Re: [Qemu-devel] [PATCH RFC 3/9] blockjob: Implement AioContext drain ops

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Wed, Nov 29, 2017 at 10:49:50PM +0800, Fam Zheng wrote:
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  blockjob.c | 47 ++++++++++++++++++++++++++++++-----------------
>  1 file changed, 30 insertions(+), 17 deletions(-)
> 
> diff --git a/blockjob.c b/blockjob.c
> index ff9a614531..86d060c89c 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -148,6 +148,23 @@ static void block_job_attached_aio_context(AioContext *new_context,
>                                             void *opaque);
>  static void block_job_detach_aio_context(void *opaque);
>  
> +static void block_job_drained_begin(void *opaque)
> +{
> +    BlockJob *job = opaque;
> +    block_job_pause(job);
> +}

This is buggy because block_job_pause() increments a counter.  Remember
the .drained_begin() semantics are that it can be called any number of
times (see comment in previous patch)!

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