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See http://www.infradead.org/rpr.html X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-loop: dm-devel@redhat.com Cc: "axboe@kernel.dk" , "linux-block@vger.kernel.org" , "linux-raid@vger.kernel.org" , "snitzer@redhat.com" , "linux-api@vger.kernel.org" , Pavel Tide , "linux-kernel@vger.kernel.org" , Christoph Hellwig , "song@kernel.org" , "dm-devel@redhat.com" , "agk@redhat.com" Subject: Re: [dm-devel] [PATCH v6 4/4] dm: add DM_INTERPOSED_FLAG X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Wed, Mar 10, 2021 at 08:28:12AM +0300, Sergei Shtepa wrote: > > So instead of doing this shoudn't the interposer just always submit to the > > whole device? But if we keep it, the logic in this funtion should go > > into a block layer helper, passing a block device instead of the > > device-mapper allows to create devices of any size using only part of > the underlying device. Therefore, it is not possible to apply the > interposer to the whole block device. > Perhaps it makes sense to put the blk_partition_unremap() function in the > block layer? I'm not sure that's a good thing. I suspect the answer is to not remap bios that are going to be handled by the interposer. In fact much of submit_bio_checks as-is is a bad idea for interposed devices. I think what we need to do instead is to pass an explicit bdev to submit_bio_checks and use that everywhere, including in the subfunctions. With that we might also be able to remove the separate interpose hook and thus struct bdev_interposer entirely as now ->submit_bio of the interposer could do all the work: static noinline blk_qc_t submit_bio_interposed(struct bio *bio) { struct block_device *orig_bdev = bio->bi_bdev, *interposer; struct bio_list bio_list[2] = { }; blk_qc_t ret = BLK_QC_T_NONE; if (current->bio_list) { bio_list_add(¤t->bio_list[0], bio); return BLK_QC_T_NONE; } if (unlikely(bio_queue_enter(bio))) return BLK_QC_T_NONE; interposer = orig_bdev->bd_interposer; if (unlikely(!interposer)) { /* interposer was removed */ bio_list_add(¤t->bio_list[0], bio); goto queue_exit; } if (!submit_bio_checks(bio, interposer)) goto queue_exit; bio_set_flag(bio, BIO_INTERPOSED); current->bio_list = bio_list; ret = interposer->bd_disk->fops->submit_bio(bio); current->bio_list = NULL; queue_exit: blk_queue_exit(bdev->bd_disk->queue); /* Resubmit remaining bios */ while ((bio = bio_list_pop(&bio_list[0]))) ret = submit_bio_noacct(bio); return ret; } blk_qc_t submit_bio_noacct(struct bio *bio) { if (bio->bi_bdev->bd_interposer && !bio_flagged(bio, BIO_INTERPOSED) return submit_bio_interposed(bio); ... } Note that both with this and your original code the interposer must never resubmit I/O to itself. Is that actually the case for DM? I'm trying to think of a good debug check for that, but right now I can't think of something that doesn't cause any overhead for n -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel