Re: [PATCH v2 for-6.2 0/6] push backup with fleecing

[Vladimir Sementsov-Ogievskiy]

Consider that as RFC.

I'm preparing an alternative and more efficient fleecing scheme, based on 
special block driver, not on backing link.

So, this will be rebased, and probably some permission-related difficulties may 
be avoided.

21.07.2021 17:04, Vladimir Sementsov-Ogievskiy wrote:
> Hi all!
>
> Here is push-backup with fleecing. What is it:
>
> 1. Make fleecing scheme
>
> guest blk
>    |
>    |root
>    v
> copy-before-write filter  -------> temp qcow2
>    |                                  |
>    |file                              | backing
>    V                                  |
> active disk <-------------------------
>
> 2. Start backup job from temp qcow2 to final remote target (NBD or
>     something)
>
> Benefit in comparison with simple backup job: for remote final target
> write operations are not very fast. And guest have to wait for
> copy-before-write operations. With fleecing scheme target for
> copy-before-write operations is local qcow2 file with faster access than
> actual backup target. So, guest is less disturbed by copy-before-write
> operations.
>
> Based-on: <20210721100555.45594-1-vsementsov@virtuozzo.com>
>     ([PATCH v6 00/33] block: publish backup-top filter)
>
> v2:
> 01: changed to simply check s->target->perm
> 06: make explicit immutable-source parameter instead of auto-detecting
>
> Vladimir Sementsov-Ogievskiy (6):
>    block/block-copy: use write-unchanged for fleecing scheme
>    block/copy-before-write: require BLK_PERM_WRITE_UNCHANGED for fleecing
>    block: share writes on backing child of fleecing node
>    block: blk_root(): return non-const pointer
>    qapi: backup: add immutable-source paramter
>    iotests/image-fleecing: test push backup with fleecing
>
>   qapi/block-core.json                        |  12 ++-
>   block/copy-before-write.h                   |   1 +
>   include/block/block_int.h                   |   1 +
>   include/sysemu/block-backend.h              |   2 +-
>   block.c                                     |   3 +-
>   block/backup.c                              |  71 ++++++++++++-
>   block/block-backend.c                       |   2 +-
>   block/block-copy.c                          |  18 +++-
>   block/copy-before-write.c                   |  48 ++++++++-
>   block/replication.c                         |   2 +-
>   blockdev.c                                  |   1 +
>   tests/qemu-iotests/tests/image-fleecing     | 105 +++++++++++++++-----
>   tests/qemu-iotests/tests/image-fleecing.out |  61 ++++++++++++
>   13 files changed, 287 insertions(+), 40 deletions(-)


--
Best regards,
Vladimir