From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH -V7 3/9] vfs: Add name to file handle conversion support Date: Thu, 13 May 2010 10:20:38 +1000 Message-ID: <20100513002038.GE13617@dastard> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Aneesh Kumar K.V" , 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 To: Andreas Dilger Return-path: Received: from bld-mail13.adl6.internode.on.net ([150.101.137.98]:46680 "EHLO mail.internode.on.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752780Ab0EMAUo (ORCPT ); Wed, 12 May 2010 20:20:44 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, May 12, 2010 at 03:49:49PM -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). > > That moves the overhead to mount time instead of for each > name_to_handle() call (which would be brutal for a system with > many filesystems mounted). That will pretty much match exactly what XFS already does. Can we start by moving the XFS functionality (xfs_uuid_mount(), "nouuid" mount option, etc) to the VFS level and then optimise from there? Cheers, Dave. -- Dave Chinner david@fromorbit.com