Re: [Qemu-devel] [PATCH v4 2/5] blockjob: add pause points

[Paolo Bonzini]

On 14/06/2016 20:17, Stefan Hajnoczi wrote:
> Block jobs are coroutines that usually perform I/O but sometimes also
> sleep or yield.  Currently only sleeping or yielded block jobs can be
> paused.  This means jobs that do not sleep or yield (using
> block_job_yield()) are unaffected by block_job_pause().
> 
> Add block_job_pause_point() so that block jobs can mark quiescent points
> that are suitable for pausing.  This solves the problem that it can take
> a block job a long time to pause if it is performing a long series of
> I/O operations.
> 
> Transitioning to paused state involves a .pause()/.resume() callback.
> These callbacks are used to ensure that I/O and event loop activity has
> ceased while the job is at a pause point.
> 
> Note that this patch introduces a stricter pause state than previously.
> The job->busy flag was incorrectly documented as a quiescent state
> without I/O pending.  This is violated by any job that has I/O pending
> across sleep or block_job_yield(), like the mirror block job.

Right, we should document job->busy as a quiescent state where no one
will re-enter the coroutine.

Paolo