[Qemu-devel] [PATCH v3 0/6] block: Mirror discarded sectors

[Fam Zheng <famz@redhat.com>]

v3: Add John's rev-by in patches 3~6.
    Rewrite patch 1: discard may not suffice, use write zeroes in that case.

v2: Fix typo and add Eric's rev-by in patch 3.
    Add patch 1 to discard target in mirror job. (Paolo)
    Add patch 6 to improve iotests.wait_ready. (John)

This fixes the mirror assert failure reported by wangxiaolong:

https://lists.gnu.org/archive/html/qemu-devel/2015-04/msg04458.html

The direct cause is that hbitmap code couldn't handle unset of bits *after*
iterator's current position. We could fix that, but the bdrv_reset_dirty() call
is more questionable:

Before, if guest discarded some sectors during migration, it could see
different data after moving to dest side, depending on block backends of the
src and the dest. This is IMO worse than mirroring the actual reading as done
in this series, because we don't know what the guest is doing.

For example if a guest first issues WRITE SAME to wipe out the area then issues
UNMAP to discard it, just to get rid of some sensitive data completely, we may
miss both operations and leave stale data on dest image.


Fam Zheng (6):
  mirror: Do zero write on target if sectors not allocated
  block: Fix dirty bitmap in bdrv_co_discard
  block: Remove bdrv_reset_dirty
  qemu-iotests: Make block job methods common
  qemu-iotests: Add test case for mirror with unmap
  iotests: Use event_wait in wait_ready

 block.c                       | 12 --------
 block/io.c                    |  4 +--
 block/mirror.c                | 53 ++++++++++++++++++++++++++++++----
 include/block/block_int.h     |  2 --
 tests/qemu-iotests/041        | 66 ++++++++++---------------------------------
 tests/qemu-iotests/131        | 59 ++++++++++++++++++++++++++++++++++++++
 tests/qemu-iotests/131.out    |  5 ++++
 tests/qemu-iotests/group      |  1 +
 tests/qemu-iotests/iotests.py | 23 +++++++++++++++
 9 files changed, 152 insertions(+), 73 deletions(-)
 create mode 100644 tests/qemu-iotests/131
 create mode 100644 tests/qemu-iotests/131.out

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2.4.0