Re: [Qemu-devel] [Qemu-block] [PATCH v6 0/8] block: Mirror discarded sectors

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, May 28, 2015 at 01:29:42PM +0800, Fam Zheng wrote:
> v6: Fix pnum in bdrv_get_block_status_above. [Paolo]
> 
> v5: Rewrite patch 1.
>     Address Eric's comments on patch 3.
>     Add Eric's rev-by to patches 2 & 4.
>     Check BDRV_BLOCK_DATA in patch 3. [Paolo]
> 
> 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 (8):
>   block: Add bdrv_get_block_status_above
>   qmp: Add optional bool "unmap" to drive-mirror
>   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                    | 60 ++++++++++++++++++++++++++++++---------
>  block/mirror.c                | 27 +++++++++++++++---
>  blockdev.c                    |  5 ++++
>  hmp.c                         |  2 +-
>  include/block/block.h         |  4 +++
>  include/block/block_int.h     |  4 +--
>  qapi/block-core.json          |  8 +++++-
>  qmp-commands.hx               |  3 ++
>  tests/qemu-iotests/041        | 66 ++++++++++---------------------------------
>  tests/qemu-iotests/132        | 59 ++++++++++++++++++++++++++++++++++++++
>  tests/qemu-iotests/132.out    |  5 ++++
>  tests/qemu-iotests/group      |  1 +
>  tests/qemu-iotests/iotests.py | 23 +++++++++++++++
>  14 files changed, 195 insertions(+), 84 deletions(-)
>  create mode 100644 tests/qemu-iotests/132
>  create mode 100644 tests/qemu-iotests/132.out
> 
> -- 
> 2.4.1
> 
> 

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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