On 04/19/2017 01:45 AM, Christoph Hellwig wrote: > On Fri, Apr 14, 2017 at 07:02:54AM -0500, Goldwyn Rodrigues wrote: >> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx> >> > >> + /* Request queue supports BIO_NOWAIT */ >> + queue_flag_set_unlocked(QUEUE_FLAG_NOWAIT, q); > > BIO_NOWAIT is gone. And the comment would not be needed if the > flag had a more descriptive name, e.g. QUEUE_FLAG_NOWAIT_SUPPORT. > > And I think all request based drivers should set the flag implicitly > as ->queuecommand can't sleep, and ->queue_rq only when it's always > offloaded to a workqueue when the BLK_MQ_F_BLOCKING flag is set. > We introduced QUEUE_FLAG_NOWAIT for devices which would not wait for request completions. The ones which wait are MD devices because of sync or suspend operations. The only user of BLK_MQ_F_NONBLOCKING seems to be nbd. As you mentioned, it uses the flag to offload it to a workqueue. The other way to do it implicitly is to change the flag to BLK_MAY_BLOCK_REQS and use it for devices which do wait such as md/dm. Is that what you are hinting at? Or do you have something else in mind? -- Goldwyn
