Re: [Qemu-devel] [PATCH v10 00/14] block: incremental backup transactions using BlockJobTxn

[John Snow <jsnow@redhat.com>]

Ping!

To clarify, I *do* intend this series to be for-2.5, and I think it does
qualify as such.

If this *doesn't* go in, we have to revise our documentation just a
pinch to undo some of Kashyap's changes that have already been merged in.

Patches 5, 10, 11 and 12 are awaiting review.

--js

On 10/23/2015 07:56 PM, John Snow wrote:
> Welcome to V10!
> 
> Where'd 8 and 9 go? Private off-list missives from Fam.
> Now you, I, and everyone on qemu-devel are staring at V10.
> 
> What's new in V10?
> 
> I replaced the per-action "transactional-cancel" parameter with
> a per-transaction paremeter named "err-cancel" which is implemented
> as an enum in case we want to add new behaviors in the future, such
> as a "jobs only" cancel mode.
> 
> For now, it's "all" or "none", and if you use it with actions that
> do not support the latent transactional cancel, you will receive
> an error for your troubles.
> 
> This version primarily changed patches 10,11 and replaced it with
> patches 10-12 that are cut a little differently.
> 
> This is based on top of the work by Stefan Hajnoczi and Fam Zheng.
> 
> Recap: motivation for block job transactions
> --------------------------------------------
> If an incremental backup block job fails then we reclaim the bitmap so
> the job can be retried.  The problem comes when multiple jobs are started as
> part of a qmp 'transaction' command.  We need to group these jobs in a
> transaction so that either all jobs complete successfully or all bitmaps are
> reclaimed.
> 
> Without transactions, there is a case where some jobs complete successfully and
> throw away their bitmaps, making it impossible to retry the backup by rerunning
> the command if one of the jobs fails.
> 
> How does this implementation work?
> ----------------------------------
> These patches add a BlockJobTxn object with the following API:
> 
>   txn = block_job_txn_new();
>   block_job_txn_add_job(txn, job1);
>   block_job_txn_add_job(txn, job2);
> 
> The jobs either both complete successfully or they both fail/cancel.  If the
> user cancels job1 then job2 will also be cancelled and vice versa.
> 
> Jobs objects stay alive waiting for other jobs to complete, even if the
> coroutines have returned.  They can be cancelled by the user during this time.
> Job blockers are still in effect and no other block job can run on this device
> in the meantime (since QEMU currently only allows 1 job per device).  This is
> the main drawback to this approach but reasonable since you probably don't want
> to run other jobs/operations until you're sure the backup was successful (you
> won't be able to retry a failed backup if there's a new job running).
> 
> [History]
> 
> v10: Replaced per-action parameter with per-transaction properties.
>      Patches 10,11 were split into 10-12.
> 
> v9: this version fixes a reference count problem with job->bs,
>     in patch 05.
> 
> v8: Rebase on to master.
>     Minor fixes addressing John Snow's comments.
> 
> v7: Add Eric's rev-by in 1, 11.
>     Add Max's rev-by in 4, 5, 9, 10, 11.
>     Add John's rev-by in 5, 6, 8.
>     Fix wording for 6. [John]
>     Fix comment of block_job_txn_add_job() in 9. [Max]
>     Remove superfluous hunks, and document default value in 11. [Eric]
>     Update Makefile dep in 14. [Max]
> 
> ________________________________________________________________________________
> 
> For convenience, this branch is available at:
> https://github.com/jnsnow/qemu.git branch block-transpop
> https://github.com/jnsnow/qemu/tree/block-transpop
> 
> This version is tagged block-transpop-v10:
> https://github.com/jnsnow/qemu/releases/tag/block-transpop-v10
> 
> Fam Zheng (6):
>   backup: Extract dirty bitmap handling as a separate function
>   blockjob: Introduce reference count and fix reference to job->bs
>   blockjob: Add .commit and .abort block job actions
>   blockjob: Add "completed" and "ret" in BlockJob
>   blockjob: Simplify block_job_finish_sync
>   block: Add block job transactions
> 
> John Snow (7):
>   qapi: Add transaction support to block-dirty-bitmap operations
>   iotests: add transactional incremental backup test
>   block: rename BlkTransactionState and BdrvActionOps
>   block/backup: Rely on commit/abort for cleanup
>   block: Add BlockJobTxn support to backup_run
>   block: add transactional properties
>   iotests: 124 - transactional failure test
> 
> Stefan Hajnoczi (1):
>   tests: add BlockJobTxn unit test
> 
>  block.c                    |  19 +-
>  block/backup.c             |  50 ++++--
>  block/mirror.c             |   2 +-
>  blockdev.c                 | 430 ++++++++++++++++++++++++++++++++++-----------
>  blockjob.c                 | 188 ++++++++++++++++----
>  docs/bitmaps.md            |   6 +-
>  include/block/block.h      |   2 +-
>  include/block/block_int.h  |   6 +-
>  include/block/blockjob.h   |  85 ++++++++-
>  qapi-schema.json           |  54 +++++-
>  qemu-img.c                 |   3 -
>  qmp-commands.hx            |   2 +-
>  tests/Makefile             |   3 +
>  tests/qemu-iotests/124     | 182 ++++++++++++++++++-
>  tests/qemu-iotests/124.out |   4 +-
>  tests/test-blockjob-txn.c  | 244 +++++++++++++++++++++++++
>  16 files changed, 1108 insertions(+), 172 deletions(-)
>  create mode 100644 tests/test-blockjob-txn.c
>