Comment 18 for bug 1837869

1a5297366f block: Fix flags in reopen queue
changes bdrv_reopen_queue_child but
 $ git log v2.11.0..v2.12.0 -L :bdrv_reopen_queue_child:block.c
wasn't very helpful to identify more.

The further context would be rather huge list around drain changes.
1a5297366f block: Fix flags in reopen queue
[...]
1a63a90750 block: Keep nodes drained between reopen_queue/multiple
44487eb973 commit: Simplify reopen of base
d736f119da block: Allow graph changes in subtree drained section
b016558590 block: Add bdrv_subtree_drained_begin/end()
0152bf400f block: Don't notify parents in drain call chain
0f11516894 block: Nested drain_end must still call callbacks
8119334918 block: Don't block_job_pause_all() in bdrv_drain_all()
 7253220de4 test-bdrv-drain: Test drain vs. block jobs
 89a6ceab46 test-bdrv-drain: Test bs->quiesce_counter
 86e1c840ec test-bdrv-drain: Test callback for bdrv_drain
 881cfd17c7 test-bdrv-drain: Test BlockDriver callbacks for drain
7b6a3d3553 block: Make bdrv_drain() driver callbacks non-recursive
9a7e86c804 block: Assert drain_all is only called from main AioContext
8e77e0bceb block: Remove unused bdrv_requests_pending
#cc954f01e3 block: Open backing image in force share mode for size probe
546a7dc40e qcow2: get rid of qcow2_backing_read1 routine
60369b86c4 block: Unify order in drain functions
5280aa32e1 block: Don't wait for requests in bdrv_drain*_end()
99c05de918 block: bdrv_drain_recurse(): Remove unused begin parameter
2da9b7d456 block: Call .drain_begin only once in bdrv_drain_all_begin()
#db0289b9b2 block: Make bdrv_drain_invoke() recursive
[...]
bd6458e410 block: avoid recursive AioContext acquire in bdrv_inactivate_all()

I hope it would not also be the new function callbacks.

Of that context we already have from 2.11-stable branch:
db0289b9b2 block: Make bdrv_drain_invoke() recursive
cc954f01e3 block: Open backing image in force share mode for size probe

We might brute force the list of changes above to check if it would even help and then try to minimize it to something SRUable later.

A second PPA version with the above started to build now in the same PPA.