From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751894Ab0HVCC3 (ORCPT ); Sat, 21 Aug 2010 22:02:29 -0400 Received: from e28smtp02.in.ibm.com ([122.248.162.2]:33705 "EHLO e28smtp02.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751796Ab0HVCC1 (ORCPT ); Sat, 21 Aug 2010 22:02:27 -0400 From: "Aneesh Kumar K. V" To: Nick Piggin , Neil Brown Cc: Al Viro , Christoph Hellwig , adilger@sun.com, corbet@lwn.net, npiggin@kernel.dk, hooanon05@yahoo.co.jp, bfields@fieldses.org, miklos@szeredi.hu, linux-fsdevel@vger.kernel.org, sfrench@us.ibm.com, philippe.deniel@CEA.FR, linux-kernel@vger.kernel.org Subject: Re: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks In-Reply-To: References: <1282269097-26166-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1282269097-26166-5-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20100820083057.GA10039@infradead.org> <20100820195303.20b17210@notabene> <20100820115135.GQ31363@ZenIV.linux.org.uk> <20100821100900.4b15fe08@notabene> <20100821083024.GB3448@amd> User-Agent: Notmuch/0.3.1-58-g6607fd6 (http://notmuchmail.org) Emacs/24.0.50.1 (i686-pc-linux-gnu) Date: Sun, 22 Aug 2010 07:32:15 +0530 Message-ID: MIME-Version: 1.0 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 Sat, 21 Aug 2010 15:12:15 +0530, "Aneesh Kumar K. V" wrote: > On Sat, 21 Aug 2010 18:30:24 +1000, Nick Piggin wrote: > > Thanks, I had both of the same concerns as Christoph with API > > change and exposing symlink fds last time I looked at the patces, > > actually. > > > > But they can probably be worked around or avoided. I think the more > > important thing is whether it is worth supporting. This is > > all restricted to root (or CAP_DAC_READ_SEARCH) only, right, and > > what exact semantics they want. I would like to see more discussion > > of what this enables and some results. > > > > For the case of avoiding expensive network revalidations in path name > > lookup, do we even need to open symlinks? Could the security issues be > > avoided by always having handle attached to an open fd? > > > > For implementing a userspace file server that use handle for > representing files (like NFS) we would require to have the ability to do > different file system operations that can operate on symlink to work on > handle too. > linkat change to take NULL path name is needed for regular files also. The file server will get a request to create a link with handle of oldpath and directory handle of new path and new name. The changes would also help in the implementation of 9P server in Qemu for implementing a fast virtualization passthrough file system (aka VirtFS) http://thread.gmane.org/gmane.comp.emulators.qemu/68992 -aneesh