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[68.160.176.52]) by smtp.gmail.com with ESMTPSA id g2-20020a37e202000000b00607e264a208sm3125054qki.40.2022.03.04.17.30.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Mar 2022 17:30:47 -0800 (PST) Date: Fri, 4 Mar 2022 20:30:46 -0500 From: Mike Snitzer To: Jens Axboe Cc: ming.lei@redhat.com, hch@lst.de, dm-devel@redhat.com, linux-block@vger.kernel.org Subject: Re: [PATCH v4 1/2] block: add ->poll_bio to block_device_operations Message-ID: References: <20220304212623.34016-1-snitzer@redhat.com> <20220304212623.34016-2-snitzer@redhat.com> <68dc8fb0-86df-effe-4ef2-8ed9c350d836@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <68dc8fb0-86df-effe-4ef2-8ed9c350d836@kernel.dk> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Mar 04 2022 at 4:39P -0500, Jens Axboe wrote: > On 3/4/22 2:26 PM, Mike Snitzer wrote: > > diff --git a/block/blk-core.c b/block/blk-core.c > > index 94bf37f8e61d..e739c6264331 100644 > > --- a/block/blk-core.c > > +++ b/block/blk-core.c > > @@ -985,10 +985,16 @@ int bio_poll(struct bio *bio, struct io_comp_batch *iob, unsigned int flags) > > > > if (blk_queue_enter(q, BLK_MQ_REQ_NOWAIT)) > > return 0; > > - if (WARN_ON_ONCE(!queue_is_mq(q))) > > - ret = 0; /* not yet implemented, should not happen */ > > - else > > + if (queue_is_mq(q)) { > > ret = blk_mq_poll(q, cookie, iob, flags); > > + } else { > > + struct gendisk *disk = q->disk; > > + > > + if (disk && disk->fops->poll_bio) > > + ret = disk->fops->poll_bio(bio, iob, flags); > > + else > > + ret = !WARN_ON_ONCE(1); > > This is an odd way to do it, would be a lot more readable as > > ret = 0; > WARN_ON_ONCE(1); > > if we even need that WARN_ON? Would be a pretty glaring oversight for a bio-based driver developer to forget to define ->poll_bio but remember to clear BLK_QC_T_NONE in bio->bi_cookie and set QUEUE_FLAG_POLL in queue flags. Silent failure it is! ;) > > diff --git a/block/genhd.c b/block/genhd.c > > index e351fac41bf2..eb43fa63ba47 100644 > > --- a/block/genhd.c > > +++ b/block/genhd.c > > @@ -410,6 +410,8 @@ int __must_check device_add_disk(struct device *parent, struct gendisk *disk, > > struct device *ddev = disk_to_dev(disk); > > int ret; > > > > + WARN_ON_ONCE(queue_is_mq(disk->queue) && disk->fops->poll_bio); > > Also seems kind of useless, maybe at least combine it with failing to > add the disk. This is a "I'm developing some new driver or feature" > failure, and would be more visible that way. And if you do that, then > the WARN_ON_ONCE() seems pointless anyway, and I'd just do: > > if (queue_is_mq(disk->queue) && disk->fops->poll_bio) > return -EINVAL; > > or something like that, with a comment saying why that doesn't make any > sense. Absolutely. The thought did cross my mind that it seemed WARN_ON heavy. Will fix it up and send v5.