From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752960Ab0EMF5G (ORCPT ); Thu, 13 May 2010 01:57:06 -0400 Received: from e23smtp02.au.ibm.com ([202.81.31.144]:44396 "EHLO e23smtp02.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752503Ab0EMF5C (ORCPT ); Thu, 13 May 2010 01:57:02 -0400 From: "Aneesh Kumar K. V" To: Andreas Dilger Cc: hch@infradead.org, viro@zeniv.linux.org.uk, adilger@Sun.COM, corbet@lwn.net, serue@us.ibm.com, neilb@suse.de, linux-fsdevel@vger.kernel.org, sfrench@us.ibm.com, philippe.deniel@CEA.FR, linux-kernel@vger.kernel.org Subject: Re: [PATCH -V7 3/9] vfs: Add name to file handle conversion support In-Reply-To: References: <1273679444-14903-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1273679444-14903-4-git-send-email-aneesh.kumar@linux.vnet.ibm.com> User-Agent: Notmuch/ (http://notmuchmail.org) Emacs/24.0.50.1 (i686-pc-linux-gnu) Date: Thu, 13 May 2010 11:26:53 +0530 Message-ID: <874oic2vkq.fsf@linux.vnet.ibm.com> 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 Wed, 12 May 2010 15:49:49 -0600, Andreas Dilger wrote: > On 2010-05-12, at 09:50, Aneesh Kumar K.V wrote: > > +static long do_sys_name_to_handle(struct path *path, > > + struct file_handle __user *ufh) > > +{ > > + if (handle_size <= f_handle.handle_size) { > > + /* get the uuid */ > > + retval = sb->s_op->get_fsid(sb, &this_fs_id); > > + if (!retval) { > > + /* > > + * Now verify whether we get the same vfsmount > > + * if we lookup with uuid. In case we end up having > > + * same uuid for the multiple file systems. When doing > > + * uuid based lookup we would return the first one.So > > + * with name_to_handle if we don't find the same > > + * vfsmount with lookup return EOPNOTSUPP > > + */ > > + mnt = fs_get_vfsmount(current, &this_fs_id); > > + if (mnt != path->mnt) { > > + retval = -EOPNOTSUPP; > > + mntput(mnt); > > + goto err_free_out; > > + } > > I don't see that this does anything for us except add overhead. This is no protection against mounting a second filesystem with the same UUID after the handle is returned, since there is no expiration for file handles. > > At best I think we could start by changing the list-based UUID lookup > with a hash-based one, and when adding a duplicate UUID at mount time > start by printing out an error message to the console in case of > duplicated UUIDs, and maybe at some point in the future this might > cause the mount to fail (though I don't think we can make that > decision lightly or quickly). I actually was looking at doing this. That is something in line of register_for_handle_lookup(struct vfsmount *mnt); Each file system will call this in their gets_sb callback after calling get_sb_bdev. ie static int ext4_get_sb(struct file_system_type *fs_type, int flags, const char *dev_name, void *data, struct vfsmount *mnt) { int retval; retval = get_sb_bdev(fs_type, flags, dev_name, data, ext4_fill_super,mnt); if (register_for_handle_lookup(mnt)) { printk(KERN_INFO, "File system won't be available or handle lookup"); } return retval; } -aneesh