Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932222AbVJQJQi (ORCPT ); Mon, 17 Oct 2005 05:16:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932223AbVJQJQi (ORCPT ); Mon, 17 Oct 2005 05:16:38 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:8788 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S932222AbVJQJQh (ORCPT ); Mon, 17 Oct 2005 05:16:37 -0400 Date: Mon, 17 Oct 2005 11:17:10 +0200 From: Jens Axboe To: Grzegorz Kulewski Cc: li nux , Erik Mouw , colin , linux-kernel@vger.kernel.org Subject: Re: A problem about DIRECT IO on ext3 Message-ID: <20051017091710.GT2811@suse.de> References: <20050831080744.GM4018@suse.de> <20051017085226.47541.qmail@web33315.mail.mud.yahoo.com> <20051017090310.GR2811@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1250 Lines: 35 On Mon, Oct 17 2005, Grzegorz Kulewski wrote: > On Mon, 17 Oct 2005, Jens Axboe wrote: > >>how to correct this problem ? > > > >See your buffer address, it's not aligned. You need to align that as > >well. This is needed because the hardware will dma directly to the user > >buffer, and to be on the safe side we require the same alignment as the > >block layer will normally generate for file system io. > > > >So in short, just align your read buffer to the same as your block size > >and you will be fine. Example: > > > >#define BS (4096) > >#define MASK (BS - 1) > >#define ALIGN(buf) (((unsigned long) (buf) + MASK) & ~(MASK)) > > > >char *ptr = malloc(BS + MASK); > >char *buf = (char *) ALIGN(ptr); > > > >read(fd, buf, BS); > > Shouldn't one use posix_memalign(3) for that? Dunno if one 'should', one 'can' if one wants to. I prefer to do it manually so I don't have to jump through #define hoops to get at it (which, btw, still doesn't expose it on this machine). -- Jens Axboe - 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/