Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763374AbZFOPvj (ORCPT ); Mon, 15 Jun 2009 11:51:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762794AbZFOPv0 (ORCPT ); Mon, 15 Jun 2009 11:51:26 -0400 Received: from e7.ny.us.ibm.com ([32.97.182.137]:40798 "EHLO e7.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762275AbZFOPvY (ORCPT ); Mon, 15 Jun 2009 11:51:24 -0400 In-Reply-To: <4A34DA30.1080201@gmail.com> To: Artem Bityutskiy Cc: Daniel Walker , Jamie Lokier , Linux Embedded , Linux FS Devel , Linux Kernel , Marco MIME-Version: 1.0 Subject: Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem X-Mailer: Lotus Notes Release 7.0 HF277 June 21, 2006 Message-ID: From: Bryan Henderson Date: Mon, 15 Jun 2009 08:51:28 -0700 X-MIMETrack: Serialize by Router on D01ML604/01/M/IBM(Release 8.5|December 05, 2008) at 06/15/2009 11:51:25, Serialize complete at 06/15/2009 11:51:25 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1569 Lines: 33 > Marco wrote: > > To enable direct > > I/O at all times for all regular files requires either that > > applications be modified to include the O_DIRECT flag on all file > > opens, or that a new filesystem be used that always performs direct > > I/O by default." > > This could be done as well by just introducing a "direct_io_only" > mount option to a file-system which would need this feature. A mount option would not be the right way. Mount options are for things that are characteristic of the way you're going to access the files. _This_ is a characteristic of the block device. So if one were to make this memory accessible with a block device, it would make more sense to have a block device ioctl. And it wouldn't ask the question, "should I use direct I/O only," but "does this device have the performance characteristics of a classic disk drive?" But it's possible that there's just no advantage to having a block device in the stack here. When unix block devices were invented, their main purpose was that they could reorder reads and writes and do buffering and caching -- all things essential for disk drives. We don't want to stretch the concept too far. -- Bryan Henderson IBM Almaden Research Center San Jose CA Storage Systems -- 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/