[Qemu-block] [PATCH v3 00/12] Fix transactional snapshot with dataplane and NBD export

[Fam Zheng]

Changes from v2, which covers virtio-scsi as well:

  - Patch 1: Review all bdrv_op_block_all callers.
             Document bdrv_op_blocker_add_notifier.
             Fix blocking in bdrv_op_blocker_notify.
  - Patch 11: Commit message and function comment update.
  - Patch 12: New.

Reported by Paolo.

Unlike the iohandler in main loop, iothreads currently process the event
notifier used by virtio-blk ioeventfd in nested aio_poll. This is dangerous
without proper protection, because guest requests could sneak to block layer
where they mustn't.

For example, a QMP transaction may involve multiple bdrv_drain_all() in
handling the list of AioContext it works on. If an aio_poll in one of the
bdrv_drain_all() happens to process a guest VQ kick, and dispatches the
ioeventfd event to virtio-blk, a new guest write is then submitted, and voila,
the transaction semantics is violated.

This series avoids this problem by disabling virtio-blk handlers during
bdrv_drain_all() and transactions.

- Patches 1~3 add the block layer op blocker change notifier code.
- Patches 4,5 secure virtio-blk dataplane.
- Patch 6 secures nbd export.
- Patch 7~10 protect each transaction type from being voilated by new IO
  generated in nested aio_poll.
- Patch 11 protects bdrv_drain and bdrv_drain_all.
- Patch 12 does the same protection to virtio-scsi dataplane.


Fam Zheng (12):
  block: Add op blocker type "device IO"
  block: Add op blocker notifier list
  block-backend: Add blk_op_blocker_add_notifier
  virtio-blk: Move complete_request to 'ops' structure
  virtio-blk: Don't handle output when there is "device IO" op blocker
  nbd-server: Clear "can_read" when "device io" blocker is set
  blockdev: Block device IO during internal snapshot transaction
  blockdev: Block device IO during external snapshot transaction
  blockdev: Block device IO during drive-backup transaction
  blockdev: Block device IO during blockdev-backup transaction
  block: Block "device IO" during bdrv_drain and bdrv_drain_all
  virtio-scsi-dataplane: Add "device IO" op blocker listener

 block.c                         | 35 ++++++++++++++++
 block/block-backend.c           |  6 +++
 block/io.c                      | 22 +++++++++-
 blockdev.c                      | 49 ++++++++++++++++++----
 blockjob.c                      |  1 +
 hw/block/dataplane/virtio-blk.c | 37 ++++++++++++++---
 hw/block/virtio-blk.c           | 69 +++++++++++++++++++++++++++++--
 hw/scsi/virtio-scsi-dataplane.c | 91 ++++++++++++++++++++++++++++++++---------
 hw/scsi/virtio-scsi.c           |  4 ++
 include/block/block.h           |  9 ++++
 include/block/block_int.h       |  3 ++
 include/hw/virtio/virtio-blk.h  | 17 ++++++--
 include/hw/virtio/virtio-scsi.h |  3 ++
 include/sysemu/block-backend.h  |  2 +
 migration/block.c               |  1 +
 nbd.c                           | 18 ++++++++
 16 files changed, 327 insertions(+), 40 deletions(-)

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2.4.0