Re: [Qemu-block] [PATCH v2 0/6] block: Mirror discarded sectors

[Stefan Hajnoczi]

On Wed, May 06, 2015 at 12:52:02PM +0800, Fam Zheng wrote:
> 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: Discard target sectors if not allocated at source side
>   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                | 12 ++++++--
>  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, 115 insertions(+), 69 deletions(-)
>  create mode 100644 tests/qemu-iotests/131
>  create mode 100644 tests/qemu-iotests/131.out

CCing Jeff Cody for block jobs

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