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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <03730b50cebb4a349ad8667373bb8127@AcuMS.aculab.com> <20230816120741.534415-1-dhowells@redhat.com> <20230816120741.534415-3-dhowells@redhat.com> <608853.1692190847@warthog.procyon.org.uk> <3dabec5643b24534a1c1c51894798047@AcuMS.aculab.com> To: Linus Torvalds Cc: dhowells@redhat.com, David Laight , Al Viro , Jens Axboe , Christoph Hellwig , Christian Brauner , Matthew Wilcox , Jeff Layton , "linux-fsdevel@vger.kernel.org" , "linux-block@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3 2/2] iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc() MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <665723.1692218114.1@warthog.procyon.org.uk> Date: Wed, 16 Aug 2023 21:35:14 +0100 Message-ID: <665724.1692218114@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Rspamd-Queue-Id: CD83812002C X-Rspam-User: X-Stat-Signature: zjujidcqepwyyedtggexu81kcksr4r5p X-Rspamd-Server: rspam03 X-HE-Tag: 1692218122-973244 X-HE-Meta: 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 LQqo2W7S 3cFYCIoUvLiGaJcUXSd4x1Xuh1jGIsKo76bIpaXFIzQe4vhIWyiYJpT3/z+Twt9p6k4/RVxdtPn7jwijHa1/uAYn+vvccqT5wjOWsxBetQqCwbTS9wGgWowvwp63OtFUBQyqmwrFZaRiPiMqUhPj1GoOIovb0ZDlpNHF0fKvuwcn5DPx3KzwAGwb3WLn5AcW+PtdEosQB2uAnjXLdvLNVVA73cxmrEhYKSlF34E9rx0o/Vw/mzUjNzMgGk7Zm8YieFHqPUcOALsnEDkw233jmzQEmR30DwoiC+dbN9dcrynJ7yTk= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Linus Torvalds wrote: > > What about ITER_BVEC_MC ?? > > That probably would be the best option. Just make it a proper > ITER_xyz, instead of an odd sub-case for one ITER (but set up in such > a way that it looks like it might happen for other ITER_xyz cases). I'm not sure that buys us anything. It would then require every call to iov_iter_is_bvec()[*] to check for two values instead of one - including in iterate_and_advance() - and *still* we'd have to have the special-casing in _copy_from_iter() and copy_page_from_iter_atomic(). The issue is that ITER_xyz changes the iteration function - but we don't actually want to do that; rather, we need to change the step function. David [*] There's a bunch of them outside of iov_iter.c.