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 43CA23EFD04; Mon, 8 Jun 2026 14:43:16 +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=1780929801; cv=none; b=k5H4jCinEcZLuGyGZggxHYGpvRb4uViVt2ZM37g9+FKXX9l1Dnh/+FKYXnQ5hQe85p1D46/kzERH4wADlaeziaIKlsP/McqJXO/4tahBc3g+8uvlDuiBsU2+p7fDi9ijh+Ld3ZCC/zNLnOxJQtw0j30M3uDaFeeJD67Z/wRgG2A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780929801; c=relaxed/simple; bh=wuZc+K7tw+E9I/jGxHgS9mrEe/FWNWNXEHO2pFPn8zQ=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=UtEcPV1AKytQbZu6YFMzqOcea/mbFrCNUkDgRhHgsRPoEbUr3v9L3+VLalUX1amYX0tUk3MEzptX6QYyhWMzgUHycyp7ecdrIPTkqB+kTVxlxyGIclMgZWeuClkVMnObVhMFr3hzmUHIXHc70rarWMFhkrFIUM1UKydlu/KrA7s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=W4i6QXqc; 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="W4i6QXqc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DEE811F00893; Mon, 8 Jun 2026 14:43:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780929796; bh=4dzy65cV98nV8e9IEBBFsdPikjXLTPrbT+oXCXkGHLY=; h=Date:From:Subject:To:Cc:References:In-Reply-To; b=W4i6QXqcwQEexyBYFUFdL6Asf/5FsbSgO4HD3O1NcnjlTFB8ltWEMXRy6gpwM2haV tDVv9CAZEgB4ypNEZHpHqsNeqGHVtcW0jE/AVTm7BNXkwysvMRNfA/GkUFcwClDeR/ SGgE4/lD7unGzEF7SsaW8Giyg2uCL1EIXWtLQrAKgotIPdNQoF1RAHQ42xRBOR3xAR vH1FjWjdogzYYOc94ME4PkgYHRB1Wta6/29OUlRpmEBBXdXC/3w20sJTDixZVyoomy 0IJBHsL7TWxDsR1p/MKKrYTuEjfgLM+so9NY0I0AVXIc9IgzeGEc8kYXcWhIrUU7Ts f0x76aq/fLOww== Message-ID: <0aa2ec2f-af87-49d8-b1a5-051720e06438@kernel.org> Date: Mon, 8 Jun 2026 22:43:12 +0800 Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Anand Suveer Jain Subject: Re: [PATCH v6 04/11] fstests: add _require_unique_f_fsid() helper To: "Darrick J. Wong" 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 References: <983ed0f63318c930379ee74220f23aa558c16d51.1779939330.git.asj@kernel.org> <20260529043056.GE6070@frogsfrogsfrogs> Content-Language: en-US In-Reply-To: <20260529043056.GE6070@frogsfrogsfrogs> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29/5/26 12:30, Darrick J. Wong wrote: > 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 ? > Correct.. I'll make it specific. >> +# 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? > Sure, that will be.. Link: https://lore.kernel.org/linux-ext4/20260409131238.GC18443@macsyma-wired.lan/ instead of the title. Thanks, Anand > --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 >> >>