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

[David Sterba]

On Tue, Oct 14, 2025 at 03:43:54PM +1030, Qu Wenruo wrote:
> 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.

What do you mean no one asking?  This was specifically asked for by
Steam to do A/B root partition mounts for recovery. It is a niche use
case but it has its users.