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Tue, 1 Sep 2026 23:32:25 +0000 (UTC) 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 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Zorro Lang References: <878a21ea507cb955ed414072c82ab5e5493b8ae0.1784949155.git.asj@kernel.org> Content-Language: en-US In-Reply-To: X-Headers-End: 1x1Xxv-0001Ig-K4 Subject: Re: [f2fs-dev] [PATCH v8 05/13] fstests: add _require_unique_f_fsid() helper X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Anand Suveer Jain via Linux-f2fs-devel Reply-To: Anand Suveer Jain Cc: djwong@kernel.org, fstests@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net 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 >> _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel