Re: [Qemu-stable] [PATCH v7 0/8] block: Mirror discarded sectors

[Fam Zheng]

On Mon, 06/08 14:02, Stefan Hajnoczi wrote:
> On Mon, Jun 08, 2015 at 01:56:06PM +0800, Fam Zheng wrote:
> > v7: Fix the lost assignment of s->unmap.
> > 
> > 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                | 28 +++++++++++++++---
> >  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, 196 insertions(+), 84 deletions(-)
> >  create mode 100644 tests/qemu-iotests/132
> >  create mode 100644 tests/qemu-iotests/132.out
> > 
> > -- 
> > 2.4.2
> > 
> 
> Thanks, applied to my block tree:
> https://github.com/stefanha/qemu/commits/block

Stefan,

The only controversial patches are the qmp/drive-mirror ones (1-3), while
patches 4-8 are still useful on their own: they fix the mentioned crash and
improve iotests.

Shall we merge the second half (of course none of them depend on 1-3) now that
softfreeze is approaching?

Fam