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 9050F35B62C; Fri, 29 May 2026 04:30:56 +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=1780029057; cv=none; b=PhPRbR734kji5UzXnfvn4l2Bn+FffVozJa8OSlmpCxmr70Qf1yLLAL+oIkbPxJeUQKrN08dr/8gnyyBI4LahDyLMWs4jbuciHn2y4kvKF038IaVQNQRcP1zDgnx2ZIb/8AyeGXesWGGO+mxh6ppsQz5pAg452CFucUHuaDgFzus= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780029057; c=relaxed/simple; bh=nR0sNMeomPmRDTFjnJZawaXlH/LQGYr4CP1PtlY1C5I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZUwHevO1SIN+UEezbzP9SBfW2fgFqzcvhIY5jEM3YWx53JQhQAgQnMIdX7sC681tvLnAF9icu0g1w1i7a/KJZ9fhm9AeMJTCuSsYczkvZodDweV/7kJLwCOpB0q2hGDZ/Yh6yRF2zMxLa3sqD6thggbA+DHFDZtcPjPOa1pDNGM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HUZJMAQ4; 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="HUZJMAQ4" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 616A81F00893; Fri, 29 May 2026 04:30:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780029056; bh=Y9i3D99952aoMze26KNO+B5RKcPVXLOJ/Le5dJq03VQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=HUZJMAQ4JW93nEK7Ak/B7yekzr0L9gilaId6xBXrCVUiqg92v5fqrUBFr8h0m5Oog iA+F1hNKwTjPIft3PnmQJLznIaw3uwRhlW/yO7iC6nc8mrwKxZ11Spi1tT+/ltMTpz 7IQPG4fRwkqsLrp7gsjSrEflI1XB+p7SzvOC1/uWggWjXTk/JblEv4qBAS+YJQcAmv 1m5mUzzgTHR4ortXnd/whkXqrlJYQ7+pU1pNwuXhBj+kA2rpGXRvx+mxNzirF6cAF+ mbVFiwiesQ8295To0Sx1dqDr+Q3kddrBX2CkGYiqz8GDTn65esC1eMNj51RB/Q+2I1 Iler0emvl6uXw== Date: Thu, 28 May 2026 21:30:56 -0700 From: "Darrick J. Wong" 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, zlang@redhat.com, hch@infradead.org Subject: Re: [PATCH v6 04/11] fstests: add _require_unique_f_fsid() helper Message-ID: <20260529043056.GE6070@frogsfrogsfrogs> References: <983ed0f63318c930379ee74220f23aa558c16d51.1779939330.git.asj@kernel.org> 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: <983ed0f63318c930379ee74220f23aa558c16d51.1779939330.git.asj@kernel.org> On Thu, May 28, 2026 at 12:05:35PM +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 | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/common/rc b/common/rc > index 937f478963b4..5446552aed92 100644 > --- a/common/rc > +++ b/common/rc > @@ -6314,6 +6314,27 @@ _require_fanotify_ioerrors() > _notrun "$FSTYP does not support fanotify ioerrors" > } > > +# Ext4 derives f_fsid from the superblock UUID, meaning clones share the > +# same f_fsid until their UUIDs diverge. Conversely, XFS, Btrfs, > +# and F2FS ensure f_fsid remains unique per filesystem instance (often by > +# deriving it from the UUID and underlying block device.) > +# > +# Across all filesystems, a UUID collision causes libblkid tools to return > +# non-deterministic device mappings. It is ultimately the responsibility "device mappings", as in /dev/disk/by-id/$UUID ? > +# of the userspace utility or use-case to enforce uniqueness when a clone > +# diverges. For details, see mailing list thread discussions titled: > +# "ext4: derive f_fsid from block device to avoid collisions". How about providing a direct lore link? --D > +_require_unique_f_fsid() > +{ > + # 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. > + if [ "$FSTYP" == "ext4" ]; then > + _notrun "Target filesystem ($FSTYP) does not guarantee unique f_fsid on clones." > + fi > +} > + > + > # 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 > >