Re: [Qemu-block] [PATCH v3 0/7] bitmaps: add inconsistent bit

[John Snow]

On 3/1/19 2:15 PM, John Snow wrote:
> Allow QEMU to read in bitmaps that have the in-use bit set, for the
> purposes of allowing users to delete those bitmaps.
> 
> This is chosen in preference to a hard error on load to minimize
> impact for a non-critical error, but to force the user or management
> utility to acknowledge that the bitmap is no longer viable.
> 
> 1. Changed wording of meaning of persistent bit, inconsistent bit
>    Declining to optimize to avoid allocations for this revision.
> 
> 2. Add Reviewed-by from Eric.
> 
> 3. Split into several patches that are more single-purpose, which
>    highlights the individual fixes more clearly;
> 
>    - Prohibit BUSY or INCONSISTENT bitmaps from being merge sources.
> 
> 4. Declining feedback to prohibit disabling or enabling readonly bitmaps,
>    on the basis that users may wish to enable/disable them prior to
>    remounting their backing storage RW.
> 
>    Decided to prohibit attempting to remove readonly bitmaps, so the
>    failure happens earlier.
> 
>    Prohibit sync=incremental backups using readonly bitmaps, because
>    they're not capable of clearing the bitmap on success.
>    sync=differential would be acceptable here. (Good spot, Vladimir.)
> 
> John Snow (7):
>   block/dirty-bitmaps: add inconsistent bit
>   block/dirty-bitmap: add inconsistent status
>   block/dirty-bitmaps: add block_dirty_bitmap_check function
>   block/dirty-bitmaps: prohibit readonly bitmaps for backups
>   block/dirty-bitmaps: prohibit removing readonly bitmaps
>   block/dirty-bitmaps: disallow busy bitmaps as merge source
>   block/dirty-bitmaps: implement inconsistent bit
> 
>  qapi/block-core.json           |  20 +++++--
>  include/block/dirty-bitmap.h   |  15 ++++-
>  block/dirty-bitmap.c           |  63 +++++++++++++++++---
>  block/qcow2-bitmap.c           | 103 +++++++++++++++++----------------
>  blockdev.c                     |  50 ++++------------
>  migration/block-dirty-bitmap.c |  12 +---
>  nbd/server.c                   |   3 +-
>  7 files changed, 151 insertions(+), 115 deletions(-)
> 

Thanks for the reviews Eric, I have staged this on my bitmaps branch. I
realize this is hasty, but it's time to get patches in for release, and
it will make reviewing the next series earlier.

Vladimir, I realize I didn't take a few of your suggestions here so I am
delaying sending the PR for this a little bit to give you a chance to
object.

--js