linux-kernel - Re: [RFC PATCH 1/1] ovl: Use fsid as unique identifier for trusted origin

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Message-ID: <fe7201ac-e066-4ac5-8fa1-8c470195248b@suse.com>
Date: Tue, 14 Oct 2025 15:43:54 +1030
From: Qu Wenruo <wqu@...e.com>
To: Christoph Hellwig <hch@...radead.org>,
 André Almeida <andrealmeid@...lia.com>
Cc: linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
 linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 kernel-dev@...lia.com, Miklos Szeredi <miklos@...redi.hu>,
 Amir Goldstein <amir73il@...il.com>, Chris Mason <clm@...com>,
 David Sterba <dsterba@...e.com>, Anand Jain <anand.jain@...cle.com>,
 "Guilherme G . Piccoli" <gpiccoli@...lia.com>
Subject: Re: [RFC PATCH 1/1] ovl: Use fsid as unique identifier for trusted
 origin

在 2025/10/14 15:09, Christoph Hellwig 写道:
> On Mon, Oct 13, 2025 at 10:57:07PM -0300, André Almeida wrote:
>> Some filesystem have non-persistent UUIDs, that can change between
>> mounting, even if the filesystem is not modified. To prevent
>> false-positives when mounting overlayfs with index enabled, use the fsid
>> reported from statfs that is persistent across mounts.
> 
> Please fix btrfs to not change uuids, as that completely defeats the
> point of uuids.
> 

That is the temp-fsid feature from Anand, introduced by commit 
a5b8a5f9f835 ("btrfs: support cloned-device mount capability").

I'm not 100% sure if it's really that important to support mounting 
cloned devices in the first place, as LVM will reject activating any LVs 
if there is even conflicting VGs names, not to mention conflicting UUIDs.

If temp-fsid is causing problems with overlayfs, I'm happy to remove it, 
as this really looks like a niche that no one is asking.

Yes, mounting cloned devices can be useful for certain cases, but with 
metadata_uuid changing the uuid should not even take a second, or one 
can just unregister the previously scanned device.

I'd say we paid too much cost for a niche that is not worthy.

Thanks,
Qu