Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754153AbbG0Jpf (ORCPT ); Mon, 27 Jul 2015 05:45:35 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:60712 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752010AbbG0Jpb (ORCPT ); Mon, 27 Jul 2015 05:45:31 -0400 Date: Mon, 27 Jul 2015 02:45:30 -0700 From: Christoph Hellwig To: Ming Lei Cc: Christoph Hellwig , Jens Axboe , Linux Kernel Mailing List , "Justin M. Forbes" , Jeff Moyer , Tejun Heo , linux-api@vger.kernel.org Subject: Re: [PATCH v7 4/6] block: loop: prepare for supporing direct IO Message-ID: <20150727094530.GA15507@infradead.org> References: <1437061068-26118-1-git-send-email-ming.lei@canonical.com> <1437061068-26118-5-git-send-email-ming.lei@canonical.com> <20150727084020.GA28336@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 863 Lines: 20 On Mon, Jul 27, 2015 at 05:41:57AM -0400, Ming Lei wrote: > > Why the hardcoded value? I suspect this should be more like: > > > > if (dio && inode->i_sb->s_bdev && > > (lo->lo_offset & (bdev_io_min(inode->i_sb->s_bdev) - 1)) != 0) > > dio = false; > > The above can't work if the backing device has a bigger sector size > (such as 4K), that is why loop's direct-io requires 512 min_io_size of > backing device. Why doesn't it work? If the backing device sector size is 4k and lo_offset is 0 or a multiple of 4k it should allow direct I/O, and my code sniplet will allow that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/