[PATCH 3/5] blk-mq: add helper of blk_mq_global_quiesce_wait()

[Sagi Grimberg]

> Add helper of blk_mq_global_quiesce_wait() for supporting to quiesce
> queues in parallel, then we can just wait once if global quiesce wait
> is allowed.

blk_mq_global_quiesce_wait() is a poor name... global is scope-less and
obviously it has a scope.


> Signed-off-by: Ming Lei <ming.lei at redhat.com>
> ---
>   include/linux/blk-mq.h | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 5cc7fc1ea863..a9fecda2507e 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -777,6 +777,19 @@ static inline bool blk_mq_add_to_batch(struct request *req,
>   	return true;
>   }
>   
> +/*
> + * If the queue has allocated & used srcu to quiesce queue, quiesce wait is
> + * done via the synchronize_srcu(q->rcu), otherwise it is done via global
> + * synchronize_rcu().
> + *
> + * This helper can help us to support quiescing queue in parallel, so just
> + * one quiesce wait is enough if global quiesce wait is allowed.
> + */
> +static inline bool blk_mq_global_quiesce_wait(struct request_queue *q)
> +{
> +	return !q->alloc_srcu;
> +}
> +
>   void blk_mq_requeue_request(struct request *rq, bool kick_requeue_list);
>   void blk_mq_kick_requeue_list(struct request_queue *q);
>   void blk_mq_delay_kick_requeue_list(struct request_queue *q, unsigned long msecs);
>