Re: [Qemu-devel] [PATCH v6 01/13] block: Add op blocker type "device IO"

[Paolo Bonzini]

On 28/05/2015 13:44, Fam Zheng wrote:
> > The reason for doing it in the block layer is that it's in one place and
> > we can be sure that it's applied. We can still in addition modify
> > specific users to avoid even trying to send requests, but I think it's
> > good to have the single place that always ensures correct functionality
> > of the drain instead of making it dependent on the user.
> 
> How to do that for the synchronous blk_write callers that don't run in
> a coroutine?

They would be completely oblivious to it.

Their call to blk_co_write would queue the request.  Then blk_write
calls aio_poll, which ultimately would result in blk_resume and unqueue
the request.

Paolo