Re: [Qemu-devel] [PATCH 11/11] blockjob: use deferred_to_main_loop to indicate the coroutine has ended

[Stefan Hajnoczi]

On Wed, Apr 19, 2017 at 04:42:19PM +0200, Paolo Bonzini wrote:
> All block jobs are using block_job_defer_to_main_loop as the final
> step just before the coroutine terminates.  At this point,
> block_job_enter should do nothing, but currently it restarts
> the freed coroutine.
> 
> Now, the job->co states should probably be changed to an enum
> (e.g. BEFORE_START, STARTED, YIELDED, COMPLETED) subsuming
> block_job_started, job->deferred_to_main_loop and job->busy.
> For now, this patch eliminates the problematic reenter by
> removing the reset of job->deferred_to_main_loop (which served
> no purpose, as far as I could see) and checking the flag in
> block_job_enter.

The defer_to_main_loop API was originally written as a utility that
could be called multiple times, not just during the final phase of the
block job.  In practice we only use it to complete the block job.

I suggest integrating it more deeply into blockjob.c so that all jobs
automatically invoke it once and only once.  There should be a
BlockJobDriver.main_loop_finalize() callback and the defer_to_main_loop
shouldn't be callable outside blockjob.c to prevent misuse.

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