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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <20260902112743.GA11999@lst.de> <1819786.1787768317@warthog.procyon.org.uk> <1895550.1787777192@warthog.procyon.org.uk> <350212.1788514937@warthog.procyon.org.uk> To: Keith Busch Cc: dhowells@redhat.com, Christoph Hellwig , Jens Axboe , Hannes Reinecke , Alexander Viro , Paulo Alcantara , netfs@lists.linux.dev, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] block: Fix start and length check added to iov_iter_extract_bvecs() Precedence: bulk X-Mailing-List: netfs@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Sat, 05 Sep 2026 17:26:40 +0100 Message-ID: <1183138.1788625600@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 X-Mimecast-MFC-PROC-ID: N3s8CkkHhWoCac8_3GhkQ0QcaEOKbbtagtZKEdjcOg4_1788625607 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-ID: <1183137.1788625600.1@warthog.procyon.org.uk> Keith Busch wrote: > If a block device behind an RDMA NIC really wants to DMA a single byte > at a time, we can't describe that capability today. That would require a > 0 mask, which is currently treated as "unset" and overridden with a > default 512b mask. The thing is, Christoph said: Massage __bio_iov_iter_get_pages so that it doesn't need the bio, and move it to lib/iov_iter.c so that it can be used by block code for other things than filling a bio and by other subsystems like netfs. but unless it can have a 1-byte alignment, it's not actually much use for netfslib (I have to be able to support "unbuffered writes", which are almost exactly like DIO writes but without alignment restrictions). Do block devices really need an aligned "start memory address" or just an aligned "start file position" (whatever that means for a blockdev). David