[RFC PATCH 0/8] Refactor bdrv_try_set_aio_context using transactions

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

The aim of this series is to reorganize bdrv_try_set_aio_context
and drop BDS ->set_aio_context and ->can_set_aio_ctx callbacks in
favour of a new one, ->change_aio_ctx.

More informations in patch 3 (which is also RFC, due to the doubts
I have with AioContext locks).

Patch 1 just add assertions in the code, 2 extends the transactions API to be able to add also transactions in the tail
of the list.
Patch 3 is the core of this series, and introduces the new callback.
It is marked as RFC and the reason is explained in the commit message.
Patches 4-5-6 implement ->change_aio_ctx in the various block, blockjob
and block-backend BDSes.
Patch 7 substitutes ->change_aio_ctx with the old callbacks, and
patch 8 takes care of deleting the old callbacks and unused code.

This series is based on "job: replace AioContext lock with job_mutex",
but just because it uses job_set_aio_context() introduced there.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Based-on: <20220706201533.289775-1-eesposit@redhat.com>

Emanuele Giuseppe Esposito (8):
  block.c: assert bs->aio_context is written under BQL and drains
  transactions: add tran_add_back
  RFC: block: use transactions as a replacement of
    ->{can_}set_aio_context()
  blockjob: implement .change_aio_ctx in child_job
  block: implement .change_aio_ctx in child_of_bds
  block-backend: implement .change_aio_ctx in child_root
  block: use the new _change_ API instead of _can_set_ and _set_
  block: remove all unused ->can_set_aio_ctx and ->set_aio_ctx callbacks

 block.c                            | 288 +++++++++++++++--------------
 block/block-backend.c              |  65 +++++--
 blockjob.c                         |  50 +++--
 include/block/block-global-state.h |  16 +-
 include/block/block_int-common.h   |   5 +-
 include/qemu/transactions.h        |   9 +
 util/transactions.c                |  29 ++-
 7 files changed, 266 insertions(+), 196 deletions(-)

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2.31.1