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 8176247D95E; Tue, 1 Sep 2026 23:32:26 +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=1788305550; cv=none; b=ddH1l6WJkMB86ZLEqnGCcmLq19RRvjc9mU8aQTCUCX6xTmxtRwztzID41v+XtUqd0g7Y7LzXI5y/0jUOM5iLXeWGKFFypwha0YCKrjDBwz5vD61bldWfDIT7jYHF3W83OVmw0pogsmBgYMdrwuwAK1tqvh4v0ZIdPwi5SMRf6ms= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788305550; c=relaxed/simple; bh=LjmVvqDf6srXlfpo5QzsQs336GnWASUPZVD6tiEk+Io=; h=Message-ID:Date:MIME-Version:Subject:To:References:Cc:From: In-Reply-To:Content-Type; b=JyiM/NwQhj7f4uLJpPIyzkhy+Zmt3ZNEa/dH7mi5n2NJrbqup3OmThIFGXSdomkluqDo2uQVMvaWq4aK+QICe4O06PZlKdIc0pmmL/OvFrc8fIQtV6cWxkEuLnQr1cToD2KxVXysukxUWQ3045C02SsjVeVBXrMJFTi/QCgo/BU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FXGk34vk; 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="FXGk34vk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A14F31F000E9; Tue, 1 Sep 2026 23:32:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788305545; bh=03+cdQH6OSkJOrqr1DanmXDylDD6Vi1Wng3BzGHUVu4=; h=Date:Subject:To:References:Cc:From:In-Reply-To; b=FXGk34vkpiY0LoHcsYDs7HMl0oV93yvwYDiuF2nT/9etACREQSwVhUxOl0cN2bVMd w1iXNl1Yv599cQuFeWjal/+9Bx6NMi8iv0tkQGVe5wVylk/nYVUtldcb0nZWdkE6xp pLuEo/hN7UizSLQ7bX8hhTlZfBoTV7HvROpWOYPAoLGM5YCWYHIpseZYlS+MKLgaC7 BHa4bmYha8Esgvfs5PPyOkM/Q6pm4FmijTJomkuWjVH8s8lUPevKbEevHUbIffU3Aq kPKpP9cG8sEQGyVBw78CwRGpDVAw6W0G95TNUzaHOsFM6VJqjrh0sAYYcKG2Ie0FeB e4y8zATwuKRmQ== Message-ID: <9832242f-cc39-46f7-847b-70871e52a373@kernel.org> Date: Wed, 2 Sep 2026 07:32:21 +0800 Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 05/13] fstests: add _require_unique_f_fsid() helper To: Zorro Lang References: <878a21ea507cb955ed414072c82ab5e5493b8ae0.1784949155.git.asj@kernel.org> Content-Language: en-US Cc: fstests@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, djwong@kernel.org From: Anand Suveer Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/9/26 00:09, Zorro Lang wrote: > 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 ($FSTYP) does not guarantee unique f_fsid on clones." >> + ;; >> + *) >> + # Conversely, XFS, Btrfs, and F2FS ensure f_fsid remains >> + # unique per filesystem instance (often by deriving it >> + # from the UUID and underlying block device.) >> + ;; >> + esac > > I would prefer to let the experts of each filesystem confirm whether their > fs guarantees a unique f_fsid. Theoretically, whether f_fsid is unique per clone depends on how it is derived. If it includes the device major:minor, it provides a unique ID per clone. Btrfs does it since commit c2a74ed0494c btrfs: derive f_fsid from on-disk fsid and dev_t > How about switching this logic to an *allowlist* > *(whitelist)* approach, where we _notrun by default and only allow filesystems > that explicitly guarantee unique f_fsid support? > > case "$FSTYP" in > btrfs|xfs|f2fs) > ;; > *) > _notrun "Target filesystem ($FSTYP) does not guarantee unique f_fsid on clones." > ;; > esac So _notrun() unless confirmed to have unique f_fsid for the cloned filesystem. Works for me. Thanks, Anand > 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 >>