From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932782Ab2KNKih (ORCPT ); Wed, 14 Nov 2012 05:38:37 -0500 Received: from claranet-outbound-smtp05.uk.clara.net ([195.8.89.38]:52679 "EHLO claranet-outbound-smtp05.uk.clara.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932117Ab2KNKif (ORCPT ); Wed, 14 Nov 2012 05:38:35 -0500 From: Tvrtko Ursulin To: Pavel Emelyanov Cc: Cyrill Gorcunov , David Rientjes , Andrew Morton , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Al Viro , Alexey Dobriyan , James Bottomley , Matthew Helsley , aneesh.kumar@linux.vnet.ibm.com, bfields@fieldses.org Subject: Re: [patch 3/7] fs, notify: Add file handle entry into inotify_inode_mark Date: Wed, 14 Nov 2012 10:38:16 +0000 Message-ID: <2092535.8S9EcgmZCZ@deuteros> User-Agent: KMail/4.8.4 (Linux/3.4.6-2.fc17.x86_64; KDE/4.8.4; x86_64; ; ) In-Reply-To: <50A36ED5.4080505@parallels.com> References: <20121112101440.665694060@openvz.org> <2105540.yeyMVrW4mH@deuteros> <50A36ED5.4080505@parallels.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 14 November 2012 14:13:41 Pavel Emelyanov wrote: > On 11/14/2012 02:08 PM, Tvrtko Ursulin wrote: > > On Wednesday 14 November 2012 13:58:12 Cyrill Gorcunov wrote: > >> On Wed, Nov 14, 2012 at 09:50:55AM +0000, Tvrtko Ursulin wrote: > >>>>> You could not use a pointer and then allocate your buffers on the > >>>>> check > >>>>> point operation, freeing on restore? > >>>> > >>>> The problem is not allocating the memory itself but rather the time > >>>> when > >>>> the information needed (ie the dentry) is available. The only moment > >>>> when we can use dentry of the target file/directory is at > >>>> inotify_new_watch, that's why i need to compose fhandle that early. At > >>>> any later point we simply have no dentry to use. > >>> > >>> But you do not fundamentally need the dentry to restore a watch, right? > >> > >> dentry only needed to encode the file handle. > >> > >>> Couldn't you restore, creating a new restore path if needed, using the > >>> inode which is pinned anyway while the watch exists? > >> > >> plain inode is not enough as far as i can tell, iow i don't see the way > >> to restore path from inode solely. or there something i miss? > > > > I don't know, as I said I was not following this at all until now. Just > > throwing in ideas. > > > > I thought, since inotify does not use the path or dentry outside the > > system > > call at all, perhaps you need a different entry point allowing you to > > restore the watch using the inode or something. Assuming life time of > > objects and stuff in C&R world would allow you that. Since you don't need > > the full path, just something 64 bytes long, I assumed that could be the > > case. > > Well, the kernel already has all the API we need but one -- it shows us > _nothing_ about the inode being watched. And we'd appreciate any > information about it. Even the ino:dev pair would work. We propose to show > the handle because we believe, that such API is better that ino:dev. You > can get the handle, call the open_by_handle_at right at once and get much > much more information about the inode with any other API (e.g. calling > fstat() will give you the ino:dev pair). Having just ino:dev pair at hands > is not that flexible. How much space does a typical file system need to encode a handle? Am I right that for must it is just a few bytes? (I just glanced at the code so I might be wrong.) In which case, could the handle buffer be allocated dynamically depending on the underlying filesystem? Perhaps adding a facility to query a filesystem about its maximum handle buffer needs? Do you think the saving would justify this extra work? Regards, Tvrtko