From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8CDEF339B32; Thu, 15 Jan 2026 08:31:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768465903; cv=none; b=dr8nvTAuVP8/6vEu/CyXoR39qLyZ9nSlbxg68xi5ajwkQpT3wCrIeyUJ5pJ/j+VwbA/f/IJbjjziW2ifgrUs4XQKiwkTbibdnhFDh9/F45lchVZZ5HaIQpZe4g3SgbffjtZ/NgN9DhqU2fSGoXd4L7EoQg2dCm+eZ8JsYQ35eyw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768465903; c=relaxed/simple; bh=QoowsZLh9gCbs7BpUDUIW6YL7UCTyh3zOWkgQP5Oeuk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CYEH6sXxgmy+cNi52h3CMjd+nJ2PGPqli9epv0k1YLr8XdJA56j9qI+qiflK1NaiUeDZaDR1oAMdLfK46xZt7gyK5roQldmh3cJmZS2zlblMd0BDwUivM8kvhH8mTvwQDzAYp7W+sZKcI5moSh5KKmiQCjYCJHU9tN2UkYHln+o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 8FAEE227AA8; Thu, 15 Jan 2026 09:31:31 +0100 (CET) Date: Thu, 15 Jan 2026 09:31:31 +0100 From: Christoph Hellwig To: Qu Wenruo Cc: Christoph Hellwig , =?iso-8859-1?Q?Andr=E9?= Almeida , Chuck Lever , Jeff Layton , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Carlos Maiolino , Amir Goldstein , Chris Mason , David Sterba , Miklos Szeredi , Christian Brauner , Alexander Viro , Jan Kara , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-unionfs@vger.kernel.org, kernel-dev@igalia.com Subject: Re: [PATCH 3/3] ovl: Use real disk UUID for origin file handles Message-ID: <20260115083131.GA12267@lst.de> References: <20260114-tonyk-get_disk_uuid-v1-0-e6a319e25d57@igalia.com> <20260114-tonyk-get_disk_uuid-v1-3-e6a319e25d57@igalia.com> <20260114062608.GB10805@lst.de> <5334ebc6-ceee-4262-b477-6b161c5ca704@igalia.com> <20260115062944.GA9590@lst.de> <633bb5f3-4582-416c-b8b9-fd1f3b3452ab@suse.com> <20260115072311.GA10352@lst.de> <461fc582-71ba-4238-9696-3d8bdd8a0207@suse.com> Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <461fc582-71ba-4238-9696-3d8bdd8a0207@suse.com> User-Agent: Mutt/1.5.17 (2007-11-01) On Thu, Jan 15, 2026 at 06:39:05PM +1030, Qu Wenruo wrote: >>> Then for those SINGLE_DEV fses, disable any multi-device related features, >>> and use their dev_t to distinguish different fses just like EXT4/XFS, >>> without bothering the current tempfsid hack, and just return the same fsid. >> >> dev_t is not related to the uuid in any way for XFS, and while I'm not >> an expert there I'm pretty sure ext4 uses the same not dev related uuid >> generation. > > My bad, by dev_t I mean bdev holder, which is a pointer to the super block > of the mounted fs. (And btrfs just recently join this common usage) How is that related? That prevents multiple callers from exclusively using a block device. Cloned file systems will sit on different devices. > Yeah, although it's possible to mount different devices with same fsid > separately, I don't think it's really that a good idea either. > > Thus I really prefer to have special flags for those "uncommon" use cases, > other than the current automatically enabled tempfsid feature. For XFS we require the nouuid option to allows additional mounts of file systems with the same uuid. I think that is the equivalent to what btrfs calls the fsid.