From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7AF5C6FA82 for ; Fri, 23 Sep 2022 15:29:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232578AbiIWP3t (ORCPT ); Fri, 23 Sep 2022 11:29:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48818 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232607AbiIWP3r (ORCPT ); Fri, 23 Sep 2022 11:29:47 -0400 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B34A26110; Fri, 23 Sep 2022 08:29:45 -0700 (PDT) Received: by verein.lst.de (Postfix, from userid 2407) id 9479867373; Fri, 23 Sep 2022 17:29:41 +0200 (CEST) Date: Fri, 23 Sep 2022 17:29:41 +0200 From: Christoph Hellwig To: Kanchan Joshi Cc: Christoph Hellwig , axboe@kernel.dk, kbusch@kernel.org, asml.silence@gmail.com, io-uring@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, gost.dev@samsung.com, Anuj Gupta Subject: Re: [PATCH for-next v7 4/5] block: add helper to map bvec iterator for passthrough Message-ID: <20220923152941.GA21275@lst.de> References: <20220909102136.3020-1-joshi.k@samsung.com> <20220909102136.3020-5-joshi.k@samsung.com> <20220920120802.GC2809@lst.de> <20220922152331.GA24701@test-zns> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220922152331.GA24701@test-zns> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Thu, Sep 22, 2022 at 08:53:31PM +0530, Kanchan Joshi wrote: >> blk_rq_map_user_iov really should be able to detect that it is called >> on a bvec iter and just do the right thing rather than needing different >> helpers. > > I too explored that possibility, but found that it does not. It maps the > user-pages into bio either directly or by doing that copy (in certain odd > conditions) but does not know how to deal with existing bvec. What do you mean with existing bvec? We allocate a brand new bio here that we want to map the next chunk of the iov_iter to, and that is exactly what blk_rq_map_user_iov does. What blk_rq_map_user_iov currently does not do is to implement this mapping efficiently for ITER_BVEC iters, but that is something that could and should be fixed. > And it really felt cleaner to me write a new function rather than > overloading the blk_rq_map_user_iov with multiple if/else canals. No. The whole point of the iov_iter is to support this "overload". > But iov_iter_gap_alignment does not work on bvec iters. Line #1274 below So we'll need to fix it. > 1264 unsigned long iov_iter_gap_alignment(const struct iov_iter *i) > 1265 { > 1266 unsigned long res = 0; > 1267 unsigned long v = 0; > 1268 size_t size = i->count; > 1269 unsigned k; > 1270 > 1271 if (iter_is_ubuf(i)) > 1272 return 0; > 1273 > 1274 if (WARN_ON(!iter_is_iovec(i))) > 1275 return ~0U; > > Do you see a way to overcome this. Or maybe this can be revisted as we > are not missing a lot? We just need to implement the equivalent functionality for bvecs. It isn't really hard, it just wasn't required so far.