From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753001Ab2D3GzN (ORCPT ); Mon, 30 Apr 2012 02:55:13 -0400 Received: from out1-smtp.messagingengine.com ([66.111.4.25]:53753 "EHLO out1-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750705Ab2D3GzL (ORCPT ); Mon, 30 Apr 2012 02:55:11 -0400 X-Sasl-enc: TVtUTYitdAkCCdk+cvFAqnG98o5/rHnqAgI9JsLHhtAtA1cNNTn43Z5Eqg 1335768910 Message-ID: <1335768906.2281.16.camel@perseus.themaw.net> Subject: Re: autofs: make the autofsv5 packet file descriptor use a packetized pipe From: Ian Kent To: Michael Tokarev Cc: Linus Torvalds , "H. Peter Anvin" , Linux Kernel Mailing List , Alan Cox , Thomas Meyer , autofs@vger.kernel.org Date: Mon, 30 Apr 2012 14:55:06 +0800 In-Reply-To: <4F9E3474.2050405@msgid.tls.msk.ru> References: <20120429205429.63CCD7C0064@ra.kernel.org> <4F9DD994.70202@zytor.com> <4F9E30BF.4030704@msgid.tls.msk.ru> <4F9E3474.2050405@msgid.tls.msk.ru> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 (3.2.3-2.fc16) Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-04-30 at 10:43 +0400, Michael Tokarev wrote: > On 30.04.2012 10:27, Michael Tokarev wrote: > >> On 04/29/2012 01:54 PM, Linux Kernel Mailing List wrote: > >>> However, a prettier solution exists now thanks to the packetized pipe > >>> mode. By marking the communication pipe as being packetized (by simply > >>> setting the O_DIRECT flag), we can always just write the bigger packet > >>> size, and if user-space does a smaller read, it will just get that > >>> partial end result and the extra alignment padding will simply be thrown > >>> away. > > > >> +static inline int autofs_prepare_pipe(struct file *pipe) > >> +{ > >> + if (!pipe->f_op || !pipe->f_op->write) > >> + return -EINVAL; > >> + if (!S_ISFIFO(pipe->f_dentry->d_inode->i_mode)) > >> + return -EINVAL; > >> + /* We want a packet pipe */ > >> + pipe->f_flags |= O_DIRECT; > >> + return 0; > >> +} > >> + > > > > @@ -376,7 +376,7 @@ static int autofs_dev_ioctl_setpipefd(st > > err = -EBADF; > > goto out; > > } > > - if (!pipe->f_op || !pipe->f_op->write) { > > + if (autofs_prepare_pipe(pipe) < 0) { > > err = -EPIPE; > > fput(pipe); > > goto out; > > > > I've one more concern. I'm not sure but I think there's some > > risk still. This packetizing gets applied to all VERSIONS of > > the autofs PROTOCOL. Which means it will be applied to the > > lowest supported version (3) TOO, but did that version read > > whole packets too? > > I think this is a false alarm. I checked autofs v3 and v4 > userspace code (found on http://www.kernel.org/pub/linux/daemons/autofs ) > and they both read whole packet at once, not piece-wise. > > I didn't test if any of these actually work with any current > kernel, however ;) Yep, all the autofs releases use a sizeof() the relevant structure when reading the kernel pipe, so that should be ok. Ian