Re: [PATCH RFC 1/3] block: add flag 'nowait_requests' into queue limits

[Christoph Hellwig]

On Mon, Jun 01, 2020 at 03:37:09PM +0300, Konstantin Khlebnikov wrote:
> Add flag for marking bio-based queues which support REQ_NOWAIT.
> Set for all request based (mq) devices.
> 
> Stacking device should set it after blk_set_stacking_limits() if method
> make_request() itself doesn't delay requests or handles REQ_NOWAIT.

I don't think this belongs into the queue limits.  For example a
stacking driver that always defers requests to a workqueue can support
REQ_NOWAIT entirely independent of the underlying devices.  I think
this just needs to be a simple queue flag.