Re: [PATCH v5 21/45] block: add bdrv_try_set_aio_context_tran transaction action

[Vladimir Sementsov-Ogievskiy]

On 6/8/22 14:49, Hanna Reitz wrote:
> On 30.03.22 23:28, Vladimir Sementsov-Ogievskiy wrote:
> > To be used in further commit.
> >
> > Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
> > ---
> >   block.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 48 insertions(+)
>
> Looking at bdrv_child_try_set_aio_context(), it looks like 
> bdrv_can_set_aio_context() were supposed to be the .prepare action, and 
> bdrv_set_aio_context_ignore() should be the .commit action.  Can we not use it 
> that way?


The difference is that we want the whole action be done in .prepare stage, not 
only the check. It's generally better: when do several actions in a 
transaction, actions usually depend on result of previous actions.

And I think it's necessary for graph update. Graph relations are changed during 
other actions .prepare phases, so I can't imagine how to postpone aio-context 
update to .commit phase.


But I agree, that having both _can_ / _set_  and *tran APIs don't look good. 
May be we can refactor it.. But not in this series I think)

--
Best regards,
Vladimir