Re: aio-context question

[Dietmar Maurer]

> If it doesn't have any effect because it just does what will be done
> later anyway, it can be removed, but that doesn't buy us much.

I think that code is simply unnecessary (no effect).
But it is quite hard to read and understand, so I think removing
that code helps to simplify things.

> If it results in preventing some case (like the one fixed by 30dd65f3),
> we need to check whether this case is actually safe. If it is safe, we
> can remove the lines and get a new feature from it.
> 
> In both cases, I think a test case should be written together with the
> removal of the code. And if we find out that it's unsafe, we should even
> more write a test case that makes sure that the operation fails.

Yes, a test case would be great. Especially one that test backups with
io-threads. 

I am hunting a bug for more than a week now. Seems bdrv_drain hangs 
sometimes when running a backup job on drives using io-threads ...

But I still haven't found a reliable way to reproduce it.
Sometimes takes me several hours to trigger it again... 

I will try to write a test case if I can really find that bug...