From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 47FBE3314D0; Tue, 7 Apr 2026 05:22:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775539338; cv=none; b=BxJ6EnbtvJa3dsX8gjGWI2K7L6lWCJ2+ceb/BdKUTYILF591YfC/DgSU4ciceCvK/ZaPS0qNmTYILoYVUAyyrmy7j5BCS1z/52nhvJkIRemGkK8q2rwF1JYfKnTJZD2FuY9SzjMD1WSmkglQWQiBBOTjq4LHq+kuPK2O7QJOst0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775539338; c=relaxed/simple; bh=wWelZyIKNqYzhsz42ROzMJtwaT4UqNEfxVRfSUhyelA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qTVI8xg7ZBfuNwXe26CCJaP863Nj3GulMuVFCbltHHPb/JvRJRfiBWjdA88SQ5dWPVdyJ1nIFoEM8omjHAY6abYEkc3q6BdXkNy2DSUAG4jgGHmGHXSwyaQH4gyF1Tfj45Sciz1Bmg6MpDHgdrZs+cq0h0dkntjo5/rC09dtdjI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=jNGZIpn3; arc=none smtp.client-ip=198.137.202.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=bombadil.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jNGZIpn3" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=LNwJPq2PzoXENMaFsFevQJSHbENECqvI5gUJFL8NwIw=; b=jNGZIpn3NBs9neRTPgIjC91Kmg /67JNs7o9hoteY1YyH5uthK2/KWCjvUr8obZXiWpUKXkOY1/0JmPxXZi3o6Ys6SbFjZI7cPATNPCP aErP3w2aa3/3wrSOyoL1zWfYDHAlzbr6rqFK/+6fRT7NAG573S8E+Y9LaGUqTfAfajhKTtSUJjqub 4DOpGDjcQRKuAelFq2+2HDkmjRqThP4Bvhpvpn74AJca5hcYnO6P0IzkLUXv1pB1JZKSI0TVDpRCu vthrnJn7DHULPouq2oUnT59Mw12ygtQOuM2mQPVm12cGLYE+olU90rRlNJGp+Me98uBNINLg3qUZ/ +3a6kCDQ==; Received: from hch by bombadil.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1w9ytE-00000005uM2-2NTQ; Tue, 07 Apr 2026 05:22:16 +0000 Date: Mon, 6 Apr 2026 22:22:16 -0700 From: Christoph Hellwig To: Anand Jain Cc: Theodore Tso , Christoph Hellwig , "Darrick J. Wong" , linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org, Anand Jain Subject: Re: [PATCH v2 3/3] ext4: derive f_fsid from block device to avoid collisions Message-ID: References: <33e8eb64c304a4d42b60f608c26497bf9a2e9e19.1774092915.git.asj@kernel.org> <20260323041624.GA11453@mac.lan> <5bda3d00-df35-4ea1-b313-2fef6e5c5682@gmail.com> Precedence: bulk X-Mailing-List: linux-ext4@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: <5bda3d00-df35-4ea1-b313-2fef6e5c5682@gmail.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html On Sat, Apr 04, 2026 at 04:59:08PM +0800, Anand Jain wrote: > Context: > Currently, ext4's f_fsid is consistent across reboots but fails to be > unique when dealing with cloned filesystems (sharing the same UUID). Per > statfs(2) [1], the primary requirement is that the (f_fsid, ino) pair > uniquely identifies a file. The man page makes no explicit guarantee > regarding consistency across mount cycles or reboots. > > Proposal: > With this fix, f_fsid becomes f(uuid, dev_t). This ensures OS-wide > uniqueness and maintains consistency as long as the underlying dev_t > remains stable. > > Dilemma: > While statfs(2) [1] suggests f_fsid is "some random stuff," we know > userspace (NFS, systemd) often treats it as a persistent handle. > > Do you prefer one of the names above, or is there a more idiomatic ext4 > naming convention I should follow? > > Given the ambiguity in the man page, is gating this behind an -o option > necessary, or should we consider making uniqueness the default behavior? > My take is that anything that should persist should be an on-disk feature flag, not a mount option. But I'm not in charge for ext4.