From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oleg Drokin Subject: Re: FS-specified FSID for non-device based filesystems? Date: Sat, 15 Apr 2006 00:41:31 +0300 Message-ID: <20060414214131.GK10907@linuxhacker.ru> References: <20060414204543.GE10907@linuxhacker.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org, neilb@cse.unsw.edu.au Return-path: Received: from linuxhacker.ru ([217.76.32.60]:65152 "EHLO shrek.linuxhacker.ru") by vger.kernel.org with ESMTP id S1751427AbWDNVlw (ORCPT ); Fri, 14 Apr 2006 17:41:52 -0400 To: Bryan Henderson Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hello! On Fri, Apr 14, 2006 at 02:32:44PM -0700, Bryan Henderson wrote: > >From my reading of the code it seems that fsid is composed of device's > >minor/major and export point's inode ino. > >I propose to replace (if supported by fs) device's minor/major by > >some unique number returned by fs itself. > >Should be no worse than what we have now. > That's for a device-based filesystem. But isn't your proposal primarily Yes. Device-based fs has root->s_dev. For non-device based (and for device-based too, if they would like) - method to get some sort of unique id to be used in the same way root->s_dev is used. > about non-device-based filesystems, and replacing a user-supplied value > with this filesystem identifier? It isn't so clear that that can't make > things worse. No, replacing whole fsid= with fs-supplied value would have implications like that you mentioned - we might have two different points in filesystem exported and we do not want those to have same id. > But I don't actually remember the specific cases in which the fsid was > considered insufficient; only that someone (probably Neil) did find that > it was. (Before Linux had export IDs, you simply couldn't export a > non-device-based filesystem at all, so we had to make a fake device on > which the filesystem could "reside." The user managed the device number > of that device as the filesystem ID). We still have those "fake devices". In fact non-device based fs can set REQUIRES_FS_DEV in fs_flags and it can be exported after that without manually specifying fsid. (yeah, I tried). But distributed filesystems would like to have same device id on different nodes. Bye, Oleg