From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 09F1A440652; Tue, 1 Sep 2026 16:09:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788278984; cv=none; b=Js9Ssn8Db/U8oaVUDrEH9Z6w0M6kw6J0g0BLOKPIzXNMzJ2GZRP5t/hM/jGhk2+4kS3R9siUrhN3VVriG9lFclPIQcLzapHFYSli4fFW8QaiPq7O987WbujisG1EGsBwduE/2r20ovybOVrnECWlHZDLrcd3fPnYCQZL8PbjxZc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788278984; c=relaxed/simple; bh=3ScCW9zb7Ytm1fQ5HgRbaOC3JRk8a9y6/M5gPInI+r8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dsoRggneN0sjnJx2BqqSWoIGMcDbTyILaBI756tE/oMRLvG9n27SFekYwicwGj0++mK7Fk7oYfhXloyPp2ACncmJyOpALO4bRklivFcqcIWTHKkRAY5CI9v66sr3u8RO5cXb/GyQQNXhXBEbpdjEERKPgnDlxz2NqU4alS6viGk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=m1Tz6oRt; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="m1Tz6oRt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 753F51F000E9; Tue, 1 Sep 2026 16:09:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788278982; bh=9CE5RSBHk34ry3w4PuiZHGozADtZbhYGgw45lpA0o2o=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=m1Tz6oRtFZ0zUWOQmm82EJl+t4YdeTXhXnnxypQmE9R6Ru0zkt0Hso2BJowL+tSNT pZAW9+UGBe2OXzNpyJPIVyejvTQoRCwqFR6UOShqbLh1KEA4oVMMzAbC2vUqJxjjo5 ahtQ3Z6ajxhqhsQwLedC1wGjJ4dPpKAtO1Zd1ViJ3ET0wv7lhKbv+izI0OIYMPH1KY MkZHbpY5MDwrOuE3Nm7Lb06drbVK5har0KcGJUVSFMWfYiUwY8NCm9/Leumz0OwmHm pPfbpBXXENrKeo36Y6e+YJt3nv7/odzaDiHakUXIgsu8ePE1TFyiGwJ4C20dyl10EC UPQuRVM6uVcEQ== Date: Wed, 2 Sep 2026 00:09:35 +0800 From: Zorro Lang To: Anand Jain Cc: fstests@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, djwong@kernel.org Subject: Re: [PATCH v8 05/13] fstests: add _require_unique_f_fsid() helper Message-ID: Mail-Followup-To: Anand Jain , fstests@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, djwong@kernel.org References: <878a21ea507cb955ed414072c82ab5e5493b8ae0.1784949155.git.asj@kernel.org> Precedence: bulk X-Mailing-List: linux-xfs@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: <878a21ea507cb955ed414072c82ab5e5493b8ae0.1784949155.git.asj@kernel.org> On Sat, Jul 25, 2026 at 03:39:02PM +0800, Anand Jain wrote: > Add a helper to check if the target filesystem supports unique f_fsid > tracking across cloned or snapshot instances. > > Certain filesystems like XFS, Btrfs, and F2FS ensure unique f_fsid > identifiers per filesystem instance. However, Ext4 derives its f_fsid > directly from its superblock UUID, which leads to identical f_fsid > values on cloned images until the UUID is manually modified by userspace. > > Introduce _require_unique_f_fsid() to allow test cases requiring strict > f_fsid uniqueness to skip gracefully on unsupported filesystems. > > Signed-off-by: Anand Jain > --- > common/rc | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/common/rc b/common/rc > index 21b516accdf7..f73251365a60 100644 > --- a/common/rc > +++ b/common/rc > @@ -6356,6 +6356,33 @@ _require_fanotify_ioerrors() > _notrun "$FSTYP does not support fanotify ioerrors" > } > > +# Skip the test if the filesystem does not enforce unique f_fsids > +# natively. Checking this dynamically requires recreating a clone > +# layout, so we use a static lookup based on FSTYP. > +# > +# Across all filesystems, a UUID collision causes libblkid tools to return > +# non-deterministic device mappings. It is ultimately the responsibility > +# of the userspace utility or use-case to enforce uniqueness when a clone > +# diverges. For details, see mailing list thread discussions: > +# Link: https://lore.kernel.org/linux-ext4/20260409131238.GC18443@macsyma-wired.lan/ > +_require_unique_f_fsid() > +{ > + case "$FSTYP" in > + ext*) > + # Ext4 derives f_fsid from the superblock UUID, meaning > + # clones share the same f_fsid until their UUIDs > + # diverge. > + _notrun "Target filesystem ($FSTYP) does not guarantee unique f_fsid on clones." > + ;; > + *) > + # Conversely, XFS, Btrfs, and F2FS ensure f_fsid remains > + # unique per filesystem instance (often by deriving it > + # from the UUID and underlying block device.) > + ;; > + esac I would prefer to let the experts of each filesystem confirm whether their fs guarantees a unique f_fsid. How about switching this logic to an *allowlist* *(whitelist)* approach, where we _notrun by default and only allow filesystems that explicitly guarantee unique f_fsid support? case "$FSTYP" in btrfs|xfs|f2fs) ;; *) _notrun "Target filesystem ($FSTYP) does not guarantee unique f_fsid on clones." ;; esac Thanks, Zorro > +} > + > + > # Computes a percentage of the available space in a filesystem and > # returns that quantity in MB. The percentage must not contain a percent > # sign ("%"). > -- > 2.43.0 >