Re: [PATCH RFC v2] fhandle: expose u64 mount id to name_to_handle_at(2)

[Christoph Hellwig]

On Wed, May 29, 2024 at 09:40:01AM +0200, Christian Brauner wrote:
> Yeah, that's exactly what I figured and no that's not something we
> should do.
> 
> Not just can have a really large number of superblocks if you have mount
> namespaces and large container workloads that interface also needs to be
> highly privileged.

Again, that would be the most trivial POC.  We can easily do hash.

> Plus, you do have filesystems like btrfs that can be mounted multiple
> times with the same uuid.

Which doesn't matter.  Just like for NFS file handles the fs identifier
identifier plus the file part of the file handle need to be unique.

> And in general users will still need to be able to legitimately use a
> mount fd and not care about the handle type used with it.

I don't understand what you mean.  If we hand out file handles with
fsid that of course needs to be keyed off a new flag for both
name_to_handle and open_by_hnalde that makes them not interchangable
to handles generated without that flag.