logics to implement device recover
- notify qourum driver of the broken states from the child driver(s)
- dirty track and sync the device after it is repaired

Thus quorum allow VMs to continue while some child devices are broken and when
the child devices are repaired and return back, we sync dirty bits during
downtime to keep data consistency.

The recovery logic is based on the driver state bitmap and will sync the dirty
bits with a timeslice window in a coroutine in this prtimive implementation.

Simple graph about 2 children with threshold=1 and read-pattern=fifo:
(similary to DRBD)

+ denote device sync iteration
- IO on a single device
= IO on two devices

                                      sync complete, release dirty bitmap
                                         ^
                                         |
  ====-----------------++++----++++----++==========
     |                 |
     |                 v
     |               device repaired and begin to sync
     v
   device broken, create a dirty bitmap

  This sync logic can take care of nested broken problem, that devices are
  broken while in sync. We just start a sync process after the devices are
  repaired again and switch the devices from broken to sound only when the sync
  completes.

For read-pattern=quorum mode, it enjoys the recovery logic without any problem.

Todo:
- use aio interface to sync data (multiple transfer in one go)
- dynamic slice window to control sync bandwidth more smoothly
- add auto-reconnection mechanism to other protocol (if not support yet)
- add tests

Cc: Eric Blake <eblake@redhat.com>
Cc: Benoit Canet <benoit@irqsave.net>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>

Liu Yuan (8):
  block/quorum: initialize qcrs.aiocb for read
  block: add driver operation callbacks
  block/sheepdog: propagate disconnect/reconnect events to upper driver
  block/quorum: add quorum_aio_release() helper
  quorum: fix quorum_aio_cancel()
  block/quorum: add broken state to BlockDriverState
  block: add two helpers
  quorum: add basic device recovery logic

 block.c                   |  17 +++
 block/quorum.c            | 324 +++++++++++++++++++++++++++++++++++++++++-----
 block/sheepdog.c          |   9 ++
 include/block/block.h     |   9 ++
 include/block/block_int.h |   6 +
 trace-events              |   5 +
 6 files changed, 336 insertions(+), 34 deletions(-)

-- 
1.9.1