From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753406Ab2D3GnF (ORCPT ); Mon, 30 Apr 2012 02:43:05 -0400 Received: from isrv.corpit.ru ([86.62.121.231]:43886 "EHLO isrv.corpit.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751375Ab2D3GnD (ORCPT ); Mon, 30 Apr 2012 02:43:03 -0400 Message-ID: <4F9E3474.2050405@msgid.tls.msk.ru> Date: Mon, 30 Apr 2012 10:43:00 +0400 From: Michael Tokarev Organization: Telecom Service, JSC User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:10.0.3) Gecko/20120329 Icedove/10.0.3 MIME-Version: 1.0 To: Linus Torvalds CC: "H. Peter Anvin" , Linux Kernel Mailing List , Alan Cox , Ian Kent , Thomas Meyer , autofs@vger.kernel.org Subject: Re: autofs: make the autofsv5 packet file descriptor use a packetized pipe References: <20120429205429.63CCD7C0064@ra.kernel.org> <4F9DD994.70202@zytor.com> <4F9E30BF.4030704@msgid.tls.msk.ru> In-Reply-To: <4F9E30BF.4030704@msgid.tls.msk.ru> X-Enigmail-Version: 1.4 OpenPGP: id=804465C5 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 ;) Thanks, /mjt