On Wed 19-04-17 10:21:39, Goldwyn Rodrigues wrote: > > > On 04/19/2017 01:45 AM, Christoph Hellwig wrote: > > > >> + if (bio->bi_opf & REQ_NOWAIT) { > >> + if (!blk_queue_nowait(q)) { > >> + err = -EOPNOTSUPP; > >> + goto end_io; > >> + } > >> + if (!(bio->bi_opf & REQ_SYNC)) { > > > > I don't understand this check at all.. > > It is to ensure at the block layer that NOWAIT comes only for DIRECT > calls only. I should probably change it to REQ_SYNC | REQ_IDLE. Ouch. Checking 'REQ_SYNC' for this is a) unreliable hack b) layering violation You just don't care why someone marked bio with REQ_NOWAIT at this place. Just obey the request if you can, return error if you cannot, but advisory REQ_SYNC or REQ_IDLE flags have nothing to do with the ability of the block layer to submit the bio without blocking... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html