Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759203AbZA2EVb (ORCPT ); Wed, 28 Jan 2009 23:21:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755478AbZA2EVW (ORCPT ); Wed, 28 Jan 2009 23:21:22 -0500 Received: from blaine.gmane.org ([80.91.229.8]:42542 "EHLO hugh.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755464AbZA2EVV (ORCPT ); Wed, 28 Jan 2009 23:21:21 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:reply-to:in-reply-to:references:date:message-id :subject:from:to:cc:content-type:content-transfer-encoding; b=fGS39qWSMhBZFTBGNL7MOXT0T/9KY678ubxRkFyVtU0B447rJU6/oHLrXFT4NJ8idG dtfZ4+FMjrGiWxzxJ2xCB+n11AoR2MySALZuDxYDpt53zIzNePGAlbxAS3Sjgrd2rFWd AXltDVuvUrSy6h8xyfZjvolHkZGQ1u//1qPys= MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: <20090129011758.GA26534@kroah.com> References: <20090128213322.GA15789@kroah.com> <4980FB4D.9090009@shaw.ca> <20090129011758.GA26534@kroah.com> Date: Thu, 29 Jan 2009 15:59:12 +1300 Message-ID: Subject: Re: open(2) says O_DIRECT works on 512 byte boundries? From: Michael Kerrisk To: Greg KH Cc: Robert Hancock , Greg KH , public-mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@hugh.gmane.org, public-linux-man-u79uwXL29TY76Z2rM5mHXA@hugh.gmane.org, public-linux-kernel-u79uwXL29TY76Z2rM5mHXA@hugh.gmane.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TMDA-Confirmed: Thu, 29 Jan 2009 05:21:05 +0100 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1793 Lines: 53 On Thu, Jan 29, 2009 at 2:17 PM, Greg KH wrote: > > > > On Wed, Jan 28, 2009 at 06:41:49PM -0600, Robert Hancock wrote: >> >> >> Greg KH wrote: >>> In looking at open(2), it says that O_DIRECT works on 512 byte boundries >>> with the 2.6 kernel release: >>> Under Linux 2.4, transfer sizes, and the alignment of the user >>> buffer and the file offset must all be multiples of the logical >>> block size of the file system. Under Linux 2.6, alignment to >>> 512-byte boundaries suffices. >>> However if you try to access an O_DIRECT opened file with a buffer that >>> is PAGE_SIZE aligned + 512 bytes, it fails in a bad way (wrong data is >>> read.) >>> Is this just a mistake in the documentation? Or am I reading it >>> incorrectly? >>> I have a test program that shows this if anyone wants it. >> >> Well, it sounds like a bug to me.. even if it's not supported, if you do >> such an access, surely the kernel should detect that and return EINVAL or >> something rather than reading corrupted data.. > > It doesn't. It says the read is successful, yet the data is not really > read into the buffer. Portions of it is, but not the amount we asked > for. Greg, Can you post your test program? Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- 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/