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

[Anand Jain]

On 14-Oct-25 12:39 PM, Christoph Hellwig wrote:
> 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.

We needed cloned device mount support for an A/B testing
use case, but changing the on-disk UUID defeats the purpose.

Right now, ext4 and Btrfs can mount identical devices,
but XFS can't. How about extending this to the common
VFS layer and adding a parameter to tell apart a cloned
device from the same device accessed through multiple
paths? I haven't looked into the details yet, but I can
dig it further.