Re: [Qemu-block] [PATCH v9 07/11] block: Add QMP support for streaming to an intermediate layer

[Alberto Garcia]

On Tue 03 May 2016 03:23:24 PM CEST, Kevin Wolf wrote:
>> c) we fix bdrv_reopen() so we can actually run both jobs at the same
>>    time. I'm wondering if pausing all block jobs between
>>    bdrv_reopen_prepare() and bdrv_reopen_commit() would do the
>>    trick. Opinions?
>
> I would have to read up the details of the problem again, but I think
> with bdrv_drained_begin/end() we actually have the right tool now to fix
> it properly. We may need to pull up the drain (bdrv_drain_all() today)
> from bdrv_reopen_multiple() to its caller and just assert it in the
> function itself, but there shouldn't be much more to it than that.

I think that's not enough, see point 2) here:

https://lists.gnu.org/archive/html/qemu-block/2015-12/msg00180.html

  "I've been taking a look at the bdrv_drained_begin/end() API, but as I
   understand it it prevents requests from a different AioContext.
   Since all BDS in the same chain share the same context it does not
   really help here."

Berto